No not a thirdgen, its my Vette but the corvetteforum hasn't been that helpful and since more thirdgenners wrench on their own car i figured you'd be more knowledgable.

I have a 93 LT1, auto with 57K miles. The car has slp shorties, slp cold air, hot cam kit, stage 2 heads, and a ported/polished/coated intake. The tune was done by Nathan Plemons for the third time (Thank you sir :-))and it still doesn't run right.

I am very doubting that the tune is causing the problem because you can start the car up and it will idle and run fine, then turn it off and restart it and then the troubles begin. The car will idle rough and die if you put it in gear without giving it some gas, it also dies at stop signs and has these other symptoms: extended cranking to start, rough idle, sputtering, backfiring, trouble reaching higher rpm, black smoke from exhaust. There is also a misfire from and above ~5300 rpm no matter how the car is running.

The car does not throw any codes and the only thing mechanically that may not be set 100% is the roller rockers (they're loose if anything). I know the above symptoms are for a bad opti but it doesn't make sense its a bad opti if the symptoms are intermitent, although they all do occur every time. The plugs and wires have less than 7K miles and the modifications were done less than 1K miles ago.

The car went from running consistent 14.0's at 99.9 to 13.7's, 13.8's 13.9's at 101...great improvement for $2K lol. It did however put down 323 rwhp and 343 rwtq on the dyno.

All questions, comments and suggestions are greatly appreciated.

Thanks in advance,

Dave

 

Swap the Opti, sounds like the optical sensor is crapping out which is generally what happens.

 

wooooohoooooooooooo, opti of doom

 

would you guys say that both problems are being caused by the opti? wouldn't it just go out and not be intermittent like this?

 

Not really, I have talked to a couple of people who say that when the optical sensor starts to go, it can be intermittant. The biggest thing that points to the opti is the misfire above 5300 which is about a 98% happening.

 

i love this site and how knowledgable you guys are!


so what do you recommend i replace the opti crap with?

stock opti can be had for $350

dynaspark runs $600ish

ltcc or the delteq are $600+ but don't really remove the opti

so which one should i go with???

 

Go back with the opti, I know someone who has a built 383 in his Z28 and went with the delteq and it still isn't running right, the opti is good for about 6500 RPM

 

i'm willing to swallow the $250 difference and go for the dynapark but i'm not sure if it is all that superior. a couple of people have gotten bad opti's off of ebay latley.

 

I think you have a couple of problems, one being the opti, possibly only the rotor.

I would check grounds for the ecm and have the ign module checked.

The opti , in my experience, will give a high and mid rpm miss regularly, but act like youre talking if any moisture is around.

Usually if it acts up too bad it throws a high or low pulse code.

 

Are you still running the stock O2 sensor? Sounds like when she reaches closed loop, you're problems then begin.

 

it does the same in open and closed loop

 

You mentioned that you'll start the car up, and it will idle and drive just fine. Are you saying that it only acts up after you shut it down, and then restart it?

 

Sorry if i mislead you... I can start the car up one day and it idle problem isn't there. I can start it up the next day (car is cold both days, weather is exactly the same) and it runs like ****. It also sometimes clears itself up and sometimes gets worse.

The high rpm miss is there no matter what.

Thanks again,

Dave

 

I'm still pointing toward the opti, either the cap/rotor, or the optics mainly because it's a '93 which is a non-vented unit that can get alot of moisture built up.

 

i'm trying to get a GP going on the Dynaspark unit over at the corvette forum....you guys think anyone on here would be interested?

 

I agree with Klortho then, in reference to a shot opti-spark. If you're constantly missing during high RPM, it's somewhere in you're ignition (especially with no codes being prevalent).

As for this tempermental symptom, one day good, one day bad, have you tried changing any sensors yet?

My buddy had a similar problem, only he had a 98 Grand Am, and the car would sometimes start, sometimes wouldn't.... sometimes drove excellent, sometimes stalled every other block....

No code was being thrown, but despite this, it was because of a bad sensor. My point? Don't rule out the possibility of a faulty sensor just because the SES light doesn't light up...