I'm STILL chasing ignition problems with the T/A. I've replaced so much but the problem continues.

One thing I haven't replaced is the voltage limiter on the back of the gauge cluster. What does this do? Just supply power to the temp and gas gauge?

Thanks

Just reduces 12v to 5v for the gauges. Doesn't affect anything else.

Explain the problem again. Intermittent no start right? No start or no crank? Is it auto or manual trans?

Starts every time when cold.
Once driven and sitting (warm) it turns over but will not start under load (key all the way forward).
Will occasionally start when you let off the key, on that last turn of the engine.
While having this issue it will consistently start with key forward and jumped from starter relay.

I have replaced the following with NEW parts:
Complete dash harness
Both engine compartment wiring harnesses
ECM
voltage regulator
starter relay
ballast resistor
coil
cleaned all grounds

I have a new, in the box ignition switch which I can plug in and turn the car but it still won't start.

I have not replaced the distributor.
Thanks

I would check the ignition switch and it's connectors because that's about the only thing left that might cause your issue.

I had an issue similar to that and it was one of the connectors to the ignition switch was melted and black, it usually worked when cold but when things got warm it would crank over but not start after pulling my hair trying to figure it out a friend of mine figured it out for me and it only took him a couple of minutes whereas I had been fighting it for quite sometime.

Like I said, I have a new ignition switch which I have plugged in (not installed). It doesn't make a difference,

Dad had one that would quit when it got hot. The coil in the dist had a winding that opened up when it got hot.

Check the neutral safety switch, might be a bad connection or bad wire.

Check the one on the clutch pedal. On the 1970 B-body's its a green wire.


Did you replace the battery cables? Some reproduction cables are not properly sized (gauge wise) and when they heat up because they cannot handle the amperage and they can lose connection usually in the terminal ends. Try running jumpers to see if that corrects the issue.

It cranks fine. It doesn't start with the key when hot but WILL start when jumped.

Have you used a test light to verify power on the brown wire when the key is turned to START? Pull the yellow wire off the starter relay while you test. This will prevent the starter from engaging. When it acts up, test the brown wire. That wire should power the ignition during START.

And check the connection for that wire at the bulkhead connector.

I'll check. All the harnesses are brand new.

And if it does put the yellow wire back on and repeat the test again verifying power is present

What are you jumpering from and to?

Once running, does it stay running when the jumper is removed?

What ignition system do you have?

An intermittent ground could also be an issue. Make sure they are all clean, bare metal contact and tight, especially on the distributor control box

If I read right it cranks but wont start mostly hot?Then you say if you jump it it starts.Seems like low voltage hot as starter draws more hot.Id almost say check the battery cables.If it was a bad ign switch Id think it would start hard all the time.That or your dropping lots of volts hot crank.Did the battery get load tested?Even if not old or new they acn be bad and start cold not hot.Rocky

When the car is warm and will not start, what is your voltage (while the engine is cranking) at the positive side of the coil?

Dual Ballast Resistor it would seem? Correct
One side of ballast is the "START" circuit (completed when key all forward (crank/start)
Other side is the "RUN" circuit (completed when key releases to the normal Run position.

If start side is bad: engine cranks, but no start
But if key is released quickly, the run circuit may kick in to run engine,
while it is still just cranking.

Those coils within ballast can loose continuity when hot, & appear good while cold.

Worn/sloppy ign switches can exhibit same symptoms, but you said you replaced with new.

Really converts a steady 12vdc signal into a pulsed signal, that should average out to that 5 volts.
Basically a mechanical type voltage regulator.

Use an analog meter on that output & you'll observe the pulsing.
Digital's will average it outright or do not have a quick enough response time to indicate it.

.

I agree with several, but Budar's suggested follow up test is the most logical next step.

Budar wrote:
.

Just to make this clear.
The 'brown wire' is the one that gets power when the key is in Start. The service manual shows this as "Ignition 2"
It goes from the key switch through the bulkhead connector to the ballast resistor(s) to the coil.

"Yellow Wire" to the relay also gets power when the key is in Start.
Schematic attached to post.

So the test procedure suggested is this:
Remove the yellow start wire at the relay.
Then connect a test light to the brown wire connection at ballast resistor.
Or, maybe better, back probe that connections with a voltmeter. Other lead of voltmeter connect to ground.
With key in start position voltmeter should show battery voltage. To know what battery voltage is during start you must measure it at the battery with key in start.

Maybe I'm just ignorant on the T/As, but based on what I know, the ECM and distributor are modifications. Therefore, I am assuming this is single ballast resistor set up and a 4 wire ECU harness. Is this correct?
Phillyrag asked the same question, but he assumed it was a dual ballast harness.

This could be important to the follow-up steps to the diagnoses if there is full power available at the brown Ignition 2 wire during start.

Just because stuff is new doesn't mean its good or correct. I trust genuine old stuff more than most new stuff (sad).

First schematic is typical stock setup for '70. Little details will vary from year to year and model to model. For example 'Run' wire may go to VR before ballast.
Second one is a common arrangement when a magnetic pickup distributor and Chrysler type ECU is added.

My dad's car had a hot start problem caused by a too-wide reluctor gap in the Mopar electronic distributor. We closed it to around .008 and that fixed it. I'm not sure if that fits with your other symptoms, but as long as you're checking things it couldn't hurt to check that too if you have something like a business card around that thickness you can slip in and check.