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Thread: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

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    Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    This morning when my girl started her car up, she said the tach "wiggled all weird" and jumped straight to the top of the gauge. The engine speed didn't change at all, and shifting into gear made no difference in the tach reading. Turning the car off causes the tach to drop back to zero. Occasionally it will read correctly for a few seconds, then smash back up to redline. Whiskey tango foxtrot is going on here?



  2. #2
    2.0Si User Hazwan's Avatar
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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    Mine is jumpy too but never as bad. People suggested its the dizzy but I don't know for sure. Mine started doing that when I replaced my cap and rotor and wires so it has to be one of them.

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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    I'd make sure the wiring to the coil and the distributor are clean, and yeah, maybe toss on some new cap and rotor goodness. It could be that something in the gauges has a bad ground, and so some power flow is reversing back through the tach's ground. Doesn't sound like it's going to be a terribly easy fix. But check the wiring under the hood first. That's the easy part. Clean up any corrosion you might have going on there, and make sure all the ground wires under the dash are good. Maybe check out your fuses too. I know when I had some old shitty fuses in my car, it caused lots of weird random problems. Replacing even the fuses that seemed to be good fixed a lot of problems.

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    Dr_Snooz's Avatar
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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    On the 3g's, a failing ICM will cause tach bounce.
    Dr_Snooz

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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    I finally am getting around to buying parts for this problem. I'm buying a new cap and rotor, new spark plugs/wires, new distributor lead. I found a few ICMs on Rockauto, cheapest is $30 and the most expensive $120. Quite the disparity there. Any way to test the ICM if it is failing, or should I just buy the cheap one and replace it because it might fix the problem?

    Hazwan: From what you described, there is probably some sort of ground problem somewhere. I know that there is a little green cable with a molex connector that runs along the firewall that connects somewhere around the carb that got caught in the hood and broke through the insulation a bit so I will patch that.

    2ndgenguy: Already did a couple fuses that were blown, I'll just redo all of them and any relays I can get cheap.

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    Dr_Snooz's Avatar
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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    I keep looking for a way to test ICM's, but no luck so far. If you find a way, definitely post it up for us.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    If it runs good then I doubt it's the icm, I would replace the other things and see how it goes so you know which thing actually fixed it.
    ... but i would replace or test the little condensor slash radio filter by the coil. All the lights work on the car?

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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    2oodoor: Which condenser do you mean? Is it near the ignition coil? What does it look like? All lights work on the car, including the brake lamps, but the brake lamp light is on. Haven't cleaned the contacts on those bulbs yet. The rear window defogger button lights up when depressed, but the defogger doesn't do a damn thing. Possibly related?


    I ended up getting a new ICM, they all look the same from the pictures, and I went for a name brand ignition coil. Doing the work as soon as she gives me the damn car for an afternoon.

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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    Looks like I don't have to replace the ICM - doing the other ignition components solved the problem. It had the original spark plugs, original dist cap and rotor, and original ignition coil. The dist was all rusted out, and the post the rotor sits on was completely orange. I hit it with a bunch of contact cleaner and a shop rag, and got it nice and shiny again. The car used to be loud as shit, now it's quiet and runs way more smoothly. Still vibrates at idle, but I'll have to find a working rebuilt Keihin to fix that... there are a few shot springs on the carb around the lambda linkage and I don't want to mess with it. I'd stick a Weber on but it needs to pass CA emissions.

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    Re: Tach jumps straight to redline - 1980 Accord w/ 3 spd auto

    Awesome man! Glad you got it figured out! Sometimes just cleaning up the crud does wonders! Let us know how the carburetor debugging goes!

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