Trouble shooting a rev counter





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  1. #1
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    Default Trouble shooting a rev counter

    Hi guys

    Hoping someone is able to give me some advice please.

    I have a 72 Chev El Camino, my pride and joy.

    I want to install a rev counter in the dash. I have the replacement cluster of the same era, so its second hand and I do not know whether its working or not.

    I have tried to test whether it works but the rev counter needle does not move.

    I have a HEI distributor installed which has a pin for the tach. I have wired 12volts when ignition is on, wire to the tach pin and grounded it, still no luck.
    I have looked to see if one of the resistors on the rev counter is blown but all looks good.

    Is there some way of testing whether the tach pin is actually sending out a signal firstly and is there a way to test the rev counter.

    I prefer not outsourcing my work for the El Camino as have been burnt too many times by so called experts.

    I am by no means an auto electrician, a car enthusiast at best.

    Will appreciate any advice given.
    Thanks in advance

  2. #2
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    Default Re: Trouble shooting a rev counter

    A standard tach/dwell meter will work to check distributor RPM at the TACH Terminal while running...

    ...not sure the US electrical schematic will help, but can try to look it up for you tomorrow
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    Default Re: Trouble shooting a rev counter

    What type of HEI distributor do you run? Build in module or remote. Most of them have a terminal that pulse the rec counter.

    The way you have connected it seems fine. Make sure you have the correct terminal should be a negative pulse as the rev counter for the El Camino were designed for the old dizzies with contact breaker.
    It is not what you buy its what you build.

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    Default Re: Trouble shooting a rev counter

    On a lighter note.

    Bit sleepy still...did double take in forum feed.
    What the heck, somebody has trouble (trying to) shooting his rev counter

    ...then light bulb moment. He trying to troubleshoot his rev counter

    What a difference a little space makes

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    Default Re: Troubleshooting a rev counter

    Quote Originally Posted by grips View Post
    What type of HEI distributor do you run? Build in module or remote. Most of them have a terminal that pulse the rec counter.

    The way you have connected it seems fine. Make sure you have the correct terminal should be a negative pulse as the rev counter for the El Camino were designed for the old dizzies with contact breaker.
    Its a big cap dizzy, with the module on the top of cap. The pic above is basically the same design. Yes the old Chevy was originally designed with a points dizzy, but was replaced with HEI due to it being faulty.

    My understanding is that the rev counter would still work with the HEI. I have seen guys at car shows that have the setup I am chasing with the same gauges but off course not sure whether they have had to modify anything on the rev counter.

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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by Prof View Post
    On a lighter note.

    Bit sleepy still...did double take in forum feed.
    What the heck, somebody has trouble (trying to) shooting his rev counter

    ...then light bulb moment. He trying to troubleshoot his rev counter

    What a difference a little space makes

    Lol......that what happens when I am so tired of trying to figure out something and it does not work. I paused to take a breath and hit the space button

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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by kavesh View Post

    Is there some way of testing whether the tach pin is actually sending out a signal firstly and is there a way to test the rev counter.
    You can test for a signal/pulse with a simple LED test light. Very easy to make.
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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by wiel View Post
    You can test for a signal/pulse with a simple LED test light. Very easy to make.
    Thats awesome, please explain how to make this easy LED test light

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    Default Re: Trouble shooting a rev counter

    A LED light have two legs. The anode + and the cathode-. The anode is the longer one of the two. Solder a 600 ohm 1/2 whatt resistor on any of the two legs (the LED is only 2V and the resistor limits the current from 12V).
    Solder about 500mm of thin electrical wire to the cathode leg and attach a crocodile clip to it. Solder thin electrical wire to the anode leg and attach a sharp needle or something similar to it(to pierce through insulation).

    I took a old pen casing and fitted everything inside it .The LED at the top, and the sharp pin at the bottom. The wire for the crocodile clip comes through the side of the pen casing.

    To use as a normal test light, you connect the crocodile clip to negative and the needle to positive. The LED will come on. It will not come on if you swop it around, only when there is a pulse.
    To check a negative pulse, connect the crocodile clip to POSITVE and the needle to negative. If there is a pulse, the LED will flash according to the pulse rate.

    So to test the tacho pin for output, you connect the crocodile clip to battery positive and press the needle on the tacho pin. Crank the engine and if there is a pulse, the LED will flash.
    You can do the same to test a coil, injectors or anything that have a negative pulse.
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  13. #10
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    Default Re: Troubleshooting a rev counter

    Quote Originally Posted by kavesh View Post
    Its a big cap dizzy, with the module on the top of cap. The pic above is basically the same design. Yes the old Chevy was originally designed with a points dizzy, but was replaced with HEI due to it being faulty.

    My understanding is that the rev counter would still work with the HEI. I have seen guys at car shows that have the setup I am chasing with the same gauges but off course not sure whether they have had to modify anything on the rev counter.
    Does the engine run now?

    Any tachometer that can be used on a V8 should be able to work with the GM HEI system...

    If itís a real GM HEI (or most Chinese knock offs) the ignition coil is in the cap and the module is attached to the distributor advance plate.

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    Default Re: Trouble shooting a rev counter

    You can try using an aa battery on the terminals of the tach to see if the needle moves, you can swop the battery around if it doesn't move but just touch the terminals to test don't keep it on for too long.

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    Default Re: Troubleshooting a rev counter

    Quote Originally Posted by AardvarkNV View Post
    Does the engine run now?

    Any tachometer that can be used on a V8 should be able to work with the GM HEI system...

    If itís a real GM HEI (or most Chinese knock offs) the ignition coil is in the cap and the module is attached to the distributor advance plate.

    Module Delco P/N D1906
    Yes the engine runs. I just want to enhance how the instrument cluster looks.

    Its not a genuine GM HEi. Its an aftermarket one and I would be lying if I told you brand. I got the dizzy from a guy that imports V8 parts for a living. Its a few years now that I have it and there was no branding on the dizzy itself.

    You are correct, the coil is in the cap, and you seem to know about the location of the module, I cannot be sure. I assume you correct.

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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by HobieDave View Post
    You can try using an aa battery on the terminals of the tach to see if the needle moves, you can swop the battery around if it doesn't move but just touch the terminals to test don't keep it on for too long.
    So which pins on the tach should I use, the power 12v pin and ground or the pin for the dizzy?
    This is great, thanks, will definitely test and advise results.

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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by wiel View Post
    A LED light have two legs. The anode + and the cathode-. The anode is the longer one of the two. Solder a 600 ohm 1/2 whatt resistor on any of the two legs (the LED is only 2V and the resistor limits the current from 12V).
    Solder about 500mm of thin electrical wire to the cathode leg and attach a crocodile clip to it. Solder thin electrical wire to the anode leg and attach a sharp needle or something similar to it(to pierce through insulation).

    I took a old pen casing and fitted everything inside it .The LED at the top, and the sharp pin at the bottom. The wire for the crocodile clip comes through the side of the pen casing.

    To use as a normal test light, you connect the crocodile clip to negative and the needle to positive. The LED will come on. It will not come on if you swop it around, only when there is a pulse.
    To check a negative pulse, connect the crocodile clip to POSITVE and the needle to negative. If there is a pulse, the LED will flash according to the pulse rate.

    So to test the tacho pin for output, you connect the crocodile clip to battery positive and press the needle on the tacho pin. Crank the engine and if there is a pulse, the LED will flash.
    You can do the same to test a coil, injectors or anything that have a negative pulse.
    I will have to print this and study it before I decide if I am able to do this.
    Just to confirm is that a 600ohm half watt resisitor?

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    Default Re: Troubleshooting a rev counter

    Quote Originally Posted by kavesh View Post
    Yes the engine runs. I just want to enhance how the instrument cluster looks.

    Its not a genuine GM HEi. Its an aftermarket one and I would be lying if I told you brand. I got the dizzy from a guy that imports V8 parts for a living. Its a few years now that I have it and there was no branding on the dizzy itself.

    You are correct, the coil is in the cap, and you seem to know about the location of the module, I cannot be sure. I assume you correct.
    Ok, if itís running I would look to the tach as the issue (wiring or part failure)
    Do you have the GM part number of the tach?
    Can you take a picture of the tach front and back? Iíve got access to most North America GM parts and wiring diagrams to verify...
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  19. #16
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    Default Re: Trouble shooting a rev counter

    Quote Originally Posted by kavesh View Post
    I will have to print this and study it before I decide if I am able to do this.
    Just to confirm is that a 600ohm half watt resisitor?
    Correct.
    98 Hilux 2.8D D/C 4x4

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    Default Re: Trouble shooting a rev counter

    We have three v8 powered vehicles with Mallory HEI distributors. Two of them with aftermarket instruments no problems.
    Had to install a Dakota interface to make the rev counter on the South African Ranger to work 100%

    https://www.dakotadigital.com/index....od/prd1192.htm
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    Default Re: Troubleshooting a rev counter

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    Quote Originally Posted by AardvarkNV View Post
    Ok, if it’s running I would look to the tach as the issue (wiring or part failure)
    Do you have the GM part number of the tach?
    Can you take a picture of the tach front and back? I’ve got access to most North America GM parts and wiring diagrams to verify...

    Please see pics attached. I have also attached a pic of the distributor. Let me know if you require better pics.

    No sure how much of a difference this makes my Elcamino is based on on the Australian Holden vehicles. The gauges are VDO as far as I understand.

    The Rev Counter would have originally been fitted to a Chevy SS or Holden Monaro GTS. My El Camino is very similar in that the front is identical to the vehicles mentioned except mine is a bakkie and the others are coupes, the sport vehicle.
    Last edited by kavesh; 2020/03/25 at 10:02 AM.

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