Ignition Coil failure
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Ignition Coil failure
How do ignition coils fail? Do they slowly lose their spark as they age?
I've got '78 F250 with a 351M and it seems to be slightly missing. Sometimes the whole engine shakes and trembles with the oscillation and shakes the whole truck.
I've rebuilt the carb (it needed it badly), replaced the plugs and wires. But, I'm not sure about the strength of the spark.
A week ago, the truck died on me. I thought it was the fuel, as it was rather low. But even starter fluid wouldn't catch. We jiggled the ingition coil plug wires and it eventually started up.
I'm about to go on a 1200 mile round trip in this truck, through some harsh terrain, and I'd like for it to be as reliable as possible.
Should I swap out the ignition coil just for good measure, or is that a waste of time?
I've got '78 F250 with a 351M and it seems to be slightly missing. Sometimes the whole engine shakes and trembles with the oscillation and shakes the whole truck.
I've rebuilt the carb (it needed it badly), replaced the plugs and wires. But, I'm not sure about the strength of the spark.
A week ago, the truck died on me. I thought it was the fuel, as it was rather low. But even starter fluid wouldn't catch. We jiggled the ingition coil plug wires and it eventually started up.
I'm about to go on a 1200 mile round trip in this truck, through some harsh terrain, and I'd like for it to be as reliable as possible.
Should I swap out the ignition coil just for good measure, or is that a waste of time?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Don't spend money on anything unless you know the old one is bad. You want to look at the resistance of the primary and secondary windings of the coil. Make sure the truck is off and disconnect the coil. Check the resistance between the two smaller posts (primary winding) and it should be around 1 ohm or less, but not zero. Next check the resistance between either of the small posts and the large middle post (secondary winding) and you should see in the ballpark of 10,000 ohms.
The only real failure a coil can have is with the windings. Resistance can go up as the windings age. Resistance can go down if the windings short from heat failure. A significant variation in the ratio of effective turns between each winding will affect the output voltage. Check the resistance and if the numbers are reasonable, then you're in good shape. There could be other things to look at. You could have a vacuum leak or a timing issue instead.
The only real failure a coil can have is with the windings. Resistance can go up as the windings age. Resistance can go down if the windings short from heat failure. A significant variation in the ratio of effective turns between each winding will affect the output voltage. Check the resistance and if the numbers are reasonable, then you're in good shape. There could be other things to look at. You could have a vacuum leak or a timing issue instead.
Last edited by fmc400; Aug 13, 2007 at 07:29 PM.
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From: Virginia
Two failure modes I have seen is the cooling oil leaks out(this is visible as the coil gets wet), and corrosion in the terminal where the high tension lead plugs in. The corrosion caused a no start condition only on rainy days.
Make sure your egr valve is not leaking and all the vacuum lines are ok. This will cause a random shake at idle. Also, what condition is the engine in? If you have a lot of blowby, I have seen all that oil smoke from the PCV valve cause the engine to idle rough.
Make sure your egr valve is not leaking and all the vacuum lines are ok. This will cause a random shake at idle. Also, what condition is the engine in? If you have a lot of blowby, I have seen all that oil smoke from the PCV valve cause the engine to idle rough.
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Originally Posted by BottomFeeder
How do ignition coils fail? Do they slowly lose their spark as they age?
I've got '78 F250 with a 351M and it seems to be slightly missing. Sometimes the whole engine shakes and trembles with the oscillation and shakes the whole truck.
I've rebuilt the carb (it needed it badly), replaced the plugs and wires. But, I'm not sure about the strength of the spark.
A week ago, the truck died on me. I thought it was the fuel, as it was rather low. But even starter fluid wouldn't catch. We jiggled the ingition coil plug wires and it eventually started up.
I'm about to go on a 1200 mile round trip in this truck, through some harsh terrain, and I'd like for it to be as reliable as possible.
Should I swap out the ignition coil just for good measure, or is that a waste of time?
I've got '78 F250 with a 351M and it seems to be slightly missing. Sometimes the whole engine shakes and trembles with the oscillation and shakes the whole truck.
I've rebuilt the carb (it needed it badly), replaced the plugs and wires. But, I'm not sure about the strength of the spark.
A week ago, the truck died on me. I thought it was the fuel, as it was rather low. But even starter fluid wouldn't catch. We jiggled the ingition coil plug wires and it eventually started up.
I'm about to go on a 1200 mile round trip in this truck, through some harsh terrain, and I'd like for it to be as reliable as possible.
Should I swap out the ignition coil just for good measure, or is that a waste of time?
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