Check Engine light comes on, tach bounces, check engine light goes off, then runs ok

Rick_Leuce

Registered User
Hello,
My 1993 SC a few months ago would sometimes have its check-engine light come on for 1-2 minutes. I bought an OBD-1 code reader, but I always passed the test with no codes. I didn't think much of it, especially since my headgaskets blew and I figured there was a chance that as we were replacing the gaskets that we might have fixed whatever was causing that.

Now hat my gaskets have been replaced, I took it for a drive to town and back. Everything was working fine until I was 2 miles from my house. Suddenly the check engine light comes on, but all my gauges read normal. Then I gave the car some gas, and my tach jumped and the car sort of hesitated, then accelerated, then hesitated, then accelerated. It was sort of jerky and the first thing that went through my mind was that it might be the cam sensor, but I had already replaced that last year. Also when my cam sensor was bad (in my 1990 and 1993) the jerkiness was much worse and I don't think the check engine light came on.

It startled me, so I stuck the car in neutral (it's a 5-speed) then I watched my tach bounce multiple times (the engine was not revving). Before I had a chance to pull over, the check engine light went away. So I kept driving and the car immediately did the accelerate-hesitate-accelerate-hesitate thing one more time and it didn't do it again for the rest of the 3-minute trip home. It seems to me like this could be a worn out sensor or a bad connection. I don't remember if my car was making the tach bounce before, but I definitely had a mysterious check engine light that came and went before the head-gasket replacement.

It's a little difficult to explain, maybe I'll drive my car with a GoPro strapped to my chest and I'll try to record it happening. But I'll wait to see what some of you think before driving it again in case it's serious and driving could be dangerous or make the problem worse.

Thanks,
-Rick Leuce
 

KMT

Registered User
Unplug the cam sensor, fire it up (might take more than one or two tries), and see how it runs then.

Inspect the front harness for cuts, oil spoiling, pin corrosion, etc.

Confirm minimum 12.5 volts running.

Confirm engine grounds, small wire at header in front of battery, larger cable from pass. side engine mount to body, injector ground at back of driver side head, clean bolts & dielectric past on DIS.

tach bounce

Tons of threads here on this classic symptom, not much more to say that hasn't already been discussed, so feel free to browse ;)

Good luck.

Ken
 

decipha

Registered User
kinda sounds like an intermittent crank sensor but dont overlook the ecu relay or the ignition switch as well

very odd the CEL came on with the jerkyness seems like the ecu lost the crank input for a second there maybe
 
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