Severe miss at 2000 to 2800 RPM

[bluewhale54]

As a new registered member, although I have been browsing this forum for the past couple of years it pains me to be asking for HELP so soon.

I have a 1995 LT1 coupe with a 6spd. Various modifications have been made to improve the power and power delivery.

I am now totally confused and stumped.

The car starts fine, runs fine in all gears, accerates beyond believe, except from exactly 2000 RPM until exactly 2800 RPM it developes a very nasty miss, regardless of what gear is selected. Downshift to ensure you are not at the dreaded 2000-2800 and all is well with the world.

Before anyone asks I have changed the wires, plugs, fuel filter but it still happens.

Any ideas

 

[B17Crew]

Anybody here think it could be bluewhale54s' Optispark acting up?

I've heard of a "missing" that can occur due to an Opti that was going bad, but that was on higer mileage cars.

B17Crew

 

[SPANISHVETTS]

but that was on higer mileage cars.

It is water, not miles that kill the Opti. Has the motor been washed recently?

Has the chip been reprogrammed?

Is it throwing any codes? If so post them here.

More info needed.

 

[bluewhale54]

The motor has not been washed recently and it is not throwing any codes. The one thing that I have noticed is that the problem gets worse as the tempeture goes up but it still only happens between 2000 and 2800 RPM.

The dealers (3) say OPTI spark but I would think that if this was gone or going that the problem would be at any and all RPM's not at a very specific RPM?

Talked with my young son last night and he had, basically, the same problem with his TransAM. His problem only showed up under load at around 2000 RPM. He replaced the plugs then the wires and finally the coil. He then went back and put the old plugs and wires back in and the problem went away. This means that it must have been the coil.

Does it seem reasonable that it is the coil? Again if it was a bad coil I would expect the problem to be there through the entire RPM range, not at a specific RPM only.

 

[vettin1]

I had the EXACT same problem. Since I have an 85, I'm not sure about the opti spark. My problem, after a LONG time of searching, finally was one of the spark plugs was corroded causing a miss at 2000-2700 or so rpm, no matter what gear (I checked the fuel pressure, filter, EVERYTHING). I had put in bosch platinum +4's in my car about a month before, and NEVER thought it could be the spark plugs. Then a tech from zip-corvette helped me out, told me it HAD to be the plugs, changed them to platinums (the regular ones) and everything was fine. He said that platinum +4's aren't really reliable in vettes. Plus, mine didn't throw any codes since there's no sensor for that.

That's my little $.02, hope it helps!

 

[darrellwest]

I had the same problem no codes and the hotter it get the
more it mess up and it got worse has time went on replace the opit spark now it runs like a LT1 should:cool :cool

 

[vee93]

Oh boy...
I had- and now once again have this problem with my '93 automatic-LT1.

After much searching- diagnostics checking for vacuum leaks, water pump failure, fuel pump failure, bad gas, dirty air filter, fuel injection system checked & cleaned with 'Run Rite', timing checked, checks for intake manifold leak, timing chain checked, PCV valve checked, ERG valve checked for leaking, ignition timing checked, checks for leaky/-ing head gasket-*whew* this particular gremlin is back! After a $1400+ tune-up, all was well for a while.

Now, after the car warms up, say after an hour or two of driving, if I hit the go-pedal at around 35/40mph @ 1800-2000rpm, the car will buck like the gas is cutting off.

All I can think to do is have the plugs, distributor and connectors checked-AGAIN!!!

The one thing no one thought of was the actual opti-spark, including me. I guess I assumed when the ignition timing was checked, that included this. And I thought the tune-up would include this check too.

Hey, never friggin' assume a g%#$@* thing!

 

[B17Crew]

I was thinking the opti was the culprit; bluewhale54s’ problem sounds exactly like an affliction my ‘94 six-speed coupe developed. It turned out to be the opti, my problem occurred above 3,000 rpm. I had around 68,000 miles on the car. I had never washed the engine either, I think that if you live in an area with high humidity, the ambient moisture is going to take its toll on the opti.

In the summer of ‘93, I bought an off the showroom floor new ‘93 six-speed coupe, I put 3,000 miles on it a year.

One night, it leaves me stranded. The opti had a major malfunction, it was replaced under warranty. Never washed the engine, this car saw only the best sunshiny days.

Right after this had happened, I was at Corvettes at Carlisle, at one of the tents, you could meet Corvette engineers, I asked one of them about my opti failure and he had said that opti failures were common due to improper venting. He said GM had a fix on the way, but I wanted to let him know -- I sure was not happy after shelling out all that money and after only 2,000 miles, my opti had died! (He was a great guy to talk to, I could’ve listened to him talk about Corvettes for hours).

Hopefully through this forum, people are picking up on the advice that washing your engine will drastically shorten the life of your opti.

I hope that whatever the gremlin is, you chase it down soon so you can enjoy your ‘95! Please keep us informed bluewhale54.

B17Crew

 

[Bonnell]

I had exactly the same problem with my 1988 L98. Once I hit about 2K rpms under load, it would miss badly.

The dealer intially said that it sounds like the optispark but the '88 does not have one. They changed the plugs and wires, fuel filter and air filter and it runs great.

 

[bluewhale54]

Well just to let everyone know te out come of this problem.

I replaced the coil, not a very friendly process since you have to drill out some rivets which must have been forged by Thor. Once this was done the problem went away, for about 500 miles.

After about 500 miles the problem returned, or at least it seemed to return but at between 3000-3200 RPM. Frustration set it in and I took the car, very slowly since I could not exceed 80 KM (50 MPH) without a severe miss, to my vette mechanic.

The Optispark was TOAST. Wether the problem was originally the Optispark or the coil I can not be sure but the coil fixed the problem for 500 miles or a tank of gas so I can not be 100% sure what the problem was. All I know for sure is that I am out $1,250 (Canadian) for a new Optispark, installed.

 

[B17Crew]

bluewhale54,

That is a lot of cashola, Canadian or U.S., glad to hear that this is probably the fix that will let you get back to enjoying your Corvette!

Thank you for keeping us posted, this is a great place for contunued learning about Corvettes.

B17Crew