94 ss

Ok i have a 94 lt1 with 270,000 miles, just replaced the plugs(ngk tr55s), wires(msd 8.8 custom fit), o2 sensors, racetronix fuel pump and wiring harness, 52mm throttle body, iac motor, and the opti about 8 months ago. The car runs great before it gets to operating temperature and full throttle.
It idles rough after it gets to operating temp, and under partial throttle it back fires through the intake, and the gas milage sucks about 13 mpg in city or hwy. The car has a tune by mad z28 for the gear change, headers, cat back, cold air intake. Ive tried everything and the car still idles rough, back fires through the intake, and no low end power from a dead stop.
Any help will be appreciated.
Thanks in advance.

kinglt-1

iTrader: (26)

OPTI, if it has not been replaced!

97Z28LT1

iTrader: (3)

SES light on?

Sounds like its the opti, especially considering the majority of all the other ignition parts are new. Might check the ICM, but I don't think that would be causing it to backfire. You could also check and double check that you don't have any of the plug wires on the wrong cylinders just to rule that out.

LM97Z

iTrader: (4)

He did mention that the Opti was replaced about 8 months ago, i couldn't even begin to tell you what it could be, because it could be a number of things, just start with the basics.

94 ss

No SES light. The plug wires are one the right plugs. And i just replaced the ICM. THe motor mounts are the factory ones with 270,000 miles, might need replaced but not sure. Anyone think i might need to get it retuned for the new fuel pump and throttle body?

97Z28LT1

iTrader: (3)

I really doubt that's your problem. I know that you replaced the opti not long ago, but it still sounds to me like an opti problem. That's not to say that I'm totally wrong and its your tune.

I'd start simple. Duplicate the problem, and then check fuel pressure and spark while its acting up. After you have one of those isolated, start brainstorming and post what you found out. I'd also check to see what cylinders are missing, and whether those cylinders are missing all the time, or if the miss is intermittent.

94 ss

i dont think its the opti because i replaced it 5 times in the last 2 years because of a intake leak at the front of the motor now it stays dry. any one think it might be the msd blaster coil?

fergymoto

iTrader: (129)

Does it ever ping? You could have installed the opti on the wrong spline being it is a 94. I would look into that. It may be advanced a spline or two.

Fixxer99TA

iTrader: (5)

What opti did you reaplace your old one with exactly?

Lots of companies putting out junk replacement parts these days...

94 ss

the opti came from oreilly auto parts. anyone think it could be the harness instead of the opti its never been replaced and has 270,000 miles

Fixxer99TA

iTrader: (5)

If its from oreillys I would seriously start looking at the opti, you wouldent believe how many people have posted here with the same exact problems. The optispark isnt something that you can skimp on, it will bite you. A GM AC replacement is the very least I would tell anyone to do, or else you might find yourself doing it twice.

It could also be the harness, but you would be able to visually see the damage on the wires if there is any (and causing them to short).

94 ss

ttt....

97Z28LT1

iTrader: (3)

Check for corrosion on the harness and clean it as necessary. Considering you bought an O'Reilly's opti, I would definately not rule that out.