JetJock

I have a 91 L98 Vette that has seen plenty of mechanics. Problem is that the car starts up fine and drives around great but punching it, it acts like I have a plug not firing. It hestitates on accleration. I've replaced the plug wires because one of them was torn up and also put new plugs in it. I also checked the fuel injector wiring with a noid light. Everything looks good. New injectors were put in from FIC. It's not a fuel problem as in contaminated fuel. I have gone through the service manual troubleshooting. Only thing that I haven't done yet is undo the plug wire and see what happens. Any ideas?

antfarmer2

New o2 or old fpr.

JetJock

fpr? By the way no codes.

antfarmer2

Either one can happen with no codes. FPR fuel pressure regulator. Or vacumm leak.

VikingTrad3r

i had an 85 L98 that would do exactly as you said. for me it must have been an air leak.

in the process of diagnosing to find it out, i discovered a leaking head gasket and toasted trans. Among other things. So much was changed i dont know what actually fixed it.

have you taken your cap off to inspect the rotor?

ex-x-fire

The first thing you should check is the fuel pressure.

jimmers

. Sounds like a fuel issue to me. I had a similar issue a few years ago, turned out to be the fuel pump.

aklim

Check fuel pressure. Turn it on a run with the FPR hose off and see what kind of pressure you get. Shut it down and see how long it holds. Next day, take it for a WOT run and while you are doing that, see how the fuel pressure holds. It might have a slight dip but it should get back to full pressure pretty quick.

aklim

The ECM is kinda primitive so it might do something but still not throw a code. Don't be too reliant on the codes. As mentioned, check the fuel pressure. If you like, remove the FPR hose, cap the nipple at the manifold and that will give you full pressure when you do a WOT run. If the pressure falls flat, you have a supply issue. Report back with the fuel test results and we can go further.

Also, what about ignition? Have you checked for a blue flame? How old is the cap and rotor?

JetJock

The engines acts like it's missing on acceleration like one of the plugs isnt firing. On start up, it sounds normal until I punch it. Then it acts kinda weird and then starts to pull but sounding like a leaking exhaust gasket or a missing cylinder. I have to leave town for a few days but that gives me something to check after I'm back.

JimLentz

Are you sure all of the wires are routed to the right plugs/cylinders?

aklim

What happens when you start it cold and instantly do a WOT run in gear?

JetJock

Yes.

JetJock

Haven't tried that yet.

desertmike1

Have you done an compression test yet?

ryank9398

Sounds like mine. My coil was leaky

kael

Sounds exactly what happened to mine as well, ran fine until pushing the pedal hard. Got worse over time. Turned out to be the fuel pump for me.

Basics first!

cardo0

Well you have an L98 motor and ECM but that's how my LT1 behaves like when I put regular low octane fuel in it. The LT1 ECM pulls back enough timing advance to make it buck and surge just trying to get on the freeway.

Replacing parts is no way to troubleshoot. You need to capture a real time scan so you can look at the sensors like the knock counts. Have you even checked for codes yet? Some DTC will stay in history but not light the MIL/SES - scanner needed to read history. Obtaining a FSM w/diagnostic charts is a good purchase if you plan on maintaining the car yourself.

Good luck.

JetJock

I had to replace the plug wires because one was torn up and disconnected from the boot and another one was burned. I had to replace the spark plugs because the wrong ones were in it. I did a noid check so I know the harness is good. I did check the fuel regulator back a couple of years ago but that doesn't mean anything. I just got back from Florida so I will do the fuel pressure check tomorrow. I trying to sell the car and trying to get it to run halfway decent.

I don't know how old the cap and rotor are.

The injectors were put in about two years ago.

JetJock

I did the fuel pressure check. With key on and engine not running, I got 41 psi of fuel pressure. With engine running, it dropped to 37 psi. It maintained 37 or so from idle to 2000 rpm. I ran it twice, same results. It's holding about 37 psi with engine off and key off. I did notice the miss while running it. I'm thinking that it might be the ignition system. I'm going to pull the cap and rotor and take a look at them.

According to the service manual, that is a satisfactory check.