Intake backfire ONLY in open loop mode
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 46
Likes: 0
From: PA NJ
Intake backfire ONLY in open loop mode
Weird problem that has persisted the past few months. The car runs like total @ss in open loop mode, hesitation upon acceleration and backfiring through the intake if you really push the throttle down.
Once the car is in closed loop mode, it runs great, no hesitation, no misses or backfiring. The opti and entire ignition system, including the knock sensors and module were replaced last month and did not resolve the problem what-so-ever.
I also ran TTS datamaster and there are no apparent problems in open loop mode.
The car is a 95.
Once the car is in closed loop mode, it runs great, no hesitation, no misses or backfiring. The opti and entire ignition system, including the knock sensors and module were replaced last month and did not resolve the problem what-so-ever.
I also ran TTS datamaster and there are no apparent problems in open loop mode.
The car is a 95.
Last edited by MyFatNutz; Jan 23, 2006 at 05:57 PM.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
hmmm.. The good news is that once you hit 'closed loop', your O2 sensors are operative, and are feeding back the correct info. so the ECM can adjust to correct AFR. What does your exhaust look like and smell like during 'open loop' ?
IMHO, your O2 sensors are in a mode of compensating for another sensor which has crapped out...
TPS, MAP, MAF problem?
IMHO, your O2 sensors are in a mode of compensating for another sensor which has crapped out...
TPS, MAP, MAF problem?
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 46
Likes: 0
From: PA NJ
I replaced the O2 sensors before the cat, they are both reading within the range they should, millivotes within each other.
As far as the sensors, none of them are reporting errors.
The LTerm Counts are consistantly green in the 135 + range. I have the file if anyone could interpret anything odd here:
http://www.dooleez.com/test.uni
(datamaster file)
As far as the exhaust, dosnt smell unusual. I'll pay more attention to that tomorrow morning and get back to ya.
As far as the sensors, none of them are reporting errors.
The LTerm Counts are consistantly green in the 135 + range. I have the file if anyone could interpret anything odd here:
http://www.dooleez.com/test.uni
(datamaster file)
As far as the exhaust, dosnt smell unusual. I'll pay more attention to that tomorrow morning and get back to ya.
Last edited by MyFatNutz; Jan 23, 2006 at 09:23 PM.
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 59
From: Fremont Oh
Has anyone reprogrammed your chip?
I'm thinking that either your mods have now made the engine lean in a particular area or the rogramming when they perhap leaned things out a bit may have gone to far.
I don't have TT so I can't see your log, but if you look at the O2's and if they are say below 800 ish while you are in OPEN loop that should steer you in the right direction. Generaly on warmup the engine will be in open loop for "period" of time before switching into closed loop.
I would look at the power enrichment, or if you have had no programming done, you may have a vacuum leak somewhere. As the computer will go into open loop if you run say above 60 % throttle it will go from closed to open loop... which could mean when you are not under heavy throttle the leak could still be there, and it is apparent once you are into the throttle more...
I hope this helps...
I'm thinking that either your mods have now made the engine lean in a particular area or the rogramming when they perhap leaned things out a bit may have gone to far.
I don't have TT so I can't see your log, but if you look at the O2's and if they are say below 800 ish while you are in OPEN loop that should steer you in the right direction. Generaly on warmup the engine will be in open loop for "period" of time before switching into closed loop.
I would look at the power enrichment, or if you have had no programming done, you may have a vacuum leak somewhere. As the computer will go into open loop if you run say above 60 % throttle it will go from closed to open loop... which could mean when you are not under heavy throttle the leak could still be there, and it is apparent once you are into the throttle more...
I hope this helps...
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Originally Posted by MyFatNutz
This has been a problem only in the last few months, the modifications were done in 2002.
You might want to pull all 8 plugs to see how they look. If the problem is isolated to a cylinder or two, the plugs would show that, and could help track the problem down. Checking for vacuum leaks is a good idea, too.
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 46
Likes: 0
From: PA NJ
Sorry for reviving this old thread, but I just wanted to follow up.
I replaced all the plug wires, and the open loop backfiring has been significantly reduced, but somewhat still there. I also adjusted the throttle cable from the ASR, it was only going to 80% now its back to 100% when the peddle is floored. I am going to do a vacuum test and then a compression test.
Again, the car rides great in closed loop, the only problem is open loop when the car is cold.
Could it be a map sensor?
I removed all the plugs and they looked good too (I am using bosch platinums).
Someone was behind me on the highway and said when I got on it, there was some smoke (not blue) coming from the drivers side only (maybe condensation). I'm thinking unburnt fuel. None of the plugs were wet eaither and I have no issues with coolant.
I replaced all the plug wires, and the open loop backfiring has been significantly reduced, but somewhat still there. I also adjusted the throttle cable from the ASR, it was only going to 80% now its back to 100% when the peddle is floored. I am going to do a vacuum test and then a compression test.
Again, the car rides great in closed loop, the only problem is open loop when the car is cold.
Could it be a map sensor?
I removed all the plugs and they looked good too (I am using bosch platinums).
Someone was behind me on the highway and said when I got on it, there was some smoke (not blue) coming from the drivers side only (maybe condensation). I'm thinking unburnt fuel. None of the plugs were wet eaither and I have no issues with coolant.
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Drifting
Joined: May 1999
Posts: 1,478
Likes: 3
From: Sacramento, CA Money can't buy happiness - but it's more comfortable to cry in a Corvette than a Yugo.
I would hazard a guess of injector(s) leaking or most likely a fuel pressure change due to the fuel pressure regulator having a problem. You are seeing smoke at the exhaust when accelerating due to a rich condition. Under acceleration to WOT you go back to open loop and the smoke is seen. Same is true for the backfiring at the intake in open loop. Too much unburned fuel. When in closed loop, the ECM/PCM is generally able to make the needed adjustments to lean out the mix and this bring things under control.
Check your fuel pressure with key on engine off and the fuel rail pressurized, during engine operation, and after shutting the engine off to see how long it takes for the pressure to drop. Let us know what you find.
Check your fuel pressure with key on engine off and the fuel rail pressurized, during engine operation, and after shutting the engine off to see how long it takes for the pressure to drop. Let us know what you find.
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 46
Likes: 0
From: PA NJ
Sorry for the super late response here, turns out the MAF was bad!
I disconnected the MAF and the car ran great with just the MAP. NOw that the MAF had been replaced car runs as smooth as it did when I bought the car six years ago (except for the sh!!tty edelebrock IAS shocks).
Car has not driven this good in at least 2 years! Thx for the help
I disconnected the MAF and the car ran great with just the MAP. NOw that the MAF had been replaced car runs as smooth as it did when I bought the car six years ago (except for the sh!!tty edelebrock IAS shocks).
Car has not driven this good in at least 2 years! Thx for the help
