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First post here, definitely glad I found this place!
I've got a '92 olds 88 with a series 1 in it, about 199k miles on her now.

Start up great, runs great for a about a minute, and then begin the problems.

Starts missing at low rpms at about 25% throttle or more. Cruises fine at all speeds, and accelerating gently it runs virtually perfect, but under medium acceleration, especially from a dead stop, it's missing and backfiring. Sounds like a backfire into the intake to me at least, can't get it to do it while I'm under the hood... Nice pop though, more than a knock. It also does a little knocking when it's "spazzing out" though. It seems to be an on/off problem, rather then one that comes about in a linear fashion, which seems to rule out a mechanical issue.. MAF, TPS, Temp sensor, plugs, wires, fuel filter, air filter, and o2 sensor are new. I found a coil pack to be failing, and replaced it, but the problems remain. (Delco ign, BTW) Injectors all impedance test OK. All the sensors mentioned have clean connectors. IAT has been cleaned... I'm gonna compression check soon just to be sure no valve seat or ring problems..

Now... When I unhooked the 02 sensor, the ecm didn't notice. I even drove it around without it and it drove the same... And the old one (very caked) had to be toasted, and replacing it made no difference. At all... But more interestingly, even after restarting and driving it again with no 02 sensor, the ecm never threw a light OR a code... It still notices every other sensor I've checked...

Sorry for writing a book, but I'm pretty stumped right now... Advice MUCH appreciated!
 

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First post here, definitely glad I found this place!
I've got a '92 olds 88 with a series 1 in it, about 199k miles on her now.

Start up great, runs great for a about a minute, and then begin the problems.

Starts missing at low rpms at about 25% throttle or more. Cruises fine at all speeds, and accelerating gently it runs virtually perfect, but under medium acceleration, especially from a dead stop, it's missing and backfiring. Sounds like a backfire into the intake to me at least, can't get it to do it while I'm under the hood... Nice pop though, more than a knock. It also does a little knocking when it's "spazzing out" though. It seems to be an on/off problem, rather then one that comes about in a linear fashion, which seems to rule out a mechanical issue.. MAF, TPS, Temp sensor, plugs, wires, fuel filter, air filter, and o2 sensor are new. I found a coil pack to be failing, and replaced it, but the problems remain. (Delco ign, BTW) Injectors all impedance test OK. All the sensors mentioned have clean connectors. IAT has been cleaned... I'm gonna compression check soon just to be sure no valve seat or ring problems..

Now... When I unhooked the 02 sensor, the ecm didn't notice. I even drove it around without it and it drove the same... And the old one (very caked) had to be toasted, and replacing it made no difference. At all... But more interestingly, even after restarting and driving it again with no 02 sensor, the ecm never threw a light OR a code... It still notices every other sensor I've checked...

Sorry for writing a book, but I'm pretty stumped right now... Advice MUCH appreciated!
The way you describe the issue, it sounds like a LEAN CONDITION. It's hard to guess.... I would scan the PCM/ECM data and see what shows up, If it is a lean condition(usually from lack of fuel delivery). You should also be aware this kind of condition can cause piston damage...... My GTP ran to lean from a bad fuel pump and burned up pistons and the block was almost wrecked. Luck for me I know a good machinest and he fixed the block.....along with a new set of FORGED PISTONS. I sure hope you can avoid this scenario before more drastic damage occurs. If you have any more questions, post the situation on this forum. There are several guys and gals with plenty of knowledge of this issue also. Some....LIKE ME .... found out the hard and expensive way....live and learn and remember. Get back with any other info or help you might need....... Mr Goodwrench (Jake)
 

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You could have valve intake leak, but also sounds a lot like my problem which like someone else, after I removed the spark heat shields it eliminated 90% of the problem. Another said if that cured the problem then the wires have an issue.
I still have some missing but only when the engine gets hot and using boost. It's easy enough to remove the shields and see if that makes the difference tho.
 

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You could have valve intake leak, but also sounds a lot like my problem which like someone else, after I removed the spark heat shields it eliminated 90% of the problem. Another said if that cured the problem then the wires have an issue.
I still have some missing but only when the engine gets hot and using boost. It's easy enough to remove the shields and see if that makes the difference. Maybe consider a new set of top shelve plug wires also.
One other thing to do is to use a COLD HEAT RANGE set of autolite 103 plugs..... Make sure all the plug wires are in great condition also.
 

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One other thing to do is to use a COLD HEAT RANGE set of autolite 103 plugs..... Make sure all the plug wires are in great condition also.
I should have taken my own advice and got a new set of wires earlier. Solved all misfires. I still backfire after boost ends but that's almost certainly a leaky straight pipe.
 
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