03 2500HD 8.1 misfiring

marr-ta · May 31, 2006

Hey everyone. I am looking for possible explainations for my trucks misfirings. I just bought it about a month ago from a local dealer g-r-e-e-n-b-r-i-e-r d-o-d-g-e. I put that in there so you guys can avoid them if you live in the Tidewater VA area . I wont go into the details on how bad the experience was but if you are thinking about dealing with them and want me to elaborate then pm me.

Anyways, the truck has an intermittent misfiring issue. When it is doing this I can go to WOT and it doesnt miss a beat so I believe it is a sensor. I've seen other posts concerning the CAM or Crank sensors causing trucks to just die and have to be restarted but that hasnt happened to me. I have seen the battery light flash when it happens and I have seen the check engine light flash as well when this happens but according to the above dealership there were no codes stored. Would those 2 sensors cause a code to be stored or keep the CEL to remain on? The truck has a bit over 80k on it and I plan on changing the plugs and fuel filter this week but with it not misfiring at WOT I dont think these 2 items are the problems. Thanks...

Supercop8100 · May 31, 2006

Cracked ignition coil grounding out at low RPM's.

k3500CC8.1 · May 31, 2006

Cracked ignition coil grounding out at low RPM's.

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My 2001 8100 had the same problem at around 75K miles. Had to replace the #4 coil.

marr-ta · May 31, 2006

Cracked ignition coil grounding out at low RPM's.

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My 2001 8100 had the same problem at around 75K miles. Had to replace the #4 coil.

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Thanks for the replies. When I'm changing the plugs I will check them out.

Supercop8100 · June 1, 2006

Beter do some good checking, most of the time you cant physically see the crack....

marr-ta · June 1, 2006

I havent done a plug change on this engine yet. Are the coils on the plugs? If I dont see anything noticable I may just bring it in to GMC service and have them check over the ignition system.

Draenor · June 1, 2006

Are the coils on the plugs?
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Yup, Four mounted each side on the valve covers.

Supercop8100 · June 1, 2006

I guess it could maybe possibly be a bad wire, but im betting on the coil.

marr-ta · June 3, 2006

Well I went to the dealer to get some parts today and it was acting up. I dropped it off with service and waited for it and of course it was running perfect when they looked at it and when I drove it off. Anyway, the service adviser said they checked for stored codes, checked out the wires, plugs and coils and couldnt find anything. So I am at sqaure one again. I did an oil change, changed the air, oil and fuel filters today. I plan on changing the plugs tomorrow and will post follow ups until its fixed.

Steady Eddie · June 4, 2006

Now you're not going to believe this, but follow along....

Your problem could be either bad battery cables, or connections,

or a "sometimes" shorted battery cell..if you have another

available 12v battery with the right posts, swap it into

your truck.

Do this FIRST, it is free...

The PCM will flash a SES/MIL

light at a lower-than-OEM battery voltage and the battery light

will flash (come on) during a split second of a short circuit.

I think to run, misfire free, your 8.1 L needs 10.5 volts DC bare minimum.

Also, (on edit) If you are not losing the voltage on the power side,

you could very well be losing it on the ground side. Which means you'll

have to start checking grounds beginning with the negative post to cable,

cable to chassis ground, etc.

marr-ta · June 6, 2006

Now you're not going to believe this, but follow along....

Your problem could be either bad battery cables, or connections,

or a "sometimes" shorted battery cell..if you have another

available 12v battery with the right posts, swap it into

your truck.

Do this FIRST, it is free...

The PCM will flash a SES/MIL

light at a lower-than-OEM battery voltage and the battery light

will flash (come on) during a split second of a short circuit.

I think to run, misfire free, your 8.1 L needs 10.5 volts DC bare minimum.

Also, (on edit) If you are not losing the voltage on the power side,

you could very well be losing it on the ground side. Which means you'll

have to start checking grounds beginning with the negative post to cable,

cable to chassis ground, etc.

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Actually, I had another truck that had a bad battery cell and it ran like crap so I'd buy that. But I had the battery load tested already and it was fine. I think the problem is solved Last weekend I was changing some fluids and swapped the fuel filter and I was checking out how hard the plugs would be to change and found a connector on one of the plugs not totally secure. I went on a 180 mile trip on Sunday and the truck didnt miss a beat. So I dont know for sure if the fuel filter or if the connection was loose enough to cause the issue. Thanks for all your input...

Steady Eddie · June 6, 2006

Actually, I had another truck that had a bad battery cell and it ran like crap so I'd buy that. But I had the battery load tested already and it was fine. I think the problem is solved Last weekend I was changing some fluids and swapped the fuel filter and I was checking out how hard the plugs would be to change and found a connector on one of the plugs not totally secure. I went on a 180 mile trip on Sunday and the truck didnt miss a beat. So I dont know for sure if the fuel filter or if the connection was loose enough to cause the issue. Thanks for all your input...

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I am glad you have solved your problems. Could have been a combo of both

issues....