OK, full background:

84 318, stock ignition except for MSD coil

Truck ran and drove fine. Washed engine and blew off with compressor. Started up fine. Drove 20 minutes without issue. Shut off.

Came back an hour or so later, won't start. Cranks cranks cranks catches cranks catches cranks cranks cranks... you get the idea.

I unplugged the wire from the coil at the cap and had someone crank the motor while I held it near a bolt. The spark was orange; no blue at all. I have orange spark at all the plugs too.

I tried a new coil, new ballast resistor, new cap and rotor, new ignition control thing (with the round transistor on it) and nothing changed this problem.

Battery reads 12.8v.

From the negative battery terminal to the negative side of the coil reads 0.00 resistance so the ground is good.

With the key turned to ON I get 3.42v when I connect the multimeter to the - and + sides of the coil. This should be 9v, correct?

When I test the pink side of the ballast resistor against ground I get 12.2v. The resistor gets WAY too hot to touch too.

I noticed my coil was warm too. Not too hot to touch, but definitely warmer than I thought it should be.

What the heck could it be??

 

did you try pouring gas down the carb?

 

No offence... but did you read the whole post?

Not sure how more gas would fix a weak spark.

 

Voltage measured at the positive terminal of the coil and a good ground should be within one volt of battery voltage. They used SCC and ECU systems on some of these trucks. Do you have a 4, 5, or 10 pin connecter on the engine controller? Do you have a single or dual pick-up coil system in the distributer?

I am not sure what ignition system is on your truck but some of that year with SCC systems got coil voltage from the starter relay. Could you have gotten moisture in the relay?

 

It's an 84... I don't have any computers or anything. If the engine controller is the box with the round transistor it has 5 pins on the round connector with a screw in the center.

Might have a bad relay... where could I find it?

I just don't get what would cause less than 4v at the coil. That's what's stumping me!

 

You have one of the 3 types of SCC (Spark Control Computer) engine control systems. If I am to help you we need to ID your system so please answer all of these questions. Do you have 2 wires and 1 connecter at the distributer or 4 wires and and 2 connecters? Do you have a single or dual ballast resistor? Do you have 4 or 5 wires At the 5 pin connecter on the SCC controller? Do you have a service manual for the truck?

All of the SCC controllers used the same 5 pin connecter but some had 4 wires and some had 5 wires. If you have a 5 wire system you have an early SCC system with a dual ballast. The 2 later 4 wire systems use a single ballast and either a single pick-up in the distributer or a dual pick-up.

Power to the coil comes from the battery to the ignition switch to the resister and then to the positive side of the coil. The negative side of the coil is connected to pin 2 of the SCC controller. Do not directly ground the negative side of the coil.

 

I have a two wire connection at the distributor.

I have a single ballast resistor.

There are 5 wires but 4 pins on my SCC (if I'm looking at the right thing).

I do not have the service manual.

 

If you have an ohm meter check the resistance of the ballast resistor. It should be 1.1 to 1.8 ohms. Check for voltage at both terminals on the resistor.

Just for info. Your system does not have anything to do with the starter relay. You have an SCC system with single ballast and single pick-up coil.

 

1.1ohms or 1.1kohms? Need to make sure I'm using the right scale on the multimeter.

What should voltage be at the resistor? 12v?

 

The book says ohms not kohms. Voltage at the resistor should be battery voltage within 1 volt.