Intermittent Tachometer
10-06-2008, 01:43 PM
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Intermittent Tachometer
The tach sometimes works properly and sometimes doesn't. One day it'll read 900RPMs when idle, and the next day it'll read 100-200RPMs.
I've changed the dist. rotor and cap, spark plugs and wires, oil and filter, and oxygen sensor. The tach problem still continues.
If I drive the car 20-30 minutes, the tach will read 1,200RPMs when it should read more around 3,500RPMs or more...and then back down to 200RPMs at idle when it is more around 900RPMs.
Could it be speed/reference sensors? I don't have any start up problems, and the car runs fine. I did disconnect them and tested with a multimeter (there is output signal) and cleaned the terminals.
The tach does not bounce when the engine is cranked over. Does this sound like a gap issue? Maybe a DME computer issue?
The puzzling part is that I don't have any engine starting or running problems, and the tach will sometimes start working correctly for a couple of days.
Any suggestions or advice is much appreciated - thanks in advance!
I've changed the dist. rotor and cap, spark plugs and wires, oil and filter, and oxygen sensor. The tach problem still continues.
If I drive the car 20-30 minutes, the tach will read 1,200RPMs when it should read more around 3,500RPMs or more...and then back down to 200RPMs at idle when it is more around 900RPMs.
Could it be speed/reference sensors? I don't have any start up problems, and the car runs fine. I did disconnect them and tested with a multimeter (there is output signal) and cleaned the terminals.
The tach does not bounce when the engine is cranked over. Does this sound like a gap issue? Maybe a DME computer issue?
The puzzling part is that I don't have any engine starting or running problems, and the tach will sometimes start working correctly for a couple of days.
Any suggestions or advice is much appreciated - thanks in advance!
10-06-2008, 03:23 PM
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Welcome to the troublesome early 944 tach 
Mine is dead at start up, then a few minutes later will pop on and sometimes read the correct rpm, sometimes read low.. sometimes it'll stay on till I shut the car off, sometimes it will drop to 0 if I accelerate hard..
"most" of the time, if you have this behaviour, there is a cold solder issue on the tach that is repairable if you are so inclined.. seems easier to me to just replace the tach since they are cheap and easy to find..
If you've already checked the basic plug in points and the tach is intermittent, I'd replace it (that's what I'm doing)
Do a search for "early tach" and "intermittent tach" and you'll get dozens of hits..
Good luck~
Mine is dead at start up, then a few minutes later will pop on and sometimes read the correct rpm, sometimes read low.. sometimes it'll stay on till I shut the car off, sometimes it will drop to 0 if I accelerate hard..
"most" of the time, if you have this behaviour, there is a cold solder issue on the tach that is repairable if you are so inclined.. seems easier to me to just replace the tach since they are cheap and easy to find..
If you've already checked the basic plug in points and the tach is intermittent, I'd replace it (that's what I'm doing)
Do a search for "early tach" and "intermittent tach" and you'll get dozens of hits..
Good luck~
10-06-2008, 06:15 PM
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Man, you really think it's just a bum tach that I have? How difficult is the solder procedure? I imagine removing the tach is a PITA?!?!
Are there any "easy fix" procedures that I can try? I haven't removed my speed/reference sensors yet - would doing that help at all? What about the DME...do my symptoms lead back to that at all?
I'll continue to search previous posts and see what others have tried and suggest. Thanks for the inpu!
Are there any "easy fix" procedures that I can try? I haven't removed my speed/reference sensors yet - would doing that help at all? What about the DME...do my symptoms lead back to that at all?
I'll continue to search previous posts and see what others have tried and suggest. Thanks for the inpu!
