Electronic ignition troubleshooting help

[MoparLeo]

Go with what it shows. A ballast resistor is a very minor thing. If you have a dual you can still use it. Only connect to one side.

 

[RJRENTON]

The dual ballast resistor is comprised of 2 sections: one section was 0.5 ohms which feeds the coil primary and the other ballast section is 5.0 ohms, which fed the 5th terminal of the control box, which is no longer required. So, nothing will be conbected to it. You can connect the ballast resistor using the harness as in tended.
The clearance between the pickup coil pole piece and the reluctor (gap) is 0.006" - 0.008" measured with a brass feeler gauge, so not to be influenced by the magnetic field of the pick up coil). You can temporarily jump out the ballast resistor to prove if its functional, if still no spark, consider substitution of the control box first then the coil. Insure that the control box is securely grounded.
BOB RENTON

 

[Curt Chambers]

Was out of town for a couple days. Back troubleshooting this.

Thanks guys, that helps clear it up. The box and resistor were purchased from different sources who both claimed it was correct for my vehicle. But my setup doesn't exactly match the diagrams.

Air gap is .010" with a little resistance, which is what the FSM said it should be. ECU is grounded. Still getting 10.5v at the coil with ignition on and around 9.5v with it cranking. Absolutely no spark at the coil secondary lead.

A new box is fairly cheap so I guess I'll start with that.

 

[Curt Chambers]

Update. Installed a new ECU from Classic Industries. Started right up.

 

[Curt Chambers]

I guess I celebrated too soon. Won't start today. It has spark. So now I'm guessing a fuel issue. But it won't even fire up with starting fluid (doesn't even really sound likes it's trying to).

So with spark and fuel there, what else can I look at?

 

[Dave6T4]

December 2020 issue of Mopar Action has a pretty good article about electronic ignition with wiring diagram and tuning tips.

 

[Curt Chambers]

I have good spark at the distributor tower, so I think the ignition system is working.

 

[Curt Chambers]

Something is very wrong here. I need to go back to square 1.

I installed a single ballast resistor instead of the dual (this was done prior to successfully starting the car a few days ago). So the ignition system is currently wired exactly like the diagram in the link in Post #19.

Battery voltage is 12.4v (new battery). With ignition on, there are 10.5v at the Ign 1 terminal of the ballast resistor and 10.5v at the ECU. That seems a little low but a poster in this thread said it should still start at that voltage. Now here's the weird part. With ignition switch on, there are 3.2v at the coil, and 3.2v at the Ign 2 terminal of the ballast resistor. I was not cranking the car at this time.

Next, I removed the Ign 2 connector at the BR, and now the BR terminal volts read normal (10.5v, same as the other side). But as soon as I connect the Ign 2 wire to the BR, the voltage drops to 3.2v. In addition, I noticed the BR was getting extremely hot. So I guess there's a short somewhere. Just to check, I temporarily installed my new dual BR and had the same results.

I hate these kinds of wiring issues. I'm just going to start tracing things backwards but if anyone knows of a likely suspect to save some time, I'm open to suggestions.

Thanks

 

[Bee1971]

Your car left the factory with a Dual Ballast Resistor like Bob mentioned earlier

Now your saying you installed a Single Resistor - What did you do with the dual resistor wiring harness black plastic connectors and pins ?

What OHM Reading Ballast Resistor are you running now ? Check it cold and hot with OHM Meter

All these aftermarket resistors are all over the map , both single and dual resistors as far as OHMS

They make all different OHM Reading Ballast Resistors , so depending on resistance , will effect voltage going to the positive side of coil

3.2V is very low , however once the car is running and the charging system is working what is the voltage on ignition 2 side of the ballast resistor and then positive side of the coil in run

6 - 8 Volts ?

Also what Ignition Coil part # or brand are you running ?

It is completely normal for the resistor to get

 

[Curt Chambers]

Your car left the factory with a Dual Ballast Resistor like Bob mentioned earlier

Now your saying you installed a Single Resistor - What did you do with the dual resistor wiring harness black plastic connectors and pins ?

I had asked about this earlier in the thread but didn't get a response. The parts suppliers list a 4-Pin ECU and a dual ballast resistor as being correct for my vehicle. Yet that combo does not match the FSM wiring diagram, nor do they really connect to each other. The ECU harness I'm using has 5 wires going to it, so one does connect to the dual resistor aux side. But there is no 5th pin on my box so it doesn't do anything.

I may not have expressed the issue correctly in my last post. There is 10.5v going to the BR at the Ign 1 terminal with the ignition switch in the "ON" position. If nothing is connected to the other BR terminal, that terminal reads basically the same voltage (10.2v). But as soon as I connect the Ign 2 harness to it, voltage drops to 3.2v. This is still with ignition switch on but not cranking.

I interpreted that as meaning that there is a short circuit somewhere in the ignition switch wiring. But I'm really at a loss on how to proceed at this point. A few days ago the car started fine with this exact same setup. Now all of a sudden have this massive voltage drop from somewhere.

 

[Bee1971]

Your car left the factory with a 5 pin ECU and a dual ballast resistor

Yes a 4 pin ECU replacement will work with the factory dual ballast resistor

A voltage short and a voltage draw are two completely different actions

When your connecting to the ignition 2 side of the ballast resistor you now have created a voltage draw with the positive side of the ignition coil and the wiring harness and and

Are you getting any spark if you where to remove a spark plug wire from the plug or the ignition coil high tension wire from the distributor cap and apply a ground path to either while cranking ?

 

[Bee1971]

"But as soon as I connect the Ign 2 harness to it, voltage drops to 3.2v. This is still with ignition switch on but not cranking."





We want to know the voltage to the positive side of the coil in the CRANKING POSITION , trying to start

 

[RJRENTON]

As best I remember, the 4 terminal ballast resistor's wiring harness, on the inlet side to the resistor has an orientation projection, that matches the ballast resistor's connection, that connects the resistor correctly, to the 0.5 ohm (coil's feed connection) and the 5.0 ohm ECU's supply. Since your ECU, has only 4 pins, the origional harness connector with 5 wires will fit but the 5th wire that goes to the 5.0 ohm part of the ballast resistor will not be connected to anything.
With the ignition switch on, but not cranking the engine, there will be approximately 12 -13 volts on one side and the ballast resistor and approximately 8.0-9.0 volts on the other side of the same section of the resistor. Since the 5.0 ohm section of the resistor is not in the circuit, the same voltage will appear on both connections and no voltage drop will be noted. On the 0.5 ohm section that feeds the coil, there will be a voltage drop and the resistor will get very hot to the touch....this is normal.
When cranking the engine, the ballast resistor is bypassed, applying full voltage to the coil, approximately 12 volts, to produce max spark energy during cranking. The transistor on the ECU, is normally biased ON allowing current flowing to the coil. ITS WHEN THE TRANSISTOR IS TURNED OFF, by the internal components of the ECU and the pulse generated by the magnetic pickup coil in the distributor, the coil generates the spark. As soon as the engine starts and the key is released, the current flows thru the ballast resistor thru the ECU's transistor to the coil. The reduced voltage to the ECU and coil helps to reduce the heating of the components and extends their life.
IMO....if your car started and ran b4, but not now, suspect a failed ECU. Insure that the ECU is securely grounded, as the ECU's transistor must be grounded to allow the coil's primary current to flow.
Just my opinion of course.
BOB RENTON

 

[Curt Chambers]

Thanks for the replies. I have spark at the high tension lead to the distributor, but it is yellow and I read that's not good. I will get a cranking voltage for you tomorrow and double check the ECU ground. I sure hope it hasn't failed already. It's only a week old.

 

[Bee1971]

It hasn’t failed if you have spark


Cranking voltage like you said taken at the positive lead on ignition coil

And how old or what brand coil are you running

 

[RJRENTON]

It hasn’t failed if you have spark

Not all together true....if the output transistor turns ON, to switch 12v to the coil (and turns OFF to produce the spark), perhaps something in the INTERNAL dwell timing network (programmable PUT-Programmable Unijunction Transistor) has failed, preventing accurate on/off timing of the ECU. its a combination of WHEN and HOW LONG the ECU controls the coil.

Cranking voltage like you said taken at the positive lead on ignition coil

And how old or what brand coil are you running

Chinese manufactured ECU's have a dubious reputation for being short lived and high failure rates.
Just my opinion of course.
BOB RENTON

 

[Curt Chambers]

Battery voltage = 13v
Ignition switch on, BR Ign 1 voltage = 10.8v
Ignition switch on, voltage to ECU = 10.8v
Ignition switch on, Coil + = 3.8v
Cranking voltage at Coil + = 7.1v

Although it was cranking OK the other day, today the battery really struggled to crank the engine. So my starter may be on the way out as well. If it helps diagnose this, I also did the cranking test with a remote starter switch, Ign On, and had 3.8v at the coil +.

As for the coil, I have no idea how old it is. It's just something the guy who sold me the distributor had laying around (along with the previous non-functional ECU).

 

[RJRENTON]

Battery voltage = 13v
Ignition switch on, BR Ign 1 voltage = 10.8v
Ignition switch on, voltage to ECU = 10.8v
Ignition switch on, Coil + = 3.8v
Cranking voltage at Coil + = 7.1v

Although it was cranking OK the other day, today the battery really struggled to crank the engine. So my starter may be on the way out as well. If it helps diagnose this, I also did the cranking test with a remote starter switch, Ign On, and had 3.8v at the coil +.

As for the coil, I have no idea how old it is. It's just something the guy who sold me the distributor had laying around (along with the previous non-functional ECU).

IMO...
1. The voltages seem a little low. The first reading ign on, 10.8 volts should be close to battery voltage perhaps due to a bulk head connector that is going bad
2. The voltage to the ECU is the same as #1...OK
3. Ign on coil+ = 3.8v. Seems low should be around 8-9 volts because the power is going thru yhe ballast resistor. The voltage would be reduced in the run state but slightly variable because of the ballast resistor will change its resistance due to current flow.
4. Cranking voltage at the coil should be approximately the same as #1 because the ballast resistor is bypassed during cranking.
Current draw and subsequently voltage measured at the coil will depend on the coil's primary winding resistance. Lower resistance = more current flow and more voltage drop.
The coil, ballast resistor and ECU must be compatible and in conjunction. Arbitrarily changing, say, to a higher voltage coil, in search of "more horsepower ", often results in strange voltages being measured and failure of the ECU or coil or both.
BOB RENTON

 

[Curt Chambers]

Thanks for the reply and your patience.

What does it mean for the coil, resistor, and ECU to be "compatible and in conjunction"? How do I determine this? FWIW, nothing was arbitrarily changed. All the components (except for the new replacement ECU) were purchased from the same vendor as a working system (or so I thought).

Would a bad starter affect that cranking voltage?

 

[RJRENTON]

Thanks for the reply and your patience.

What does it mean for the coil, resistor, and ECU to be "compatible and in conjunction"? How do I determine this? FWIW, nothing was arbitrarily changed. All the components (except for the new replacement ECU) were purchased from the same vendor as a working system (or so I thought).

Would a bad starter affect that cranking voltage?

Compatibility means the coil's requirements (current) cannot, or should not, ecxeed the ECU's switching or current handling capabilities. Likewise, the resistance of the ballast resistor, if too low, will cause too much current to flow thru the ECU and the coil. Brand names are not important as the electrical specifications. Sometimes, vendors package components based on profit or what is in stock vs component compatibility.

Re your other question, YES...IF the the starter is failing, due to an internal shorted commutator bar or brush holder or bad field coil, this would cause a severe voltage drop while cranking. IF, you are going to replace it, consider a "mini" starter as they have permanent magnet fields in lieu of windings, consume less current produce more starting torque.
BOB RENTON