I have a 91 rs that the rpm is readin close to double what its suppose to, does anyone heard of this before? my dad is one of the best machanics in the area and he cant figure it out. let me know of what to do or someone whos knows!!!

 

If its a tach for a V6 and a V8 is in it, thats why. Im not sure if there is a wire you can cut on a factory tach to mess it up or not. If its the original motor then its something electrical

 

My dad try and work with and say its not the eletics. i dont know whats wrong wit it?!
p.s. its a V8 if that tells u anything
Kreg

 

Mines 600 rpms off been like that since i bough it. I plain on replaceing the tach or getting all new gages.

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91 RS Camaro 5-speed black w/t-tops 305 TBI now TPI
MODS: SLP cold air intake w/K&N, air foil,Accel 19 LB injectors, March aluminum under drive pullies, Alburn pro posi, Aluminum drive shaft, Random Technology 3'' cat-back, 8.5mm MSD wires, 160 thermo, jet fan swich, Custom chip with 91 vette computer, SSBC slotted rotors, optima battery in the rear, BMR adjustable lower control arms and panhard rod, Kenny Brown strut tower brace, TB bypass, no egr, no air

 

[QUOTE]Originally posted by Blacamaro91:
I have a 91 rs that the rpm is readin close to double what its suppose to, does anyone heard of this before? my dad is one of the best machanics in the area and he cant figure it out. let me know of what to do or someone whos knows!!![/

im not sure but i think there is a gear in the transmission that is resposible for sending the rpms to the gauge

i know thats where the spedometer gear is located

 

Hey,I have the same problem on my 89RS w/305 and 5spd. My car idles at 1400rpms on the factory tach. I hooked up an after market one and found that the factory unit was a good 500 to 600 rpms off. I would also like to know what causes this? I didn't leave the ext tach hooked up, because I like the factory gauge set up. I just keep in mind that is off. I wonder if changing the whole gauge set up(speedo incl) will fix the problem? Is the tach getting it's input from the computer? I know it gets the orginal signal from the coil, but does it go to the computer before going to the tach?

 

I have the exact same problem on a newly acquired 90 RS V6. I am told there is a white wire on the distributor that has some sort of electronic 'filter' in series with the tach signal. I'm also told that if this filter goes whacko it can make the tach read 2X the actual RPM. I'm a few days away from troubleshooting mine, but will share what I find.

Gerry-
Norfolk, VA
96 Impala SS
90 Camaro RS

 

Well.... I have traced this down inch by inch and if there's anything like a 'filter' in line with the tach wire, I don't see it. Maybe thats MY problem, but my tach is reading 2X what it should be ( 90 V6 RS ).

There is a drawing in the service manual that shows where each wire comes into the instrument cluster, and the 305 and 350 come in on a different pin than the V6. I know that this dash has been apart, just don't know how far.

Anyone every had the cluster out and moved any of the wires around ?

-gerry