Home Forums Gear Hunting Trucks and Four-Wheel Drives diesel mechanics...

Here's a question for you about an incident I had today.

2008 Dodge Cummins, 6 spd manual. It has a DPF delete. It uses a chip to reset the computer each time you start it.

I was coming down a long, steep hill. Pulling a trailer that grossed under 2500lb. I'd been averaging 30 mph, pushing against the compression brake most of the time, usually in 4th gear. I'd gone 15 to 20 miles like this when I got a huge puff of WHITE smoke out of the exhaust. It was 1/4 mile before I could pull over and by that time it was clearing up. By the time I got stopped, it was pretty much done. It never did it again. The oil pressure and temp were fine.

Any ideas what could cause that? Could the compression brake cause it?

Not a mechanic but I think white smoke usually indicates water.

That was my thought, too, but if it started leaking water into a cylinder, it wouldn't quit like it did. Usually white smoke will smell like antifreeze, too, and this didn't.

White smoke out of a diesel is unburned fuel usually. The grid heater on my 98 dodge diesel hasn't worked in years, when I first start it in the cold weather it'll pour white smoke until it warms up to operating temperature.

It sounds like something caused it to overfuel while you were coasting against the exhaust brake. I don't know enough about the electronic common rail setup to know why it would do that in that situation, but it sounds like the computer gave it more fuel than it needed at the time.

You need to have an injector balance test done. If you have one that's not sealing when closed, it will accumulate unburned fuel. Bad news on a diesel, can result in a torched piston and oil dilution. Check your oil level too. If it's "making" oil, it's a problem.

when injectors crap out engines usually will run rough. i had a duetz diesel that had an injector stick open and wash fuel down by the rings and "make" oil as alluded to above you could definitely hear something up. pure white smoke is usually indicative of a turbo/aftercooler issue in my experience, but the fact that it came out of it is puzzling. Aftercoolers do make condensation because they cool the air that is entering the turbo. usually there is a valve that drains that condensation off before it enters the engine but if the water is being burned off white smoke will occur.

Yup. Common rail injection on the Cummins engines can behave a little differently though. Fuel pressures vary from about 8000psi at idle to 29000psi at WOT, and it's always present at the injector. The injectors aren't pressure activated, but are electronically triggered up to 5 times per compression stroke, and some leakage when "closed" can accumulate without combusting if the engine is running against compression. Not saying it isn't an oiling problem (Bad turbo shaft seals perhaps), but in light of what unmanaged fuel will do to a diesel, still worth checking.

Since this happened, I've put nearly 100 miles on without a hiccup. It's running great. For that matter, as soon as the smoke cleared, it was running great. I just think it had something to do with running against the exhaust brake for so long and hard but I don't know enough about how they work to even guess what it would be.