My Tach is begining to act funky. It will bounce sometimes 200 rpm and sometimes it will bounce between 2k and 4k. Am I correct in assuming the pickup sensor on the harmonic balancer is the culprit?

 

Can't help you with that problem, but I never know when mine is going to work

 

if you notice that your amp guage fluctuates with the tach i would almost bet that the crank trigger is the problem. i found that out once when i accidently smashed the trigger wires behind the fan bracket....truck would start and run but no tach and no alt. voltage....... when warm and the intake heater is not cycling it should read a bit over 14 on the guage... i may be wrong but just trying to help.. maybe infedel can help a bit more...

 

I know that my amp gauge is working because I keep an eye on it since I lost an alt last month. Mech, does your cruise work when the tach is not. I don't need the tach it is very annoying that everytime the rpms jump it turns off the cruise.

 

My cruise works seldom. Sometimes I can play with it and it will work, only to drop out a mile down the road. Never really paid attention if they don't work together.

 

If the engine speed sensor was the problem you would have more problems than just the tach. The cruise wouldn't work at all and voltmeter would fluctuate in time with the tach.

I'm thinking the problem might be a poor connection or ground behind the tach itself.

 

Every time the tach jumps it kills the cruise.

 

What's the voltmeter doing when the tach jumps?

 

Nothing. It started doing it last night and I made it a point to look at the voltmeter. It didn't fluctuate once but the tach was jumping by 50 to 100 RPMs. Why would the tach affect the voltmeter?

 

charging is controlled by the pcm and the pcm uses the crank sensor to tell if the engine is running and therefore charging.....

 

The thing is the rpms are not dropping. When the tach fluctuates it is jumping up 500-1000rpms not down.

 

that sure sounds like a faulty but not yet failed sensor to me. also check connections at harnesses