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Discussion Starter #1
I bought an 04 impala ss back in October. It was not running. Blown head gasket and the owner had everything torn apart. So I pulled the engine. Sent the head to the machine shop. They came back good according to them. I put it all back together and installed it into the car.
It started right up. But idled rough, once it warmed up the rpms got worse and would shut off. On restart the rpm jumped from around 1200 to 400 until it shut off again.
When I installed the engine I put New spark plugs, new wires, new air filter, new fuel filter. After I got the p0300 code I put a new fuel pump swapped ICM and coils off of a known working car. I also swapped the cat, MAF, IAC and fuel injectors with rail. There is no vacuum leaks. I just installed a pcm from zzp no luck. O2 seems to be working its fluctuating like normal.
I hooked up hp tuner to it and could see all cylinders are misfiring. The o2 is fluctuating like it is supposed too. The only code I get is p0300.

Misfire history
#1 1346
#2 59
#3 4504
#4 108
#5 58
#6 335

This was the highest misfire count I read. Other attempts where in the 300 to 500 hundred range.
 

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Did you do a compression check on all cylinders after putting the head on? Guessing it was the front? Usually good to do both when something caused them to leak originally (overheating, overboost, improper install, etc.).

Sounds like you've chased alot of things and spent money before fully diagnosing it.
 

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Discussion Starter #3
My next day off monday. I'll do a compression check and fuel pressure check. And any other suggestions anyone has. As for parts didn't really cost me anything. I got a 2005 monte carlo ss supercharged and a extra l67and transmission sitting so I have a few parts around. Thanks for the input
 

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Discussion Starter #4
I just did a compression check on the front 3 cylinders.
#1 160 psi
#3 185 psi
#5 160 psi
I will try to get to the back 3 when I get some time but at this point I don't really think I need to. Since the cylinders with the most misfires was on the front 3. Im also reading on other threads on this forum that I should see between 140-160 psi and that anything lower than 100 is bad. Based on that I dont think my #s are bad. If I had a bad MAP sensor I would have a DTC set right? Im asking because I did notice a difference between the stock boost gauge on my monte to impala and when I rev the monte the boost gage to move half way up and the impala only goes a 1/4 of the way up?

Thank again for any advise
 

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Those gauges are poorly calibrated "fun meters" while the actual data is the raw reading from your MAP sensor (in kPa) and a reliable vac/boost gauge like AutoMeter, etc. The dash displays interpret the MAP signal with varying methods for different 3800SC cars, but it's not a go-to tuning or troubleshooting reference.

Anywho, I'd check over your work and see what else might have been the culprit. A) blown head gaskets aren't usually an issue, LIM gaskets have been known for 25yrs now to be a primary issue, and they get misdiagnosed by shops for causing similar symptoms. B) you dug into the entire engine to do this work, and basically touched everything, which now introduced a laundry list of possibilities that you need to check off.
 
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