Not firing except when starter is turning

[jetsg4]

Last year about this same time, my '75 wouldnt get fire except when i was turning it over. it turned out to be the ignition box. i replaced it, hit the key and boom... everything has been fine ever since. today, same shit.

i went and bought a new ignition box, and will be putting it in tonight. hopefully it's the problem. how often do these things go out? is there a way to test them?

Thanks

 

[DirtDonk]

Not sure just how to test them, but I'm sure there's a way.
Other than the box though, there is another possible cause. The ignition switch itself has to supply power to the coil and module, so if either the switch or the wire between it and the ignition goes bad,

So first (if you haven't already that is) check for power at the appropriate wires. If you're not sure which ones those are, I'll try to come up with some colors for you.

As for why the modules fail, well, it's hit-and-miss really. Unless something in the vehicle is sending spikes to burn it out, sometimes they just get old.
There does seem to be one correlation though. The less you spend on one, the shorter it's life-span. I paid $30 for two or three from the local parts store and they lasted a very short time. Paid $200 for one from Ford Racing and never had to replace it.
I've also had, and seen on other's trucks, the original Ford modules still working. Just sold an '83 F150 last year and it still had the original box on it.
Go figure.

Good luck. Hope you can track down all the issues, if it's more than one.

Paul

 

[GrillMaster]

I had the same problem and it was just a wire going from the box to the key/switch. test the wires. Your ignition boxes may be fine. My MSD 6A must be 20+ years old.

 

[GrillMaster]

if its a MSD there is a way to test it. find the manual online and read up testing and the FAQ section too.

 

[TBS-POPS]

I would say it's not the ign box but rather a voltage supply issue. If it only fires when on the start circuit then it is drawing voltage only from the "I" terminal on the solinoid. Start checking connections and wires with a volt meter for proper supply in the ign/run position. Just changing the box last time could have wiggled a bad connection. Boxes shouldn't go out every year...

 

[DirtDonk]

Because he has a '75, I was just "assuming" that he was talking about a stock type Duraspark module, which does have a separate wire to tell it when the engine is cranking. This circuit will run the whole show too though, so it's possible for an engine to fire from just while starting with a bad Duraspark box.
Then again, it can still be a wire that's partially bad, and the simple act of disconnecting the old one and re-connecting the new one may jiggle the wires enough to work for a year.

Is yours Duraspark only jetsg4? Or do you have other boxes there as well?

Paul

 

[Hoppy]

The I side of the starter switch will only give full 12volts for a quick jiffy
find a better spot to get 12volts on run and start
I have gone threw 2 msd boxes because of the above.

 

[jetsg4]

Because he has a '75, I was just "assuming" that he was talking about a stock type Duraspark module, which does have a separate wire to tell it when the engine is cranking. This circuit will run the whole show too though, so it's possible for an engine to fire from just while starting with a bad Duraspark box.
Then again, it can still be a wire that's partially bad, and the simple act of disconnecting the old one and re-connecting the new one may jiggle the wires enough to work for a year.

Is yours Duraspark only jetsg4? Or do you have other boxes there as well?

Paul

stock rig. i replaced all the wires last year when i went through this. i'm fairly confident it's the box. even removed the wiring from the switch and have it all hotwired, just to eliminate that possibility.

 

[Jerseydevil]

I had a very similar problem last week. On my truck, there is a purple wire that runs from the if switch to the starter selinoid. The terminal was broken. I Replaced it, then checked my ignition fuseand it was blown, so I changed that too. Good luck.

 

[Explorer]

I ran across this a while back. Hope this works, never loaded a pdf. file on here.