digital meter

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Shenango

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I tried this thread on the Corvette forum but no one wanted to answer. If you read further on you will see it works well on my 70 Swinger 340. Maybe the Mopar guys are smarter or less stuck up than the Vette boys.

My actron digital meter will not read RPM on my 75 Vette with HEI distributor, it flashes wildly and will not settle down. I have tried the tach wire both in front of and after the capacitor and the coil ground. In all instances my meter negative was tried on the carb, engine ground and alternator ground. It works great on my 70 Dodge A body with 340 engine, electronic distributor and external coil using coil minus and carb ground. Are these new digitals not capable of functioning on the HEI units? My original dash tach works but I suspect it of being 200 to 400rpm high and I just want to verify that discrepancy and have an accurate tuning tool.
Thanks for any help, Jerry
 
Have you tried searching that particular model number Actron for similar posts / problems on the net?
 
Doesn’t the gm hei have a specific tach output terminal off the coil? At least from what I remember.

It does not familiar with what your using but maybe it needs connected to the tach output. Your in dash may need to be connected to the same. Not sure.

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i have one of those acton digital meters and in order for it to work on my 72 340 duster with msd ignition i have to hook the positive lead to the tach output on the 6al box.
 
All the tach wire actually is on a "real" (GM) hei is a connection to the coil NEG terminal. I have no answer unless it was RF interference. Try twisting the test leads, position the meter away from the HEI, lay the leads down along the engine, and clip them to ground and the tach connection with as little "untwist" that you can manage.

Can/ have you tried it on another vehicle?
 
i have one of those acton digital meters and in order for it to work on my 72 340 duster with msd ignition i have to hook the positive lead to the tach output on the 6al box.

A 6AL is a different breed of cat. They are capacitive discharge. An HEI works "more similar" (LOL) to breaker points or Mopar ECU........it switches the coil NEG to ground
 
I don't know if this will help but here goes;
I saw this on a SBM with an Orange box and a reversed pick-up polarity; The Idle timing was Ok, but as soon as I revved it just a little, the strobe on my inductive dial-back timing light, went wild, and the tach read erroneously.
I cut the wires and reversed them close to the connector, then hit the Key. The base timing was way off, but the strobe had returned to normal.And the tach along with it.
 
All the tach wire actually is on a "real" (GM) hei is a connection to the coil NEG terminal. I have no answer unless it was RF interference. Try twisting the test leads, position the meter away from the HEI, lay the leads down along the engine, and clip them to ground and the tach connection with as little "untwist" that you can manage.

Can/ have you tried it on another vehicle?

RF interference sounds like it could be my problem. I do have a real HEI with a 65,000v coil. My tach lead feeds a capacitor/choke then through the fire wall to my dash tach. I have tried my meter lead on both sides of the capacitor. Also the meter works properly on my 70 Dart with 340 and orange box ignition. I may try wire extensions with shielded coax and set my meter on the work bench.
Thanks to everyone for the suggestions, MOPAR guys are cool beans. Jerry
 
My tach lead feeds a capacitor/choke then through the fire wall to my dash tach.

Where did this come from? Those components could very well be affecting the ignition system itself. Did the tach manufacturer recommend it, or is this factory equipment?

The point is that rf interference from the tach wire to other components aside, LOL, you cannot filter the tach wire "too much" or you won't have a pulse at the other end for the tach to count!!

IE you would need to select those components carefully to not cause problems themselves
 
Where did this come from? Those components could very well be affecting the ignition system itself. Did the tach manufacturer recommend it, or is this factory equipment?

This is a factory installed piece of equipment. The tach is also GM supplied and is built into the dashboard.
 
I am out of ideas, other than Google around your meter / model and look for other user's reviews/ problems, etc

You have any access to coax, TV, or CB? Not critical. Cut two pieces each one about a "handy" length for your measurements. Buy some Banana plugs on Egag to fit your meter. Tape the two coax together (or zip tie) and tie the shields together at both ends

At the meter end, with the shield of the two pieces connected, tape that shield off. Strip out some of the center conductor and hook the banana plugs up to connect to the meter

At the engine end, you want a short ground clip on the shield. This will connect near the dist. to engine ground. Hook the appropriate center coax lead to the dist. tach connection, and the remaining coax center lead to whatever the meter wants......12V, ground, whatever it should be

This creates what is known as a "Faraday shield"

============================================

You could also do this with a scrap ethernet cable.......they are 8 conductor IE 4 pair. Select one pair and use them for the meter connections.

Take all other wires at tape them off at the meter end, same as the coax, above

At the engine end, twist all unused wires together, put a clip on them and connect to engine ground. That is your shield
 
I am out of ideas, other than Google around your meter / model and look for other user's reviews/ problems, etc

You have any access to coax, TV, or CB? Not critical. Cut two pieces each one about a "handy" length for your measurements. Buy some Banana plugs on Egag to fit your meter. Tape the two coax together (or zip tie) and tie the shields together at both ends

At the meter end, with the shield of the two pieces connected, tape that shield off. Strip out some of the center conductor and hook the banana plugs up to connect to the meter

At the engine end, you want a short ground clip on the shield. This will connect near the dist. to engine ground. Hook the appropriate center coax lead to the dist. tach connection, and the remaining coax center lead to whatever the meter wants......12V, ground, whatever it should be

This creates what is known as a "Faraday shield"

============================================

You could also do this with a scrap ethernet cable.......they are 8 conductor IE 4 pair. Select one pair and use them for the meter connections.

Take all other wires at tape them off at the meter end, same as the coax, above

At the engine end, twist all unused wires together, put a clip on them and connect to engine ground. That is your shield

You were right on the money 67. I constructed a Faraday shield from a pair of 2 1/2 ft lengths of 4 conductor telephone wire. Grounded the 6 shield wires close to the distributor and connected the meter pair to the output of the tach filter. I grounded the meter negative lead to the alternator and hooked the meter positive to the tach filter pair. Thank you for suggesting the shield, it worked beautifully.
Jerry
 
!!COOL!! Always good "when a plan comes together" LOL
 
i have one of those acton digital meters and in order for it to work on my 72 340 duster with msd ignition i have to hook the positive lead to the tach output on the 6al box.

Just a FYI, With the MSD, be carefull, connecting ANY test equipment to the coil. The MSD supplies several hundred volts to the coil (not 12 volts), and can burn out some test equipment.
 
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