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View Full Version : What supplies signal to the tach?



stevenwsanborn
05-05-2012, 05:58 PM
My 89 SC keeps randomly dieing while driving, when it happens the tach instantly drops to zero even though the motor is still turning, oil pressure gauge won't move either. It's been getting more frequent recently but starts normally after 5-10 minutes or so. I'm thinking that the ecm is the only possibility with a common connection to tach and oil pressure gauges?

DeanWinchester
05-05-2012, 06:15 PM
Crankshaft position sensor is likely effing up. That or your harmonic balancer is wobbling.

stevenwsanborn
05-05-2012, 06:26 PM
Why would the oil pressure gauge die? It doesn't even move while cranking until the "ghost" goes away.

RalphP
05-05-2012, 07:01 PM
Why would the oil pressure gauge die? It doesn't even move while cranking until the "ghost" goes away.

Could be unrelated - the oil pressure sender is in the same general area (front of motor), and the connector is known to work loose after years of operation.

I'd first treat them as two separate problems - fix the tach problem and see if that fixes the oil pressure problem.

RwP

stevenwsanborn
05-05-2012, 09:12 PM
Replaced cam sensor and dis, still same issue.

stevenwsanborn
05-05-2012, 09:32 PM
Where is the ecm located?

DeanWinchester
05-05-2012, 11:22 PM
Replaced cam sensor and dis, still same issue.

I could have told you that. The cam sensor doesn't have anything to do with the tach. The crank sensor on the other hand does.

XR7 Dave
05-05-2012, 11:30 PM
I could have told you that. The cam sensor doesn't have anything to do with the tach. The crank sensor on the other hand does.
Au contraire. A crank sensor problem will kill the motor instantly, but when the motor continues to run while the tach drops to -0-, it is often the cam sensor or DIS that is the cause.

{edit} Sorry, misread the first post. :o If the engine is dying also, then crank sensor is a common cause. If your upshift light stays on while the engine is cranking, then that's a sure bet. Oil pressure will be at -0- because - well - if the engine isn't running, it won't have oil pressure.

stevenwsanborn
05-06-2012, 01:50 AM
I appreciate all the input. Only tried cam sensor and dis cuz they were readily available and I was stranded. Don't think its wiring cuz moving things around never makes a difference.