oifcombatvet

1989 Corvette L98 with 6 speed.

New:
plugs
wires
fuel pump
fuel strainer/sock
fuel filter
TPS: tested at .054
fuel pump relay

ALSO: No SES light

No matter whether wide open throttle or easier acceleration my car stumbles, hesitates, starting at 3200rpms. It seems like it just won't go any higher, it does stumble up and down to the high 3000's when it first starts but that is about it.

Need some advice/starting point/what have you don to solve this problem. Any help would be greatly appreciated.

Thank you all.

jesredvette

I went through the exact same symptoms last year with my '88.

Disconnect your MAF sensor plug and try it. If it runs noticeably better, that is your problem. Rebuilt replacements (Autozone, etc.) are fairly inexpensive; new ones are quite pricey. Rebuilt worked fine for me.

theadmiral94

Hi oifcombatvet,

Has the distributor cap and rotor been replaced?

Has the coil been checked?

Has the distributor ignition module been checked?

Does it only happen under load, or does it happen in the driveway/garage too?

what does the exhaust smell like when it stumbles (rich gas smell or lean). Could indicate fuel issue caused by injectors or sensors PCM uses to control fuel (e.g. MAP, O2 sensors).

Cliff Harris

Check the plug wires to make SURE they're on the right distributor terminals.

The car will run just fine on 6 cylinders, which it will do if you have two wires crossed (you don't need to ask how I know this). Try this little helper:

hemivett

A bad o2 sensor will do the same thing. Runs fine when you first start out, but the more throttle you give it, the more it noses over. h

oifcombatvet

Distributor cap/rotor has not been replaced.

Coil has not been checked

It will do it under load or when I rev it in the driveway up to 3200 rpms

I have not smelled the exhaust yet,

oifcombatvet

I will check the MAF.

I also double, triple checked the firing order and that is good to go.

Thanks everyone for their input so far.

oifcombatvet

*Quick Update*

Unplugged the MAF and it still stuttered/hesitated/stumbled at 3200rpms.

coupeguy2001

a lot of the time, when you replace the plug wires, they will need some hearty pushing on to make them " click" onto the posts.The rubber pushes the wires up off the dist. posts with vibration and some heat. Then they have an excessive air gap, and it stumbles. works the same on the plugs as well.

aklim

Have you checked fuel pressure at that RPM? Maybe tape a fuel pressure gauge to the windshield and hit it hard and see how far it drops off. Sure, you are having your new fuel pump relay but what if the wires to the pump are bad and not giving it the full current?

Also, what is the quality of the spark? Is it blue? Have you checked for spark leaks using a spray mist bottle of water at night?

oifcombatvet

Fuel pressure is 34-36.

I took it to a Corvette shop in my town and they ran their tests on it and told me it was the EGR Valve. They wanted an arm and a leg to replace it so, but I believe I can do it myself.

Along with the EGR Valve replacement, what are some other good things to do with the plenum off? I believe it would be best to take advantage of a crappy situation.

I read alot about adjustable fuel pressure regulators. How do you adjust these? Do they adjust automatically or do you have to tune them?

Thanks everyone.

aklim

Pressure is a little low. 45 would probably be better. I would check what it is at wide open throttle. If you have the stock one, how long does it take to bleed down after shutdown? Adjustable unit means YOU adjust it with a gauge.

I would definitely take the injectors to FIC for cleaning and testing.

bjankuski

Check your cap and rotor, this sounds like an ignition issue.

oifcombatvet

Alright here is the new issue:

Installed a new EGR Valve today. Hooked everything up, vacuum lines, sensors, etc.

All it does is crank. I pressed down on the Schraeder Valve and it is just bubbling...barely. It will turn over but never fires. I can here the fuel pump turn, fuel pump fuse is good.

I CAN hear a sucking/hissing noise while the fuel pump turns on when you turn the key. When the fuel pump turns off, the noise stops. It sounds like it is coming from the FPR/EGR/Under Plenum area. All vacuum hoses are connected from what I can tell.

Any ideas???? Thanks.

oifcombatvet

I looked back over, and I found that the plastic hose that goes from the FPR into the plenum was on the wrong port. I switched the hoses to the correct ports on the plenum and it is still having the same issue.

coupeguy2001

you need to take fuel pressure again,

but on the EGR thing, over on the right exhaust manifold, there is the hot air tube screwed on with 2 screws/bolts. loosen them up, get some roofing flashing or thin piece of aluminum, and loosen the screws and slide a little piece of metal in between the joint, and tighten the screws. That effectively eliminates the EGR gasses from the intake, and so if the Egr valve was a problem, this is an effective way to stop the flow of gasses to check the valve.


On the hissing, check to see that you hooked up your power brake booster line correctly.

oifcombatvet

I will probably have to buy a new fuel pressure gauge. Last week I tried to check pressure, unscrewed the Schraeder Valve and put the fitting in, hooked up to my gauge and it didn't register any pressure.

I'll check the brake booster line. I know it's screwed in good to the part of the plenum. I'll recheck the check valve.

oifcombatvet

Brake Booster is good to go.

The hissing/sucking/shhhhhhh sounds like it is coming from the FPR/Plenum/EGR area.

aklim

Clamp off the return line at the tank and see if it builds up pressure.

oifcombatvet

Which line is the return? I know there are three that all connect into the sender.

Thank you. I can't wait to get off work and try and fix this!