1985 F150 spark problem
jmikalh
10-10-2007, 02:06 PM
I have a 1985 F150 with a 351. It is not fuel injected. It will not get spark all the time. Sometimes it will fire up but other times there is no spark. Any ideas?
CanukGMC
10-10-2007, 08:39 PM
I have a 1985 F150 with a 351. It is not fuel injected. It will not get spark all the time. Sometimes it will fire up but other times there is no spark. Any ideas?
Is it rainy out when you don't get spark? I had a truck that had a crack in the distributor cap that allowed water to splash inside and short the spark connection causing it to not start or even stall when driving. You best bet is to locate where the spark stops. When the problem appears again have an extra spark plug handy and disconnect the plug wire that runs from the coil to the distributor at the distributor end, plug the spark plug into it and ground the plug to somewhere good (metal not painted) and have someone crank the engine, if you still have no spark then you know that the problem is from the coil back and not distributor or plug wire related. Check the plug wires themselves for proper connection and ensure the one on the coil hasn't rotted away, put some dielectric grease inside the boots to ensure a true connection.
If there is NO spark from the coil then you know the problem lies either with the coil itself or possibly the ICM, if the 85's had an ICM, I'm not sure on that one. An ICM is an ignition control module, it's normally found screwed into the distributor, it's a computer chip that tells the coil when to fire. Mine fried on my 89 and the thing stopped dead on the road. Yours could be on it's way out if it's coming and going. Hope some of that helps.
Is it rainy out when you don't get spark? I had a truck that had a crack in the distributor cap that allowed water to splash inside and short the spark connection causing it to not start or even stall when driving. You best bet is to locate where the spark stops. When the problem appears again have an extra spark plug handy and disconnect the plug wire that runs from the coil to the distributor at the distributor end, plug the spark plug into it and ground the plug to somewhere good (metal not painted) and have someone crank the engine, if you still have no spark then you know that the problem is from the coil back and not distributor or plug wire related. Check the plug wires themselves for proper connection and ensure the one on the coil hasn't rotted away, put some dielectric grease inside the boots to ensure a true connection.
If there is NO spark from the coil then you know the problem lies either with the coil itself or possibly the ICM, if the 85's had an ICM, I'm not sure on that one. An ICM is an ignition control module, it's normally found screwed into the distributor, it's a computer chip that tells the coil when to fire. Mine fried on my 89 and the thing stopped dead on the road. Yours could be on it's way out if it's coming and going. Hope some of that helps.
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