Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: Chuck & Jeannie on July 13, 2014, 07:08:35 pm
Title: Fuel System Science Project
Post by: Chuck & Jeannie on July 13, 2014, 07:08:35 pm
I have been recently gathering the materials to conduct a evaluation of my fuel system. I have just completed the project, and will report my findings in this thread. I will make a separate post for each step in the operation. I hope this info will be of value to the Forum membership, especially those with the C-8.3L Cummins (mechanical) engine. I am extremely pleased with the outcome of my project!
My 8.3L engine was pretty much all original when we purchased our U280SE last November. It seems to run fine to me, but since I have zero experience with diesel powered vehicles, I have no basis for comparison. Because my coach has 163,000 miles, and 3900 hours on the engine, I felt it likely that some of the original fuel system components were probably "getting tired". The goal of my project was to ascertain the current condition of my fuel system, and if a problem was found, to hopefully correct it.
According to several online sources, one of the best fuel system diagnostic tools is a fuel pressure gauge that takes its reading somewhere between the lift pump (also called a transfer pump) and the fuel injection pump. Also according to the experts, (for the C-8.3L with P7100 injection pump) at idle this pressure should read somewhere between 15 and 25 psig. Anything below this range indicates a "problem" somewhere between the fuel tank and the injection pump. So the first step in my project was to install a fuel pressure gauge. The parts I used are listed below, along with a few photos. The installation was pretty simple. When I started the engine and went back to view the gauge, my fears were confirmed: fuel pressure at idle was only 3 psig! Definitely not good, so on to step 2, and hopefully an improvement in this critical number.
Parts list: TORK TEK CUMMINS 14MM X 1.5 PRESSURE GAUGE SNUBBER CBS010 - Tork Teknology (http://www.torkteknology.com/products/TORK-TEK-CUMMINS-14MM--X-1.5-PRESSURE-GAUGE-SNUBBER-CBS010.html) JEGS Performance Products 41057 JEGS Braided Stainless Steel Mechanical Gauge (http://www.jegs.com/i/JEGS-Performance-Products/555/41057/10002/-1) Valley Instrument Grade A Back Mount 2 1/2in. Glycerin Filled Gauge — 0-30 (http://www.northerntool.com/shop/tools/product_413320_413320?cm_mmc=Housefile-_-SHIPPED-_-1206-_-CONF)
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 13, 2014, 08:22:23 pm
Chuck,
You are on the right path. The fuel pressure gauge should be installed between the secondary filter and the injection pump so it can detect any restriction in the filters as well as fuel pump pressure. A deluxe setup would have another gauge on the discharge side of the fuel pump so you could compare readings and verify your fuel pump as well as the secondary filter.
I installed a fuel pressure gauge on the discharge side of the secondary filter as well as one on the primary filter so I can check how well the hand pump is working and see if there is a air leak between the hand pump and the fuel tank.
Another gauge was installed on the discharge side of the secondary filter on the generator. It will tell if the electric pump is working as well as filter restrictions. The 4 psi is about normal from the electric pump with or without the engine running.
Our engine pressure are not the same as we have different engines. The 30 psi is residual pressure (engine off) and the idle pressure is normally about 60 psi.
Pierce
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 13, 2014, 08:32:06 pm
What repairs, if any, have you made to the fuel system components?
Is everything original? New fuel lines? Lift pump?
Could you list the fuel pressure as you increase the engine speed while not in gear?
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 13, 2014, 08:39:54 pm
Chuck,
Depending on where the pressure gauge is installed, the low pressure could be caused by a weak or dirty fuel bypass ball and spring on the return line out of the injector pump. That line could be clamped off and the pressure reading compared to before. Follow the link to a diagram of a typical Bosch mechanical injection pump. The part that can sometimes causes trouble is #200 in the photo at the link below. The other problem is that it is usually located on the back side of the pump next to the block and hard to get at if you have big hands. diesel bypass fuel injection pump valve - Google Search (https://www.google.com/search?q=diesel+bypass+fuel+injection+pump+valve&rlz=1C5CHFA_enUS504US504&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=piTDU-LUMdW2yASEioF4&ved=0CBwQsAQ&biw=1358&bih=647#facrc=_&imgdii=_&imgrc=A_BHSXixYVxcVM%253A%3BAatLML021OkiRM%3Bhttp%253A%252F%252Fwww.peachparts.com%252Fshopforum%252Fattachments%252Fdiesel-discussion%252F65103d1236613446-fuel-injection-pump-starvation-good-lift-pump-diesel-bypass-valve_868g6546t498j.jpg%3Bhttp%253A%252F%252Fwww.peachparts.com%252Fshopforum%252Fdiesel-discussion%252F247039-fuel-injection-pump-starvation-good-lift-pump.html%3B371%3B309)
You also need to see what your fuel pressure at the gauge is at full throttle. Either a sensor with a wire to a remote gauge, a video camera or someone in the compartment while you are going up a hill at full throttle. :D
Pierce
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 13, 2014, 09:01:12 pm
Thanks for the replies - as you continue reading, you will see I have covered most of these points.
Step 2. The lift pump (transfer pump) is one potential source of trouble, and low fuel pressure. My lift pump was original. It was seeping fuel from the "prime button", so was due for replacement. That was done using the parts listed below. It is a fairly simple task, except for the awkward working position. I strongly recommend the use of studs rather than bolts...makes it into a "one-handed installation". Unfortunately, when I started the engine after mounting the new pump, my pressure still read the same: 3 psig. On to step 3!
Fuel Transfer Pump Alliant Power Stock Replacement Dodge Cummins 1994-1998 5.9L (http://www.thoroughbreddiesel.com/stock-replacement/dodge-94-98-fuel-transfer-pump.htm) Larryb - LarryB's EASY Stud Mounting Kit for Lift Transfer pump, 12 valve (http://www.fostertruck.com/easy-stud-mounting-kit-for-lift-transfer-pump-12-valve-cummins.html)
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 13, 2014, 09:45:37 pm
It's been years since I did a lot of Bosch inline pump work. I think we were looking at about 7 psi going into the injection pump. The fuel at 3 or 7 psi goes into the body of the pump and then the pistons take it and send it up to the injectors at somewhere around 3000 psi. With a restriction from a partially clogged filter or other reasons, it's easy for the injection pump to run away from it's supply of fuel with a resulting loss of power. Too low fuel pressure may cause cavitation where the fuel makes the transition from the low pressure to the high pressure part of the pump. These Bosch pumps have not changed that much in about 100 years. The pump in my previous link had the lift pump mounted on the side of the high pressure pump body. They almost never fail.
Pierce
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 13, 2014, 10:04:23 pm
Here is an excellent link on the overflow/bypass valve with great photos. The guys here modify the valve for racing but you get the idea. New ones are pretty inexpensive. How to modify the overflow valve OFV - Competition Diesel.Com - Bringing The (http://www.competitiondiesel.com/forums/showthread.php?t=99725)
You also get the idea how big hands don't work here. If changing or cleaning it, there is a a copper washer that is easy to drop and it needs the washer.
Pierce
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 13, 2014, 11:24:42 pm
Step 3. Another item that can cause low pressure at the injection pump is clogged filters. The lift pump has to suck fuel through the primary filter, and push fuel through the secondary filter. Blockage at either one will lower pressure. I changed the primary filter, and started the engine. Pressure still 3 psig. Then I changed the secondary filter, and..........STILL 3 psig! So the filters were probably in good shape, but it never hurts to have new ones in place. Time to move on to step 4.
Step 4. As Pierce has been explaining (with excellent links provided), the overflow valve is another factor in the fuel pressure equation. They are very simple and fairly reliable, but they DO fail. The spring can become weak, or the valve seat can erode, or trash can foul up the works. Since my injection pump was original, and the overflow valve had obviously never been changed, this was the logical next step. In the case of my engine, the valve is VERY difficult to access. It is tucked under the AC compressor mounting plate, wedged between the injection pump and the cylinder head, and held in place (even when un-screwed) by a metal fuel line. The hardest part of the operation was loosening the little bolt that holds the fuel line bracket. I thought I would never get it to break free, but it finally did. There is JUST enough space to unscrew the valve, then slide the fuel line and valve together out from between the pump and cylinder head. It is NOT a fun job.
Once out, you can see (in the photos below) that my original valve does not have a retainer bolt for the valve spring, and therefore cannot be "modified". No matter - I already had a new adjustable Tork Tek valve ready to install. Even though the two valves are shaped slightly different, there was still enough room to install the new piece. Getting it and the fuel line slid back in place was just as difficult as removing it, but it can be done...very slowly...very carefully. Once it was installed and the fuel line was reconnected, it was time for the test. I cranked the engine, walked to the rear hatch (AGAIN) and looked at the gauge: 19 psig at idle!!!!
I believe I have found the root cause of my low fuel pressure. If the new overflow valve had not cured the problem, the next step would have to be replacing the fuel line from the tank to the primary filter. You can probably guess that I am glad I did not have to go to step 5. I still have to take the coach out for a test run, to see if the higher fuel pressure results in any noticeable improvement in engine performance. Like I said in the beginning, I haven't had any problems driving it up till now, so I don't expect a dramatic change. After the test drive, I will close out this thread with a final report.
Title: Re: Fuel System Science Project
Post by: TAS69 on July 14, 2014, 12:14:23 am
Thanks for the research! We have virtually identical motors so this will definitely carry over to our coach in the coming months!
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 14, 2014, 12:19:47 am
Any thoughts as to whether the 19psi is too low compared to TorkTek's literature saying that typical idle would be 23psi?
I've been busy with other things and haven't had a chance to hook up my gauges but will post my numbers here when I get a chance.
Also, did you have to remove the AC compressor bracket for overflow valve removal?
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 14, 2014, 12:31:45 am
Chuck,
Nice job with the photos and good logic figuring the pressure problem out. And glad you explained how tough it is to get a wrench back there to get the fitting off. Every time we would put a turbo on a normally aspirated engine, we would have to R&R the pump to add fuel, otherwise, the turbo just dropped the EGT with not much increase in HP. The pump is a real devil to get off. First, there is a single bolt at the far end to stabilize it and then you need a 1/4" ratchet with a tiny universal, about an 8" extension and a 13mm socket. I would wrap electrical tape around the universal so it wouldn't move too much and then try to get my hands down there to remove the 3 nuts holding the pump onto the engine block.
The Bosch injection pumps only get about 5 minutes on the calibration stand at the factory and to get the best idling and running Cummins (or Mercedes, etc), having a shop put it on the stand to calibrate it can make a difference. When installed on the Bosch test stand, it gets spun for an assigned amount of revolutions. It then disconnects and the amount of fuel in clear, graduated glass vials is measured for each cylinder. This is done at several different speeds and the end result is a smooth running engine from idle up to the governor limit. It is also necessary to check so each injector gets it's fuel at the precise number of pump degrees.
This video best shows the irregularities a stock pump can have. This is much like the machine we used. YouTube injection pump calibration at: Fuel pump test stand - YouTube (https://www.youtube.com/watch?v=FCcc-jE-o4U) To do a pump right, it took an hour and a quarter or a little more unless new parts were needed.
When it was done, the cars were faster, smoother and didn't smoke like a lot of chipped PUs do now.
Pierce
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 14, 2014, 08:42:29 am
Any thoughts as to whether the 19psi is too low compared to TorkTek's literature saying that typical idle would be 23psi?
Also, did you have to remove the AC compressor bracket for overflow valve removal?
I have seen a wide range of "recommended" numbers for fuel pressure on this engine (both the 5.9 and the 8.3). For a stock, unmodified application anything around 15-25 psig (at idle) seems to be commonly accepted as OK. Also, at the bottom of the the Tork Tek installation instructions it says (I added the underline):
"NOTE: Set the fuel pressure to OEM specs. 17 to 22 PSI at idle. Our valve typically idles at 25 to 26 PSI. Pressure at 2500 NO LOAD RPM is 29 to 32 PSI. Tork Teknology is not responsible for injection pump leakage or damage from running excessive fuel pressure or the use of a HP overflow valve."
Even though I'm not getting the 25 to 26 they say their valve "typically" produces, I AM right in the middle of what they say is OEM specs. I'm happy with that. Also, I have not had the chance to check the pressure at higher RPM - my DW was not available to manipulate the gas pedal yesterday when I was working on the installation. I want to see what the pressure reads at higher RPM before I think about changing anything. If I do decide I need to adjust the valve setting, at least it is now easy to do!
And to answer your second question, no, I did not remove the AC compressor. After "eyeballing" the job I decided there was enough room to work around the AC mounting plate. It would probably be easier with the AC bracket removed, but it's not absolutely necessary.
Title: Re: Fuel System Science Project
Post by: wa_desert_rat on July 14, 2014, 09:52:58 am
Excellent piece of troubleshooting and repair. Nice work. I have the 5.9 engine on my U225 (with about 70,000 miles) and should look at this as a job for next spring.
Thanks for posting this (and for the great photos). And thanks to Pierce for significant commentary. :)
Craig
Title: Re: Fuel System Science Project
Post by: Gary Bouland (RIP) on July 14, 2014, 10:32:27 am
Chuck, On most of our FT's you can increase idle speed using the set and increase switches on your cruise control. On My 95 you used the increase switch in increments to set idle where you wanted it. May differ on some models. Gary B
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 14, 2014, 10:48:52 am
Gary,
First of all, let me say how happy I am that you finally found a buyer for your coach. I know that is a load off your mind. But I also hope, like many others, that you will stick around the Forum and continue to provide the benefit of years of experience with Foretravel products. I was always especially interested in your comments, since we shared similar model coaches. Don't go away - we need you here!
As to using the cruise control to set idle speed, I have read on the Forum about this "optional" function but cannot get it to work on my coach. Either my unit does not support this mode, or something is not working right. The CC seems to work fine going down the road, so don't know...
I'll just have to rely on my DW (as usual) to provide assistance.
Title: Re: Fuel System Science Project
Post by: krush on July 14, 2014, 01:20:58 pm
You can just reach around and pull on the throttle to speed up the engine. I can reach it from standing behind the coach reaching in the engine cover.
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 14, 2014, 01:38:46 pm
krush, Thanks for that info! I know old school carburetors, but I don't know squat about diesel fuel injection. Today I am installing a new fuel shutoff solenoid. While I'm "under the hood" I will get a good look at the injection pump linkage, and determine what or where I should push/pull to rev up the engine.
Title: Re: Fuel System Science Project
Post by: krush on July 14, 2014, 07:56:47 pm
It will be very obvious. The cable from the King Controls box goes to it. Pull/push it....just like a carb!
Were you having problems with the shut-off solenoid? I can't help but feel that sometimes people over-replace stuff. Remeber, there's tons of these engines out there on trucks going much further and working much harder than in our RV's.
Title: Re: Fuel System Science Project
Post by: Gary Bouland (RIP) on July 14, 2014, 08:02:35 pm
HEY ALL ......... If you reach around from the rear and move the fuel arm make very sure that you do not have a loose sleeve or anything else that can contact the belts or pulleys running, IT CAN BE PAINFUL.
GaryB
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 14, 2014, 09:56:23 pm
Were you having problems with the shut-off solenoid?
It was due to be retired. See "new" and "old" photos below:
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 15, 2014, 06:36:55 pm
New shutoff solenoid is installed.
Note to those who are planning on upgrading this item: I encountered a problem during installation. The new solenoid and the new bracket that comes with it fit perfectly - no problem there. HOWEVER, due to the larger size of the new solenoid, my throttle cable bracket would not fit. On my engine, it is held by two of the same bolts that attach the solenoid bracket. Basically what I had to do was modify the throttle cable bracket so it could be moved "inboard" (toward the injection pump) about 1/4". This required drilling 2 new mounting holes, and removing some material from the bracket. Not a big deal - can be done easily with basic hand tools. Your setup may be different, and you might not have the same problem. Just thought I'd mention it. Photo of new solenoid and modified bracket below.
Title: Re: Fuel System Science Project
Post by: Barry & Cindy on July 15, 2014, 11:30:49 pm
The injector pump 'overflow' fuel return flows directly back to fuel tank. Each injector also has a fuel return hose connection that seems to daisy chain from injector to injector.
Where does the last daisy chain of the injectors flow to?
One electric fuel pump I am looking at, the installation instruction says to tie injector fuel return with injector pump fuel return, and I don't know what they are referring to.
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 15, 2014, 11:35:43 pm
Daisy chain goes into the return line.
Pierce
Title: Re: Fuel System Science Project
Post by: Barry & Cindy on July 15, 2014, 11:59:31 pm
Pierce,
I thought our fuel return rubber hose came directly from the injector overflow fitting. Where does the daisy chain connect to the return line, or does it connect to injector pump and then flow out the overflow valve?
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 16, 2014, 01:39:15 am
Good question Barry. There are two sources of excess fuel. The first comes from the high pressure injection pump. The fuel/lift pump produces more pressure than the overflow/bypass valve on the back side of the injector pump is set for. So, the excess fuel goes past the ball valve and out the fitting toward the tank.
The fuel injectors have a certain amount of internal leakage and the extra fuel is daisy chained either through metal lines or in fabric covered rubber lines from one injector to the next where it picks up a little more to the next and so forth. Once it leaves the last injector, it goes to a fitting where it meets the excess fuel from the injector pump and adds to the total amount of fuel returning to the main fuel tank. The main fuel injection pump has to take into account the small amount of fuel loss at the injector when it is calibrated so the proper amount of fuel is injected into the combustion chamber or pre-combustion chamber.
The returning fuel from the injectors and injection pump is warm so you can feel it when you put your hand against the tank after it has been running for any length of time.
In the case of a Detroit 2 cycle, there are no injector pipes or fuel lines or even a single injection pump. All fuel travels inside the cylinder head(s) to each cylinder where there is a fuel injection pump and injector all in one compact package called a unit injector. All excess fuel is VERY hot and carries quite a bit of heat back to the main fuel tank. Putting your hand on a tank that is only partially full can almost burn your hand. That's why Detroits are so clean looking on the outside. Everything to do with the fuel system is internal in a very complex cylinder head.
Below is a diagram of a Bosch style inline injection pump with the lift pump mounted on the side of the main injection pump. An electric or engine driven lift pump remotely mounted may also be utilized. Engine manufactures may design the system in different ways but they all get the excess back to the tank. The returning fuel is under very low pressure.
Since we don't have a Cummins, I can't describe exactly how or where the connections are made. I used the diagram below as it is the one I am most familiar with. This closely matches a Bosch pump mounted on a Mercedes 300SD engine. One of the differences is a primary filter is installed ahead of the lift pump (between the lift pump and the fuel tank) and there is only one secondary fuel filter.
Pierce
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 16, 2014, 09:12:43 am
Where does the last daisy chain of the injectors flow to?
I can answer this one!
On my engine (may be different on others), the drain from each injector feeds into a manifold that terminates at the inlet fitting for the secondary fuel filter, where it joins the supply line from the lift pump. The two lines are attached with a double connection banjo bolt. The drain manifold is constructed of metal tubing "T's", one for each injector. The "T's" are connected by thin plastic tubing that is a simple press fit onto the metal tubing. It all looks pretty flimsy to me, and is obviously not meant to contain any appreciable pressure. I think the excess fuel basically just "runs downhill" until it gets to the filter inlet, where it rejoins the flow into the filter. There is a one-way check valve (banjo bolt #21 in the second drawing) at the double connection, I suppose because line #6 is under pressure from the lift pump. In the first drawing below, fuel line #6 comes off the lift pump to the secondary filter. In the other drawing, drain manifold #20 terminates in a banjo fitting, which is stacked on top of #6 at the fuel filter inlet.
(Photos from Cummins QuickServe Online)
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 25, 2014, 10:51:11 pm
So I got my GlowShift gauge temporarily hooked up with wires run through the living area rather than fished underneath for a few days.
I was getting 9 psi with the stock overflow valve at idle. After changing out the valve, it is between 15 and 17 depending on exactly what speed I set the idle at. 17 psi occurs at an idle of 725 rpm, any lower idle speed results in a fluctuation of 15-16 psi.
These numbers are still low from what I've read on other Cummins truck forums, especially considering that this is supposed to be a higher pressure overflow valve than stock, and I'm trying to figure out if there is something that should be looked at. I'm also going to pick up a cheap mechanical gauge to compare to the GlowShift reading. I'll probably fill up a 5 gallon tank of diesel and hook directly to the injection pump to see if there is anything in the fuel tank line causing the pressure drop.
I'm going to see if there are any leaks in the lines that go into the transfer pump. I do have a spot down on the right side of the injection pump, when looking at it from the side, that is a bit wet. It appears to be a vent but I'll be investigating it tomorrow.
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 26, 2014, 11:21:21 am
Robert,
I haven't had a chance to get my coach out for a test drive since I changed the overflow valve (and both filters). I don't know yet if there will be any improvement in driving performance, but I'm hoping for some noticeable change. One thing that did definitely improve is my cold startup action. For the past several months I have noticed a degradation in cold starts - my engine would start immediately as soon as I turned the key, but after about a minute it would falter and die. Then it would require 2 or 3 re-starts before it would finally run smoothly. After that, no problem. After I changed the filters and overflow valve, this behavior has completely disappeared - every start, hot or cold, is immediate and flawless. Idle seems smoother, also.
As to your pressure concerns, here is what I have observed. Right after startup (as soon as I see good oil pressure, I get out and walk to the back of the coach) my fuel pressure reads around 22-23 psig. As the engine warms up, it gradually drops to around 18-19 psig at 750rpm, and holds steady there. So allowing for the difference in our two gauges, we are probably pretty close on the readings at idle. I have not checked mine at higher RPMs yet. I do not have any leaks in my system, at least none that I can see. I will be interested in hearing the results of your further investigation.
Did you install the Tork Tek adjustable overflow valve? If so, you could try raising the fuel pressure, but be careful. I have read warnings about going too high, and causing damage to injection pump. I plan to leave mine alone for now, and see how it drives. I'm REALLY happy with the improved startup performance!
Title: Re: Fuel System Science Project
Post by: pocketchange on July 26, 2014, 01:52:58 pm
Service bulletins (& forums) on the diesel in your machine will point you in the right direction.
In my case (5.9L HO Dodge) after learning that lift pump issues were common 100%, I replaced the fuel lift system with a FASS HD (electric) fuel lift delivery system which ended this problem.
Injection pumps have a light duty fuel lift feature which if compromised w/low pressure from the lift pump, stresses the injection pumps' separate lift feature. If this goes away the injection pump will no longer function.
A gauge (fit in the injection pump) will tell how much lift (pump) pressure is getting to the injection pump.
A gauge on the low pressure side of your high pressure injection pump is money in the bank. If you have a starting problem.. (PLEASE) check the fuel system.
Keep the agenda thing in mind. Cummins, Caterpillar and ALL the other manufactures will be happy to repair fueling problems. pc
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 26, 2014, 03:00:53 pm
Thanks, pc. I'll keep that info in mind.
I got back from a drive to a local campground to dump my tanks which has provided more useful information. I'll probably end up crashing the FT since I've been staring at the 3in1 gauge with EGT, boost, and fuel pressure nonstop and noting how the values change based on terrain. I do have some slight doubts about the accuracy of the gauges due to almost 50' of 16 gauge wire but I'm going to perform some comparisons in the engine area, without all the extra wire, to see if there is any change.
The trip was at 500' above sea level and mostly flat land though there are a few longer hills. It was slightly windy.
As noted, I'm idling at about 725 rpm and have approx. ~16psi fuel pressure. During my trip (and assuming that the gauges are reading correctly with no voltage drop due to the length) I saw a maximum of 23psi of fuel pressure and a low of 7psi. The high pressure of 23psi, along with the highest readings in general, occurred when I had just let off the gas after aggressive acceleration and it did not last long before dropping. The lowest pressure, along with all of the other lowish readings, occurred during hard acceleration and high boost.
The average cruising psi at highway speed at about 1800rpm was in the 10-14 range which seems lower than ideal from my research. This is with a new lift pump from Cummins, new fuel lines, new and clean fuel filters, etc. I did note that after changing to the TorkTek overflow valve that the engine has more power and is more responsive. I hit a maximum of 22psi of boost during the trip and slightly over 1100 degrees of EGT measured from a port drilled in the exhaust manifold.
There was an inverse relationship between fuel pressure and boost/EGT, when one went up-the other went down.
I'm going to do some testing to see if there is any voltage drop causing incorrect readings and trying to see if I can find any leaks at all. If I can't find any problems and the readings are correct, I may end up playing around with the adjustable overflow valve to see if I can bring the values up closer to the recommended values.
Edit- the higher pressure of the overflow valve also seems to have smoothed out my engine a bit and the addition of the additional aluminized insulation over the top of the old and worn out insulation made a rather larger difference in sound.
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 26, 2014, 06:12:45 pm
After testing with the gauges temporarily hooked up back at the engine, I feel comfortable saying that whatever differences there may be due to the length of the wiring are very small, if any, and that my numbers from my earlier post are correct.
I clamped off the return fuel line a bit and the fuel pressure went up to the 30s prior to letting off the clamp so I feel comfortable that there aren't any issues with the transfer pump.
I'll probably start playing around with the adjustment on the fuel overflow valve to see if I can get it up to 25psi in the next day or two.
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on July 26, 2014, 06:38:57 pm
Robert,
Be sure to post your results from increasing the fuel pressure. The way I understand it, when the engine is under heavy load, the closer you can get to holding 30 psig at the injection pump inlet, the better off you are. Supposedly, anything over that is either not beneficial (with a stock engine), or can be harmful.
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 27, 2014, 09:55:24 pm
One electric fuel pump I am looking at, the installation instruction says to tie injector fuel return with injector pump fuel return, and I don't know what they are referring to.
Is this the FASS HD 150 unit, Barry? From everything I hear that thing is LOUD.
I definitely think that you should be the guinea pig for the electric fuel pumps and tell us how it all works out ;).
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on July 27, 2014, 11:45:27 pm
As noted, I'm idling at about 725 rpm and have approx. ~16psi fuel pressure. During my trip (and assuming that the gauges are reading correctly with no voltage drop due to the length) I saw a maximum of 23psi of fuel pressure and a low of 7psi. The high pressure of 23psi, along with the highest readings in general, occurred when I had just let off the gas after aggressive acceleration and it did not last long before dropping. The lowest pressure, along with all of the other lowish readings, occurred during hard acceleration and high boost.
If your fuel pressure drops to 7 psi under high load, either the lift pump can't supply the volume or you have a restriction somewhere between the tank and the injection pump. Your fuel pressure from normal cruise to full throttle should see little fuel pressure change on the low pressure side of the injection pump.
We used an alternate fuel source for the injection pump and then had the lift pump fill a graduated container and measured it against factory specs. They may provide the liters/minute/rpm information online.
Pierce
Title: Re: Fuel System Science Project
Post by: rsihnhold on July 28, 2014, 06:11:22 pm
In my case (5.9L HO Dodge) after learning that lift pump issues were common 100%, I replaced the fuel lift system with a FASS HD (electric) fuel lift delivery system which ended this problem.
Do you have anything to say about the FASS, positive or negative? Was it worth it?
Title: Re: Fuel System Science Project
Post by: Caflashbob on July 28, 2014, 09:12:46 pm
Do you have anything to say about the FASS, positive or negative? Was it worth it?
Pittsburg power mentioned a .4mpg improvement and a handful of power increase when I called them recently.
Good videos on their site. Depends on how much air and/or water is in your fuel I guess
Title: Re: Fuel System Science Project
Post by: rsihnhold on August 13, 2014, 10:36:47 am
So after my last trip to dump my tanks and with a bit more turning of the adjustable overflow valve, I'm currently at ~23-24psi at idle in neutral along with a drop in pressure at higher RPMs. cajk reported that he has gotten similar readings.
I'm still getting a major drop at WOT under load but now I'm bottoming out at about 9psi rather than the 7psi I was getting before. Most highway driving results in low teens fuel pressure.
I'm not sure how much further this valve will let me turn it but I'm going to find out. The Cummins manual says that the P7100 injection pump can take up to 50 psi.
On a side note, the turbo intake v-clamp was not lined up quite right which was causing a bit less boost than I am getting now. The correct and full connection actually looks slightly off, like it is crooked, and I found that the sealing o-ring had slipped out of its groove and was preventing a good seal. I'm now up to the occasional flash of 24 psi and a continuous 22-23psi.
On a side, side note. The new engine compartment insulation has made an enormous difference in keeping the heat and noise in the engine compartment and out of the bed/bedroom. The rear air basically never kicked on during my trip and the bed didn't seem to be warm at all.
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on August 13, 2014, 10:56:06 am
Trying to finish our engine compartment insulation this week. How about a photo of what you have done?
If you are dropping fuel pressure on the freeway and further on grades, I suspect you either have a restriction somewhere in the fuel supply or the lift pump is deficient. Depends on what fuel pressure Cummins says you need at full load/max RPM.
Turbo boost would seem to be pretty good.
Pierce
Title: Re: Fuel System Science Project
Post by: rsihnhold on August 14, 2014, 09:07:43 am
Trying to finish our engine compartment insulation this week. How about a photo of what you have done?
If you are dropping fuel pressure on the freeway and further on grades, I suspect you either have a restriction somewhere in the fuel supply or the lift pump is deficient. Depends on what fuel pressure Cummins says you need at full load/max RPM.
Pierce
I didn't do anything fancy at all with the engine compartment, just covered the old stuff with new insulation and aluminum tape like a few other people here have done like Barry and Cindy.
It seems to be fairly well acknowledged around the Dodge Cummins 5.9 guys that the stock mechanical fuel pump can't keep the fuel pressure up under load. Only real path to take is the electric pumps which I'm thinking more and more about though it doesn't sound like it is quite as critical for us with the P7100 pumps as it was with the slightly later VP44 pumps.
Title: Re: Fuel System Science Project
Post by: Pierce & Gaylie Stewart on August 14, 2014, 11:09:47 am
Looks good and will keep the foam from falling down on the hot engine.
Sounds like you have done your homework pretty well.
Pierce
Title: Re: Fuel System Science Project
Post by: krush on August 14, 2014, 03:41:57 pm
What did you use for the insulation? It looks great!
Title: Re: Fuel System Science Project
Post by: rsihnhold on August 14, 2014, 05:08:09 pm
What did you use for the insulation? It looks great!
It took about 2.5 rolls of this stuff-
Amazon.com: Thermo-Tec 14120 48" X 72" One Sided Thermo Guard Flame Retardant: (http://www.amazon.com/Thermo-Tec-14120-Sided-Thermo-Retardant/dp/B001GFQ1XI/ref=sr_1_fkmr0_3?ie=UTF8&qid=1408049667&sr=8-3-fkmr0&keywords=thermotec+flame+resistant)
They make a version that has both sides aluminized but I'm not sure its needed but I know thats what Barry and Cindy used. Amazon got my order mixed up and sent me one of each when I ordered it and I didn't feel like sending it back so I ended up using a mixture of both types. There isn't any difference other than the one has two aluminum sides.
If you install it with two people it would probably look a bit nicer and certainly be easier to hold in place while starting out. The spray adhesive didn't provide enough initial grab to support the weight of the material so I was trying to put the screws in with one hand while holding the sheet up with the other.
Title: Re: Fuel System Science Project
Post by: rsihnhold on September 26, 2014, 03:39:02 pm
So I'm midway through my trip to North Dakota and I figured I'd update this post with current numbers.
I've got the adjustable fuel pressure regulator at the highest value I can muster without removing the AC compressor bracket. I'm currently still at ~24psi idle though I'm sure the pressure could be raised if the valve were removed and adjusted but I've been too busy with other things at the moment.
Since installing the valve, I've also replaced the stock 4" exhaust system with a 5" Magnaflow Hushpower muffler and piping. This has allowed me to be able to sustain long term boost pressures on hills of 24 psi and have occasionally hit 26. The larger exhaust seems to take longer to get to 22+psi compared to the stock 4" but has seen higher overall peak numbers though the higher numbers only really happened on longer hills than I ever tested the stock 4" setup on. I recall somebody on here dyno'ed their rig with a C8.3 and found that the 4" setup produced more power and torque.
The downside to this extra boost is the fuel pressure at WOT drops to a low of 7-8 psi which is just below the 9 psi maximum value I had with the old, worn out original valve. When I get around to removing the AC bracket, I'd like to end up with fuel pressure in the double digits and WOT. Hopefully the valve has enough adjustment left in it to make that happen, I imagine idle will probably be around upper 20s for that. In the meantime, this C8.3 is clearly moving much quicker than it did before the fuel pressure and exhaust system upgrades. My dreams have been filled with Holset Super 40s and electric fuel pump upgrades lately.
I also haven't managed to kill myself by staring at the 3in1 gauge yet while driving, surprisingly.
Title: Re: Fuel System Science Project
Post by: Barry & Cindy on October 13, 2014, 06:07:17 am
We are back on our fuel project after a few months delay from traveling. I have re-read every Forum posting and checked out many links. We thank all who told their story and responded to our questions earlier this year. I have gleaned our needed parts from what others have used.
I think that making the step to an electric fuel lift pump at this time adds too many questions and may not be needed, so it is on hold.
Our Cummins C8.3 is running just fine, but we plan to install new preventative parts:
mechanical lift/transfer pump - wonder if there are improved & recommended aftermarket brand lift pumps, instead of Cummins part, how is Allliant? Are all new lift pumps manufactured with rubber internal parts that can withstand BioDiesel?
Jegs gauge damper hose kit p/n 41057 2nd snubber 1/8" male/female, assuming more snubbing is better for gauge sender.
Fuel Pressure Gauge:
We prefer a dash mounted electric digital fuel pressure gauge with high/low memory, but are not sure what gauge to buy. I have looked at many gauge brands and find only Cyberdyne has high low memory, but it does not have good PSI ranges. I do see other digital gauges without memory that look pretty good, like GlowShift MaxTow DoubleVision 0-30psi.
If anyone has put in an electric digital gauge, we would appreciate your experience and review.
Wow, can't believe we are getting ready to order parts as this has been a very large thoughtful project.
Thanks again. . . Barry & Cindy
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on October 13, 2014, 08:04:42 am
...aftermarket brand lift pumps, instead of Cummins part, how is Allliant?
Barry,
When I got ready to replace my lift pump, I emailed "LarryB" and asked about recommended brands. He said they are all made in China now, even the replacements sold under the Cummins brand. So basically, just take your pick. I went with the ALLIANT-AP4988747, and the best price I found was at Thoroughbred Diesel, $84.16 with free shipping + they give you instant $5.00 off with your first order from them:
Alliant Power 5.9L Dodge Fuel System Components (http://www.thoroughbreddiesel.com/alliant-power/5.9L-fuel-system-components.htm)
I don't know about the BioDiesel compatability - only time will tell. Installation was easy with the stud kit. I did have to add a reducer bushing to the inlet port to adapt to my existing fuel line. The pump has been working great - instant starts, smooth idle, good power, no leaks.
Title: Re: Fuel System Science Project
Post by: pocketchange on October 13, 2014, 05:17:00 pm
We are back on our fuel project after a few months delay from traveling. I have re-read every Forum posting and checked out many links. We thank all who told their story and responded to our questions earlier this year. I have gleaned our needed parts from what others have used.
I think that making the step to an electric fuel lift pump at this time adds too many questions and may not be needed, so it is on hold.
Our Cummins C8.3 is running just fine, but we plan to install new preventative parts:
mechanical lift/transfer pump - wonder if there are improved & recommended aftermarket brand lift pumps, instead of Cummins part, how is Allliant? Are all new lift pumps manufactured with rubber internal parts that can withstand BioDiesel?
Jegs gauge damper hose kit p/n 41057 2nd snubber 1/8" male/female, assuming more snubbing is better for gauge sender.
Fuel Pressure Gauge:
We prefer a dash mounted electric digital fuel pressure gauge with high/low memory, but are not sure what gauge to buy. I have looked at many gauge brands and find only Cyberdyne has high low memory, but it does not have good PSI ranges. I do see other digital gauges without memory that look pretty good, like GlowShift MaxTow DoubleVision 0-30psi.
If anyone has put in an electric digital gauge, we would appreciate your experience and review.
Wow, can't believe we are getting ready to order parts as this has been a very large thoughtful project.
Thanks again. . . Barry & Cindy
I like the idea of leaving a fully functioning system alone.. pc
Title: Re: Fuel System Science Project
Post by: krush on October 13, 2014, 05:19:32 pm
mechanical lift/transfer pump - wonder if there are improved & recommended aftermarket brand lift pumps, instead of Cummins part, how is Allliant? Are all new lift pumps manufactured with rubber internal parts that can withstand BioDiesel?
I do see other digital gauges without memory that look pretty good, like GlowShift MaxTow DoubleVision 0-30psi.
If anyone has put in an electric digital gauge, we would appreciate your experience and review.
Are you sure that you need the stud kit? My 98 already had the studs installed with the original lift pump.
As I've mentioned before, I've got the GlowShift 3in1 gauges. I'm very happy with it and it allows fuel pressure readings up to 60psi. After having the electric gauges, I wouldn't feel that it was necessary for the low/high memory since you are able to get consistently repeatable results. There was really nothing to the install other than either running a few wires front to back or using the extra existing wires. Just the snubber and an extra length of hose at the inlet to the injection pump with the sender attached to it and mounted higher than the injection pump to keep a pocket of air to dampen the pulses.
No idea about the mechanical lift pump options, I'm using a new unit bought from Cummins.
Title: Re: Fuel System Science Project
Post by: John Haygarth on October 14, 2014, 10:40:08 pm
I hope I do not have to work on the lift pump on our coach as it sure is in a lousy location for people with back issues. I do have a kit for it with the seal/etc that is good for ULS fuel as was able to get it from Cummins before they stopped selling them and having to buy whole pump. JohnH
Title: Re: Fuel System Science Project
Post by: Barry & Cindy on October 14, 2014, 11:56:51 pm
Robert, great idea, I will look to see if we already have studs. I saw that you had the 3-in-1 gauge that you can't take your eyes off. Since we already have a boost gauge and a great unique pyrometer, I figure that a single gauge will do it and since I can't find any with memory, I have put my eye on the Glow Shift Max Tow 30psi electric fuel pressure gauge with digital readout and sweep hand. Thanks for the idea to mount sender higher than pump, as it makes sense.
John, our C8.3 has a different fuel pump than your ISC8.3, which had the gasket problem and ours is on the curbside. It is still difficult to reach pump, hope not worse than reaching the fuel shut off solenoid for replacement.
Thanks for the replies.
Title: Re: Fuel System Science Project
Post by: Alan & Gerri Ortiz on October 15, 2014, 06:53:43 am
call, had to have my high pressure pump rebuilt. They replaced duel shut off solenoid (FSS), fuel shut off valve, etc. While doing the job. I saw the replacement FSS identical to the new one in the picture. When we picked up our unit (1996 Cummins C8.3) I noticed the throttle "feel" had changed. It now feels like it is binding at initial foot pressure and then releasing making it very tough to control low speed action in tight places. I will get out to my up unit and see if the mechanic ignored the increased size of the new FSS and its effect on the adjacent throttle cable.
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on October 15, 2014, 08:25:41 am
It is still difficult to reach pump, hope not worse than reaching the fuel shut off solenoid for replacement.
Replacing the fuel pump is about the same as doing the shut off solenoid. I did both of mine from "above"...one foot on the bell housing and other foot on the frame member along side the engine. Once you convince your back to bend sufficiently, you have pretty good access to the pump. My original factory lift pump came off easily - the bolts were not much more than hand tight. I think the factory engine paint was holding everything together!
Title: Re: Fuel System Science Project
Post by: Chuck & Jeannie on October 15, 2014, 08:59:19 am
see if the mechanic ignored the increased size of the new FSS and its effect on the adjacent throttle cable.
If your throttle cable bracket is the same as mine, the mechanic HAD to make some kind of "modification" to get it back on with the new FSS. What he did is the question... There are 2 items connected to the bracket (and to your throttle lever): throttle position sensor (for Allison transmission), and the actual throttle cable. If the bracket was badly bent or otherwise "jury rigged" to make it fit, very possible something is in a bind.
OR, it could be something they did, or did not do, in the process of rebuilding the injection pump.
OR, it might be something in the throttle pedal itself, or the throttle control air valve under the floor, causing the "binding" feel.
Title: Re: Fuel System Science Project
Post by: TGordon on February 08, 2021, 01:56:16 pm
You also need to see what your fuel pressure at the gauge is at full throttle. Either a sensor with a wire to a remote gauge, a video camera or someone in the compartment while you are going up a hill at full throttle. :D