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Roy, import/domestic specialest
Category: Chevy
Satisfied Customers: 4343
Experience:  ASE master tech for 40 years
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Chevrolet 3500 diesel dually: I have a 96 Chevy 3500 6.5 turbo

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I have a '96 Chevy 3500 6.5 turbo diesel. 235000 miles. Noticing momentary surging when 55 to 65 mph after engine has been running a while. Occasionally get a little jump while sitting at light. Surge will cause rpms to jump for a second or two and then it falls back to where it was. Black smoke seen after surge.
Truck is easy to start, little bit of white blue smoke on ignition. Otherwise I generally don't have smoke unless I have been sitting a t idle a while then hard acceleration.
Does not stall. Does not runaway. Does not show issue at lower speeds or in cooler weather.
Reading about PMDs and other causes, like waste gates, vacuums etc. My PDM is mounted on a FSD Heat Sync attached to intake. I have pulled nothing apart. I don't have diagnostic tools.
Looking for a little guidance and info
Good afternoon my name is XXXXX XXXXX I will try to assist you today.

Back smoke is unburnt fuel usually the result of an injector. It could be the spray pattern being off not delivering the correct amount of fuel. They do need to be serviced but not as frequently as the gas motor injectors. In my fleet of dura max, I use diesel injector cleaner for just this reason. It works very well to clean up the tip of the injectors to give it a better spray pattern. I am not a big believer in fuel additive s in gas motors but I am a strong believer in diesel cleaners.

With no codes and it runs well, I would not look for any off the wall issues. Lets start at basics first. It can and most likely will be this simple from your description.

White smoke is from burning coolant. This can occur from a bad egr cooler, or head gasket. Once again, if it runs well and has no unexplained loss of coolant, I would not think there is a cooling system issue.

Customer: replied 3 years ago.

No noticeable loss of coolant.

I typically add injector cleaner with fuel. Will the spray pattern cause the surge? Not a good feeling to have the truck accelerate on its own, even if its just a second or two.

Is my best bet to go to dealer for test coding, to see what shows up?


Spray patterns need to very exact in these motors as too much fuel will cause engine damage from no combustion chamber and too little will cause missfires.

Have the system checked for codes to see if there is anything showing. You can go to a parts store for a free code check rather than spending money at the dealer.

Customer: replied 3 years ago.

I know this may not be a fair question in this type of format, but will an uneven spray pattern be a cause for the surging issue I'm having?
Will a code check tell you if there are dirty injectors or the spray pattern is off? Thanks.


yes, it will cause erratic engine operation just as in a gas motor.

It will not code just for that. The pcm constantly tries to adjust mixture all the time from input from the O2 sensors, mass air flow among some of the inputs.

Computers are not that smart yet to detect dirty injectors or mass air flows.

Roy, import/domestic specialest
Category: Chevy
Satisfied Customers: 4343
Experience: ASE master tech for 40 years
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