Tachometer doubling
Thread Starter
4th Gear
Joined: Oct 2005
Posts: 4
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Tachometer doubling
I have an automatic 91 coupe. My engine is at 720 rpm, (accordind to the scan tool ) and the tach in the cluster shows 1400 rpm. It is reading almost twice as high. At 2000 rpm the tach indicates almost 3800-4000 rpm. Everything else works fine. Anyone know where are who could recalibrate this cluster ?
Pro
Joined: Nov 2004
Posts: 677
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From: Frisco TX
Originally Posted by flying91
I have an automatic 91 coupe. My engine is at 720 rpm, (accordind to the scan tool ) and the tach in the cluster shows 1400 rpm. It is reading almost twice as high. At 2000 rpm the tach indicates almost 3800-4000 rpm. Everything else works fine. Anyone know where are who could recalibrate this cluster ?
I am all ears on this one... My dads 91 has the exact same problem. Shows that he is shifting around 6200 RPMs (off the scale) with an L98 motor.
Tim
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
Without having intimate knowledge of the L98 system, a faulty tach filter might cause this problem. On the LT1 it is a small black module (about 1 inch in size) that comes off the coil grey connector. The tach filter is basically a capacitor that cleans up the signal noise before it heads to the tach and ETBCM.
FYI, pink wire if I remember goes to the tach itself and the white goes to the ETBCM. They were about six foot long, I spliced them into the existing wires. Wasn't going to tear the whole wiring harness and into the instrument panel.
Here is a picture:
FYI, pink wire if I remember goes to the tach itself and the white goes to the ETBCM. They were about six foot long, I spliced them into the existing wires. Wasn't going to tear the whole wiring harness and into the instrument panel.
Here is a picture:
Last edited by 93JetJocky; Oct 11, 2005 at 05:23 PM.
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
I doubt it would be missing. I just looked in the Ecklers catalog and under Elecrical wiring harnesses and hardware section in the back it shows a tach fiter 84-89 OE style and repl. $59 and 29 respectively. Interesting it skips for years 90-91?
Le Mans Master
Joined: Oct 1999
Posts: 6,366
Likes: 34
The tach filter on my 90 was mounted on the back of the divers side head. The 91 should be the same.
My tach filter went out on me in 3 days. at first the tach was slightly off, then it started bouncing around, then it was useless. I have an MSD box, so I cut the tach filter out, and ran the "tach out" on the msd box to the wire at the tach filter that was left over (which goes to the tachometer). havent had a tach issues since.
My tach filter went out on me in 3 days. at first the tach was slightly off, then it started bouncing around, then it was useless. I have an MSD box, so I cut the tach filter out, and ran the "tach out" on the msd box to the wire at the tach filter that was left over (which goes to the tachometer). havent had a tach issues since.
Cruising
Joined: May 2005
Posts: 14
Likes: 0
My 91 also has a bad tach with the same symptoms as listed here. I tried to purchase a tach filter at the local Autozone but they looked at me as if I was crazy. I am still a bit confused about the location of the filer and where to purchase a new one.
Thanks for the help. (sbonds@visus.jnj.com)
Thanks for the help. (sbonds@visus.jnj.com)
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