C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

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C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

October 15, 2015, 11:09:38 pm

I noticed that recently our 1997 C8.3-325 was frequently taking longer than "normal" to start the first time for the day of travel. Historically, it started very quickly at the turn of the key. Recently it has frequently taken several seconds to fire up on many occasions. Coincidentally, historically, I filled the fuel tank near the end of each travel day, but recently have been postponing fill ups for a few days to take advantage of lower fuel prices along our travel route. On our most recent trip, I observed that it started immediately in the morning after a fill of the tank just before stopping for the night. If the tank was down a bit from full, the first morning start was slow. Each of these "coincidences" happened at least twice during the trip. The starting behavior shows no correlation to ambient temperatures, but does correlate directly with the level of the fuel in the fuel tank.

I plan to check with Berndt Ramspeck in NAC regarding the issue. Does any reader of the forum have experience to clarify the issue or suggest a solution?

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #1 – October 16, 2015, 06:08:40 am

Mine was the Winn systems air leaks then replacing all the rubber fuel line hoses that the low sulphur fuel had dried out.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #2 – October 16, 2015, 06:23:41 am

Have you had your fuel lines changed out yet?

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #3 – October 16, 2015, 07:06:24 am

For the price of fuel filters I would change both of them.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #4 – October 16, 2015, 08:17:17 am

JD,

Like others said if you have Winn I'd look at reworking it or preferably replacing it with the Racor with integrated prime pump. Great unit. Other than that, since your symptoms are obviously fuel related, checking the lines to and from the engine fuel pump might be a good call. Look at fuel line fittings as best you can.Takes a couple of fittings but not too hard to do is installing a clear vinyl line temporarily between primary and secondary filter. That'll show you if you're sucking air from a bad fuel line, fitting, pickup tube etc. Does your engine have the mechanical fuel pump or electric?

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #5 – October 16, 2015, 08:51:54 am

the 8.3 usually doesn't have a "Winn" system. The 1997 8.3 has a mechanical lift pump.

The problem sounds like air getting in the fuel lines or a failing and/or failed lift pump.

Do it do it with fuel tank full and engine parked downhill?

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #6 – October 16, 2015, 09:08:31 am

If you find cracking in the lines around the hose fittings (even if that is not the cause) wrap some Rescue silicon tape around the end tightly (or the cloth electrical tape) and that will prevent air entering and give you time to get lines changed. I did all of mine (even on top of tank) when I had a hole cut in floor for inspection just to be on the safe side-but had almost no cracks too.
Another way to stop air entering is what I did a few weeks ago on the 2 lines that come and go from Cooling system filter when it was pouring out of there while on this trip. I cut some new small diameter rubber rad' piping and sliced it down one side then wrapped it around leaking ends and used 3 clamps on each one to squeeze this new hose slightly over all the cracked area. I have done 1k miles since and not a drop of fluid lost since, so I know it would do the opposite and seal any air leaks on fuel lines. I hope it lasts till we make it home, but will at some time soon get a couple of new lines made up and change them out when I have the chance to get under the rear again.
Just and idea that does work- for me right now.
JohnH

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #7 – October 16, 2015, 09:57:42 am

Rescue tape and tie wraps can do wonders. Or Rescue tape and hose clamps.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #8 – October 16, 2015, 10:08:42 am

All fuel lines were changed about three years at FOT. They replaced the rubber lines with plastic lines. They pulled the fuel tank and replaced all the fittings at the fuel tank.

R B Services (Bernd Ramspeck) tweaked a couple of the fittings on the fuel lines and repaired a leaking injector line about two years ago.

The mechanical lift pump was changed one year ago by R B Services.

The fuel filter is a simple spin on filter with a sight glass at the bottom. I think there is only one fuel filter. It is located passenger side near the start batteries. There is no priming or purging device in the fuel system.

I've seen no signs of fuel leaks since R B Services repaired the leaking injector line.

The coach always remains level when parked. I know it starts quickly with the tank full. It requires some cranking to get it started after sitting overnight when the tank is more than 50 gallons down from full.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #9 – October 16, 2015, 10:34:42 am

FYI, I think there is a secondary fuel filter mounted on the engine...I believe on the passenger side. It often gets overlooked.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #10 – October 16, 2015, 10:40:37 am

That's a tough one. If there is absolutely no sign of fuel leakage, you've got an air leak into fuel system somewhere that is allowing air to enter and fuel to siphon back to the tank. The easiest, and probably first place to check is at your fuel filters, including the drain valve on primary. You should have a secondary filter though, typically located very close to mechanical fuel pump on side of engine. Are proper gaskets installed on filters?

Does anyone know....I've heard oblique reference to a check valve in the engine fuel system somewhere. Is there such a valve?

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #11 – October 16, 2015, 10:43:17 am

The secondary filter is a fleet guard FS1251 FORMERLY a fs1226.
If you change these d'ont forget to fill with fuel.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #12 – October 16, 2015, 11:22:35 am

yes on my Cummins it is on pass' side abpout mid pont of engine. Be very carefull there though as behind it is the wiring for ECM and the connection pins and that is what caused all my problem last winter. If you are removing it DO NOT use anything other than a thin metal strap type filter wrench.
JohnH

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #13 – October 16, 2015, 11:41:54 am

Thanks to all for suggestions and education. I'll seek out the "other" fuel filter so that I know where it is. I think I have spares in the coach, but have never personally changed or tweaked them.

I agree that the symptoms indicate some drainage to the fuel tank. The level of fuel in the tank would affect the "suction" on the fuel supply system when the engine is off. Drainage would require some air to replace the volume of fuel. A "less than full" tank might be required to such a bit of air into the system.

The problem is currently more of a curiosity than a "show stopper." I'm due for some services on the engine and coach. Those services will be done by people in NAC who know the systems. I'll see if the behavior changes after the filters are changed.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #14 – October 16, 2015, 11:57:47 am

You may laugh at this but see if the fuel tank in the mornings is under suction?

Mine had non vented fuel fill caps on it. Overflowed up steep hills from the pressure buildup and after the hot fuel cooled off the tank was under suction from the reduced volume.

Needs to be a vented cap as far as I know.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #15 – October 16, 2015, 12:05:16 pm

I believe the OEM fuel cap is non vented. When I fill up while travelling I hear/feel the pressure in the tank release.

Roland

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #16 – October 16, 2015, 12:10:24 pm

Quote from: Roland Begin – October 16, 2015, 12:05:16 pm

I believe the OEM fuel cap is non vented. When I fill up while travelling I hear/feel the pressure in the tank release.

Roland

Mine shot fuel out after going up cajon pass and out of grapevine, ca with non vented caps.

Same hill, vented caps, no overflow and smells and fuel all over the road.

No idea what was supposed to be there but as I drive mine harder than most those were my results.

Bought two new locking vented caps and the overflow isdues went away.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #17 – October 16, 2015, 12:45:03 pm

The first thing I would have checked is the fuel return check valve on the injection pump.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #18 – October 16, 2015, 12:58:32 pm

TORK TEK CUMMINS ADJUSTABLE OVERFLOW VALVE OFV010 - Tork Teknology

The first thing I would have checked is the fuel return check valve on the injection pump.
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Yes I agree high failure rate on oem return fuel line check valve. I replaced mine with the following...

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #19 – October 16, 2015, 01:21:07 pm

I just checked the engine compartment from above using a small flashlight to illuminate dark areas. I found the secondary fuel filter high on the side of the engine, toward the front (of the coach), on the passenger side. I could see no evidence for fuel leakage anywhere on the engine or fuel systems.

The only designation on the fuel tank caps was "Diesel Fuel Only." I saw no holes in the cap, but I think they may be vented. In the section that screws into the filler pipe, there appear to be some ports in the molded plastic and there may be some kind of venting system. The tank never "exhales," nor "inhales" when I remove a cap. It must be vented somehow.

After I get the engine started one time during the day, it starts very quickly thereafter. The only "slow" starts appear to be after the coach has been idle overnight with a partial tank of fuel. That situation takes a long time to reproduce. We'll see what happens with new filters installed by experienced mechanics. I will also inquire about check valves in the system that might affect the starting issues.

Thanks for contributing to my continuing education.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #20 – October 16, 2015, 02:12:49 pm

Any change in starting habits usually goes hand in hand with either air being introduced into the system or a restriction. Overnight system pressure drop could also be related to a fuel return valve but less likely. A DOA heated intake screen is another possibility if you have one. A tank of fuel with a low cetane rating will make for poor cold morning starts as cooler weather approaches and may contribute to slower starts.

Anytime a coach is driven up a relatively steep incline with a tank less than half full, it should be fast idled for a couple of minutes to insure no air has been picked up in the tank before shutting down. This has caught several members.

Pierce

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #21 – October 16, 2015, 02:43:22 pm

When I helped tear apart a 2000 u270, I finally got to see the vent. It comes along the front bulkhead right in the middle of the coach. It was a small hose with a screen on the end. Never would have seen it, but the entire front end was gone and converted to a 5th wheel.

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #22 – October 16, 2015, 03:30:56 pm

Our U300 vent is set for 2-4 psi so has a fairly good "whoosh" when the cap is removed.

Pierce

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #23 – October 16, 2015, 06:45:18 pm

JD,
A longer crank time after it sits makes me think that fuel is leaking back from the engine toward the tank requiring more cranking to bring the fuel back.
If you have changed your fuel lines that should eliminate that.
Did this start since the last fuel filter change? Oil filters have a check valve to keep them from leaking down, l'm not sure if fuel filters do. If this started after the last filter change you might consider changing them again. Save the ones you take off if they are new and don't solve the problem.
JD

Re: C8.3 Starts Quickly on Full Tank of Fuel, Slowly on Partial Tank

Reply #24 – October 16, 2015, 08:48:32 pm

If your 295 has aqua hot their is a one way in its fuel supply line I am told.

If the aqua hot lines are cracked and the one way is bad then fuel can be sucked from the engine.

Not an expert on the exact connections in there and I may have mis stated exactly how it's hooked up but something to consider.

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