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Discussion Starter #1
I have a 94 SS and so far I've changed the plugs, wires, fuel pump, fuel filter, MAF, optispark, and injectors but the car still backfires and sputters under load! Any advice you could give me would be much appreciated!
 

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Take the car to someone who can properly diagnose the problem.
"Firing the parts cannon" only adds more variables.
 
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They are thinking? Take it to a place that will DIAGNOSE vehicles, not make guesses.

The Opti only bolts on one way and upside down isn’t possible so there is no 180 outing it.
 

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Thanks Sinister! I'm picking it up tomorrow, I could tell the guy was clueless after speaking to him. He couldn't get a reading on the obd1 so now he THINKS I have a wiring problem!
 

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Thanks Sinister! I'm picking it up tomorrow, I could tell the guy was clueless after speaking to him. He couldn't get a reading on the obd1 so now he THINKS I have a wiring problem!
Make sure that you have the wires correctly connected to the Optispark.
196441
 
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I have a 94 SS and so far I've changed the plugs, wires, fuel pump, fuel filter, MAF, optispark, and injectors but the car still backfires and sputters under load! Any advice you could give me would be much appreciated!
You need a new vacuum hose & restricter assembly that runs from the opti-spark to the intake plenum. See picture
196472
opti-spark vacuum-01.jpg
 

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A common request by reply-ers ends up being to ask what exactly prompted the flurry of throwing parts at it in the first place. The same "backfires and sputters under load", or something else?

To madamorr's point I claim a perfect record of getting EXACTLY 2 wires wrong every time I replace them.

I take "I've changed" as meaning you did all the work up til now yourself. If so, the perfect way to spend your time and $$$ the best is to invest in the Fact. Serv. Manuel for its great diagnostic trees on running issues.
 

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Thanks Sinister! I'm picking it up tomorrow, I could tell the guy was clueless after speaking to him. He couldn't get a reading on the obd1 so now he THINKS I have a wiring problem!
Unfortunately finding folks who can and have the tools to scan 94/95's right is very rare.

-Brian
 

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Discussion Starter #12
A common request by reply-ers ends up being to ask what exactly prompted the flurry of throwing parts at it in the first place. The same "backfires and sputters under load", or something else?

To madamorr's point I claim a perfect record of getting EXACTLY 2 wires wrong every time I replace them.

I take "I've changed" as meaning you did all the work up til now yourself. If so, the perfect way to spend your time and $$$ the best is to invest in the Fact. Serv. Manuel for its great diagnostic trees on running issues.
Thank you!!
 

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I've read (on this forum) that ALL Impala SSes got the vented harness, regardless of year. Confirm on your own at will.
 

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Thanks a lot, I'll try it!
The symptoms that you initially had were identical to what I had on my 94 9C1, and just as you stated, I "threw" all the "parts that just had to fix it" except for that vacuum assembly. At the time I did not know that the LT1 could not run correctly without the restricter valves & hose assembly. What I over-looked was that the larger valve had 'blown out' the restricter portion which then allowed un-metered vacuum into the intake. Check Hamilton Chevrolet on Ebay:
 

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… ALL Impala SSes got the vented harness, regardless of year.
Fixed it.
Seriously, until parts sources learn better, it needs to be common knowledge someplace, so it might as well be common knowledge here.

ALL '94-'96 Caprices, Impalas SS, Roadmasters, Fleetwoods (anydcommercial chassis) with L99 or LT1 V8s used externally vented Opti-Sparks and NEED a Vent & Vacuum Harness to work properly.
 

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Discussion Starter #18
The symptoms that you initially had were identical to what I had on my 94 9C1, and just as you stated, I "threw" all the "parts that just had to fix it" except for that vacuum assembly. At the time I did not know that the LT1 could not run correctly without the restricter valves & hose assembly. What I over-looked was that the larger valve had 'blown out' the restricter portion which then allowed un-metered vacuum into the intake. Check Hamilton Chevrolet on Ebay:
Thank you, I just ordered it! I hope this is Edg
The symptoms that you initially had were identical to what I had on my 94 9C1, and just as you stated, I "threw" all the "parts that just had to fix it" except for that vacuum assembly. At the time I did not know that the LT1 could not run correctly without the restricter valves & hose assembly. What I over-looked was that the larger valve had 'blown out' the restricter portion which then allowed un-metered vacuum into the intake. Check Hamilton Chevrolet on Ebay:
Thanks, I just ordered it! Hopefully this is a lifesaver, thanks again!
 
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