Hey guys I'm new to the forum and look forward to some help. I have a 2004 srx 4.6 I bought for the wife and it had a hard misfire cylinder 7. I through new oem plugs in and full set of coils and fuel filter. Cleaned throttle body. I noticed a slight skip at idle. Very little shake but it was there. Under heavy load at about 4500rpm it through a p0300 and a p0303. Here's the weird part. The pcm disabled that cylinder 3 completely. Until I shut it off and restarted it and then it was back on. I thought maybe vac leak so I did intake gaskets.i noticed some intake seats on the head had been replaced. Im assuking timing chain had broke. But not sure where to go with this. Compression tests were all good at 122 within 10% I checked fuel pressure at idle and it was 50. My tester isn't long enough to check it under load and still wouldn't explain the m issue at idle. Any input be great

 

It maybe that the PCM has failed and is dropping #3. When car is restarted PCM is reset. The PCM should only disable cylinders when traction control is active.

 

I'd be curious on the random misfire also. I do see that it could be a failing driver in the pcm. I just did a wot pull and at 4500rpm it stopped accelerating for a second and then started skipping as if fuel pressure faded off. I'm gonna make a way to lengthen my gauge and read fuel pressure during wot. But that still doesn't explain the slights shake at idle. Ty for the quick response also

 

If the fuel pressure falls out there would a lean code(s) set since the engine doesn't stall. Old R12 hoses work for to lengthen fuel gauge. Do you have a scanner to read PCM data?

 

nothing like a tech 2 scanner or anything just a code reader. I can watch long and short term fuel pressures and some others pids though. Injectors is another thought but that would also show lean. It drives great except on a short hard pull or like long steep hill on Highway woth and extended light pull.

 

It would be worthwhile to get a OBD2 scanner some are inexpensive. They won't do all a tech2 will do but they will do enough. With OBD2 EPA had it so manufacturers had to run the data stream so a generic scanner would read all the basic parameters.

 

I can watch quite a few different pids on my bluedriver but misfire count isn't one of em. I'll watch the 02s in the am and fuel trims. And check vac at idle also. Hopefully after that and fuel pressure it's narrowed down. I kinda wondered about fuel being aerated a little because when I drained it it seemed bubbly. Unlikely though since it's all pressure from pump up

 

You could add 5-8 gallons of fuel and see if it corrects condition.

 

just filled it with high test. I drove car a few days and only noticed a light misfire until a trip on Highway last night and long uphill climb it decided to stop firing number 3 cyclinder

 

so I noticed while sitting waiting for wife that it had that slight shake at idle and if I short stocked the brake pedal and kept pumping it to dump off some va*** the shake went away. And when I stopped idle would drop to 400 and then spring back up