Starting spark frequency? (ignition issues...)

[NukeBass]

(Long story, question at the end)

I have a 73 Duster with a 340 and an electronic ignition. Three weeks or so ago the car started and drove fine. Tuesday I went to drive it and it did not start. I checked for spark at the #1 spark plug with a spark tester and didn't see any spark. Then I checked all of the voltages I found recommended in other posts with the key in the run position. I had 12 volts on the ignition wires (there is a dual ballast resistor, but it's been wired to so that the bottom and top resistors have been bypassed), 12 volts on the positive side of the coil and 12 volts on the negative side of the coil. I checked continuity between the ECU harness and the locations on ballast connectors, distributor connectors and coil connectors and everything checked out. The 12 V on the negative side of the coil led me to believe that the ECU might be bad and, since I didn't have a backup anyway, I ordered one.

The original ECU was a REV-N-NATOR (in the process I found these are out of stock) and I replaced it with Carquest premium module. After I installed it, the car still did not start, but I measured and now have 1-2V on the negative side of the coil. Somewhere in the process I read to check the AC volts coming out of the distributor and read 0.2-0.3 VAC which seemed a good bit lower than the 1VAC mentioned in other posts. So I thought maybe the pickup had shifted or gone bad so today I took out the distributor (a firecore model from the RT garage) and the air gap seemed fine if I was using my feeler gauge correctly. I spun it by hand and never read above 0.5 VAC on my meter. I also have an older MP distributor and it measured upwards of 0.8-0.9 VAC with a gap > 0.010". I adjusted that one and, spinning by hand, got voltages greater than 1 VAC, so I decided to put the MP unit in the car.

I got everything hooked back up and the car still wouldn't start. I did check for spark at the coil at the distributor side of the HT wire (I had to buy another tester since my other one didn't seem to be configured for this wire) and got a spark. We tried a few more times to start it and when we backed off the key the engine would spin backwards for a second or so. This clearly wasn't right and figured I either messed up when I put the distributor in or cross wired something. I rotated the engine back to about 15 degrees BTDC, reset the distributor cap and hooked the wires back up. After this we tried to start the car. The first time was nothing. The second time the car fired right up and idled fine.

We let it run for a while and I checked the timing. Everything was going fine so we shut it off and I plugged the vacuum advance so I could check the mechanical advance and the car would not restart. We tried multiple times and it would never restart (it never ran backwards during this evolution so that was an improvement). I still had the timing light connected and it would occasionally flash, but it seemed to take a good bit of time for the flashing to occur. But I have no reference point for how often it should spark when the engine is being turned by the starter.

How often should the coil spark during starting? It seemed to take five or more seconds for the coil to fire a spark and 30 or more seconds to fire at the #1 cylinder as indicated by the timing light. This just seemed long to me. Maybe the distributor still isn't sending a consistent signal to the ECU?

What should I do next to troubleshoot?

Thanks for all your help.

 

[67Dart273]

Here is the deal on the voltage on the NEG side of the coil. First, I am NOT familiar with the "revanator" modules. I know of them, but not familiar
All Mopar "factory like" modules draw coil current with key in "run." This means the coil is switched "on" that is grounded through the module transistor, and will pull the coil NEG low, down to a volt or two

Some ignition modules such as GM HEI do NOT draw current with the key in "run." This means that since the module is NOT grounding the coil NEG, the coil NEG will be "high" or battery voltage.

So what you measured there "may be normal" for some aftermarket specialized modules

 

[67Dart273]

How to check spark

First it is important to understand how Mopar ignition switches work. The "run" position is hot in run, and feeds power to the coil through the ballast. On older "5 pin" ignition boxes, which require a "4 pin" ballast, the second ballast also feeds reduced voltage to the module, as well as "full battery" V to one other pin

The "run" voltage GOES DEAD (a function of the ign switch) when twisted to "start." The ONLY voltage to the ignition system in "starting" is provided by the IGN2 circuit, normally brown, which goes to the coil+ side of the coil, and feeds "full battery" to the + side of the coil. It ALSO "backfeeds" V through the ballast and to the module during this time. That is, during start, the module works on reduced voltage

The reason I'm telling you this is that if you test spark and you bypass the starter relay with the key "in run" this sets up a "false condition" which can lead you down the wrong path. ALWAYS try and test by using the key to crank, unless you realize the difference

So "rig" a spark gap out of the coil tower using a solid core wire, not a radio resistor one, and use a large gap plug or other means for a gap. Crank using the key. A properly working system will make nice blue sparks at least 3/8" and typically more like 1/2" long



Always suspect the dist. connector. Turn key to run, pull dist connector apart, and rig a spark gap to the coil HV tower. Take the engine harness half of the connector and repeatedly tap the bare terminal of the connector to ground. A nice single "'snap" spark should happen each time

Dont be afraid, generally, to wiggle test connectors, and to work them in/out several times to scrub the terminals as well as "feel" for tightness. There's even been a few guys here have had trouble with the big connector on the module, so don't put that out of your mind.

The module absolutely MUST be grounded to operate. Scrape around the bolts remount using star lock washers

Inspect the dist. reluctor/ pickup for rust/ debri/ damage. Inspect the shaft for wobble and loose bushings. Hook your multimeter to the dist connector and spin dist. or crank engine. On AC low volts, the dist should "generate" about 1v AC

 

[Dana67Dart]

there is a dual ballast resistor, but it's been wired to so that the bottom and top resistors have been bypassed)

This is troubling to me.

If you have a standard coil and a standard mopar electronic ignition system you still need a ballast resister.

IIRC the older 5 wire ECUs need a ballast resister for their power feed and the coil needs it's ballast resister

The newer and I suspect all replacement ECUs are 4 wire and the ECU does not need a ballast resister on its feed. BUT you still need the ballast for the coil.

So if you bypassed both the top AND the bottom ballast resisters you might be cooking the coil.

Now if you have aftermarket coil, dist, and ECU they may have internal protections and be specifically designed to run on full battery voltage.

 

[NukeBass]

To test the coil tower, I used this tester at the 10 mm distance and it gave a good spark when it sparked. For the spark plug spark checks I used the Lisle inline spark tester. All of my spark tests have been done with the key (using either my son or my wife to help).

I'll rerun the AC tests in the morning. The meter I've been using is auto scaling and may not be sensitive enough for lower AC readings so I'll try a different one.

Thanks!!

 

[67Dart273]

Doesn't your meter have a function to disable "auto?"

 

[67Dart273]

To test the coil tower, I used this tester at the 10 mm distance and it gave a good spark when it sparked. For the spark plug spark checks I used the Lisle inline spark tester. All of my spark tests have been done with the key (using either my son or my wife to help).

I'll rerun the AC tests in the morning. The meter I've been using is auto scaling and may not be sensitive enough for lower AC readings so I'll try a different one.

Thanks!!

If it is getting good spark at the coil tower there is no need to do anything else except for the high voltage side of the dist. itself . Frankly, the "big" items at that point are carbon tracked cap or rotor, rotor "punch through" which causes a ground through to the dist. shaft, or just a bad coil wire. It can take what "seems" a long time to come around on one spark plug. Bear in mind the crank must make TWO revolutions between each spark at one plug

 

[NukeBass]

This is troubling to me.

If you have a standard coil and a standard mopar electronic ignition system you still need a ballast resister.

IIRC the older 5 wire ECUs need a ballast resister for their power feed and the coil needs it's ballast resister

The newer and I suspect all replacement ECUs are 4 wire and the ECU does not need a ballast resister on its feed. BUT you still need the ballast for the coil.

So if you bypassed both the top AND the bottom ballast resisters you might be cooking the coil.

Now if you have aftermarket coil, dist, and ECU they may have internal protections and be specifically designed to run on full battery voltage.

The story behind this is the guy who restored the car couldn't get it to start with the ballast so he bypassed it. This was one of the things I was eventually going to try to figure out why (it doesn't make sense to me why, but it would not run with a ballast) so now is as good a time as any. I currently have the coil from RT Garage that is matched to the REVNNATOR, but they say you should use a ballast, too.

 

[NukeBass]

Checked this morning and only have 300 mVAC from the plug on the distributor side of the connection. Is this enough to trigger the control module?

However I did notice the car acted like it wanted to start after the key was released and a little smoke came up through the carburetor. Not sure what this means.

I'm going to get something to label my plug wires at the distributor and then take a look under there. After I charge the battery I'll also check for starting voltage of the brown wire from the starter relay. I wonder if something is going on there since, based on what was said above, the ballast should have nothing to do with starting at all.

 

[67Dart273]

Be for certain (that is, check it) that the coil is getting 12V during cranking

300mv if your meter is accurate is quite low. If you have not done so, check the reluctor/ pickup visually, and get yourself a .008" (inches not metric) BRASS feeler and set the reluctor gap. The pickup adjusts similar to breaker points with a clamp screw

 

[NukeBass]

I went back out and checked the voltage during cranking and the meter read essentially 0 (200 mV) which was odd since it started yesterday. I checked voltage at the brown wire at the ballast during cranking and found 0 volts there, too. I traced that wire back to the bulkhead and made sure there was continuity there. However, during that exercise I found the alternator wire at the bulkhead was pushed out of the connector. I didn't think that would affect anything I was testing, but figured I'd fix it.

For this wire the bulkhead connector had gotten so old and loose (it never melted like some of the pictures I've seen, but you can tell where it had definitely been over heated and expanded) the dash wiring side connector wouldn't stay put so I super glued it in a couple of years ago. I guess everything wasn't lining up right and over time the female connector pushed the wire out of the engine side connector. I went ahead and spliced in a connection through the bulkhead connection to fix that. While I was under the dash I also checked for continuity between the ignition switch side connector brown wire and the connection at the firewall. Everything there checked out so I knew the wire was good and the ignition connections were good.

I tried to start the car, figuring I would eventually check the brown wire voltage at the firewall, and it fired right up. I stopped and started it a few times to ensure it wasn't fluke like last night and it started right up every time. I checked the AC volts at the distributor during cranking and it was between 0.8 and 1.1 volts. I don't know why a bad connection of the alternator wire would have affected this circuit, but it did. I also checked cranking voltage at the brown wire at the ballast and it was 12 volts.

Then I installed the ballast resistor that RT garage sold me with the coil and checked the voltage (I didn't expect it to start) and the brown wire jumped from 12 to 9V when the car started. For the first time this setup started with a ballast resistor installed. Then I put the firecore distributor back in since I know its mechanical advance is set where I want it and the car started again (I didn't check AC volts since it started). The ballast I have on there now is a two prong ballast so I just connected the bottom portion of my two connectors.

I'll run it again tomorrow to ensure this wasn't a complete random fluke. The only current component different than it was Tuesday is the ignition control unit. I haven't installed the REVNNATOR yet, but I might do that tomorrow. If that starts the car with the ballast resistor installed then that means I've had a bad bulkhead connection for 10 years that has likely caused starting issues in the past. I have run parallel battery and alternator wires in the past and didn't think the bulkhead connection would be as important with those in place, but apparently I was wrong, and hopefully this fixed it.

If the car is now fixed and the REVNNATOR works then I just am out a backup control unit and I figure it's not a bad idea to keep that as a spare. I also have a much better understanding of how the system works.

Thanks for your help. The information here and in previous posts I read has been invaluable.