90 GSX
15+ Year Contributor
- 322
- 2
- Jun 24, 2004
-
Fremont,
California
What started out as an occasional power loss has turned into a really bad random stumble. I noticed my AIRT was acting kind of erratically and a couple days ago it started throwing code 13 (Intake air temp) on and off. When the code turned on, the temp on the logger went to -59.0*C. I automatically assumed the mas was bad so I got one from my friend that should have been good but was not verified, and it had the same intermittent data dropout except it was throwing code 12 (Mass air flow). I probed wire number 3 on the 2g harness which is the mass airflow signal voltage, and it was dropping out randomly to 5 volts (input voltage) and then returning to normal when the data returned on the datalogger.
I guess it's possible that I have 2 bad mas air sensors but I don't believe in coincidence and I don't like intermittent problems. I tried the harness wiggle, I tested the continuity of all of the mas wires to the ECU pins and they were all good.
The mas does not explain the stumble though because even when my logger says that the mas is reading normally (ie temp is in normal range compared to ambient and the mas hz are normal) it still stumbles hard but I do notice a misfire when the air temp reading jumpes around but it's different from the stumble. The stumble is very violent, and happens worse at high rpm and light throttle. It is completely random. The car also feels very sluggish at all rpm and load including wide open throttle at all times in addition to the misfire. It's not slow to the point that you can't move - the car drives well enough to get you to timbuck too, but your back will hurt after being jolted by those damn misfires. When you try to give it gas it moves like a fast honda rather than a fast DSM, I don't know how better to explain it. You can even hear it in the exhaust tone, it sounds like it's struggling to give me that honda power. I could post a log but it would be useless, all you would see is that occasionally the o2 voltage drops close to or all the way down to zero when the car stumbles (does that mean no gas was in the cylinder or that the spark didn't ignite it?). I'm stumped... I have checked and verified literally everything. This problem is insidious, it is random and it developed slowly over a period of weeks.
These are the things I have checked:
-Plugs (BR7ES gapped at .028 and verified, wires are brand new stock wires with separators, coil and power transistor came off of a well running car. I just replaced the well gaskets too as they leaked and killed my accel300+ wires)
-CAS came from a running car
-No boost leaks
-No short circuits (running an ammeter in series with the negative battery terminal, I got <0.01A with the car off).
-No grounding issues
-ECU - there is no visible damage and the caps are practically brand new
-Battery and alternator are brand new
-EPROM chip is good
-Compression is 180-185 across the board (2g pistons)
-Fuel pressure
-Fuel filter
The list can go on... I take very good care of the car. I don't know what else to look for... please help me, I will have to sell the car if I can't fix it I'm completely stumped.
I guess it's possible that I have 2 bad mas air sensors but I don't believe in coincidence and I don't like intermittent problems. I tried the harness wiggle, I tested the continuity of all of the mas wires to the ECU pins and they were all good.
The mas does not explain the stumble though because even when my logger says that the mas is reading normally (ie temp is in normal range compared to ambient and the mas hz are normal) it still stumbles hard but I do notice a misfire when the air temp reading jumpes around but it's different from the stumble. The stumble is very violent, and happens worse at high rpm and light throttle. It is completely random. The car also feels very sluggish at all rpm and load including wide open throttle at all times in addition to the misfire. It's not slow to the point that you can't move - the car drives well enough to get you to timbuck too, but your back will hurt after being jolted by those damn misfires. When you try to give it gas it moves like a fast honda rather than a fast DSM, I don't know how better to explain it. You can even hear it in the exhaust tone, it sounds like it's struggling to give me that honda power. I could post a log but it would be useless, all you would see is that occasionally the o2 voltage drops close to or all the way down to zero when the car stumbles (does that mean no gas was in the cylinder or that the spark didn't ignite it?). I'm stumped... I have checked and verified literally everything. This problem is insidious, it is random and it developed slowly over a period of weeks.
These are the things I have checked:
-Plugs (BR7ES gapped at .028 and verified, wires are brand new stock wires with separators, coil and power transistor came off of a well running car. I just replaced the well gaskets too as they leaked and killed my accel300+ wires)
-CAS came from a running car
-No boost leaks
-No short circuits (running an ammeter in series with the negative battery terminal, I got <0.01A with the car off).
-No grounding issues
-ECU - there is no visible damage and the caps are practically brand new
-Battery and alternator are brand new
-EPROM chip is good
-Compression is 180-185 across the board (2g pistons)
-Fuel pressure
-Fuel filter
The list can go on... I take very good care of the car. I don't know what else to look for... please help me, I will have to sell the car if I can't fix it I'm completely stumped.
