sprint48

1992 Vette, LT-1, A/T ~ 85K miles, K&N panel filter, chip and a gear change. Plugs were changed about 1000 miles ago.

Car had been running a bit rough like it didn't have enough fuel so I changed the inline filter and put in a new fuel pump and filter element. It ran about the same for a few weeks. One day I went to pass a car and it backfired, stumbled and would not get over 2500 rpm. I can get it to pull to 4000 rpm in Low gear, and can 'nurse it' to about 60mph in Drive but it takes a long time.
I've got a set of Ford Racing 28# injectors for it and a replacement Opti-Spark sitting here but I wanted to see if this was perhaps a sensor issue or something in the computer before I started changing parts. I've got the factory service manual but couldn't find anything specific. Local parts store can't use their code reader, but there hasn't been any Light on the dash indicating a problem. HELP!!

My direct email is
legalearnings@aol.com

and I would greatly appreciate any help or suggestions since I'm NOT driving the Vette and that needs to change fast!

Thanks!!

I Hate Rice

Sounds a lot like fuel delivery...but you've already changed most of it. The next thing I would say would be the injectors but if you switch to a bigger injector like that without changing the tune you might encounter another set of problems (running very rich). Have you tried a fuel injector cleaner of any sort? Also have you checked fuel pressure at the rail? Always best to try the cheapest easiest stuff before throwing money out the window when its not going to fix the problem....I've learned that the hard way . Good Luck and keep us posted.

Jerris

Sounds like a weak coil or a ICM going bad but my money is on the coil putting out a weak spark.

If the coil tests new my second guess would be plugged cats.

RRT vette

500hp

I had a '93 TA that did this and it ended up being the front half of the cat element was dislodged and sideways. BUT this was a SINGLE cat car, so essentially the ENTIRE exhaust system was restricted. As for the usual suspects: Fuel, ignition, and EGR.

sprint48

Not sure the cat's could do it since it will go to 4000rpm in Low. It acts like low fuel since it backfires when the throttle is slammed open, then stumbles.
The Ford 28# injectors should be close to factory for this setup, but as mentioned I don't want to swap them until the rest of the problem is cured.
I've tried injector cleaner.

Coil is a good suggestion but again it pulls stong without hesitation in LOW so the issue seems to be in DRIVE like it is either a sensor or the ECM

Originally I wondered if it could be the chip in the ignition key but I think the key just shuts down the high performance curves.

Keep those cards and letters coming!!

Thanks!

aminnich

Get a scanner and check codes, otherwise you are throwing $$ away.

RED92LT1

Did you check compression?

Jerris

A weak coil will often work under less load like low gear but when there is more load on the engine and the mixture is fattened up by the ECM it can no longer light off the mixture.

It is NOT the chip in the ignition key.

Bradley1

I had the same similar problem with my 92 vert about a year ago. I had to change out the optispark distributor including the cap. The spark plugs and both oxygen sensors. I also had to change the map sensor. The distributor had gotten water in it and was corroded inside and the timing was way off. The cap electrodes were broken off and burned out. Remember you must get the timing marks lined up right before you put on the new optispark or you will get a no start condition like I did. I had to take mine to a shop because I couldn't figure it out. Now my car has no problems. Also seal the distributor with some gasket sealant around the outside so no water can splash up into it. I drained the coolant and took off the waterpump myself to save the labor cost. Take it to a reputable shop and let them change out the optispark.

Alvin

Have you put some sort of chip in this car? Alot of times if you install a chip backwards (with an adapter) it will do the same thing.

Jerris

Good to know as I also have a 92 LT1.
What kind of adapter are you referring to, the stock one just plugs into the slot in the ECM. Would this be for a non stock chip?
Thanks

REDC4CORVETTE

What's the fuel presure?
Have you taken a flash light to see if the weep hole is leaking under the opti?

sprint48

Glad to know it's not the key -
The chip was already in the car and tuned when I got it.

I'm leaning toward the optispark since the problem just happened suddenly. I've got another one and think I found a good shop to install it and troubleshoot it since time is an issue with racing season approaching.

I'll post whatever I find out!

Daniel DK

i would put my money on the cat

sprint48

If it was the Cat, why would it still accelerate hard and smooth to over 4000rpm in Low? Since fuel and air flow (ie exhaust) is a function of engine speed rather than mph, it should have the same problem in all gear ranges (A/T)

Same w/ plug wires - they should react the same in any gear.

I need to find the code reader and see if that shows anything

ittlfly

I'm with Jerris on this one. A coil on its way out will break up under load at the higher RPM's. I would test the coil first and the module before throwing money at the problem. ... ie: opti.

VetteUSA

I had similar problem to you, weak spark, above certain rpm , my car would bog and die... and it was my ignition coild that was bad.

Check your ignition coil. you can check the ignition coil by probing it with an ohm meter. Primary resistance for ignition coils typically reads from 0.5 - 1.5 ohms. Secondary resistance tuypically reads from 8000 - 12,000 ohms. If those specs aren't in check with your ignition coil, then the coil is bad.

I recently replaced my ignition coil. My bad coil's primary resistance read 0.8 ohms, however, my secondary resistance was out of spec at 145,000 ohms. (the excessive value indicated that there was an open within the ignition coil unit). I replaced with a new coil from NAPA and my car is back to normal.

Also, first thing you should do is check for any trouble codes.