Well i just finished rebuilding my 4+3, and sure enough, another problem has risen!

First noticed it last week (when in second gear), accelerating from around 1200rpm it would stumble and hesitate a little. No backfires, but i could feel it stop and go, even though i was on the pedal steady.

Now, it has gotten worse. In every gear, i feel it hesitate, and even when im holding 40 mph in 4th, i can feel it hesitating as i go. For the most part, it only does it once the engine is nice and hot (does it a little when cold but not much). I am not getting any trouble codes, and no service engine light coming on.

I have replaced the fuel filter today and stills does the same thing. I also drove it around with the o2 sensor unplugged, and it didnt seem to change much at all (although that brought the service light on, code 13 and 22).

Should i replace the o2 sensor, or maybe could i be looking at the tps or even fuel pump? Thanks

I have been having a similar problem with my 85. I'm thinking it might be the fuel injectors but I'm not really sure. I haven't been driving the car much lately but I want to get it running good.

Im not thinking injectors because the problem just started, and has gotten considerably worse everyday (total of about 150 miles since last week when i first noticed).

It seems like its being starved of fuel, but i didnt think that the fuel pump could slowly lose pressure. Figured it would either work and be dead. Maybe tomorrow i will get my hands on a fuel pressure gauge and check it out. (although when my f350's fuel pump crapped it, it slowly started to lose life, like i am having now).

FYI the car throttles fine in neutral, just hesitates when driving under load.

i had an f150 that did exactly what your describing it would hesitate and get worse when the motor warmed up. turned out to be just a fouled spark plug try checking them:beerbang:

You need to verify your fuel pressure is 55 psi. If it's not, you need to find out why. How many miles do you have on your fuel pump? If you have over 100,000 miles on it, you might as well change it based on miles alone.

Ok i will be checking fuel pressure tonight after work. The car has 69,000 miles, and i imagine its the original fuel pump. 55 psi at the schrader valve on the rail??

Checked the fuel pressure. Was idling at 35psi, and when i throttled it up to about 4000 the pressure went to about 41 and then would drop down to around 20 quickly(regulator dropping the pressure?). Is this normal?

Also, i changed the spark plugs and got a noticeable difference. Maybe plug wires and coil? The wires are original.

that fuel pressure seems low to me, that could be part of the issue.

Sorry i had a typo there. I meant to say that when i throttled it up, the pressure would rise to about 40-41psi.

Manual says 34-39 psi so it seems fine.

The only reason i believe the fuel pressure isnt a problem, is because the car starts fine and runs 90% normal when cold, but after driving for 10-15 minutes and it gets hot, the car runs horrible.

well it's definetely not the fuel pressure then, that is good pressure numbers, I would check the 02's. Good luck my friend!

Changed the oxygen sensor and its still doing it. Car stumbles and hesitates when i am slowly speeding up, and when i am holding a constant speed i can feel it on & off (a little more on hills and when i first get on it a little).


BUT, if i put the pedal down to the floor, it will stumble for a second and then take off like a bat out of hell, so im figuring its not a fuel pump problem.

Any other ideas, maybe plug wires, tps, vacuum problem?? Thanks everyone

Changed the oxygen sensor and its still doing it. Car stumbles and hesitates when i am slowly speeding up, and when i am holding a constant speed i can feel it on & off (a little more on hills and when i first get on it a little).


BUT, if i put the pedal down to the floor, it will stumble for a second and then take off like a bat out of hell, so im figuring its not a fuel pump problem.

Any other ideas, maybe plug wires, tps, vacuum problem?? Thanks everyone

It could be any one of these things that you mention. The fuel pressure is right where you want it to be, although you haven't tested it under load yet (something you might want to do). When was the last time a complete tune up was done? Where the car is 24 years old it wouldn't be a bad idea to give it a complete tune up.

Good idea. Ill be working on it today, looks like we've got some rain coming and ive got the entire day off. :chores013:

This sounds like a clogged vacuum port somewhere. Try cleaning the throttle body and if you have gaskets pull the egr and clean out it's passages. Another is that the cold start injector might be partly open and messing with the mixture??? That would be a giant problem since i still haven't found a source for new ones.

there should be someone out there called the "Vette Doctor" and all this person would do is fly all over the U.S. and know how and then fix all Vette issues. Wheres the Vette Doctor when you need him!

I usually dont have any problems when it comes to fixing the vette (which is often lol), or any other vehicles at that. But this ones got me a little stumped. Maybe im just not being patient enough.

I just might have found the problem. After looking under the hood while she was running, i noticed a faint ticking/sparking noise. When i looked real carefully, i noticed a spark plug wire cap was arching out intermittently (about 8-15 sparks every 10 seconds) against the manifold. Gonna go pick up some new wires and change them this afternoon. Ill let everyone know how it goes after. :burnout:

Edit- Every time it was sparking out, i could hear the engine bog down and idle real choppy, and then when it stopped for a few seconds i would hear the engine pick up and sound smoother.

Manual says 34-39 psi so it seems fine.

The only reason i believe the fuel pressure isnt a problem, is because the car starts fine and runs 90% normal when cold, but after driving for 10-15 minutes and it gets hot, the car runs horrible.


I'm sorry I gave you the incorrect figure of 55 psi. I just re-checked the manual and found out 34-39 psi is the pressure you need. The best way to check fuel pressure is to put the pressure gauge on your windshield, tape it down with strapping tape, THEN take your car out for a drive. Then you can observe what's happening to your fuel pressure when you give it full throttle. The pressure should hold steady at the 34-39 psi at ANY throttle opening or engine load.

Well the bad spark plug wire was the problem. Now she runs stronger than ever, and my fuel mileage is back to where it normally was. Also, she holds a perfect idle (only varies 10 rpm). :banana: :beerbang: :friday:

Well the bad spark plug wire was the problem. Now she runs stronger than ever, and my fuel mileage is back to where it normally was. Also, she holds a perfect idle (only varies 10 rpm). :banana: :beerbang: :friday:

I am glad that you got it fixed buddy!:cheers: