Multiple Misfire Cylinder 1 and 6 2000 GMC Sierra

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Lenny

Multiple Misfire Cylinder 1 and 6 2000 GMC Sierra

Unread post by Lenny » Wed Feb 20, 2013 9:22 am

My 2000 GMC Seirra C-1500 with 5.3L engine is tripping a code 0300, random multiple misfires. When I checked the data with a Mac Mentor, I found that cyl 1 & 6 are the cylinders are misfiring. I have had the injectors cleaned, replaced spark plugs and wires, cleaned the throttle body, and have swapped the coil pack from cyl 1 with cyl 3, and still show that cyl 1 & 6 are misfiring. I think that the crankshaft position sensor might be the culprit, since the firing of these 2 cylinders is 180 degrees apart from each other, but am not sure. What else do these 2 cylinders have with a common link? What do you think is my problem? This has been happening for about the past 3 or 4 months and getting progressively more frequent.

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ProTech
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Re: Multiple Misfire Cylinder 1 and 6 2000 GMC Sierra

Unread post by ProTech » Wed Feb 20, 2013 6:24 pm

Are they misfiring constantly, like a dead hole? Or does it only happen at start up and get better as the truck warms up? I really doubt the crank sensor is bad, because if it was, the truck wouldn't run at all. You could be experiencing a vacuum leak at the intake gaskets, as that's a very common problem on the 5.3 engines, and will cause a misfire. It does usually clear up a bit once the truck is warm, that's why I asked.

Otherwise, since the plugs and wires are new, and you swapped coils...that only leaves an injector problem, or a mechanical issue (like a broken valve spring, or bad lifter). One other thing to check is the fuel pressure regulator for leaks. I've seen leaking fuel pressure regulators cause weird misfires as well. You can remove the vacuum line from the regulator when the truck is warm and look for any fuel discharge, that would tell you it's bad.
GM Dealer Technician For 18+ Years
In the automotive industry for 20+

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