I was driving downt the road 70mph and the car started to cut out a little, i got about another mile down the road and it went to way worse and hardly will run at all if you dont keep your foot on the pedal. I was able to get it home and cant seem to figure out the issue. It runs REALLY rough and barely idles without dying. I checked the fuel pressure thinking it may be the fuel pump but it is at 40 ( a little low but consistent) about where it should be. I had some new O2 sensors so i put those in thinking it may be that but it didnt help at all. Its a 94 with 39000 miles. Could it be the MAP sensor? Optispark? Ideas?

 

How does it run now? Will it start right up? Does it run better cold/hot?
Codes? Are the air intake tubes tight on the MAF/Throttle Body?

Just for grins and giggles with they key off, unplug the MAF and try to start and see how it runs. This WILL throw the ECM into open loop and turn on the CEL and fans.

 

Speaking from experience, it is probably the Optispark that is corroded out due to water seepage.

 

It starts right up without issue and it doesnt make any difference if it is hot or cold. It idles as bad as it runs. I took it up to a local shop but they dont have any way to read codes on this car i was going to take it to a chevrolet dealership in the morning. From reading about MAP sensors on the forums here it sounds like that may be whats wrong with it but i am not sure. As far as seapage from the waterpump i replaced it with a new waterpump back in febuary so i dont think that is it unless it is leaking from under the pump itself although i have never seen a drop of coolant on the garage floor.

 

Find a new shop, your car has the OBDII port and any decent scan tool should be compatible. I have a used "entry" level professional scan tool that works on my 93 for crying out loud. You can pull any codes that there maybe your self via the Instrument Cluster. Do a search you may find many posts on this.

FYI, keep in mind a 94 has a MAP and a MAF. The MAF has primary control the MAP serves as a backup. The MAF is the one in the air intake tubing. The MAP is on the manifold itself behind the throttle body and much smaller.

 

You want to throw parts at it?
ICM, Coil, Harness from opti to the passenger side connection, opti, wires, plugs, fuel pump, fuel filter

Otherwise get thee a factory service manual and follow the trouble tree for your problem.

 

It was running really rich and dripping black out of the exhuast when i started it earlier and the exhuast tips are really black on the outer edge as well.

 

Just a thought to get a simple thing out of the way.

Check the digital temperature gauge on the speedometer cluster. Does the temperature seem correct for the engine at ambient and higher running temperature. That sensor that drives that display also drives the PCM for A/F fuel management. If the temperature is wrong, the PCM will be doing some very weird things along the lines of making things rich.

Probably not an issue but also check the vacuum line for the FPR to make sure it is not leaking fuel back into the engine.

 

If it is the original Optispark unit, that would be my guess.

Pull codes and see what comes up, I think autozone might be able to do it for free?

 

Digital guage shows 194-198 and i just replaced the sensor that goes to the dial gauge about a week ago and it is constant at about the same as the digital or a little higher. They did a smoke test for vacuum leaks and came up with nothing this afternoon. I am leaning towards the ignition coil and am going to get it to the chevy dealership tomorrow i think. There is alot to read on these forums and throwing parts at it seems a bit costly.

 

Most of the zone personal will come out with a OBD2 reader and then try to figure out why they can't get the codes and establish communications. They don’t have a OBD1 reader with the necessary OBD2 connector. Nor do they have the knowledge to get the codes from the on board diagnostics.


Scottermis
If you have you car at a dealership, surly they should be able to tell you if there are any codes. May or may not help but a starting point.

If you have the engine running, then you should be able to pull a plug wire and check for spark. You should be able to pull a 1/2 inch white spark. If that looks pretty good the coil and ICM are probably OK even though it is basically a quick opinion judgment test. The dealership should also be able to give you this information, ask them.

 

It was the MAF sensor. I never took it in to the dealership i just replaced it on a hunch and that was the culprit. While i was at it i changed out the MAP but when i went to unplug the wiring harness from it the housing that has the clip on it fell apart in my hand. Guess i am going to need another one of those too!

 

What a hunch. Educated guess or plain luck if you have it fixed that what counts.

There was lots of suggestions but 93Rubie was on the right track. This problem did not have any of the usual standard symptoms and I thought it was a bit more complex. I was not close either. I just wonder if there were any codes that would point this out.

 

Glad to hear you got it fixed.

I always say, start simple. Unplugging the MAF because it is SO important is a easy simple start if it runs the same or worse you can assume the MAF is probably NOT the issue. However, if you had unplugged it and it ran much better you have at least an idea that it runs better without it or at least it runs better in open loop. This would only take literally seconds to do.

The other thing to drivability diagnostics is to NOT assume ANYTHING. Come at the problem with a blank slate. Use only logic and specific testing to find the issue. Guessing rarely works. Hence the crys of ICM, Opti-Spark and other usual suspects. Forums are great but take everything with a grain of salt. Trust but VERIFY for yourself on YOUR car, before replacing parts. Just because similar/same symptoms occurs on one car does NOT mean the same fix is needed on YOUR car. Trust but verify.

Start simple get more complex as you go. I am a strong believer in hunches especially if your a experienced diagnostician. Sometimes it is dumb luck but if it fixes it, whatever works.

FYI, I've been wrenching for 4 years for a living and am a ASE Master Certified Technician, so I have half a clue, which is half more than the average person. NOT trying to belittle anyone, but I'm saying I've been there, saw that, done that, on a daily basis.

 

this happened to me one time, drove me nuts for a day or two, till i figured out one of my spark plug wires was touching a header and burnt through. replaced and problem solved

 

I put a cardone reman MAF in the car because it was all i could find in stock anywhere for a replacement. The car runs MUCH better now but it still has some issues i think. It is a bit groggy at low rpms for some reason and i cant seem to figure out why. I ordered an AC Delco MAF but it wont be here until probably tuesday or wednesday i am hoping it is as simple as that.