6thVetteC4

Hey what's up fellas,... Picked up a pretty nice 93 40th Anniversary coupe last week. Car has 87k original miles, previous owner just had a new fuel pump, starter, alternator and battery installed. First couple of days I had the car it would launch hard off of an easy roll, as of yesterday the car launches and then falls on its nose, picks back up for a couple seconds and does the same thing. Car idles perfect and runs like new otherwise, does not do this at 45 mph or above when you get on the gas. I have tried it with the ASR on and off and no difference, anyone have any idea where to start trouble shooting this issue? Thanks in advance.

Tom400CFI

Check the fuel level in the tank....then check fuel pressure if it's got enough gas.

6thVetteC4

Ok, I've been keeping it full, it's between 3/4 and full at the moment, could it possibly be the throttle position sensor? Seems the random searches I've been pulling up have kinda pointed in this direction as well.

fake

Opti senses low resolution and back fires ignition coil. Sounds like car ignition system mine did the same thing and found reluctant wheel completely corroded when i took opti apart. Car was once in a rail storm in 93 and i have had it since but could not believe 24 years and the failure,but water pump was leaking on it and shaft would not turn unless you applied water pumps to shaft!

Tom400CFI

That would not be the first thing that I would check. I would check fuel pressure first. Even with a new pump...I'd check pressure.

ddahlgren

Seems odd they did not change the fuel filter with the pump change from your list. I wonder if the tank sock has been changed or cleaned or something. The other odd thing on the new parts list is they are all high current electrical things.

billschroeder5842

Tom is correct- this sounds like fuel pressure issue. Pump, filter, FPR then injectors.

Congrats and have fun!

6thVetteC4

Thanks everyone, I changed the fuel filter tonight and now it runs even worse, won't take off at all, thinking it is either electrical or an injector. I have a good friend that is a Master tech, trying to get it arranged for him to have a look at it. And it was actually the crummy original fuel filter on it, I was surprised to see.

pcolt94

So the fuel pump was replaced…..…why. Possibly there was a problem and the pump was changed to correct it. The problem might be still in there.

Before I changed the fuel filter again if clogged, I would get it down to 1/2 tank and pull out the pump sending unit and inspect it well. Then take a good flashlight and look real well in the tank to see if there is any debris in the tank.

You can also drive with the fuel pressure gauge on the windshield to monitor it.

Hot Rod Roy

"Crummy original fuel filter"? That's a strange description. What did you find "crummy" about it? Are you talking about the In-Tank filter, or the filter behind the RF wheel?

aklim

Check the fuel pressure and spark quality. Check wires. Eliminate those first.

Tom400CFI

This.^ This is what you need to do. Otherwise, you're just guessing and throwing parts at it.

fake

Lets face it the opti or coil chech contact base on passenger side by pulling off coil wire If corroded replace but clean first . Start car and give it gas if it runs at idle with no hesitation ,warm it up and wait till it goes into close loop (180) degrees on car gauge . If car bucks after warm change coil because with your high mileage it breaks down with heat and grease on it and it is a lot easier than opti. Also on water pump you have a two wire connector (it is in the three oclock position), check that connector is secure . That can be bench checked if you remove it with a meter. Good luck

Purple92

Another vote for checking fuel pressure while running - If it dips - you need to figure out why - if it doesn't you can eliminate the fuel supply system as the problem.

I'd also pull a few of the easier to get at plugs - they are probably original as well, and their looks might tell you a few things about what's going on with the engine.