Hi everyone. I'm new to the Z33 world, but not new to Nissan. I've been a B13 guy for a long time.
Anyhow I just wanted to share my story as I was not able to find useful information on the issue I was trying to resolve. I figure what I went through can help somebody in the future.
I purchased an 03 Enthusiast 6MT about a year ago. The car is a fixer upper. The major problem being that the engine was not working well. Long story short my problems were due to a bad ECM.
-The car ran rich you could smell it
-Pressing the throttle heavily would result in a stall and also some misfire
-Misfire codes P0300, P0304, P0305
-02 Heater Codes P0032, P0037
Things that I tried and checked for troubleshooting:
-New 02 Sensors (The P0032, P0037 codes did not go away)
-I replaced the Camshaft Position Sensors and Crankshaft position sensors with some junkyard spares (This did not do anything)
-New Coil packs ( Initially I bought a single spare coil pack for Cylinder 4 due to the P0304. It did nothing. I later bit the bullet and bought 6 brand new coil packs. The new coil packs did not fix the misfire)
-Removed the front 02 sensors. ( I did this to check for clogged cats. The cats were not clogged. This did nothing)
-Replaced injector harness and knock sensor with a junkyard spare from a G35 sedan ( I found a mouse nest under the intake manifold. I thought maybe the mice had messed with some wiring. This did not fix anything)
-Cleaned the fuel injectors that came with the car ( I decided to send out the injectors to Deatschwerks for cleaning. The injectors were fine no major difference from before to after. This did nothing)
-Replaced original injectors with junkyard spares. (After installing the cleaned original injectors my misfire codes went from P0300/P0304 to P0300/P0305. I thought maybe despite cleaning one of my original injectors was still probably screwed up. Use of the junkyard injectors did not fix the issue.)
-Cleaned the MAF that came with the car. (This did nothing)
-Swapped my MAF with a known good MAF. (I swapped the MAF from my 2.5L Frontier that was known good. This made no change)
-Checked fuel pressure going into the rail. (My fuel pressure was ok within the range specified in the service manual.)
-Checked wiring between ECM, coils, 02 sensors and fuel injectors. (I used the service manual a multimeter, and a logic light to check for continuity, resistance, correct voltage, shorts to ground, and shorts to power. Everything checked out OK. Visually and with instruments my wiring between ECM and engine checked out.)
-Sensor Checks with Multimeter. ( I checked my important engine control sensors with a multimeter. They checked out OK according to service manual specs.)
-Replaced Coolant Temp Sensor. (I replaced the coolant temp sensor because during my troubleshooting I noticed that if I would feather the throttle I could get the car to not misfire. Eventually when the engine was warm enough it would idle well. I thought maybe the misfire might be temperature related so I replaced the temp sensor with a junkyard spare. This did nothing)
-Compression Check. (I ran a compression check cold and warm. Compression numbers during the warm check were in spec. My cylinder compression checked out)
-Leakdown CHeck. (I ran a leak down and it came back ok. No serious drops in PSI. No air bubbles visible in the coolant)
-Vacuum Gauge CHeck. (I connected a vacuum gauge to my intake manifold during idle. The vacuum was where it should have been. No signs of valve problems, bad rings, clogged cat, or blown headgasket)
-Throttle Pedal Released Learning, Throttle Body Closed Position Relearn, Idle Air Volume Learning. ( I tried these out but they did nothing to fix my misfire and poor idle)
-Replaced ECM. (This was my last step. I didn't go here from the start because ECMs usually don't go bad. I replaced my ECM with an ebay spare. This finally fixed my misfire and poor idle. The engine runs great now
-I learned that if I started the car while holding the throttle in a feathering position I could get it to stay at 2k rpm. This allowed me to warm up the car. Once warmed up it held idle on its own. Also on many occasions the misfire went away once warmed up. I would be able to apply heavy throttle with no misfire. I'd come back the next day after the car sat overnight and the poor idle and misfire would return.
-Being able to warm up the car and have it idle was very useful. Compression and leak down tests are best when done on a warm engine. Vacuum gauge and fuel pressure checks are easier to interpret with a good idle.