Yep.
backfires now when letting off gas
Thread Starter
Team Owner
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backfires now when letting off gas
When I am in 1 or 2 gear and floor it then let off it now pops and fires. This thinjg never did this before. I have put on a corvette ram air cold air intake with sensor and dual straight pipes with dynomax muffs, it has a hypertech chip in it and is auto . I realize the chip is no good really, but is this affected now? or timing? searched other threads some say too rich which seems to meit is. others say it is lean pops. is the computer not ready for these changes? help
Le Mans Master
Joined: Sep 2006
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From: Phoenix AZ
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pops
check to see that one or both air pump check valves on the exhaust manifolds are good.
If the check valve is bad, it pops n spits.
Also check to see that there's no codes, and that the O2 sensor is still plugged in and the wires are good.
If the check valve is bad, it pops n spits.
Also check to see that there's no codes, and that the O2 sensor is still plugged in and the wires are good.
Le Mans Master
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From: H-Town Texas
If by poping and fire you mean a burbbling kind of sound with a popping in between, that is the sound you paid for with the intake and the exhaust. This means these parts are doing what they are supposed to do. If by fire, you mean a loud bang, like gun fire that makes people dive for cover, then you have a timing problem.
Thread Starter
Team Owner
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yes I have had cars with straights before and its not the rap, its like a pop pop pop likeits loading up or something. I thought to rich now or not enought timing. but I have a hypertech chip so afraid to up the timing.
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Le Mans Master
Joined: Dec 2006
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From: H-Town Texas
Does it "pop" at idle, or only when letting off from higher RPMs. When you suddenly let off at high rpm, there is still alot of cylinder pressure and that is what you hear releasing. You just didn't hear it before because the back pressure from your stock system kept in. If you had a timing issue the pop would be more consistant through out the rpm range I would think. I believe if you were so rich it would cause backfire, I would think that you have a little hesitation or stumbling when revving.
Did you put the exhaust, intake, and chip all in at the same time? I would not rule out the Hypertech chip, but I don't think they affect timing enough to cause a mis-fire. I could be wrong though.
Did you put the exhaust, intake, and chip all in at the same time? I would not rule out the Hypertech chip, but I don't think they affect timing enough to cause a mis-fire. I could be wrong though.
Le Mans Master
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Check the resistance of your injectors. I suspect one or more is going bad.
If your '90 is like my '89, there is only one O2 sensor on the driver's side. And, the injectors fire in batch mode (simultaneously) vs sequentially.
If any injector goes bad on the driver's side, the ECM sends more gas to ALL injectors. Because the O2 can only monitor what one group of four injectors are doing, it is forced to ASSUME what every injector is doing. One lean/bad injector on the driver's side lowers the amount of unburnt "fumes" going to the O2 sensor. The ECM can only respond by sending more gas to every injector. Now you have 1 (or more) bad/lean injectors plus up to 7 rich injectors! From that, you can assume at least one of the following will result:
The "performance" chip you purchased could "aggravate" the problem by asking the ECM to deliver a richer burn (in addition to a possible injector issue). Again, quieter exhaust systems muffle those types of pops -- making them difficult/impossible to hear. That's how your mods could make it seem like they created a problem that was already there.
If your '90 is like my '89, there is only one O2 sensor on the driver's side. And, the injectors fire in batch mode (simultaneously) vs sequentially.
If any injector goes bad on the driver's side, the ECM sends more gas to ALL injectors. Because the O2 can only monitor what one group of four injectors are doing, it is forced to ASSUME what every injector is doing. One lean/bad injector on the driver's side lowers the amount of unburnt "fumes" going to the O2 sensor. The ECM can only respond by sending more gas to every injector. Now you have 1 (or more) bad/lean injectors plus up to 7 rich injectors! From that, you can assume at least one of the following will result:
- The good injectors (pumping more gas) cause a rich condition. More fumes are entering a HOT exhaust pipe where they can explode/pop. Additionally, ODB1 computers are "slower" to react. Therefore, I have to assume a slow ECM may not terminate/adjust injector pulses fast enough (on decel) to prevent extra gasoline from entering the exhaust stream. The ECM may be fast enough to minimize outright popping with a factory exhaust -- but not with compensating injectors and an open exhaust system.
- Bad injectors can reach a borderline were a "lean miss" occurs. Not enough fuel enters that cylinder for proper combustion. But, fuel could enter the HOT exhaust pipe where detonation can occur.
The "performance" chip you purchased could "aggravate" the problem by asking the ECM to deliver a richer burn (in addition to a possible injector issue). Again, quieter exhaust systems muffle those types of pops -- making them difficult/impossible to hear. That's how your mods could make it seem like they created a problem that was already there.
Last edited by GREGGPENN; Oct 7, 2008 at 06:40 PM.
Thread Starter
Team Owner
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it runs good at idle , and driving, but when i wind it up in first then let off as the r'ss come down it pops like 2-3 times.
the chip was in it , I only changed other things. some times happens if I rev it all the way up period.
so sounds like -no back pressure- timing is to advanced somehow- bad injectors(buying fic)
so you guys think I should retard the timing?
the chip was in it , I only changed other things. some times happens if I rev it all the way up period.
so sounds like -no back pressure- timing is to advanced somehow- bad injectors(buying fic)
so you guys think I should retard the timing?
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Melting Slicks
Joined: May 2007
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From: Warwick RI
The only time that I have really seen this was on bikes and the fix was to go up on the low speed jets to allow a little more fuel when the throttle was closed. Maybe someone experienced with this issue will chime in to tell you how to richen it up a little when the butterflies are closed. The intake change will probably fix it anyway so I wouldn't stress over it right now, do the intake and then stress
