Installed new coil, now the tach acts funny

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Believe me electrical can be confusing. I threw my hands up and our 67 has sat for a few years now.
I always ASK, well almost always lol, before doing something that I dont understand, OR something that could affect driveability. There are LOTS of aftermarket goodies out there that alter/cripple the way that these mopars work unless done properly or modified.
There is another electrical thread going on that I cringed at as the OP posted "he hired a mechanic/shop" to install elec ignition and now it doesnt run worth a ****. Licenced mechanics arent electricians lol. Anyway sorry for the ramble, glad ya got another one ordered. You meaning tach?
Perseverance pays off. There are a few electrical whizbangs on here that will get you on your way.:thumbsup:
 
Installed the replacement tach and connected it to the gray signal wire, as Autometer directs. I still have the same problem - needle reads zero at RPMs 1200 and lower. I called MSD, and they said installing a new coil shouldn't have affected tach performance. Other than saying that, he could not help me.
 
Hook your replacement tach up to the neg side of the coil and see if it works. Since your tach worked before the coil replacement, something else is happening here; maybe created a ground some place, the new coil smoked the ECU or something but stuff doesn't just break on its own, something occurred when you replaced the coil.
 
Any ideas how I can troubleshoot the ignition module? I’m fairly ignorant when it comes to electrical work.
 
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I'm no help,(sounds like MSD isnt either)but if it were me, everything would go back to stock and start from there.
Sorry you're having issues and bought 2 tachs....
 
Have you tried an MSD tach adapter? If you're interested, I have two different models new in the packages. PM me with your email & I'll get some pictures.
 
The reluctor gap in the dist is not a player in tach operation. The reluctor gap of about 0.008" is reqd to fire the coil, & the coil generates the signal to operate the tach.

This is a most unusual problem, since the Mopar ign box is inductive ign, which most tachs should work with when correctly hooked up. The tach signal wire should go the coil [-] terminal, which in my old MP book is a black/yw wire.
 
Demonracer said:
Have you tried an MSD tach adapter? If you're interested, I have two different models new in the packages. PM me with your email & I'll get some pictures.
Click to expand...
I'll PM you. I will say that I asked the MSD guy if he thought an adapter would help, and he was doubtful. When I called Autometer, they said their tach needs a square wave to read the signal properly. My best guess would be to obtain an oscilloscope to confirm the waveform. Does the adapter change the waveform? Because that may well be what I need.

Bewy said:
The reluctor gap in the dist is not a player in tach operation. The reluctor gap of about 0.008" is reqd to fire the coil, & the coil generates the signal to operate the tach.

This is a most unusual problem, since the Mopar ign box is inductive ign, which most tachs should work with when correctly hooked up. The tach signal wire should go the coil [-] terminal, which in my old MP book is a black/yw wire.
Click to expand...
After reading your reply, I double checked my wires going to the coil, and I've got a brown one going to the positive terminal, and a black/yellow going to negative.

At first, I connected the tach to the negative coil terminal as it was prior to changing coils, and when I noticed the tach starting to function strangely, I referenced the Autometer literature and found this:

"If you have a Mopar Orange or Chrome Box ignition system on your vehicle, rather than connecting the Green signal wire of your tachometer to the negative side of your ignition coil, instead locate the Gray wire running between the Ignition Box and the Distributor. Connect your tach's Green signal wire to this Gray wire for a proper engine RPM signal."

So I connected it to that gray signal wire like they said, same problem. I thought I had fried the tach, so I bought a new one and I had the same behavior.

I'm not normally someone to give up on something, but I'm starting to question whether I even need a tach in the first place. The Scamp is anything but a race car....
 
I feel your pain. You said you have "old tach"? And when hooked to "old" coil it worked? What are they? Try those.
 
You need to make certain that "whatever color" that the power wire from the ballast goes to coil +
And that "whatever color" the coil - goes to the ECU

Something you might try "shot in the dark"

Unplug the regulator and see if the tach works

With everything connected normally

With the engine running "fast idle" Check charging voltage at the battery. With the engine warm and the battery "normalized" you should see 13.8--14.2

If so turn on the headlights. Heater if you have it. Voltage should not drop much, not below 13.2--13.5

Now, turn your meter to AC volts. Measure right at the alternator output stud with engine still running on fast idle. You should have a very very low reading, almost zero. I would say over .3V (3/10 of 1 volt) is too much. This is AC ripple caused by bad diode(s) etc.

If you have "anything" for a radio supression cap, install at the coil+ to ground.
 
Well this gets even stranger.
As far as I am aware, the only wires going to the dist on Chrys Electronic ign dizzies are the p/up wires. So, AM is saying to hook the tach wire to one of these?
For a start, never heard of any aftermarket tach that gets a signal from the p/up.
And the p/up output is a sine wave, not a square wave??
 
@4spdragtop I'll give that a shot. The coil will be easy, I've been dragging my feet on trying the old tach simply because i'm not excited about ripping up all the wiring work I did.

@67Dart273 That sounds like a good diagnostic test, will be trying that out tomorrow. I will say that when I added my new alternator about a month ago, I didn't know to also install a new regulator. I found this out a couple days ago when the car started acting like either the alt or battery were bad. Turns out it was the voltage regulator. I thought I would mention this since it all sort of ties in with the parts to be tested.

@Bewy & @KitCarlson After returning the first tach, I tried the second - brand new straight out of the box - connected to the gray wire like Autometer said. Same problem. It does work, but only at higher RPM.
 
Keep at it. They'll get you sorted out. One thing I will say, in my opinion start at the beginning. With testing/verifying alt and vr. By the sounds of it that's when problems started.
:thumbsup:
 
Can you post the [a] instruction hook up info that came with the tach or model number.
 
I have the AutoMeter 2893 tach. I've attached the install instructions that came with it (note the warning near the bottom that states the warranty will be void if connected to the coil when using an aftermarket ignition box).

Tach install.png
 
Righty if it is not system electrical noise cause by something such as the charging system, the only thing left is "something odd" going on with the ignition box. I would try to find SOMETHING to substitute, such as a working junkyard Mopar ECU or a GM module which you could easily "rig" if nothing else temporarily. This is my "infamous" emergency ignition---a coil, an GM 4 pin, to clip leads, and a Mopar dist. connector

This circuit, nicely drawn by a great member here

4pin-jpg-jpg.jpg


in this box

hwlcfa-jpg.jpg
 
I cannot stress enough to check for possibility of some sort of electrical interference, EMI/RFI. The destructions were talking about triggering it off the pickup which is a VERY low voltage, low power source. This means the tach is quite SENSITIVE. A long meandering pickup wire to the tach may be too close to some other wiring which is inducing interference, including secondary (spark plug/ coil high tension) wiring.
Check the thing is properly grounded, and that it is not grounding through the lighting circuit.

Try to "dress" the pickup wire close to ground, along the column, near the firewall, etc, which is as clos as you will get to a "ground plane" and will help reduce noise.
 
67Dart273 said:
You need to make certain that "whatever color" that the power wire from the ballast goes to coil +
And that "whatever color" the coil - goes to the ECU

Something you might try "shot in the dark"

Unplug the regulator and see if the tach works

With everything connected normally

With the engine running "fast idle" Check charging voltage at the battery. With the engine warm and the battery "normalized" you should see 13.8--14.2

If so turn on the headlights. Heater if you have it. Voltage should not drop much, not below 13.2--13.5

Now, turn your meter to AC volts. Measure right at the alternator output stud with engine still running on fast idle. You should have a very very low reading, almost zero. I would say over .3V (3/10 of 1 volt) is too much. This is AC ripple caused by bad diode(s) etc.

If you have "anything" for a radio supression cap, install at the coil+ to ground.
Click to expand...

Well here's an update.

Unplug the regulator and see if the tach works
Tach does not work at all with regulator disconnected

With everything connected normally

With the engine running "fast idle" Check charging voltage at the battery. With the engine warm and the battery "normalized" you should see 13.8--14.2
Battery voltage was 13.83 and climbing

If so turn on the headlights. Heater if you have it. Voltage should not drop much, not below 13.2--13.5
Headlights only. I have no heater, no radio, nothing else to add load. Voltage 13.42

Now, turn your meter to AC volts. Measure right at the alternator output stud with engine still running on fast idle. You should have a very very low reading, almost zero. I would say over .3V (3/10 of 1 volt) is too much. This is AC ripple caused by bad diode(s) etc.
I don't quite know how to measure at the output stud, so I tried several configurations. I tended to get 2 readings: 32-33 volts and/or 0.6 volts. I'm guessing the 0.6 volt reading was the configuration I was going for.

If you have "anything" for a radio supression cap, install at the coil+ to ground.
Radio suppression capacitor is connected to coil positive.

The fellas at the parts store "loaned" me a couple different ignition modules so I could perhaps troubleshoot my current one. The only ones they could source were the 4-pin and 5-pin chrome boxes. I have a 4-pin orange box. My car started after lots of cranking on the 5-pin box, but the tach performed even worse. No start at all on the 4-pin box.

I'm going to contact AutoMeter one more time via email so that I have this all in writing, but I'm pretty sure I'm giving up on at least this particular model.
 
OK there is no way that the tach should quit when you disconnect the regulator. Something is amiss there

The reading at the alternator is troubling. Can you detail how you came up with 33v?

You might try that again. You do know what I mean, right, the output stud of the alternator is the large black wire and this is hot at all times. This is what goes in, through the ammeter, and back out to the battery

With the car running on fast idle, hook one lead of the meter to ground, and the meter set on AC volts. Now hook the remaining meter probe to the stud. Again, you should get a very small voltage reading, the less the better.

"While you are there" also take that same reading with the meter in DC volts. Note the reading and take it again with headlights turned on.

Is the tach now reconnected to coil NEG? And have you made certain that is the wire going to the ECU? (Not the power wire) If there is any question of that, one way to find out is to pull the connector off the ECU box, disconnect the coil NEG wire and measure power at the coil + You should see battery voltage. If not the wires are reversed at the coil
 
67Dart273 said:
OK there is no way that the tach should quit when you disconnect the regulator. Something is amiss there

The reading at the alternator is troubling. Can you detail how you came up with 33v?

You might try that again. You do know what I mean, right, the output stud of the alternator is the large black wire and this is hot at all times. This is what goes in, through the ammeter, and back out to the battery

With the car running on fast idle, hook one lead of the meter to ground, and the meter set on AC volts. Now hook the remaining meter probe to the stud. Again, you should get a very small voltage reading, the less the better.

"While you are there" also take that same reading with the meter in DC volts. Note the reading and take it again with headlights turned on.

Is the tach now reconnected to coil NEG? And have you made certain that is the wire going to the ECU? (Not the power wire) If there is any question of that, one way to find out is to pull the connector off the ECU box, disconnect the coil NEG wire and measure power at the coil + You should see battery voltage. If not the wires are reversed at the coil
Click to expand...
Here's where my ignorance may really start to surface. You're talking about the voltage regulator, correct? the regulator mounted on the firewall? That's what I disconnected, and when disconnected, the tach did not work at all.

When I was probing the alternator, I had my meter set to AC, and wasn't sure which of the probes should go to the output stud, so I tried both. (one at a time, of course...haha) Here's where I think I screwed up: with one probe touching the output, I touched the other to another terminal on the alternator. I don't remember which gave me the high voltage reading and which gave me the low, I'll redo the test tomorrow when I'm off work. Are you saying I should ground the meter to an engine ground and not one of the other alternator terminals?

The tach is not connected to coil neg, as I'm concerned with voiding the warranty since I have an ignition box. But I am 100% certain that the wire going to coil negative is coming from the ignition control module. The wire going to coil positive is brown and coming from the ballast resistor.

@Bewy not a and idea, I'm just not eager to disconnect it yet another time....

Apologies for my ignorance and I appreciate everyone's help here.
 
That tach is perfectly safe on coil neg. The only types of ignition you don't connect the tach to the coil are MSD or other CD ignitions Most all CD ignitions are aftermarket.

Yes I was referring to VR. That should not affect the tach. My thoughts were that with it plugged in, some problem was generating RFI/ EMI (think radio static) and causing electrical noise, triggering the tach

So far as the voltage checks yes, ground the meter. The alternator case should be grounded, but you can ground to the engine
 
Test lead on the output stud, ground lead to the body of the alternator, meter set to AC volts, fast idle, 34.4 volts.

3BB89B84-C6FD-494A-A647-E63A79483DA0.jpeg
 
IF we are not missing something, and you have the meter set correctly...........

(what does the switch position say exactly I cannot read it? EDIT looks like AC 200V?)
And what make/ model is the meter?

That is TERRIBLE. AC ripple should be less than a volt by a long ways. You likely have a--more than one--bad diode(s) or other problem in the alternator and it is causing interference in the electrical system.

I have NO idea why the tach would not work with the alternator unhooked. It should work fine.
 
67Dart273 said:
IF we are not missing something, and you have the meter set correctly...........

(what does the switch position say exactly I cannot read it? EDIT looks like AC 200V?)
And what make/ model is the meter?

That is TERRIBLE. AC ripple should be less than a volt by a long ways. You likely have a--more than one--bad diode(s) or other problem in the alternator and it is causing interference in the electrical system.

I have NO idea why the tach would not work with the alternator unhooked. It should work fine.
Click to expand...

It’s a Gardner Bender GDT-311. The lowest AC setting is 200v, so that’s where it’s set. It didn’t matter whether the ground was on the body of the alternator or grounded at the fender well or engine, I got the same reading.

I should update with the fact that I tried the tach once again with the voltage regulator disconnected, and this time it worked (to the same level it has/hasn’t been working). I must have missed something the first time.
 
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