Car is a 93 Skyline GT-R, only modification I know of is high-flow cat (I know it's not clogged, I checked) and cat-back exhaust. It had a Mine's ECU, that I didn't know about until a few days ago, but I have since traded it for a stock ECU. Has ran fine the almost 3 years I've owned it until this problem arose.
Symptoms:
Sounds like a bi-plane
Idle is a bit rough, can feel the car shaking a bit when sitting at idle, but stays fairly stead at 900-1000 rpm
Vacuum gets less (think it's usually at 500 steady and usually goes to 475 when problem occurs)
No engine/cat temp light, but it does come on when turning they key forward to ign position before starting, so I know the bulb works
Happens around 5-20 minutes of driving, well after it's up to operating temp for certain
Smells rich, saw smoke once, looked grey but couldn't tell; sometimes when I get out of the car I smell like unburnt fuel even!
Fuel mileage is horrible
Nissan Data Scan hooked up shows rear O2 not really oscillating, which leads me to believe this is the problem OR part of the problem
Diagnosing done:
Plugs are brand new OEM spec
Coils cleaned and ohmed out per FSM
New OEM coil harness
Tried to do homemade smoke tester, may try again but what little bit it worked I saw no smoke, so hopefully no vacuum leaks. Looked around for obvious torn gaskets or bad vacuum lines and saw nothing
Battery voltage fluctuates between 13.7-14.1V
MAF's look to be equal in their readings on Data scan, were a bit dirty so I cleaned them lightly
Boost or no boost seems, to have no affect on if the problem will arise. And I made sure to not go into boost at all when I left from work one day and steadily taking the rpm's up to 3-3500 in each gear, once the problem started to happen, it was almost like it was hitting fuel cut.
One morning I left my house at approximately 6:29am and the problem didn't arise until almost 6:49am on the dot.
Leaving work, I don't recall exact time (around 4:30pm), but the car sat all day without being started, so roughly 9 hours. I left work and got maybe 5-7 minutes away from work and it acted up. So time doesn't seem to be much of a factor either but it seems the longer it sits, the longer it'll go before the problem occurs.
I have a few logs, not sure how to post them up, does the board have a feature to allow NDS logs to be uploaded? Or do I need to record a video of it and do it that way?
Someone was saying that it's probably not the O2, it's a misfire making the O2 signal look flat and could I post the voltages up, but I don't know how to even get the software to show as voltages, only readings from 0-100.
Thank you for any help!
