Irratic Tachometer
Drifting
Joined: Oct 2006
Posts: 1,554
Likes: 13
From: Romeoville IL
Mine had similar problems, idle bounced around more than it should have and would go nuts when above 2500/3000 rpm. Mine was the tach filter going bad. I bypassed it and it cleaned up the tach a lot. I've since installed an ignition amp and used the tach output from that, and the gauge is rock solid.
Instructor
Joined: Sep 2009
Posts: 182
Likes: 1
From: Greenville SC
Ditto on the tach filter. However, instead of bypassing it, I bought a new one from Eckler's and installed it last night, and it fixed the problem. It wavered between erratic and non-functional.
Didn't know you could just bypass it and go directly to the tach, I thought that might not be good for the digital system.
Dave
Didn't know you could just bypass it and go directly to the tach, I thought that might not be good for the digital system.
Dave
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Instructor
Joined: Sep 2009
Posts: 182
Likes: 1
From: Greenville SC
You also might want to know that there is a way to check the filter. For this you will need a volt/ohm meter (preferably digital). I don't remember the exact protocol, it came with the filter that I bought from Eckler's, and I don't have it at hand. If no one posts this information before this evening, I will try to find those directions and get this to you.
It might be worth knowing for sure if the tach filter is for sure the culprit before you spring for one.
Dave
It might be worth knowing for sure if the tach filter is for sure the culprit before you spring for one.
Dave
Instructor
Joined: Sep 2009
Posts: 182
Likes: 1
From: Greenville SC
OK, here's the info on testing that came with the Eckler's new tach filter:
Using your ohm meter probe both lead wires. You should get a reading of about 15,000 ohms across both lead wires. If you get this reading, take one of the probe leads and touch the black ground wire. You should have close to 0 ohms. This shows that the tach filter has continuity and is not shorted to ground internally. If the tach filter passes both of these tests, the signal from the distributor will pass through to the tach. If your tach does not work, it is not because of the tach filter.
I did NOT run this test on my tach filter, but I was apparently right in assuming that it was bad, since replacing it fixed everything.
Good luck, Dave.
Using your ohm meter probe both lead wires. You should get a reading of about 15,000 ohms across both lead wires. If you get this reading, take one of the probe leads and touch the black ground wire. You should have close to 0 ohms. This shows that the tach filter has continuity and is not shorted to ground internally. If the tach filter passes both of these tests, the signal from the distributor will pass through to the tach. If your tach does not work, it is not because of the tach filter.
I did NOT run this test on my tach filter, but I was apparently right in assuming that it was bad, since replacing it fixed everything.
Good luck, Dave.
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