Recently Purchased 6.0 Misfiring

[wvamatt]

This is my first post on the forums here as I just bought a 2003 Chevy Silverado 2500HD with the 6.0 engine. The truck has 206,000 miles on it. I bought the truck off of a friend of mine who is a fleet manager at an electrical contracting company, so this truck has primarily highway miles. The truck was recently worked on before I purchased it, and I have the receipts from the following work:

• Replace battery and alternator
• Replace PCM
• Replace brake lines

The truck is in surprisingly good shape, even with 200,000+ miles. A few days after purchasing the truck, I started getting a flashing CEL during driving. The flashing CEL goes away when I return to an idle, and sometimes will go away when I run the engine in the 3,000+ RPM range. I scanned the codes, and found two active codes:

• P0300 - Multiple misfires
• P1637 - Generator L-Terminal Circuit

Can anyone give me some insight on how to further diagnose the source of the problem. I've been searching the forums, and I plan to replace spark plugs and wires. What else should I be looking at or checking, and how can I check it?

[txab]

Common issue can be intake gasket leaks,

[Formulabruce]

Totally clean the whole throttle and plates with Throttle body cleaner, dont miss a thing, then get some MAF cleaner, and clean that, then try it after clearing codes, Then you may want to mist starting fluid near intake and test for a vacuum leak . Good luck

[dewfpo]

Totally clean the whole throttle and plates with Throttle body cleaner, dont miss a thing, then get some MAF cleaner, and clean that, then try it after clearing codes, Then you may want to mist starting fluid near intake and test for a vacuum leak . Good luck

 

I agree with Formulabruce. At this mileage, the intake and intake sensors are sure to be gummed up. Cleaning the throttle body and plate and IAT and MAF sensors may alleviate some of your symptoms.

 

DEWFPO

[wvamatt]

Thanks, guys. I will clean both the throttle body, the MAF, and will probably just go ahead and do the intake gasket since it is a known issue.

 

Should I do all of the above before looking into plugs, wires, coils, etc?

[gavhughes6.0]

I am having the exact same issue. Been trying to fix it,

[Formulabruce]

Intake is plastic ( no fuel) and can bend some, I would , and have done it on a few trucks, the simple stuff first, involves Cleaning. Coils and or wires last. Plugs? make SURE you use a COPPER Never seize on them. I recommend the Original type Irridium plug ( yes the more expensive 100K plug that retains its Gap)

[wvamatt]

Over the weekend, I cleaned MAF and throttle bottle, replaced plugs, wires, and intake manifold gasket. Still throwing the P0300. I did a little more poking around the forums here, and discovered that there is a crank relearn procedure that must be done after installing a new PCM. I called the guy I bought the truck off of, and he gave me the name of the garage that did the PCM install. I called them, and found out that they never did the crank relearn after replacing the PCM. I have an appointment tomorrow at 1:00 to have the crank relearn done. I'll report back tomorrow with results. Thanks for everyone's help and support. So glad to have the resource of this forum.

[Formulabruce]

Thanks for the update!! Good luck!

[Swimmer8366]

Having same problem with my 2002. Feel mine is top end damage.... but try the crank relearn first could solve your problems with the new computer being installed and the relearn not being done.... check your valve springs after they can break and find out what cylinder it is. These engines will read multiple misfire when it is really only one due to the trailing cylinder getting a bad misfire reading.

 

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[wvamatt]

Sorry for taking so long to get back on here, but I wanted to report that the crank re-learn DID solve my P0300 misfire issue! The relearn took less than 5 minutes on their Snap-On scanner. The scariest part of the process was when they had to hold WOT for what seemed like forever to get the relearn to take. 6,000 RPMs on these engines sure do sound intense.

 

Anyway, for anyone else out there who is getting this code, but the engine otherwise seems to be running fine, you may want to look into the crank re-learn. My truck has never run better.

[Raptordude]

That re-learn process seems ridiculous to me, I wish there were a better way to do it. My crank sensor went bad a year ago, I popped a new one in and did NOT re-learn it. 7,000 miles later, haven't had an issue

 

 

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