I was told to put this here. Hopefuly you folks can help.

My 1985 F150 with a 300 6 started giving me grief lately. After some testing I found that the coil is only getting 6 volts with either the engine running or just with the ignition on. If I take the coil leads off they show twelve volts, but only 6 when attached to the coil. I swapped the coil, plug wires, cap and rotor and ignition module to no avail, still 6v. Oh, and I put a new MSD blaster coil in because that's what I first suspected and it blew up the coil after about 15 minutes of driving. Then a guy I know at the parts store tells me to test my magnetic pickup, because they are known to mess with your engine like that.

So here's my question.
A: Is this guy right or huffing gas?
B: If he is right how do I test my magnetic pickup?
C: I have a MSD 6al system that I was considering installing, would that help my problem at all?

Thanks in advance.

 

Wow, you folks were a lot of help. Sorry to sound like a dink but come on, I got better advice from my great grandfather. It's no wonder I barely ever post here.

 

Wow, you folks were a lot of help. Sorry to sound like a dink but come on, I got more advice from my great grandfather. It's no wonder I barely ever post here.

 

I heard you the first time!

I don't have a solution for you, except maybe SELL it.

 

If you have a Duraspark system, there is a “ballast resistor” in series with your coil. The ballast resistor and the coil both have about the same resistance of about 1 to 1.5 OHMS. When current flows through the circuit one haft of the battery voltage is dropped by the ballast resistor and one half is dropped by the coil. Your reading of about 6 volts on the coil indicates that the circuit is working exactly as it was designed.

The coil drops 6 volts when current is flowing through it. When the ignition module “opens” the circuit and no current is flowing, you will read 12 volts at the coil. When the engine is running the coil is being constantly switched on (6 volts) and off (12 volts). A voltmeter across the coil with the engine running will read the average between the 6 volt state and the 12 volt state for the average of about 9 volts.

If your MSD coil is designed to work without a ballast resistor, that coil may be incompatible with the duraspark ignition module which was designed to work with a ballast resistor.

You also might have the TFI system. I'm not sure if or not the TFI coil circuit has a ballast resistor like the Duraspark system. In any case, measuring 6 volts at the coil does not necessarly mean that there is a fault in the ignition coil circuit.

 

Then go ask him! Posts take time to evaluate. And everyone who reads them does not always know the answer!