I'm the owner of a '94 Z28. I have this problem that i can't figure out. If i'm in 6th gear going 70mph, and mash the gas to the floor, sometimes my car will buck and it will get jerky. The rpms jump up slightly when this happens. My first thought is a slipping clutch. But then if i mash the gas down in first gear, it pulls good, but sometimes at about 4500 rpm i'll get this hesitation where my car just stops pulling, but i really don't feel a slipping of the clutch b/c it pulls hard all the way up. Now could this be a worn clutch, or maybe a bad plug or wire causing a misfire?
P.S.-this usually happens once i've been driving for a while and the car is heated up. Hope someone can help

 

Well, you shoudlnt mash down on the gas when your in 6th, but, if it starts to vibrate it could be a transmission mount, or a loose spark plug wire or burnt one, but you would feel it in any gear.

 

i don't have to mash the gas down for it to happen, it also happens in other gears just not as bad

 

Since the problem as you said in the first post, occurs around 4500 RPM. Have you ever checked your fuel pressure when the problem occurs? Have you ever changed your fuel filter for that matter?

I would rule out the fuel system first by checking the fuel pressure, changing the fuel filter and then have the injectors professionally cleaned. Even if the pressure is good, an injector could be restricted. As fuel sits in the injector with a hot engine after shut down, deposits will form in the injectors.

 

The same thing was happening to me in my car. When doing a burnout the rpms would jump quicker than normal, and during hard acceleration (2nd gear most noticeable) the car would kind of fall on it's face.
When the clutch was removed there wasn't much left, just the disc.
Hope this helps.

 

My car would rattle and vibrate whenever i would give it throttle in any gear....checked the plugs, one of the wires was not all the way on, pushed it back on, the problem was fixed. Check the plugs and wires, if they are ok, check fuel.

 

Thanks for the help...no one thinks that this problem can be the clutch? Moslty in 5th and 6th gear the rpms will jump up, it feels like something is slipping

 

Just got back form the shop....it turns out that my opti-spark is covered in oil from my numerous oil leaks, and thats causing a misfire(thats what all the stumbling and hesitation was) For now i will get the crank oil leak fixed, full tune-up(plugs wires pcv ect..) and a new opti, he gave me a price around $900, does this sound about right to you guys out there?

 

I think just the opti itself for your car is listed at about $350-$400 in Summit, so when you add the price for fixing the leaks, materials, and labor that seems to be a fair price