Check your coil packs,sounds like you may have a couple bad ones.Hi all!
I'm still new to the Commander - I purchased mine as a project two weeks ago, and it's running rough. I have a 2006 Commander with the 4.7 V8 and QTII. 189,000 miles.
I have a code reader, and was getting a P0300 (random misfire), and bad O2 sensor codes for 3 of the 4 sensors. Here's what I've done to try to diagnose the issues.
Through trial and error, I found out that cylinders 1 and 7 (front and rear cylinders on the driver's side) are not contributing to the engine running. I pulled the power wire going to the ignition coil on plug, and got no change in RPM at engine idle.
I swapped the ignition coils with cylinders 3 and 5, which were running good.. No change.
Did a compression test on cylinders 1,3,5 and 7 (120 PSI, 135 PSI,135 PSI,120 PSI) This is only a 12% difference in cylinder compression. Based on a compression ration of 9.0:1, the actual compression spec in the manual should be 132.26 PSI, so I'm guessing mu gauge isn't perfect, but it's close enough.
I replaced all 8 spark plugs - 1 and 7 were very black/sooty. The rest looked good.
I did a fuel pressure test - 59 PSI at the fuel Rail, which is exactly what he manual calls for.
Checked and cleaned fuel injectors on 1 and 7 - no change.
Swapped 1 and 3 injectors and 5 and 7 injectors - no change.
Checked for vacuum leaks - no leaks, and there is 13-14 in Hg at the throttle body while idling.
Sprayed carb cleaner around the heads at the base of the intake to see if there was any intake leaks - no leaks found.
Checked MAP sensor readings against actual vacuum gauge reading - good.
I have removed the injectors and put an endoscope camera into the injector hole to see if the intake valves are opening - they are all opening.
I have also checked for voltage at the fuel injectors at cylinders 1 and 7 with a NOID light tester set - the light lit up, so I'm assuming the voltage is good.
I have also cleaned the battery terminals and ground lugs that attach to the body and engine.
Short of a timing issue on just those two cylinders, I can't figure out what I'm missing. Anyone run across a similar issue, or does anyone have an idea of what I should try next?
Thanks for reading and thanks for any advice!