Engine/Transmission (1994 - 1998) White smoke and stumbling

[LandShark]

Started the truck yesterday after sitting for a week. Started right up and ran smooth for about 30 seconds, then started running rough and stalled. Took about a minute to restart and it ran very rough with huge amounts of white smoke. After about a minute of this it settled down to normal and I drove it 85 miles without incident. Today it started right up and after 10 seconds of smooth running it stumbled and started blowing out white smoke; but not as bad as yesterday. After 30 seconds at high idle it settled down.

Fuel filter was changed about 1000 miles ago. Return line was replaced 15 years ago (by Dealer), and the fuel heater screen was checked about 10 years ago. Other than that the fuel supply system is all OEM stock.

I'm thinking air in the fuel line? Any ideas would be great prior to me tearing into it. Plan is to replace all rubber fuel lines and maybe swap out the lift pump with a new spare I've had for about 5 years.

 

[KRStone]

Huge amounts of white smoke?

Head gasket starting to leak?

 

[LandShark]

White exhaust smoke goes away after about a minute of running, when it settles down and runs as smooth as ever. On a restart later in the day, it starts normal (no smoke).

 

[BIGNASTY]

Low on coolant lately? water in fuel you guys have been getting quite a lot of rain? Did ya just fill up before this happend?

 

[hsmith]

My guess is an air leak, or fuel line letting air get into the supply.

 

[TBartlett1]

Let us know what you find. I'm having the same problem with my 98. I think mine might be sucking air somewhere between the tank and the fuel filter. Like yours, my fuel lines are mighty old and are probably starting to rot, thanks to the northeast winters and the salt we pour down like its free.

 

[Missouri Mule]

Usually air getting into fuel system cause hard starting and once you get it started it runs fine. Can you see any fuel leakage? Does it matter how full/empty the tank is?

 

[BDaugherty]

I worked on a truck with similar symptoms, but this one also leaked some fuel on the ground. I replaced all the fuel lines forward of the fuel tank, serviced the strainer, and installed a new WIF sensor in the new fuel filter. It now starts right up after sitting for weeks at a time.

 

[tempforce]

drooling injectors... .
the temp changes... starts and stops the condition...
get em cleaned b4 they stick...

 

[LandShark]

Here's what I've found out so far:
New fuel return line, overflow valve, lift pump and running fuel direct to the pump (totally bypassed the heater and screen) did not help. I cut into the fuel supply line at the frame rail (under driver footwell) and hooked up a small electric diesel fuel pump. The supply line did not leak any fuel when I cut into it (normal ??), but the output from the pump was frothy. I would guess about half air and half diesel. Tomorrow I will start checking the fuel supply line back to the tank and determine if I need to get into the tank. No obvious leaks.

Maybe I can figure out how to pressurize the line to help find the leak.

I don't expect much gunk in the tank as the prefilter screen was clean.

 

[tempforce]

frothing fuel, yep, you have air getting in... check the fuel line to tank connections. and anywhere the fuel line may rub...

 

[LandShark]

Update:
Today I tilted the truck bed to get access to the fuel tank top. Pulled out the module and inspected it. Filter screen looked good and no gunk in the tank. Put the module back in and ran a rubber fuel line from the module direct to the fuel pump and added a NAPA diesel filter screen. Did a little priming and the truck started in about 10 seconds. Ran rough for about 15 seconds and then settled down. I'll do a start test in the morning to see if it is really fixed. Nice to hear the roar of the Cummins after being dead for 2 weeks!

 

[Hootguy]

You might have a look at the pre-heater/pre-screen,,they are notorious for leaking air at the electrical plug in,,,everyone just removes the pre-heater and throws it away,,Doge put that ****ty thing in there NOT Cummins,,and it doesnt do much anyway,,think of how much fuel is ahead of it,,,

 

[hsmith]

Ditto^^^^^

 

[LandShark]

You might have a look at the pre-heater/pre-screen,,they are notorious for leaking air at the electrical plug in,,,everyone just removes the pre-heater and throws it away,,Doge put that ****ty thing in there NOT Cummins,,and it doesnt do much anyway,,think of how much fuel is ahead of it,,,

I totally bypassed the preheater/screen module. I removed the 1/2" rubber line at the preheater (the other end is attached to the lift pump) and angled it down, and used a 1/2" to 3/8" barb and ran the supply line from there directly to the tank module, using a NAPA diesel prefilter screen #3270 (141 micron) down near the frame.

 

[LandShark]

Truck seems to be running normal again. Here's what I did.

1. Replace overflow valve and return line to frame rail. No help.
2. Replace lift pump and preheater screen. No Help.
3. By pass preheater module. Run fuel feed line direct from tank to lift pump. Inspect fuel tank module. Fuel and screen were clean. No help.
4. Replace fuel return line from frame rail to tank. Fixed!

I was amazed at the number of possible failure points in the fuel system. Here's the fuel path starting from the tank:
1. Valve at bottom of fuel module
2. spiral plastic tube from bottom of module to top
3. metal tube thru top of tank module
4. plastic fuel line to frame
5. metal fuel line along frame rail
6. braided rubber line
7. rubber line
8. metal line to fuel heater
9. 1/2" rubber line to lift pump
10. metal line to fuel filter
11. metal line to injection pump

And now the return line:
12. overflow valve to metal line
13. rubber line
14. metal line.
15. braided rubber line to frame rail
16. metal line along frame rail
17. plastic line to top of fuel tank module
18. metal fitting thru top of module
19. plastic spiral line to bottom of module

My truck is now modified so a single rubber line runs from the fuel tank to the lift pump with a prefilter in the line (heater module is bypassed) and a single rubber return line from the overflow valve to the top of the fuel tank.