I would like your opinion, if you can help. I have a 2003 Mitsubishi Montero Sport es. And I had a mechanic replace my timing belt, water pump, spark plugs&wires,and front cam seal. He leaned on my camshaft sensor and damaged it. He replaced it but my service engine light has been on since Ive gotten it back with P300. I had 2 shops and dealer after replacing several parts say it was the ECM because the codes kept changing and they said was giving false codes. Replaced the ecm but the engine light came on again after a day with P300. At a loss, do you have any ideas? The dealer is saying that the car does not do well with aftermarket parts and said it could be my mass flow sensor, or alternator since they are not mitsubishi parts. I need something more definate than that.

 

It is true that Mitsubishi's do not like generic parts. However, if your vehicle ran fine and without issues and codes prior to timing belt change, I'd suspect that problem originates from that, rather than from the aftermarket parts. My primary suspects would be - 1. defective camshaft sensor (even a new sensor can be defective); or 2. timing being off. You can be off on timing by one tooth on ether of the banks, and you will not see a difference in driveability. However, you'll have misfires.

 

Hunter - regarding the "one tooth off on timing belt theory" any idea what measured impact the one tooth off has on compression? If you recall, I am still chasing a P0306 cylinder 6 misfire on my 2002 3.5L after rebuild. My compression test results are:

1 - 150 psi
2 - 175 psi
3 - 175 psi
4 - 170 psi
5 - 175 psi
6 - 100 psi misfire

The one tooth off theory to me would indicate that all cylinders on the affected bank would be adversely affected. In my case, the drivers side or left bank 2, 4, 6. However, in my case cylinders 2 and 4 tested fine. Specs are 171 psi standard, 127 psi minimum with 14 psi max spread.

 

I have to say i do not know the effect of one tooth miss-timing on the compression would be. Logic would suggest that all cylinders on one bank would be somewhat lower. Thinking back when I made that error with timing myself, I believe I had misfire reported on one cylinder (no 5) only. It's likely that 1, 3 and 5 were misfiring and could be at about the same rate, but it is possible that when one cylinder reached the "critical" number of misfires, it triggered a code and that's what is stored in the PCM?

I'm puzzled by the misfire you are dealing with. I doubt you have a tooth skip, since you timed the engine on the stand - much easier view of the timing marks without parallax error. Remind me - did you try the spark plug swap with another cylinder? Same goes for the coil pack swap to eliminate ignition as a source of misfire.

Also, does your compression reading improve if you add a little oil to the cylinder #6?

 

I swapped the plug wire locations on 3/6 with no effect. I then installed a new 3/6 coil with no effect. I then removed the plenum for compression testing, installed a new spark plug in cylinder 6 (removed plug was sooted) after the compression test, and installed a remanufactured injector for cylinder 6 all to no effect. I did squire some oil in the cylinder during the compression testing with no effect so pretty certain its the valves and/or valve timing. I did lap the valves while the engine was apart.

Many engines run just fine on 100 psi cranking pressure, so surprised of the miss. Yes cylinder 6 is lower than the rest and below spec.

 

You are right - if you have same low (100 psi) compression with and without oil, you have some sort of issue with the valves. Would be helpful to run a leak down test on #6. It might help to determine if it is an intake or exhaust valve. It has to be a serious valve malfunction if you are getting sooted spark plug and a severe misfire. I wish I could be more helpful Are you up to pulling off the valve cover to see if something obvious jumps out at you?

 

At the moment we are just driving it as is, once slightly off idle, runs like a dream.

Pulling the valve cover means pulling the plenum, new gasket, etc. Not sure I'm up to that task at present. When I was doing the compression test, I tried to get cylinder 6 at TDC firing and pressurize the cylinder to see if it was exhaust valves or intake but was having great difficulty finding TDC as the damper is not marked for each cylinder.

 

I had the tming belt checked, compression test, lil Oil on the spark plugs. Valve cove gasket is leaking. Service engine light Comes on when I hit 60mph misfire 0
P300

 

Are you able to see the freeze frame data from the P0300?