1996 Chevy C3500 6.5 Turbo Diesel Fuel Problem

[Tim Martin]

The situation is the truck came in with a blown engine. So, we installed a used engine which is fine. It starts fine and idles great with no smoke. The problem is, as soon as the accelerator pedal is moved off idle, white smoke rolls out the exhaust pipe, and by 3,000 rpm, raw fuel is also coming out the tailpipe. The scan tool readings at idle are: boost pressure 102 kpa (15"), accel pedal 1 .65v, ect is 185 degrees, timing is dead on, and idle speed of 750 rpm and engine load of 12%. These readings concur with other 6.5s we have worked on. One thing we noticed is that as soon as the accelerator pedal is moved off idle, engine load goes to 50% which we suspect is a calculated figure produced by the PCM. Installing another PCM does not change the numbers so we suspect there is an issue of some proportion. As engine speed increases the only scan tool readings that change are that rpm number changes and engine load as mentioned goes from 12% to 50% and stays somewhat stationary. The question is: What is producing the 50% engine load even though the accelerator pedal is hardly moved? Or, perhaps we have us another issue we are not aware of. Why the white smoke and raw fuel?

[steven kiser]

I've found that on some of these dsls with trashed engines they have to run for a long time before all the crap deposited in the exhaust from the old engine will burn away. I've had so much crap in exhausts i've drilled holes in mufflers to drain it. You could very well have a plugged cat as well. The pugged cat will cause a back pressure that could be read as a strain on the engine. Has this been allowed to reach operating temp? I'm trying to remember if this has the warm up valve in the exhaust, i don't think so but i've seen a lot of issues with these. If the fuel was being dumped into the engine before the cylinders you would have a run away unless you had a completely dead cylinder and by the readings it doesn't seem so, even if you did it would take for ever for the fuel to build up enough to drip out of the exhaust. My guess on that is it's left from all the trying to re start the blown one. You probably tried for a bit and the owned probably tried a lot. I've had ones where the either smell was so strong it filled the shop so bad we moved it outside and the owner claimed they never tried to start it even though we found two empty cans of either on the passenger floor. As it warms up the smoke gets worse is right in line with a contaminated / plugged exhaust. I've had mufflers plugged as well as cats. I have a mig with a flexable head on it so it takes me 1/2 the time opposed to removing the 02's to just cut the pipe before the cat, run it, sleeve and weld when done.

[Tim Martin]

Just an update on this one.

We replaced the crankshaft sensor with a new one and it has made a whole world of difference. At least for now. It starts up fine, runs fine, with very little smoke. We may have to tweak the injector pump timing just slightly.