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2003 2500HD Misfire

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Hey guys have been battling this truck for a wile now and I'm kinda out of ideas and I don't want to keep throwing money at it so i figured maybe someone here could help.

The truck is a 2003 GMC Sierra 2500Hd 6.0 Gas motor with 189,000 on it.

It has a intermittent misfire the only codes i pull are a U1000 and a code for the bank 1 sensor 1 02 i have replaced that sensor a few times and it always comes back to misfiring. I guess it is possible that the sensors are bad out of the box but i dont seem to think so.


I have replaced Fuel pump and filter, Injector 2 and 7 I have access to the GM scan tool and they weren't firing right. also have replaced the fuel pressure regulator, plugs wires have checked all the coil packs.


The other thing the truck has done since i have owned it when the motor is warm and you turn it off and run in to the store or something and come back out and go to restart it its hard to start like it takes two trys or its a long time turning over. so i dont know if this is related or not.


I have 4 other of these same trucks have have never had as many problems as i have with this one truck.

Any input or ideas would be great thank you.


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  • 2 months later...

Your GM scanner will tell you history on misfires. If there are specific calendars that are missing significantly more than others, those would be the focus. It sounds like you have already done that and isolated cylinder 2 and 7? It's possible that it has a bad intake manifold gasket on those two cylinders (or more). What is the O2 code? It's possible that there is a lean condition on that bank causing the code from a vacuum leak. You can use carb cleaner to spray around the intake to see if there is any change in RPM.


It's also possible that there is low compression. If spark, fuel and air are all ok, that is the only thing left. There have been a few Ls motors that have had a lifter roller seize and take out a cam. It could be another mechanical issue also.

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Long crank hot restarts usually mean a injector is leaking fuel and "flooding" the motor.

Extra fuel is not a problem on a cold motor.

I went through that with my old '99 with the CFI spider setup.

Are you using OEM O2 sensors ? Aftermarket sensors have been know to cause strange issues. IE Bosch = junk .

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