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Old 11-24-2010, 06:10 PM   #1 (permalink)
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Tach signal?

I have a 94 Accord LX. It's pretty new to me. I've noticed the tach is off. It appears that it works, in other words, it's not shakey, bouncing, or dead. It's pretty steady and it moves with shifts and everything, but it's clearly off. The car drives fine and seems to shift at the correct points. If I floor it, the tach never shows higher than 3500, when it clearly is turning higher RPMs. When I'm cruising at 75 mph, the tach is steady around 1900 RPMs.

The question I have is where does the signal for the tach come from? Can it be calibrated or is it no good? Any ideas or suggestions on how to correct the tach?
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Old 11-26-2010, 07:32 PM   #2 (permalink)
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It comes from the Distributor which will be the light blue wire at the Distributor connector harness.
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Old 11-27-2010, 11:33 AM   #3 (permalink)
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I realize that the signal comes from the distributor, but that wire sends a signal to the ECU or something which then sends it to the tachometer. Or is the signal sent directly to the tachometer unit in the dash? I haven't researched, but I think that there is a signal sent to the ECU, which dictates shift points and stuff. I'm thinking that I'm getting a bad feed from the output side of the ECU or that the tachometer in the dash is bad. I guess this is really my question, what are the possible components that can go wrong on the tachometer system?
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Old 11-28-2010, 09:40 PM   #4 (permalink)
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if it never goes higher that 3500 rpm even under full throttle...does the tach just stop moving at 3500 or does it flutter??? 1900 rpms on an automatic cruising isnt a problem...that has to due with the tourque converter and thats a whole nother story.... if it drives fine, shifts fine, and acts fine with the tach as the only exception, id say your problem is in the dizzy, the tach itself, or the wiring inbetween, yes the ecu has a rpm reading as well but if the car runs fine then the computer is getting the correct rpm readings....if it wasnt it would be reading and applying the wrong maps, and throwing codes at you
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Old 11-29-2010, 05:16 AM   #5 (permalink)
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Even under full throttle, the tach just goes slowly up but never breaks 3500, even if it gets that high. It's really strange because it doesn't shake, it just slowly and steadily fluctuates with the RPMs but it's off. I agree that the ECU is getting the correct signal. My question is, does the signal to the tach come directly from the dizzy? Meaning, does the signal from the dizzy split and send two signals, one to the ECU and another to the tach in the dash? I know the ECU is getting the right signal because it drives fine and doesn't throw any codes. I think that the tachometer itself is bad or I have some bad wires between the tach and the ECU.
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Old 12-01-2010, 05:05 PM   #6 (permalink)
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I don't quite remember, I need a wiring diagram to see where it comes and goes to.

EDIT: As I'm looking at the wiring diagram right now, it looks like its coming from the ICM inside the dizzy and through the under-the-hood fuse box then to the gauge assembly out the other side to ground.

Hope this help. I'm tried my best to keep it simple for ya.
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Old 12-06-2010, 05:25 PM   #7 (permalink)
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Originally Posted by nusdogg View Post
I don't quite remember, I need a wiring diagram to see where it comes and goes to.

EDIT: As I'm looking at the wiring diagram right now, it looks like its coming from the ICM inside the dizzy and through the under-the-hood fuse box then to the gauge assembly out the other side to ground.

Hope this help. I'm tried my best to keep it simple for ya.
Thanks
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