Help please
I have a 1994 C-4, black/black automatic with approximately 78,00 fun miles on her. I have owned for 7 years.
Recently, while driving on very hot summer days, the engine will start sputtering/bucking. This usually occurs after driving at highway speed (65-70) for a while and only when giving a little extra gas to pass or speed up and in the 1800-2000 rpm range. The water temp is around 230-235 when occurs. If I drive on cruise control, or regular it is ok. If I really get on the pedal and in higher rpm's it is ok, too. Once car is cooled, it is fine.
I have had the plugs/wires/fuel injectors checked and they are all ok. They are the originals, too. There are no codes showing. Local GM mechanic says car is fine and needs nothing. The fans come on when they are supposed to.
I have been told that maybe it's vapor lock, but I thought that was on carburators only.
I have also been told that maybe it's a computer board warping and causing problem.
This is strange and I have had at three mechanics who say I have to bring in when it does it, as they can't see anything wrong.

If anyone has suggestions, please advise.
Thanks

 

If you can't get it to do it consistently enough to have it do it for a mechanic, you have two choices; wait for it to get worse or start replacing parts, hoping to fix it. I would go ahead and replace the cap, rotor, plugs and wires. This isn't easy on an LT1, but considering the age of these parts it should be done regardless. Replace the fuel filter too, its not the problem since it runs good at higher rpm, but if its original, it should be replaced.

Good Luck, Paul

 

good advice, cant believe your still running on the original parts

 

HAHA. When I bought my '89 this past summer (96,000 miles) it still had the original EVERYTHING. Cap, wires, plugs, fuel filter, you name it. The plugs were worn so bad the gap was like .065 and the ends were worn almost to a point. Unbelieveably, the car still ran great. No codes, no misses, nothing. I still haven't had a mechanical failure. Everything I've done to the car has been modifications at will. I've been lucky.


To bullmarket......If it does happen to be a vaporlock problem of sorts, consider having a tune done to lower your fan on/off temps and maybe a 180* thermostat. By doing this your car should never go above 200 or 205 or wherever you decide to have the fans set to come on. If you never have the problem below 205 then that might fix it for you. I would to the cap, wires, plugs and fuel filter as well tho, and do them first to see if they fix the problem.

 

Thanks to all for the advice.
The fuel filter was checked and is good. I asked three mechanic's (one GM 'corvette guy') about the plugs, wires, etc.
They all said they appear ok and wouldn't change them until the required 100k miles.
I guess they don't want the business or are lazy.
I was hoping not to 'just replace parts and hope for the best', but I guess I'll start with the spark.
Thanks again.

 

mine did that also and it was the fuel pump. thats a 100 dollar fix if you can do it yourself.

 

Thanks
The fuel pump was checked out already and was told it was fine.
I'll start with the plugs, wires, etc and see how that goes.

 

My plug wires looked great on the 302 that I had spark jumping across. Couldn't tell by looking. I would do the plugs, wires, cap, fuel filter, etc. It is due for a tune up anyway. They if that doesn't fix it I would dig deeper before blindly replacing any other parts. Let us know what you find out!! Good luck.