constant backfire/stumble
Thread Starter
Joined: May 2006
Posts: 3,974
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From: Spring Hill, FL
constant backfire/stumble My 94 z28 has developed some big problem. I was just running around with my newly installed cutout. Coming down from a 110mph blast it started stuttering and backfiring. It constatly backfires, leaving from a stop it drops down to 500rpms almost before taking off. I'm thinking its my MAF, I'm having my stock unit sent to me to see. Any ideas? Its a little rough at idle, as soon as you give it some gas it freaks out! I replaced my driver side o2 sensor as it was 12 yrs. old, the passanger side o2 is 1 1/2 yrs. old. Current MAF is a Granatelli unit.
Originally Posted by camar0corey
My 94 z28 has developed some big problem. I was just running around with my newly installed cutout. Coming down from a 110mph blast it started stuttering and backfiring. It constatly backfires, leaving from a stop it drops down to 500rpms almost before taking off. I'm thinking its my MAF, I'm having my stock unit sent to me to see. Any ideas? Its a little rough at idle, as soon as you give it some gas it freaks out! I replaced my driver side o2 sensor as it was 12 yrs. old, the passanger side o2 is 1 1/2 yrs. old. Current MAF is a Granatelli unit.
Thread Starter
Joined: May 2006
Posts: 3,974
Likes: 2
From: Spring Hill, FL
Hmm its throwing no codes. If my stock MAF dosen't show back up today I will unplug the MAF and see how it runs, what does that do, make it run like a speed density setup?
Someone has also mentioned to me that the coil may cause this when its on its way out, is this also true? Thanks.
Someone has also mentioned to me that the coil may cause this when its on its way out, is this also true? Thanks.
Thread Starter
Joined: May 2006
Posts: 3,974
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From: Spring Hill, FL
Ok I don't comprehend how to get freescan to tell me anything, looks like its logging, but isn't displaying anything.
Its not the coil, I picked a new one up, made no change.
I have the cutout located right before the pipe goes up over the axle, so 2 1/2-3 ft. from the o2s, my exhaust setup is BBk shorties/y pipe, and 3" flowmaster catback.
Its not the coil, I picked a new one up, made no change.
I have the cutout located right before the pipe goes up over the axle, so 2 1/2-3 ft. from the o2s, my exhaust setup is BBk shorties/y pipe, and 3" flowmaster catback.
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Thread Starter
Joined: May 2006
Posts: 3,974
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From: Spring Hill, FL
Could this be the opti going out? I replaced the cap and rotor with msd pieces maybe 5,000 miles ago. The optical discs had some spotty rust on them I suppose. Its really dry around here though and the car hasn't been exposed to water at all.
I just don't understand why the ses light isn't coming on, it obviously has something wrong with it.....
I just don't understand why the ses light isn't coming on, it obviously has something wrong with it.....
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Verdad Gallardo The opti wont always throw codes ... it could very possibly be the opti. The optical sensors **** the brick 9 times out of 10 before the cap and rotor. They are very sensitive.
Also yes unplugging the maf would be running in a sense of speed density ... and should run correctly. So if the car acts the same with the maf unplugged then, its safe to say the maf is fine.
I personally think it is an opti issues since you didnt change the whole unit, and the cutout thing was just bad timing! It is hard to tell what these cars are doing without a good datalog sometimes.
Also yes unplugging the maf would be running in a sense of speed density ... and should run correctly. So if the car acts the same with the maf unplugged then, its safe to say the maf is fine.
I personally think it is an opti issues since you didnt change the whole unit, and the cutout thing was just bad timing! It is hard to tell what these cars are doing without a good datalog sometimes.
Thread Starter
Joined: May 2006
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From: Spring Hill, FL
ok is it true that if the tach isn't acting all psychotic that the optical sensors are probably still fine? I unplugged the maf, still acting strange, should have my hands on my stock unit today.
have you checked to see if your plugs wires are arcing at night? Mine acts very similar to what described and we have been having a hell of a time figuring it out. my opti was new ac delco 6 months ago, new plugs, and have tried a couple different sets of wires, with no change. 
Originally Posted by camar0corey
ok is it true that if the tach isn't acting all psychotic that the optical sensors are probably still fine? I unplugged the maf, still acting strange, should have my hands on my stock unit today.
http://www.gmhightechperformance.com...ing_modifying/
Symptoms:
* Car suddenly dies and won't restart
* Starts but immediately dies
* Extended cranking to start
* Rough idle
* Sputtering
* Backfiring
* Trouble reaching higher rpm
* Black smoke from exhaust
* Poor performance with car warmed up
* Weak plug wire spark
* Codes 16, 36, and 42 may be set
Thread Starter
Joined: May 2006
Posts: 3,974
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From: Spring Hill, FL
ok the stock maf didn't resolve the issue, and neither did a new coil.
Also when this constant running like crap and backfire is going on it dosen't matter if the car is warmed up or not.
The voltmeter shows constant rising and falling of voltage while the car is running this way, the only time voltage and such are fine is when the car is sitting there at idle. As soon as you touch the throttle in any manner it goes nuts.
Thanks for the responses so far.
Also when this constant running like crap and backfire is going on it dosen't matter if the car is warmed up or not.
The voltmeter shows constant rising and falling of voltage while the car is running this way, the only time voltage and such are fine is when the car is sitting there at idle. As soon as you touch the throttle in any manner it goes nuts.
Thanks for the responses so far.
TECH Resident
Joined: Feb 2006
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From: Panama City Florida
Originally Posted by ras928
Well after eliminating all of that, theres a good chance it is the opti. Are the plug wires fine?
Thread Starter
Joined: May 2006
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From: Spring Hill, FL
Ok plug wires look alright, replaced all the plugs with champions, I don't know just the cheapest plugs til I get the tr6's for the fact that I will be running nitrous. My friend saw sparks around where the opti clip is that goes into the top, would the harness spark itself or can the opti itself show sparks out of it?
Plugs on the driver side were worse than the passanger side, but I account that to the fact that side is the one that I just replaced the o2 finally, so yeah it was running on a 12 yr. old o2 sensor. Oh yeah and somehow the #1 plug wasn't the same as the other 7 plugs, I don't know how I was issued 8 plugs and one of them wasn't the same, they were AC delco Platinums.
Plugs didn't solve the issue though, so I guess its either the opti clip/harness or opti itself????
Plugs on the driver side were worse than the passanger side, but I account that to the fact that side is the one that I just replaced the o2 finally, so yeah it was running on a 12 yr. old o2 sensor. Oh yeah and somehow the #1 plug wasn't the same as the other 7 plugs, I don't know how I was issued 8 plugs and one of them wasn't the same, they were AC delco Platinums.
Plugs didn't solve the issue though, so I guess its either the opti clip/harness or opti itself????
Sounds like it could be, an arch in wires touching, wire touching headers or bad plugs. If the O2 is bad it will fowl up new and old plugs. Mine did same thing with cut in spark plug boot, but O2 was no good, so when I put new plugs and wires in it fowled up new plugs.
Thread Starter
Joined: May 2006
Posts: 3,974
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From: Spring Hill, FL
none of the spark plug wires are touching the headers, I looked at them yesterday when I put the plugs in and they seem to be fine, my friend said he saw the sparks around the wires going into the opti, or the general area of the top of the opti itself.