Engine/Transmission (1994 - 1998) Loss of Fuel Prime

[JMVincent]

Hi: I have a '96 5 speed, 16 C. M. Turbo from Piers, and modified torgue plate, as well as a Transfer Flow aux. fuel tank. About 1 year ago the truck started to miss after starting when it sat overnight, and this was particularly noticeable if it sat on an incline with the nose up. Piers Henry suggested I have Transfer Flow check the switch over valve, to see if it might be the problem. I just finished taking the truck to Transfer Flow, they spent 4 hours pressure and vacuum testing all of the fittings from both tanks up to the fuel lift pump, and could find no leaks.

Does anyone have any ideas what else could be causing the problem? Incidently, after missing for the first 1/2 mile of driving, the problem clears up and it then runs fine.

BillGaines at Transfer Flow is also interested in finding out what the problem is, and they really treated me right on trying to resolve the problem. Thanks, Jack

 

[Dieselnerd]

If you have over 70,000 miles on your truck and have never changed the lift pump, it may be the culprit. There are several check valves in the lift pump that can go bad but you must replace the whole pump. Cost about $150 from Cummins. 12 Valve Lift Pump, latest style, Cummins P/N 3936316. You might also have a bad fuel return line but the original lift pumps on the '96 normally fail around 70-75K. I speak from experience...

 

[Deezul1]

Put a pressure gauge on it you can read from in the cab and see whats up before throwing money at it. My 96 had almost 300,000 on the lift pump and my 97 has 168,000 on the original pump. I havnt heard a lot about lift pump problems on 12 valve engines but the gauge will help a lot trying to figure it out.

Good Luck

 

[redram]

Hope you've checked the obvious / most common problem on a 12 valve for losing fuel prime - that being the cracking / aging return fuel lines at the back of the engine.

 

[wcjp]

I was at a local Bomb party this weekend. Lots of great people and awesome trucks. One of the guys showed me where the return line is located. I have the exact same problem as JMVincent. The people I talked with all said the hose was the likely culprit. I'll attack it on Tuesday.



Basically, remove the fuel filter and housing, the hose is then easily identified. My theory is the hose is allowing air into the system. When the nose is pointed up the air will seek the highest level. Causing a hard or no start situation. When the nose is pointed down the air will stay in place or return to tank.

 

[JMVincent]

Losing fuel prime

Thanks, everybody, for all the helpful suggestions. You might be interested in the response I got from Jim Anderson if you also have a similar problem. Jim's reply was as follows: "Jack: If the truck runs O. K. , a fuel pressure check is not necessary. Suggestions 1 and 2 (fuel return line, and fuel lift pump) are the most common causes for this complaint. You can do a bit of troubleshooting before spending money on parts. After the truck has been parked overnight, operate the primer button on the fuel lift pump. Since it is a long reach for my short arms, I use a broom handle to push on the rubber button of the primer. Stroke it 10-20 times and observe if there are any fuel leaks, anywhere in the system, paying particular attention to the fuel return line rubber portion under the rear half of the engine intake manifold. Then start the engine. It should start right up. The fuel lift pumps fail because one of the 3 internal check valves hang open allowing fuel to drain back into the fuel tank while the truck sits overnight. Cummins offers both new pumps and a rebuild kit. Buy the new pump and observe instructions carefully for putting it on the engine. Feel the rubber of the fuel return line carefully. If its surface is rough or cracked, replace it. It fails due to heat from the engine deteriorating the rubber. I suggest using a replacement hose made of silicon rubber which is better able to withstand the heat. "

I thought Jim's comments were very helpful, and hope they help someone besides me (especially "wcjp"). I'm on the road haeaded south at the moment, so I'll check the fuel return line as soon as I reach Yuma, Arizona next week. Does anyone know where I can get a silicon rubber fuel hose in Yuma? Again, thanks for all the great imput! JMVincent