Lt1 still backfiring and missing in closed loop
02-09-2012, 02:25 AM
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Lt1 still backfiring and missing in closed loop Hi,
I have a 1994 firebird lt1 that will run fine in open loop, however, once it heats up, it starts to run like sh*t. I've replaced the ICM, Coil, EGR valve, Spark plug wires, MAF, and O2 sensors. I'm thinking its the opti now? does this sound like a reasonable explanation? If it is, how do I know what to look for in a replacement opti? Which should I buy? Please let me know. Appreciate any help. Thanks
I have a 1994 firebird lt1 that will run fine in open loop, however, once it heats up, it starts to run like sh*t. I've replaced the ICM, Coil, EGR valve, Spark plug wires, MAF, and O2 sensors. I'm thinking its the opti now? does this sound like a reasonable explanation? If it is, how do I know what to look for in a replacement opti? Which should I buy? Please let me know. Appreciate any help. Thanks
02-11-2012, 07:05 PM
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anyone? I replaced the IAT sensor and that didnt help. This only happens when the car has been for say ~15 minutes. It starts as high RPM misses, but then starts to happen with lower RPM ~1500 and lower and eventually starts backfiring at anything above ~1200rpm. What else could I try? Thanks
02-11-2012, 08:20 PM
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Check your wiring to your O2 sensors. I had a couple of O2 sensor wires get on a header and melt together. Took a while to track that down. Open loop, it ran fine. Closed loop, it would start acting up. Didn't want to idle and would bog when pulling out. If I gave it enough throttle to put it into PE, it would run ok.
02-11-2012, 08:32 PM
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the opti is original from what I know...so 18 years old I guess. It wasnt run between 2003 and late 2011 so it sat for a long time as well. I dont think its the O2s anymore as It was missing at WOT as well.
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02-11-2012, 08:48 PM
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old ignition components... opti's can last a while, but like all distributors the cap and rotor are "wear items"... and well... anything that has sat for 18 years, isn't really going to be at it's peak.
02-12-2012, 08:09 AM
#11
x3! Get a scantool and check the temps of your coolant temp sensor when cold and warm. These are prone items that go bad and when they do they send false readings to the pcm making it think its running to hot or too cold. Also would be a good idea at the the same time to check for stored trouble codes even if the check engine light isnt of. Do that first and report back before assuming its ignition related.
02-12-2012, 02:27 PM
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Well the scanner I have apparently only does codes, but it found a code 42 (Electronic Spark Timing Circuit Grounded). What does this mean? Also where would I get a scanner that reads sensors?
Edit: after looking into code 42 it appears to be related to the ICM. I replaced the ICM and coil maybe a month back when there was no spark to one I got off ebay (original GM). After I replaced them, everything worked fine. However, I heard that perhaps this could be causing the code?
Edit: after looking into code 42 it appears to be related to the ICM. I replaced the ICM and coil maybe a month back when there was no spark to one I got off ebay (original GM). After I replaced them, everything worked fine. However, I heard that perhaps this could be causing the code?
Last edited by goldylocks; 02-12-2012 at 02:35 PM.
02-12-2012, 06:32 PM
#13
being a 94 if you have a laptop you could just get a cable and use the trial version of Data master. You can then data log the car while driving and as soon as the problem occurs you can take it home and read the data log and even upload it some of the guys on here. It will cost about 100 bucks for the cable. but this shows just about every sensor input. Great tool and if you like it you can buy the program for about a 100 bucks. Other then that there are hand held scanners that can do it but the cost are usually around 250+.
