I have a Mazda CX-9 SUV 2008, 3.7L engine version - just turned 300,000 KM. The CEL come on recently and the code pointed to the VVT solenoid on bank 2. There was also a misfire on Cylinder 2. I Ohm test both VVT solenoids and the one on bank 2 was 14.1 Ohms, so almost at max of spec; bank one was around 7, well in spec. Resetting CEL, it came back, same codes.
To replace, I had to remove the valve cover, etc. Did this, no longer have CEL for VVT solenoid. However there is still a slight misfire - never stalls, and CEL comes back on misfire Cyl 2. Assuming the misfire resulted in an advancement request, which the ailing VVT could not fulfill... or two things happened to break at once.
Removed the Plenum again to get a Cyl 2 coil and swapped with Cyl 6. Few days later, CEL back on, misfire Cyl 2. So coil is okay.
So I am left with injector, plugs or compression. Now the question. All the examples I find for checking injectors involve the vehicle running and back probing injectors, etc. I cannot do this though, because this Cyl 2 is right at the back of the engine directly under the Plenum. When I remove Plenum, I can access, however can I then perform compression test and/or injector testing? With the Plenum off there are obviously large gaping opening in the top of the head.
I guess the low hanging fruit is just to pull the plugs and check gaps and condition, especially on Cyl 2.
Any advice of diagnosing Injector versus Compression versus Spark plug with the plenum removed?