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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29430
Experience:  GM Grand Master Technician 2007. 14 year experience.
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Gmc 2500hd Diesel: I have a 2004.5 GMC 2500hd diesel with 163,000

Customer Question

I have a 2004.5 GMC 2500hd diesel with 163,000 miles. When I'm sitting at a stop light, after driving on a bumpy road, my truck starts loping and blowing blue smoke. This only happens when the truck is at a complete stop. When I put it in neutral or park at this stop, it quits . The loping and blue smoke doesn't happen at a stop if I'm driving a smooth road. It's shaking something, but I've had it hooked up to a diagnostic machine 4 times, and it's not throwing any codes. Any ideas?
Submitted: 1 year ago.
Category: GMC
Expert:  Gm Tech (Cam) replied 1 year ago.
Hello, I'm Cam.
Can I get your first name please?
Sorry to hear about this issue. MY initial thought is an injector, but lets explore this further. To start with, do you still have the scanner?
Also what is the vin?
Customer: replied 1 year ago.
Hi there - I'm Marvin.
The truck is actually a 2004.5 with the LLY engine.
I don't have the scanner. And I''ve had all injectors checked while idle and while actually driving around with a mechanic.
VIN #1GTHK29234E336618
Expert:  Gm Tech (Cam) replied 1 year ago.
Okay Marvin, I'm not surprised that it didn't set any codes, however I still believe it to be an injector. Specifically I believe it to be nozzle issue. What will need to be performed as the following. when the issue is happening, we need to use the scantool in order to disable the injectors one at a time which is doing an injector balance test. Basically the injector that you disable that stops the smoking or has the least impact on the Poor running of the engine when it's happening will be the injected to replace. It's possible that more than one injector is bad, but I don't believe it's more than two or three. Again, I am 100% confident this is an injector issue.
Customer: replied 1 year ago.
Since I've already done this, and it only happens on bumpy roads, I've been told it can be electrical. But don't know what to be looking for if it is. What would be your advice for that?
Expert:  Gm Tech (Cam) replied 1 year ago.
OK, so without codes that does make it more difficult. The electrical control of the system is rather sensitive and will pick up faults quickly. I do want to ask if you did the test WHILE it was happening.
There are a couple things to check.
First the wiring that comes out of the fuel module, it attaches to the top of the module on a bracket. That wiring is known to chaff on the bracket and can cause issues.
Second are the connector to the injectors. Unplug each in turn and see if there is a gold or copper dust on the end that goes into each injector. There should not be. Each should be perfectly black and clean. I suspect you may find the front drivers side and rear passengers side to have this dust.
Check this out next and let me know what you find.