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Problem with Cheveolet diesel truck

I am trying to help my brother-in-law with repairing his truck. It is a 2002 or 2003 Chevy truck with a diesel engine. He was going down the road the other day under normal driving conditions when the motor made a racket and then white smoke started coming out of the back like a chimney. The truck will still crank and run (and smoke), and now there is a knocking or tapping noise that is coming from the engine. The engine is running kind of rough, and has the tapping or knocking sound, but it will calm down for 1/2 a second at which time the rough idle and noise stop, but quickly return. There is no engine code showing, so my code reader is useless. I once had a Chevy 350 with a spun main bearing that sounds similar, but the motor didn’t idle rough or smoke. I don’t know enough about diesel engines, so does anyone have any ideas? I was told there was a possibility of a bad injector pump or bad injector itself. Is there any way of testing this yourself, or does it require a shop trip? Thanks in advance for the help.

How many miles on it? Is this a Silverado 2500HD with the 6.6L turbodiesel?

not sure of the mileage, and I do think the rest is correct.

Get a hold of a infra-red thermal gun, and while the engine is running point it at the runners on the exhaust manifolds for each of the cylinders.

If you find a cold runner on the manifold that cylinder isn’t firing.

Tester

the truck is a 2003 2500hd 6.6l turbo duramax with 88000. I have never heard of a infra-red thermal gun, but will try to locate one.

Check your auto parts store. They may have one to loan. You have to give them your credit card # as a deposit, but they will delete the charge when you return the heat gun. Places like Advance Auto and Auto Zone have this service. I’m sure others do too.

you’re looking for something like this.

Make sure it has range of up to 1200 degrees.

Tester

Could be a blown head gasket.

I just wanted to follow up with this. I talked to my brother-in-law recently who said he got his truck fixed. Turned out the fuel filter was full of water, and after installing a new filter, the truck runs fine.