Tach Filter
Thread Starter
Racer
Joined: Dec 2004
Posts: 470
Likes: 0
From: Phoenix Arizona
Tach Filter
I have a '90 with a new GM Crate motor 350ci/ 330 hp / 380 torq with12k miles on it . On a recent trip and around town I notice that at higher speeds (freeway) the Tach needle jumps between 2k and 3k then will settles back to 2k. Is it the tach filter or should I look at something else?
Thank you
Jeff
Thank you
Jeff
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
It could be but no way to know without trying. It could be a bad ground or the resistor tach calibration chip failing or a connector to the dash. The tach filter is probably the least annoying thing to try.
Race Director
Joined: Feb 2003
Posts: 16,475
Likes: 270
From: Kingman AZ
Cruise-In VII Veteran
Cruise-In VIII
St. Jude Donor '06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
Do a search here in the big "Search" box above the postings. Lots of info. My 91 reads way over what it should. I tried another tach filter and it did not help. This fix is still on my "to do" list.
One of the fixes has you pulling the dash cluster and adding resistors to the tach circuit and also repairing some deteriorating soldered areas.
One of the fixes has you pulling the dash cluster and adding resistors to the tach circuit and also repairing some deteriorating soldered areas.
Team Owner
Joined: Dec 2000
Posts: 21,094
Likes: 282
From: Phila., PA burbs
I'm going through a similar problem with my 91 that I just put a 383 in. The car runs great, but the damn tach jumps all over the place now. I'm still assuming I left a ground unhooked somewhere, but I haven't been able to locate it 
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
http://www.thirdgen.org/techboard/el...meter-fix.html
http://forums.corvetteforum.com/c4-g...ch-repair.html
http://forums.corvetteforum.com/c4-g...-problems.html
http://forums.corvetteforum.com/c4-g...ch-filter.html
Filter replacement usually does not fix it
http://forums.corvetteforum.com/c4-g...1990-vert.html
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If your tach filter is the metal can with a ground lug, be sure that case is grounded.
After my '88 Vette engine rebuild the assembler neglected to attach the tach filter to the top bell housing bolt and the tach read higher than my scan tool showed. Jumpering the tach case to an engine ground brought the tach reading down to the correct value.
After my '88 Vette engine rebuild the assembler neglected to attach the tach filter to the top bell housing bolt and the tach read higher than my scan tool showed. Jumpering the tach case to an engine ground brought the tach reading down to the correct value.
