Engine won’t fire

[gnagrant]

Hi-

I have a 1974 duster 318 automatic. I’ve had intermittent issues with the ground on the ignition module, so normally if I take the bolts out and scrub the metal and put it back together the engine will fire right up. I drove the car last night with no issues, but this morning I can’t get the engine to fire. It is getting fuel and the ground with the ignition module seems good. I swapped out the ignition module, but same result. Where should I look next?

 

[MadScientistMat]

I put together a checklist of what to look for here: How Chrysler electronic ignitions work, and what to check if they don'
Let me know what you find!

 

[Kendog 170]

Did you check the seatbelt interlock? Or maybe try starting in neutral to see if the neutral safety switch is acting up?
NOS Mopar Seat Belt Interlock Override Switch 1974 Models - Hiltop Auto Parts

 

[dano]

Be sure the Ignition module case is grounded well as in the two mounting screw to chassis.

 

[Glen McKenzie]

Hello, I will take a stab at it. Take a look at the original module you took out. Was it a 4 prong or a 5 prong ECU? Make sure you replace with the same number of prongs you took out or it won't fire.

 

[toolmanmike]

I bought a Nutsert tool from Harbor freight and made positive attachment points for my ECU.

 

[Jeff Seighman]

I did the same with any screws that went into sheet metal.

 

[RustyRatRod]

I bought a Nutsert tool from Harbor freight and made positive attachment points for my ECU.

View attachment 1716395670

View attachment 1716395671

View attachment 1716395672

Yes sir! Now THAT'S good thAnkin!

 

[67Dart273]

Hello, I will take a stab at it. Take a look at the original module you took out. Was it a 4 prong or a 5 prong ECU? Make sure you replace with the same number of prongs you took out or it won't fire.

Nonsense. The originals were 5 prong, and most modern replacements are 4 whether they have 4 or 5 physical pins. A 4 pin will work where a 5 pin was originally.

THE ONLY DIFFERENCE is that the 5 pin was supplied power through the 2cnd resistor. A 5 pin box MUST have a 4 pin resistor.

A 4 pin box will run with either a 2 or 4 pin resistor

 

[67Dart273]

Did you check the seatbelt interlock? Or maybe try starting in neutral to see if the neutral safety switch is acting up?
NOS Mopar Seat Belt Interlock Override Switch 1974 Models - Hiltop Auto Parts

The seat belt interlock will prevent the starter from cranking, it will not prevent the engine from running, say, if you were to jumper the start relay, or LOL just reset the button

 

[67Dart273]

The checklist posted above does not go far enough. If you did those checks, next, pull the dist cap, and make sure the distributor turns with the starter. Examine the reluctor/ pickup for debri, rust, strike damage, etc. Consider checking the reluctor gap, use a brass or stainless (non magnetic) .008" (inches not metric) feeler

With the key in "run" and a spark test gap rigged to the coil tower, separate the distributor connector, and tap the bare terminal of the harness end on ground. Each time should result in a nice hot blue spark 3/8--1/2" long. DO NOT test and evaluate spark with resistor/ radio plug wire. Use a metallic core wire, even low voltage if "hung" in the air. Rig it to a plug gapped open, or buy a gap tester. Lisle makes an adjustable one.

Examine the distributor connectors for corrosion. Connect/ separate them several times, "feeliing" for tightness, and to scrub off corrosion/ oxide.

If you set your meter on low AC (NOT DC) and "rig" it to the distributor connector, it should generate about 1V AC when cranking.

You should have AT LEAST 10-10.V at the coil + when cranking USING THE KEY. With key in "run" and engine stopped, coil + will vary from perhaps 5 to 10V. If it is "same as battery, the coil/ ECU is not conducting.

 

[Lefty71]

A missing or loose body ground strap may cause you some issues, but not 100% sure on this one in particular.

 

[Glen McKenzie]

All I know is from my experience with my 1974 Dart Sport with a dual ballast resistor. It would not work with a 4-pin ECU, so I put the original 5 pin ECU back in and it solved the issue. I believe a 4 pin ECU works with a single ballast resistor, but not the dual ballast resistor. In my experience with my car, a 4 pin ECU did not work in my application.

 

[67Dart273]

All I know is from my experience with my 1974 Dart Sport with a dual ballast resistor. It would not work with a 4-pin ECU, so I put the original 5 pin ECU back in and it solved the issue. I believe a 4 pin ECU works with a single ballast resistor, but not the dual ballast resistor. In my experience with my car, a 4 pin ECU did not work in my application.

I already told you. This is NOT true. Something else is wrong. Either the 4 pin ECU was bad, or you didn't get it grounded, etc, hard to say. It is not because of the ballast.
The rule is hard and fast

The older 5 pin boxes MUST have a 4 pin ballast
The newer 4 pin boxes CAN use either 2 or 4 pin

You CAN NOT TELL if a box is 4 pin by looking at it, because many of them actually have 5 physical pins. You can only tell by checking resistance from the 5th pin to the other ones and ground.