Fuel System Science Project

Topic: Fuel System Science Project (Read 3906 times) previous topic - next topic

Re: Fuel System Science Project

Reply #25 – July 16, 2014, 09:12:43 am

Quote from: Barry & Cindy – July 15, 2014, 11:30:49 pm

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)

Re: Fuel System Science Project

Reply #26 – 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.

Re: Fuel System Science Project

Reply #27 – 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!

Re: Fuel System Science Project

Reply #28 – 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

Re: Fuel System Science Project

Reply #29 – 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.

Re: Fuel System Science Project

Reply #30 – 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.

Re: Fuel System Science Project

Reply #31 – 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.

Re: Fuel System Science Project

Reply #32 – July 27, 2014, 09:55:24 pm

Quote from: Barry & Cindy – July 15, 2014, 11:30:49 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

Re: Fuel System Science Project

Reply #33 – July 27, 2014, 11:45:27 pm

Quote from: rsihnhold – July 26, 2014, 03:00:53 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

Re: Fuel System Science Project

Reply #34 – July 28, 2014, 06:11:22 pm

Quote from: pocketchange – July 26, 2014, 01:52:58 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?

Re: Fuel System Science Project

Reply #35 – July 28, 2014, 09:12:46 pm

Quote from: rsihnhold – July 28, 2014, 06:11:22 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

Re: Fuel System Science Project

Reply #36 – 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.

Re: Fuel System Science Project

Reply #37 – 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

Re: Fuel System Science Project

Reply #38 – August 14, 2014, 09:07:43 am

Quote from: Pierce & Gaylie Stewart – 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.

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.

Re: Fuel System Science Project

Reply #39 – 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

Re: Fuel System Science Project

Reply #40 – August 14, 2014, 03:41:57 pm

What did you use for the insulation? It looks great!

Re: Fuel System Science Project

Reply #41 – August 14, 2014, 05:08:09 pm

Quote from: krush – August 14, 2014, 03:41:57 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:

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.

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Fuel System Science Project

Reply #42 – 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.

Re: Fuel System Science Project

Reply #43 – 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:

Injector pump input snubber - TorkTek CBS010 Injector pump output fuel return - TorkTek OFV020

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?

Lift pump mounting studs - LarryB's Stud Mounting Kit

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

Re: Fuel System Science Project

Reply #44 – October 13, 2014, 08:04:42 am

Quote from: Barry & Cindy – October 13, 2014, 06:07:17 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

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.

Re: Fuel System Science Project

Reply #45 – October 13, 2014, 05:17:00 pm

Quote from: Barry & Cindy – 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:

Injector pump input snubber - TorkTek CBS010 Injector pump output fuel return - TorkTek OFV020

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?

Lift pump mounting studs - LarryB's Stud Mounting Kit

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

Re: Fuel System Science Project

Reply #46 – October 13, 2014, 05:19:32 pm

Quote from: pocketchange – October 13, 2014, 05:17:00 pm

I like the idea of leaving a fully functioning system alone.. pc

I agree. There are thousand upon thousands of these engines operating around the world and they seem to be doing fine with the stock components.

Re: Fuel System Science Project

Reply #47 – October 14, 2014, 09:24:22 pm

Quote from: Barry & Cindy – October 13, 2014, 06:07:17 am

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?

Lift pump mounting studs - LarryB's Stud Mounting Kit

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.

Re: Fuel System Science Project

Reply #48 – 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

Re: Fuel System Science Project

Reply #49 – 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.

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