Electrical Demon?

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Moparmarcus

Moparmarcus

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I'm in need of help. I have a fresh 360 build in my Scamp. I have a problem with the engine stalling out. At first it appeared to be heat related and I treated it for vapor lock. But then it started to do it cold and finally got to the point where it wouldn't even start. I discovered 2 spark plug wires that were melting next to the headers and possibly even arcing, so I replaced all the wires with new Accel 8mm wires and installed a new coil. It started and ran well for about 15 minutes and then stalled again. But at least at this point I could get to start again. I noticed that most of the times it stalled I wasn't getting spark from the coil. Tried a second new coil with the same result.

The one clue is that I had test light on the positive lead of the coil and without touching anything (ignition was in the run position) the light suddenly went from dim to bright. It immediately fired right up at that point. I'm getting 9.4volts at the positive lead on the coil.

The only thing in the entire ignition system that is not brand new is the ignition switch. Could that be the source? Thanks in advance
 
What kind of ignition do you have, IE Mopar ECU, HEI, points, what, exactly?

The power you get to the coil in "run" is NOT what "starts" the car. There is a separate contact in the ignition switch which feeds what is known as the "IGN2" circuit or the "bypass." This is one brown wire comes out of the switch, goes through the bulkhead, and goes to the coil + side of the coil.

BUT WE NEED to know what you have for an ignition, and what YEAR is the car?
 
Its a 73 Scamp, '73 motor. The ignition system is ECU, OEM kit from Summit. But that reminds me that I did steal the ecu from that kit for my road runner and ordered another one. But due to shipping delays I got the replacement from ebay. The very last trouble shooting I attempted was to check the voltage at the ballast resistor from the ecu with the engine running. It appeared to be low - about 13.3 volts but then stalled after a few seconds. That was when I had to step away and about 2 minutes before I wrote the first post.

Then engine ran beautifully through break-in, then I got it settled in to a perfect 750rpm idle. The only indicator of a remaining problem was that it to acted like it was starving for fuel at 5300rpm, started to sputter. Shortly after that was when the stalling problem manifested itself and when I started thinking vapor lock. But she eventually started stalling even when cold.

Once I found the melted spark plug wires it seemed logical that was the source. Now of course my concern is did that problem burn out something else?
 
How long did the car sit while the enigne was being rebuilt? I ask since from the indication of the voltage suddenly jumping up and then the car starting, the ignition switch contacts may have oxidized a bit while sitting. BTW, when the voltage did jump up, were you turning the crank?

I am not sure I fully understand this statement: "The very last trouble shooting I attempted was to check the voltage at the ballast resistor from the ecu with the engine running." Do you mean 'from the ballast to the ecu'? At what point were you measuring this?

I would not worry too much about the burnt wires shorting anything; basically, the spark plug gaps are shorts of a sort all the time!
 
Failing ballast resistor, failing ignition switch, etc.., etc...
You could throw a lot of parts at it. In some cases that is the best route since you're replacing 40 year old parts that are destine to fail eventually anyway.
If you want to find and fix only what's wrong today, First take a close look at connectors. A white connector in the engine harness near the right valve cover is one of the usual suspects. The harness connector, also white, from the ignition switch, under dash, is another. If there is no visual evidence found,
Get a clear understanding of what voltages you should have where and when, then start diagnosing.
 
Sat for 5 years while I've had it, probably at least 5 more before that. I started to remove it and got to the point of pulling the shaft out of the column, don't have the puller. I figured before I cobble something together to use as a puller I figured I'd raise the flag of help on any other ideas. It was at this point that I read about the voltage at the ballast resistor ( you are correct - from the resistor "to" the ecu ). Just got the meter to settle on 13.3. she stalled and I hit the emotional wall. The range in the manual shows 13.8 - 14.x

Just this minute found a potential problem - I can't get a good resistance reading from the voltage regulator. It would not even register on the ohmeter. I cleaned the paint from the bolt contact areas, wire wheeled the bolt threads and added a direct ground wire over to the bolt on the ballast resistor which has a perfect 0.0 resistance back to the battery. Now the regulator ground is all over the board - from not registering to bouncing in 5-8 ohm range.
 
How old is the gas and filter ??

Did you take the gas tank out and clean it,,

Next time it stalls, look down the carb and see if it squirts gas when you move the throttle.. if it doesn't squirt,
Take the fuel filter off and see if you can blow thru it..

Your symptoms also match a progressively plugging fuel filter, or perhaps water in the fuel..

hope it helps
 
This MAY NOT be electrical, I'm not convinced either way. After the engine died, did you notice whether the carb accelerator pump would show fuel? That might have indicated a fuel problem


Both the ECU and regulator MUST be grounded, no matter what. Make sure you are stabbing through paint, chrome, rust, etc with your probe. Anyplace on the ECU or VR shell should be ground

It's not clear to me that you are or are not getting spark.

Is this a 4 or 5 terminal ECU? This is IMPORTANT because the newer 4 terminal ECU only needs a 2 terminal ballast, and can make troubleshooting that much easier.

Not all 4 terminal ECUs have 4 terminals. The 5th terminal may be a dummy. If it is NOT a Mopar OEM branded ECU it probably is NOT 5 pin regardless of pin count. Only way to tell is to resistance check the 5th pin to all the others, reverse your leads, and try again, to see if ANY of them show anything other than infinity. Also check to ground.

As Red said, I would pull ALL connectors and give them the wiggle test.

With the key in "run" ground first one, then the other distributor harness wire leading to the ignition. One or the other should produce one single spark when grounded.

With the key in "run" engine off, coil + voltage will be somewhat low, anywhere from 6-9 volts perhaps. If this voltage is near 12V check the NEG coil. A high reading there means the ECU is NOT grounded or is bad.

Probe the ballast for the "high" (KEY) sided, and check that carefully against battery voltage. When you find the high side, move your ground probe to battery positive. This will give you a very low reading, the lower the better. More than .3V (three tenths of one volt) means you have excessive voltage drop in the wiring between battery, switch, bulkhead, etc on the road to the ballast.
 
inertia - New tank, new sending unit, cleaned the existing lines with brake cleaner and air pressure (was about a week after that installed the new tank) new filter, getting 7 psi after the filter. New carb for that matter :) The bowls are full regardless of how long the engine runs or if its starting cold I get a strong supply of fuel when I work the accelerator pump.

I just noticed the dark blue wire that feeds the ballast resistor is on the bottom left instead of the top left. According to the manual it should be on the top left and the dark green/red that feeds the ecu should be on the top right. All wires except that dark blue trace out correctly. This is an aftermarket wiring harness (Evans Wire Harnesses) and in order to correctly line up the dark blue with the green/red I'd have to cut off the plastic tab that forces you to install it "correctly" Could it be that the connector was installed incorrectly by Evans? And this is burning out my coil?
 
Not all harnesses install the same. This is a PITA. This is WHY I wanted you to find out if you have a 4 or 5 pin ECU, because if you have a 4 pin, the "other side" of the ballast is not needed.

In other words, if your harness plugs in so that the "jumper" end is plugged into the end of the resistor with the U cutout, then the two wires at the opposite end must be reversed left to right in the diagram below. Think electrically, not mechanically.

Go by this diagram:

Look at the upside down "U" shaped cutout in the diagram. THIS is what identifies each section of the resistor. On a 4 pin (newer) ECU the left side of the resistor, which feeds reduced power to the box is eliminated




http://www.mymopar.com/downloads/Ignition_System_5pin.jpg


Regardless of how your harness is hooked up, the LOW RESISTANCE side of the resistor MUST hook to the coil

See here:

Top of the resistor is what feeds the ECU. The BOTTOM of the resistor is same as a 2 pin coil resistor

http://www.mymopar.com/index.php?pid=115

http://www.mymopar.com/forum_images/Ballast_Resistors.png
 
67Dart273 - NO spark from the coil after it stalls, Once I have an arc from the coil wire I plug it back into the distributor it fires right up. There is just no rhyme or reason as to why I suddenly get spark again.

You may be on to something. I just pulled the ECU connector. The ECU is 4 terminal. The space that does not have a terminal is where the green/red from the ballast resistor resides. Would this kill the coil or just make it get funky like I have been experiencing? I definite have no spark from the coil when it won't run.
 
The distributor/ECU I bought from Summit came with a single ballast resistor but the harness was connectorized for a dual. Since the manual showed a dual I bought a dual one and went from there.
 
OK, since your Summit box ONLY needs a 2 pin resistor, all you need to do is make sure that the coil is hooked to the correct side. Either that or cut off the extra harness wires and use the 2 pin resistor.

SINCE WE now know that you have a 4 pin box this makes things "somewhat" easier.

One thing you can do is when you have NO spark, try running a jumper (clip lead) directly from a battery source (starter relay) direct to the coil + wire. This will give you a nice hot spark regardless of problems in the main harness.

If it does not, you KNOW it's "right there" in the ignition somewhere, and not in the ignition switch, bulkhead connector, etc.
 
Have I mentioned I hate electrical problems? I tried a jumper from the Battery+ terminal to the coil+ terminal. Started right up and stalled after 4 or 5 minutes. So I took off the jumper and checked the voltage at the coil. I am getting 11.6v on the coil+ terminal with the key in "run" position. Also 11.6 on coil- terminal. Indicating bad ECU? (ECU ground is good) but shouldn't it have run well with the jumper if that was the case?
 
If you have that high voltage on the ECU then it is actually not grounded or ECU is bad. ALL Mopar ECUs draw current through the coil with key "on".

What you SHOULD see on NEG side of coil with key on is a fairly low voltage, perhaps 1/2 volt. The transistor on the ECU should get a bit warm, and the coil will get warm if you leave the key "on" for long. The ballast will heat up


I would CERTAINLY r r r r r r r eeeee check ground on the ECU before replacing it!!!
 
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