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Discussion Starter · #1 ·
So I've got a 98 bird with the 3.8 and 5spd. Recently got the car, and got it running. But it's running super rich. Last time I took it across town I think it averaged roughly 5mpg. At a loss as to what could be the issue. All injectors are working properly with good voltage and resistance. Any help is appreciated.
 

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Seeing that car was not running for awhile, did you check injector spray patterns. Partially clogged injectors can spray a stream of fuel, rather than a fine atomized spray pattern. Did you clean out gas tank as it could be gunked up.

Have you changed fuel filter. And do a fuel pressure check. At key on prime pressure should be in mid to high 40', Start engine and check idle pressure. Should be in 40 psi range with vacuum hose Start engine & let idle. Fuel pressure should be around 40 psi with vacuum line connected. Take car on a short drive to see if fuel pressure maintains pressure without pressure rising.

Im not sure about 3.8 fuel pressures. So go to the following link & download the 98 factory service. It will have proper fuel pressure numbers. www.mediafire.com/?40mfgeoe4ctti

How about your ignition system. Does engine misfire? Try misting the spark plug wires with some water from a spray bottle. Run engine at night and look for spark leakage Have you replaced spark plugs & wires. This is normal maintenance. If misfiring coil packs could be the problem.

Finally, get an obd 2 scanner. One that does real time sensor data. Have an assistant drive car while you check sensor I actuator readings. If you need help understanding the data, members here will assist you. And do a code check also. Because not all codes light the SES.
 

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Discussion Starter · #4 ·
Update
So turns out it was a faulty mass air flow sensor. We unplugged the sensor and the car is no longer running rich and will also hold an idle now. So we got another sensor and now it doesn't want to idle with the new sensor connected. But if I leave the MAF unplugged the car will run and drive
 

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I once unplugged a mass air flow sensor to make it run in open loop because I had a bad O2 sensor and it ran really bad when it went into closed loop. Need to check your codes. Your old mass air flow sensor may or may not be bad. It seems to like open loop.. open loop is when it runs off preset tables in the computer.. closed loop is when it runs off the sensors. Apparently you have a bad sensor somewhere
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Typically, when the MAF sensor fails completely, or is disconnected, the PCM simply defaults to the speed-density method of calculating mass air flow. This is confirmed in the factory service manual V6 engine controls section. I know the V8 controls do not default to open loop when the MAF sensor fails or is unplugged.

If it runs better in speed-density, it's because the MAF sensor is not producing accurate data. Either air is bypassing the MAF sensor, there is electrical interference on the MAF sensor wiring, s0mething is plugged up, etc. Appears you still have a problem in one of those areas. Have you scanned it for codes? Typically I would expect you to have P0101. If you haven't scanned it, now is the time to start.

I would strongly suggest you download a free copy of the 1998 factory service manual (courtesy of GaryDoug), and look at the discussion of P0101. It describes what can cause the code to set, and the typical sources of the problem. This would be a much better solution than simply unplugging the MAF sensor.


The only significant sensor that is not used in "open loop" is the O2 sensor(s). They simply don't work when they are cold, and even if they did, the AIR pump (if the vehicle is equipped with one) running at startup would cause the O2 sensors to read incorrectly. Again, referencing the 1998 factory service manual for the 3,8L V6, "In Open Loop, the PCM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on TP sensor, engine coolant (sensor), and MAF sensor inputs only".
 
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