I have this 01 Diamante 3.5L with a p0300. no communication with pcm while engine running I can with engine off. runs fine with maf disconnected. all ignition components are new. need help. Not familiar with Mitsubishi any ideas worldwide be appreciated. Thank you

 

Test the maf, chances are it is causing the misfire due to it giving off the wrong readings.

Part 1 -The Basics of Testing a MAF Sensor.

 

Clearly the MAF here. I wouldn't bother testing it, just scoop one up at a junk yard.

 

Tried. Maf from autozone same results. Reason I tried one is because with maf unplugged it ran fine when swapped ith autozone maf it did the same. My boggle here is why can't I communicate with PCM when vehicle is running? When it is on koeo I can communicate.

 

You're not supposed to be able to communicate with the engine running, only with the key in the 'on' position.

Can you describe to me how the car runs with the MAF plugged in?

 

With autozone maf same as original one, ran fine at first then issue came back a short time while road tested the car. Car runs bad but with it unplugged it runs fine. Plenty of power. If I can not communicate with PCM with engine running that is a problem simple reason in MAssachusetts state to pass emission tests it checked with engine running to check for complete monitors.

 

With autozone maf same as original one, ran fine at first then issue came back a short time while road tested the car. Car runs bad but with it unplugged it runs fine. Plenty of power. If I can not communicate with PCM with engine running that is a problem simple reason in MAssachusetts state to pass emission tests it checked with engine running to check for complete monitors.

 

Your issue is a ground wire. Check the engine grounds, and the negative terminal in general. I was working on a car that came into the shop with that issue, and I could not figure out why the new MAF only worked for a minute. Then I started to play around with the ground wires, and realized the idiot didn't have one on the engine!

That piece of equipment is a twenty thousand dollar live streaming data logger. Your hand held code scanner is nothing in comparison.

 

Well grounds are good even at the DLC pins 4&5. My equipment is not a hand held code reader it's a 10 k piece of equipment.

 

Well, without being in front of the car that's the extent of the help I can offer.