I continue to set P0305 code-misfire on cylinder 5 on my 2006 Pontiac G6 GTP

Question

I just had major work completed trying to remedy this issue. Things completed:

Measured compression after seats and valves for cylinder 5 were ground-replaced all the gaskets and seals and changed the oil.
Replaced the oil pressure switch-based on pressure test.
Engine tested 130 PSI at cranking
Swapped plugs, wires, coil towers on 2&5 and then also replaced the entire system.
Fuel injector balance test 47-35 psi on all cylinders
Swapped injectors on cylinder 5 & 6
Installed new injector harness
Leak down test and no leak when comparing to cylinder 3
Called tech assistance-advised to look at voltage drop across injector control wires on shared B+. Eliminated fuse block and harness, ran B+ directly to injector harness and all tested good.
Swapped injector control wires on 4&5 and 5&6 no change
Installed new ECM
Installed new Cam phaser solenoid
Checked for vacuum leaks both external and internal and found nothing.

What am I missing.... this was a ton of work that took over a month and I still have a slight rough idle on low RPM's (not driving) and it is setting this code.

Answer 1

Leak down test is the best test, especially after a valve and set, a compression test does not really help only if the problem is obvious. A leak down test is the best test to perfrom

Comments

Reynaldo-I apologize...I missed that in my list of things that have been tried.  The leak down test was also performed and it didn't show anything out of normal.  Still trying to understand what is missing....could it be the MAF sensor?  Silly I know...but I am grasping

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This type of engine has a Map sensor and uses a MAF, the engine can be confusing , this engine is more a speed density, right where the MAP sensor is at check to see if it has separated. And by the way it would be the MAP at idle it uses the MAP

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Reynaldo-I checked the MAP sensor-it seemed fine.  However I purchased a new one-replaced it-and it actually made the car run horrible.  The shifting became very hard and it didn't idle quite right.  I put the old sensor back on-and all of that went away.  With that said-the P305 code on cylinder 5 came right back the next day?  Could I have had a bad MAP sensor?  It was new out of the box....but it was definitely new old stock!

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If the MAP sensor fails on this vehicle it set a throttle body code and a MAF sensor code, A TPS and a MAF sensor are not suppose to set together , if the MAF sensor fails the TPS is used by the ECM and vice versa. So if there was a faulty MAP sensor you would not necessarily set a MAP code. but a TPS and a MAF going out of frequency, and the engine would not even be able to accelerate or maintain a idle. The MAP sensor that even if new could be faulty. If the MAP sensor does not resolve the problem your best be to determine the direction is either with a running compression test in comparison with another known good cylinder. being above 65 psi is sufficient , (75 is the magic number) lower than that its mechanical. Its not bad to rule out exhaust back pressure , these are known vehicle to plug catalytic convertors you can remove the 02 sensor but leave it connected and hanging in a safe manner on both banks. Being a GM vehicle it also good to realize that even if the ECM identifies number 5 as the cylinder misfire, it can be its companion cylinder which is cylinder 2, There are cases when a cylinder that is misfiring and the ECM identified it ,  and according to a ignition analyzer the problem was the companion cylinder these happens. it worth looking into cylinder 2