engine backfiring and stalling when opening it up
Thread Starter
Senior Member
Joined: Jun 2004
Posts: 741
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From: Long Island NY
Car: 1989 Firebird Formula
Engine: 5.7L 355 TPI
Transmission: 700 R4 with TCI rebuild kit and valve body mods
engine backfiring and stalling when opening it up
ok... i think i've finally figured out why i've been haiving the crappy idle every once in a while and still getting code 33 with pretty much new everything.... there are 2 clips from teh wiring harness that plug into my coil. one of the clips is broken, so it easily slides on and off the coil... i already ordered a new clip and piece of harness from the dealership to hopefully fix the problem. i was thinking it was getting a loose connection when i open it up, and then missing a spark, and having no explosion, and just stalling or backfiring due to that... what do you guys think? any other ideas if this doesnt work??? thankssss
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Joined: Jan 2000
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Your hypothesis is sound, but maybe not because of the unburned fuel. The missing spark is only another symptom of the problem.
The DTC 33 is a result of the ECM receivign MAF flow information that is higher than expected for more than 600mS. That's not very long. The ECM calculates the acceptable range of MAF flow inputs by measuring throttle position and engine RPM. The TPS supplies the throttle position data, and the distributor supplies the RPM information via the reference pulse on the purple/white wire.
What is likely happening is that the reference pulses from the distributor are being interrupted (bad connection). The ECM counts these pulses and compares them to a time base to determine engine RPM. If some of these pulses are lost, the ECM calculates a lower engine RPM. If the MAF signal is "normal" for the actual engine RPM, but the ECM is counting a lower RPM, the MAF signal would be determined to be too high for the calculated RPM. Fix the connection, and the MAF error will likely go away.
Further, the ECM also operates the injectors based on the reference pulses. If some of the pulses are lost, the ECM will not cycle the injectors on that engine revolution. That is likely causing or contributing to your backfire or afterfire, since the mixture will be very lean when the ijectors are not operating.
That may be the best connector repair you ever do for your performance.
The DTC 33 is a result of the ECM receivign MAF flow information that is higher than expected for more than 600mS. That's not very long. The ECM calculates the acceptable range of MAF flow inputs by measuring throttle position and engine RPM. The TPS supplies the throttle position data, and the distributor supplies the RPM information via the reference pulse on the purple/white wire.
What is likely happening is that the reference pulses from the distributor are being interrupted (bad connection). The ECM counts these pulses and compares them to a time base to determine engine RPM. If some of these pulses are lost, the ECM calculates a lower engine RPM. If the MAF signal is "normal" for the actual engine RPM, but the ECM is counting a lower RPM, the MAF signal would be determined to be too high for the calculated RPM. Fix the connection, and the MAF error will likely go away.
Further, the ECM also operates the injectors based on the reference pulses. If some of the pulses are lost, the ECM will not cycle the injectors on that engine revolution. That is likely causing or contributing to your backfire or afterfire, since the mixture will be very lean when the ijectors are not operating.
That may be the best connector repair you ever do for your performance.
Thread Starter
Senior Member
Joined: Jun 2004
Posts: 741
Likes: 1
From: Long Island NY
Car: 1989 Firebird Formula
Engine: 5.7L 355 TPI
Transmission: 700 R4 with TCI rebuild kit and valve body mods
well taht makes a lot of sense... i jsut took off some stuff tonight after work, getting it ready for tomorrow... i want to hopefully get the injetctors, chip, and headers all in tomorrow... that would be a really big accomplishment... also that coil wire too, they ended up ordering the wrong one, so i have to wait till tomrrow for the one i need to come in and then i have to go pick it up. ill keep you posted on the situation. thanks a lot man
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