Lookin' for some help re: tach

Doober

Moderator
Jun 2, 2003
14,704
1
38
Catalina, AZ
www.cardomain.com
http://www.442.com/oldsfaq/ofmsc.htm#MISC Tachometer Reads Incorrectly

That's about all I've been able to find regarding a tachometer acting up. I believe mine is acting funny because I never hit 4k rpm and it says I hit 5 when I took the 'Bu for a drive the other day. I looked for a "clip" or "pin" on the board for the tach, but haven't really found anything resembling either. I can get pics of the front/back of the PCB if anyone wants... I'm at a loss here... If all else fails, before I up & replace the tach I plan on trying a fairly cheap RCA cable I have. The ground/shield is more or less a foil wrapped around the signal & its insulation. I plan on using that ground connection and running it to an electrical ground on the car and running the signal conductor from the distributor cap to the 2' or so tach wire coming off of the cluster connector. What do the rest of you electrical gurus think about this, could it help?
 

ScotSea

Frequent Racer
Sep 21, 2003
381
0
0
The V6 and V8 tachs are different. The Malibus and Montes don't have the V6/V8 selector that the Olds uses.

There is a good chance that the resistors/capacitors that are used in the circuit could be getting old. The tach circuit is quite simple, and most of the resistor part is on the white 14 pin DIP that is on the circuit board behind the tach. The caps are next to that DIP.

One of the Fiero boards has the explanation of how to re-cal an errant GM tach. The author just cut a circuit line on the tach board and installed a 10 turn pot to adjust it in.

Scot
 

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