[Denon G]

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!

 

[1slow96]

Take the car to someone who can properly diagnose the problem.
"Firing the parts cannon" only adds more variables.

 

[Denon G]

Thanks, it's at the shop now and they're thinking the optispark is 180-ed...

 

[Sinister]

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.

 

[Denon G]

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!

 

[madamorr]

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.

 

[TheGarage]

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

 

[96 Black]

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.

 

[Sshockr]

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

 

[Denon G]

You need a new vacuum hose & restricter assembly that runs from the opti-spark to the intake plenum. See picture
View attachment 196472 View attachment 196472

Thanks a lot, I'll try it!

 

[Denon G]

Unfortunately finding folks who can and have the tools to scan 94/95's right is very rare.

-Brian

That's very true, unfortunately!

 

[Denon G]

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!!

 

[Denon G]

You need a new vacuum hose & restricter assembly that runs from the opti-spark to the intake plenum. See picture
View attachment 196472 View attachment 196472

I can't seem to find this anywhere for a 94, only the 95-97. Will this fit the 94 by chance?

 

[96 Black]

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

 

[Denon G]

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

Ok, I'll look into this. Thanks a lot!

 

[TheGarage]

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:

Impala SS~Opti-Spark Vent Vacuum Harness~LT1 Caprice~9C1~Buick~OEM GM~12555323~ | eBay

Genuine GM Part that will replace the one on your vehicle that has dryed out and left your Opti-Spark not working correctly. 1994 - 1996 Chevrolet Caprice 9C1. 1994 - 1996 Chevrolet Caprice SS. 1994 - 1996 Chevrolet Caprice.

www.ebay.com

 

[Marky Dissod]

… 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, and Fleetwoods - including commercial chassis - with L99 or LT1 V8s used externally vented Opti-Sparks, and NEED a Vent & Vacuum Harness to work properly.​

 

[Denon G]

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:

Impala SS~Opti-Spark Vent Vacuum Harness~LT1 Caprice~9C1~Buick~OEM GM~12555323~ | eBay

Genuine GM Part that will replace the one on your vehicle that has dryed out and left your Opti-Spark not working correctly. 1994 - 1996 Chevrolet Caprice 9C1. 1994 - 1996 Chevrolet Caprice SS. 1994 - 1996 Chevrolet Caprice.

www.ebay.com

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:

Impala SS~Opti-Spark Vent Vacuum Harness~LT1 Caprice~9C1~Buick~OEM GM~12555323~ | eBay

Genuine GM Part that will replace the one on your vehicle that has dryed out and left your Opti-Spark not working correctly. 1994 - 1996 Chevrolet Caprice 9C1. 1994 - 1996 Chevrolet Caprice SS. 1994 - 1996 Chevrolet Caprice.

www.ebay.com

Thanks, I just ordered it! Hopefully this is a lifesaver, thanks again!

 

[95CCRMW]

I am having somewhat the same issue. Under load, especially with the ac on, the car will miss and stumble while trying to accelerate or go uphill. Wondering if the new vacuum hoses fixed your issues?

 

[Marky Dissod]

EGR Valve &/or Solenoid?