79 won't start. Spark issue
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Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 49
From: Great American SouthWest
79 won't start. Spark issue
Last week, the 79 wouldn't start.
79 F-350 460 C6 4x2
Changed the plugs, wires, rotor, cap, coil and finally the ignition control module. Started many times over the following week and it ran great!
This morning wouldn't start. No spark at the plugs. When cranking, no spark at the coil; however, when you stop cranking, there's a spark. Consistently
Swapped the ignition module and coil with known good. No difference
When checking for spark, I was jumping the S on the solenoid to the battery, because I was by myself
Eventually the battery gave up, and so did I. I put a charger on it, and will attack it again tomorrow. What should I check next?
79 F-350 460 C6 4x2
Changed the plugs, wires, rotor, cap, coil and finally the ignition control module. Started many times over the following week and it ran great!
This morning wouldn't start. No spark at the plugs. When cranking, no spark at the coil; however, when you stop cranking, there's a spark. Consistently
Swapped the ignition module and coil with known good. No difference
When checking for spark, I was jumping the S on the solenoid to the battery, because I was by myself
Eventually the battery gave up, and so did I. I put a charger on it, and will attack it again tomorrow. What should I check next?
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
^^^^ Agree. Your description is a classic case of a failed or failing stator, or bad/loose wiring connections.
If the stator is going south, it will not switch the module while cranking....but releasing the key will collapse the coil which will give you a spark.
Check the stator: Resistance check between the orange and purple wires from the distributor. You're looking for 400 - 700 (maybe 1K) ohms. If it's good, check the wiring between distributor and ICM harness...jiggle, cajole, shake, etc, and try again.
If the ohms are above or below the stated range, the stator has crapped the bed. I think it's more likely a loose wiring/connection issue.
If the stator is going south, it will not switch the module while cranking....but releasing the key will collapse the coil which will give you a spark.
Check the stator: Resistance check between the orange and purple wires from the distributor. You're looking for 400 - 700 (maybe 1K) ohms. If it's good, check the wiring between distributor and ICM harness...jiggle, cajole, shake, etc, and try again.
If the ohms are above or below the stated range, the stator has crapped the bed. I think it's more likely a loose wiring/connection issue.
More Turbo
Joined: Nov 2003
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Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 49
From: Great American SouthWest
It was the pickup coil in the distributor. Swapped-in a known good one (from the 77) and it started right up
Went to O'Reilly for a new one, but the truck didn't like it. It would start, but as soon as I got on the accelerator, it'd die
Put the donor back in, and all was well
Thanks scottscott and filthybeast! Never would have thought of that-need to learn more about that system...
Went to O'Reilly for a new one, but the truck didn't like it. It would start, but as soon as I got on the accelerator, it'd die
Put the donor back in, and all was well
Thanks scottscott and filthybeast! Never would have thought of that-need to learn more about that system...
Fleet Mechanic
Joined: Dec 2007
Posts: 1,506
Likes: 339
From: Wildwood Pa
In my experience, the first thing to replace is the pickup coil when having ignition problems on these systems. They used to go bad on my Mopar 2.2 turbo years ago too.
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Postmaster
Joined: Mar 2011
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From: Taxachusetts
...and, you're welcome, Papa Bear Yuma. Glad you got her fixed.
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Thread Starter
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Cargo Master
Joined: Nov 2011
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From: Great American SouthWest
The problem was, in fact, the pickup coil. Proper and complete testing of all components would have shown it. The big clue was when I quit cranking, it'd fire.
The confusing problem I ran into was with the reluctor. The distributor shaft has just one slot for the roll pin, but the reluctor has two. There is no obvious marking for which slot is correct, and they appear to be the same. But they're not. If you use the wrong slot, the truck will be way out of time and might start, but won't run. Turn the reluctor 180 degrees, to the other slot, and everything is wonderful!
The confusing problem I ran into was with the reluctor. The distributor shaft has just one slot for the roll pin, but the reluctor has two. There is no obvious marking for which slot is correct, and they appear to be the same. But they're not. If you use the wrong slot, the truck will be way out of time and might start, but won't run. Turn the reluctor 180 degrees, to the other slot, and everything is wonderful!
New User
Joined: Nov 2016
Posts: 8
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Just for the heck of it, run a jumper wire from the ground on the battery and ground it to the base of the distributor, also check the wiring harness that goes the distributor to the module, also where the wires go into the mod, make sure the plastic piece that go into the module are the same color if you replace the module!
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