I Have a 86 L98 automatic. The car takes 15-20 seconds to start cold. when it starts it idles up and down, (1300-500). It will run for about 5-10 seconds then cut out. Once i get it to idle right (700 RPM). its fine. If i mess with the throttle, it will start to stumble, then it will jump to 1300 RPM then stumble. When it stumbles it miss-fires out the intake, and the exhaust. (which makes me think it has to do with electrical timing) sometimes it will be a pop-pop-pop. other times it will pop once. if i move the throttle a tad. it begins to stumble. When driving it will start to surge then cut out.

I purchased the car 3 months ago. at that time it ran decent. it idled high. (1100 Rpm) but not like now. I replaced the IAC, TPS, Plugs, Replaced the Altenator, the distributor cap, rotor, and coil.

I didnt realize it at the time, but it has no AIR pump, EGR, or Catalytic converters, and it has headers, I would think the computer would have to be tuned for the missing parts.

I think the car is retarding the spark then advancing it. If so, where would the problem be, what are my choices.

I Love my vette and just want to be able to drive it. If any one can help, it would be greatly appreciated.

 

Try pulling some codes first, and go on from there.

 

the guy that owned the car removed the check engine light, so i cant do the paper clip method of code pulling. if i could drive it to the corvette shop 10 miles away i would, but it wont make it there. I bet it is pulling codes.

Thanks for the help.

 

From the top, did you get kissed cause I am guessing you got screwed. What do you mean " removed the SES (check engine) light. Did he simply remove the bulb or did he rip the wiring all the way back to the ECM? Without some way to check for faults throwing parts at it is not a good thing. Can someone do a scan where it sits? Headers, does it have an 02 sensor?

 

Why don't you post your location? Someone with a scanner might be just down the road.

 

The PO probably removed the SES light for a reason....because it wouldn't go off. Which might offer us a clue as to what's ailing your car. Get the SES light working again...that's your first assignment. We can't make it feel better if we don't know where it hurts.

 

I just pulled off the Info Center and the SES light was missing. I going to buy a bulb and see what codes im pulling. The car DOES have O2 sensor, but I havent checked it yet. Im in Land O' Lakes, FL.

 

I replaced the bulb and its pulling multiple codes. I have not checked to see what each is. (Ran out of time today) The engine is miss-firing out the intake. Im thinking i might have a fuel problem.

 

MISS firing or BACK firing?

If it's back firing out of the intake, let's first run a compression check to rule out a stuck valve or the timing chain having jumped.

Then let's check ignition timing. If you can get it to run long enough, set base timing to 6 degrees BTDC with the ECM wire to the distributor disconnected.

When you replaced the cap and rotor, are you 100% positive you got the plug wires back on the correct towers? Run the firing order to verify.

Once those things are ruled out, let's start sorting through the codes and figuring out what the computer is looking for that it's not getting and go from there. Your symptoms also sound like a failing ignition module....wouldn't hurt to take it out and have it tested.

It sounds like the PO hacked up this car without knowing what he was doing. Nothing insurmountable, but it may take some time to work it all out.

 

What Frizel said. You need to backup to make sure everything you did was done correctly. Back to basics so to speak.

 

I agree with starting with the basics first. Check the wires and also did this problem start after your last stop at the gas station? Bad gas can cause the problems you are discribing..Just a thought..WW

 

i checked the plug wire to distributor order. and its correct. the timing is set to 6 degrees BTDC. The Gas I recently put in was not premium.

Thanks for the help.

 

I checked SES. Pulling code 33 (MAF) and 42 (EST). Frizel was right and I replaced the ignition module. Its running better and is no longer pulling a code 42. My friend said it could be compounding variables, MAF,EST,low fuel quality. I need to sort through a few more things. Got to love project cars.

Thanks a ton for the Help!

 

Did the new module correct the backfiring issue? And did you remember a light coating of module grease underneath it? If the backfiring stopped, we can probably rule out an internal mechanical issue and focus on the emissions system. Test the voltage on terminal C of the MAF sensor. The manual says it should be .5 volts at idle and go to 4.7 volts at WOT. I believe there is a relay for the MAF, but I don't recall where it's located on the TPI cars.

Just for sh**s and giggles and to rule out a fuel system issue, check your fuel pressure too and see what it reads, and replace the fuel filter. Should be 38-42 psi at the rail, and remain in that range through all operating paramaters.

When you shake it down, they need 3 things to run correctly:

1. Suitable compression.
2. A suitable fuel / air mixture.
3. A suitably strong spark delivered at the correct time.

That's it. If those three conditions are met, they run correctly. If not, they don't. This applies to every internal combustion engine built in the last 100 years.

Troubleshooting always comes down to finding which of the above isn't correct, and then finding out which component is causing the malfunction. I'm a huge believer in troubleshooting. I detest throwing parts (& $$$) at a problem hoping it will go away. This comes from growing up poor....when making a mistake and buying the wrong part just wasn't an option. Stuck with me 4 decades later.

At any rate, glad it's running better. Keep us posted on the progress.

 

I had something similar. I don't like just throwing parts at a problem, but.....

Try changing the coolant temp switch.....$11.00 at autozone. It fixed my 89 coupe.

Good Luck....Let us know