2007 Tahoe LTZ misfiring again.

mrfix71

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Similar issues from before https://www.tahoeforum.com/threads/07-tahoe-4-misfire.538923/
Truck starts great in the morning. When I restart later, the engine idles a bit rough but if I put her in gear she will start to misfire terribly and kick. She will die at stoplights or other inconvenient places.

Last year, took to a shop (I had no time available) who changed plugs, wires, and MAP sensor. Odd that I changed all that about a year before. But Big Blue ran great for several months. Last couple months the problem returned but I am not getting any codes from my economy scanner. Assuming OEM plugs & wires should last more than a year or so, I have tried other things like different gas stations and fuel additives. Replacing MAP sensor (warranty) felt much different but same symptoms remain.

Since there are no codes, what system is not monitored and would not detect a problem? My thought is fuel system with the filter being relatively clear after a long rest like overnight but restricted with debris after running a while? Gage read absolute Zero psi after trying several key, pressure bleed, and reconnecting. But she fired right up and had 60psi at idle. Will check fuel pressure again after running a while simulating daily commute.

* 60psi Fuel pressure after running approx 30 min, waiting 30 min, then restarting. Did not get the rough idle though.
 
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mrfix71

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Just tested the MAP sensor circuit. PCM voltage is 4.7v and drops as I apply vacuum to the sensor port. However, I am supposed to be getting 10-12v when testing the PCM ground but only get 9.4v.
 

PNW NBS Z71

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Just to be clear, there is no external fuel filter. It is part of the pump. I would attach a fuel pressure gauge to the rail and have a long enough hose that the gauge can be ran out the back of the hood and tape to w/s and do a cold start and drive and see what happens. I had a similar problem on my 05 Z71 and was the bank 1 sensor 1 O2 sensor but I replaced all 4 of them. I also had a CEL as well.
 
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