inaccurate tach?

[shotimev6]

ive noticed lately that according to the tach my rev limiter comes in around 5500 rpm. i know it has something to do with the gauge cuz it says the secondaries open at 3000 so the gauge is reading wrong. anyone encounter this problem? i replaced the cam sensor but the problem is still there. thanks guys.

beer

 

[nc89sho]

the tach gett's it's info from the crank sensor, not the cam sensor.

 

[shotimev6]

prove it

 

[SHOZ123]

Actually the tach gets it's signal from the DIS (ICM), which gets it's signal from the crank sensor. I think.

I've got a low reading tach and a miss on my '93 and haven't been able to figutre it out. The tach reads about 33% less than it should. I changed the DIS but the problem is still there.

 

[projectSHO89]

Try a new external TACH to see if it's the tachometer in the cluster or something under the hood.

Try this experiment and see for yourself what is needed to generate the TACH signal:

1) Unplug the cam sensor. Start engine (it may take several attempts, but it will start). Observe tachometer

2) Replug cam sensor. Unplug the crank sensor connectos. Crank engine (It won't start). Observe tach needle while cranking.

Reach your own conclusions.

Steve
89

 

[sdpatt]

There is a temperature affected component in the DIS that can slightly change the calibration of the tach, but only when something is really wrong can it have the effect you have seen. Since the rev limiter and secondaries appear to be functioning at the correct engine speed(?) and the tach is just indicating low, your problem is most likely to be in the tachometer or the cabling to it rather than the signal source. It could even be a corroded connector on the DIS or at the back of the instrument cluster. Check the DIS connectors first

<small>[ September 20, 2002, 08:58 PM: Message edited by: sdpatt ]</small>

 

[RI-SHO]

Steve would the same apply to a bad cam sensor? Because I wanted to check this sensor to see if it was working properly and always thought it wouldnt start if it were bad?

 

[projectSHO89]

Unplug it and give it a try

Steve

 

[ShoTime1991]

my tach just seems to be stuck at 2 grand no matter what.. sometimes it jumps around and others it works for a bout 5 seconds

 

[Slo-Sho]

The gauge itself is very easily replaced. The instrument cluster is made up of three separate units. The Tachometer, Speedometer, and the Fuel and Temperature gauges. Each one of these just "pop" out of the instrument cluster. I've taken a close look at the rear of the gauges and they're very cheap. The stepper motor for the tach is of low quality.