Cardad02

My 93 (automatic) only has 15,000 miles on it. Two years ago, I replaced the plugs, wires, fuel filter, PCV, air filter (K&N) and exhaust (Magnflow). The car ran great until the end of last summer. At approximately 40mph, the car shakes (feels like it's right under the driver's seat), acceleration disappears, and then it kicks in with a large RPM spike. After a 10 second delay, the shaking stops and the car runs fine - until I drop below 40 and it happens again. Additionally, I can not "step on it" at a traffic light - it does the same thing. If I use even, smooth acceleration (off of the line) it is fine - until I hit 40mph.

All fluids are changed religiously. Nothing is unconnected. No modifications or chips.
Any advice is truly appreciated.

DanielRicany

Okay, does the car do this when cold? Only when warm? Can you locate which cylinder it's coming from? What color are your spark plugs? If you put the car in the garage with the lights off and the engine running, do you see any arcing or spark coming from the engine bay? If it's the original Optispark on there, that's where I'm pointing my finger first.

But I'd still like to know the conditions of when it does it.

Cardad02

It is worse when cold, but it also happens when warm. I have not seen any arching or spark from the engine bay. It is the original Optispark. Is there a test that I can conduct to determine the output of the Optispark?

I have not pulled the plugs since I did the tune-up in 2012. They were NOS A.C. Delco plugs.

I am not a mechanic, but I do my best to do my own work. I just purchased a Snap-on "brick" kit (complete) and am going to run to run a diagnostic this weekend.

I do appreciate your response.

DanielRicany

When it does it when it's cold, unplug the MAF sensor. Does it get better or worse?

Cardad02

It's raining here in Seattle. I'm going to wait until it clears before taking the test drive. I will keep you posted. Thanks.

Cardad02

I checked the fuel pressure and it was only 26 PSI (ignition on, engine off). I decided to add new parts over the last two months:

Water Pump and sensor
Pettis optispark
TPS
Fuel pressure regulator
Cleaned the fuel rail and the injectors
Serpentine belt
Delphi Fuel Pump - I removed the entire unit from the tank.
Replaced every hose

Once I completed the project, the fuel pressure went up to 41PSI (ignition on, engine off). After all that work, I have the same problems.

bad-zr1

Did you use the SnapOn MT2500? It will tell you if there are any cylinder misfires and which one(s).

Cardad02

Yes. Everything indicates the car is fine. I took it out yesterday and it did the same thing, but; the lights on the the dash started to flicker and the car felt like it was going to stall.
It never stalled.

Under normal driving it sounds and runs perfect. I slowly accelerated to75 MPH (on an open back road) yesterday without a problem. Once I hit the gas for passing, the hesitation and misses happen.

I'm not a mechanic by any streach, but I took my time, purchased good American made parts and did my research. Some people are saying replace the ICM and the knock sensor? How do I test to see if they are bad? At this point, everything on this car will be new. Thanks to everyone for their help and advice.