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2015 GMC 2500HD misfires only at idle

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Old 03-12-2021, 12:23 PM
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Default 2015 GMC 2500HD misfires only at idle

So I took my truck in for a misfire code and was talked into basically rebuilding the whole top end, i.e. lifters, cam, oil pump, water pump, head/intake gaskets, plugs, etc.. He did show me the plug that came out of #2 and it was shot, after I'd only had maybe 15k mi on iridium plugs. Just got the truck back and its running rough at idle after the engine warms up. The engine will drop to around 500RPM and just barely stay running. Took the truck back to the mechanic who says got a consist misfire of #2 (had it hooked up to a scan tool). He says he did a compression check and # 2 has low compression and now needs a new block! If you give the truck gas it never hesitates and doesn't seem to misfire when driving (have go 80mph+ with no hesitation) Seems to me if the truck has low compression it should have a steady misfire from the start? Any thoughts? Ideas? I'm not ready to drop a new engine in this thing!
Thanks for the advice!
Old 03-13-2021, 01:21 AM
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It sounds like the mechanic didn't diagnose properly before suggesting rebuilding the whole top end.

What are the compression numbers?

How was compression tested?

How many miles on the car?

How many miles have you owned it?
Old 03-13-2021, 08:46 AM
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Originally Posted by CathedralCub
It sounds like the mechanic didn't diagnose properly before suggesting rebuilding the whole top end.

What are the compression numbers?

How was compression tested?

How many miles on the car?

How many miles have you owned it?
you're correct the mechanic assumed it was lifters? And the VVT causing timing issues causing the misfires. He didn't do a compression test until after it was completely rebuilt and I returned with it continued misfires.
The mechanic just said #2 had no compression. He added oil to the cylinder and the compression came up. So he thinks stuck rings. I'm doing a compression test on it today.
the truck has 145k. It only misfires at idle. Seems like rings would cause issues all the time
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