Strange ignition question

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DCDuster75

DCDuster75

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Hey guys and gals, I have a weird issue when starting ill try to explain as best I can. When starting my 318 duster, I can turn it over to start it and it will keep cranking with no hint of firing, but! Upon release of the cranking position to run position after turning it over, it will fire right up. I've never had this issue with any other mopar before. Usually I could here it firing off while cranking, but not on this one. This starts on the release of the cranking position. This is very very strange and wondering if anyone has experienced anything similar. I have installed a new ignition previously, so wondering if a wire or 2 are backwards?? Kinda perplexed here. Any thoughts? Thanks.
 
It sounds like a ballast resistor issue. Is your ballast a dual coil unit?

Ballast_Resistors.png
 
DCDuster75 said:
It sure is yes.
Click to expand...
One coil is for the start circuit and the other coil is for the run circuit. The start side is bad I bet. Test with a multimeter or replace and keep your fingers crossed.
 
I'll test it but it is brand new, and same happens with the one that was in it before. Just to add, I used the ballast resistor in my dodge van to test an issue in the van and started fine in it, that said though, I will test it and put up what I find. Appreciate it
 
OK.
Don't change the parts unless they are bad.
The photo is wrong.
Take a multimeter, set to Ohms, lowest scale if there is a choice.
Touch the probes together and adjust zero (analog) or write down the number if its digital and not showing zero.
Key off, remove the connectors and measure the resistance across each resistor.
One should be 5 ohms, the other should be 0.5 Ohms

If the resistors measure correctly then they are not the problem.

The two resistors were used with factory ECU through the later 70s, maybe beyond.

Later ECUs and most aftermarket do not need the 5 ohm resistor, although it does hurt to leave it there.
People often call these 4 pin ECUs versus the original factory units that used all 5 pins on the connector.
 
I agree that it could be key switch or wiring fault. Specifically the Ignition Start wires (J3).

1975 model year wiring can be a little different than earlier years.
The key switch power feed comes from a splice in the alternator's output wire (R6-12Black).

That shouldn't effect the ignition wiring, but something to be aware of when tracing wires.
1683993045795.png
 
I put a new ignition in but the problem was that the new ignition wire coloring is different than the original. So I'm thinking maybe that may be the issue is that 2 wires are reversed?
 
DCDuster75 said:
I put a new ignition in but the problem was that the new ignition wire coloring is different than the original. So I'm thinking maybe that may be the issue is that 2 wires are reversed?
Click to expand...
Explain more.
A new ECU should take the same pentagon shaped connector plug.
 
Was this car equiped with the seat belt interlock?
its been posted here that some early '75s had it.

Below is a sketch of a standard '75 without the seatbelt-starter interlock.
1683997783897.png


I don't have a full wiring diagram but the open circle in the J3 circuit I beleive is an 'engine connector'.
This is maybe a four cavity connector that also has the J2 feed to the alternator and choke.
It's on the engine.

If you have multimeter or test light, disconnect the grounding wire(s) on the starter relay.
Then turn have someone turn the key to start while the lamp or meter (set to volts ) checks for power at the J3 connections.
First check at the coil and then at the engine connector and then the firewall connector if you can slip a probe in.
 
As far as wiring, if there's no interlock wiring, then its pretty simple.
Look at the pentagon connector.
The two wires on the right of the pentagon connect with the distributor. They are not interchangable. That signal is amplified by the ECU and used to switch on/off current through the coil. That's the left pin (black w/ yellow wire originally) which must connect to the coil negative.

The pin at the top of the pentagon connects to power. Bottom left is to control the power on the original ECU's. That pin connects to the 5 ohm resistor. Red and green wire originally.
 
Mattax said:
Explain more.
A new ECU should take the same pentagon shaped connector plug.
Click to expand...
My plug was disintegrated as well as the new plug was the same shape but different size. I can't be only that "that" has happened to. Lol but I read the aftermarket parts did have an issue with wiring color as well as it wasn't installed into the plug, was in the box with the ignition
 
You say you replaced ignition in post 10. Are you referring to the ignition switch?
 
DCDuster75 said:
My plug was disintegrated as well as the new plug was the same shape but different size. I can't be only that "that" has happened to. Lol but I read the aftermarket parts did have an issue with wiring color as well as it wasn't installed into the plug, was in the box with the ignition
Click to expand...
Ahh.

Well those are the two possiblities I can think of, assuming no seat belt interlock system. While that AFAIK was only for the starter motor it did have J3 connections.
To be clear, the two possibilites are:

1. The J3 is not getting power with key in start. It should be at the same voltage as the battery when the key is in start. If the battery is 12 V, then all of J3 should be 12 V. If the battery is at 9 Volts with key held in start, then J3 should be 9V. That's also enough to light a test lamp as long as the connections are half decent.

2. Distributor signal wires are backwards. They may trigger but the timing will be scattered or off.

Most likely J3 is not getting power in start. The connections from the ballast resistor to the coil positive and coil negative to the ECU are probably good since it does run.
 
This may or may not be related to your problem, but it's still worth noting. In 1975 the ignition switch connector is different from earlier years. For reference purposes, do an eBay search for: 3746936 NOS. Examine all 5 photos and you will see where the black and red wires have a separate connector.
 
Thanks to all for chiming in, The help was much appreciated. Had some time to get out in the car and explore the ignition switch wiring today. Turned out that the run wires for starting and running were reversed. Tested and functioning properly now. The biggest confusion was the after market switch's coloring is different than the original. easy mistake to make as the new switch had no reference to priority of wire functions.
 
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