If it's not really about tuning or wiring. Then it belongs in here.
Have a friend's 350z I'm trying to help fix - the car is running really rough (missing) and really down on power.
You can hear it "missing" on idle, it's kind of inconsistent as sometimes it would start perfectly fine but that is getting rarer. When you accelerate while in neutral it seems to rev out ok and sound normal but when driving and having the motor under any load it will missfire and just run really poorly. It will kind of "jump" through the rpm range, if you went WOT instead of a nice smooth quick response up to redline it will kind of hesitate then jump a few around.
Things I have tried;
Spark plugs are not that old - all look good colour wise.
Tested resistance on coil pack pins - all seemed very close to each other, not sure if this is a way to 100% rule out faulty coil packs though?
Unplugged coil packs while running - instantly begins misfiring heavily.
MAF looks clean.
compression test results were excellent
Not really sure where to go from here, it's not throwing any obd codes being an Aussie model apparently the obd is not 100% implemented like the overseas models.
Kind of leaning towards a intake leak somewhere but have checked all the hoses and have not found anything, unless there are some hidden ones?
Can hear an air suction type noise right near the PCV- is this normal?
Honestly kind of stumped - Thinking it's a bad sensor or vac leak? I know the engine is healthy from a comp test and that would also indicate valve timing is good too, so thinking either coils/sensor/vac leak?
Hopefully someone has seen this before and can help :)
I would at least swap in crank and cam sensors to eliminate that. If it doesn't fix the problem, you should have spare ones anyway for this type of diagnosis.
Air should be getting passed through the PCV at idle, so some noise isn't unexpected, but you could try cleaning it with some carb' cleaner.
Might be a good idea to double check grounds and connections - if there's a problem it may be worsened by the engine rocking at rough idle.
I agree with you David, but I hardly work on these cars and am really only doing this as a chop out for a mate, find it hard to justify the expense of $300 on potentially dead money.
Cleaned out the PCV hasn't made any difference, grounds all look good - my friend did report that it did throw a engine lean condition code at one stage while he was driving as it missfired really badly.
From the color of all the spark plugs I had seen, i am almost suspecting it is a cam or crank related sensor causing the car to have poor ignition timing - do you think this would be a plausible theory ?
I am assuming the car wouldn't run with a bad Crank angle sensor ? Possibly one cam sensor?
The way to avoid throwing parts at it, is to get the correct diagnostic equipment. So find someone with a Picoscope that can connect to the cam/crank sensors and recreate the problem. That will tell you if they are the problem. Next look at the coils. Again, an oscilloscope can diagnose a bad coil but you have to know what you're looking at. MAF, Injectors, and on down the line.
I have very little experience on engine troubleshooting, so the quality of my advice is questionable, but at this point I would consider testing the fuel pressure.
The logic is as follows: we assume that air, ignition, compression, timing are ok, because there are no air leaks, coils are ok, compression is good, engine runs ok with no load. So it must be either bad fuel supply or bad data going to/from ecu. Its easier to check fuel pressure first.
Normally I would start from checking the trouble codes and in your case I find it quite strange than none showed up. At least I would expect seeing P0300.