intermitant loss of tach signal and rough running

fhrrmc

Registered User
I have an 89 SC w/ a 5 speed transmission 160,000 miles. When driving there is a momentary loss of tach signal and what seems like 1/2 the cylinders stop firing causing the car to buck and jump. the car will still idle but under power it is very, very rough, suddenly the tach signal returns and the car runs smoothly. The frequency and duration is increasing. The last couple of times, this lasted for several miles before smoothing out again.
Some history, I have had a broken Harmonic balancer (twice). The first time the bracket that holds the crank position sensor also was broken and subsequently repaired. I have not replaced either the cam sensor or the crank sensor. About a year ago I did replace the ignition control module and the ignition coil.
 
Sounds like a bad cam sensor based on what you've described. I took a quick video of when my 89 went bad - I'd either lose the tach completely or it would do the following.

https://www.youtube.com/watch?v=2VXdWZmKgkw

Sounds like you have a good grasp on this issue - it's usually Cam/Crank/DIS or the wiring itself. An easy way to also test it - unplug the sensor. The car will start off the computer usually after 3-4 tries of trying. You'll be able to drive around (no tach at all)...but if the issue goes away it gives more direction before you start buying parts.

-Tim
 
A Tim notes, typical symptoms of an issue w/the cam sensor and/or it's connector/wiring. The stumble is when the computer toggles between using default sensor values and checking for real signal to see if the sensor has come back online.

Best to read the codes, first, if you can, rather than risk firing the parts cannon at it ;)
 
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