I posted this on the 80-86 forum but is seems that this is probably an electrical thing so I thought I would ask all of you. I have a 1983 F250 w/460, carb. The truck starts right up when the engine is cold. When I drive it around, get the engine up to normal temperature, let it sit for twenty minutes, it will not start. No spark at the coil. I replaced just about everything ignition wise, coil, pickup coil, module(second one in 1 year. Had them both tested at Auto Zone.) I checked/cleaned and/or replaced ground wire on battery and engine to firewall. I also put spacers between the module and the fender to try to keep that cooler. It (so far) only happens when I am trying to start it when it is warm. It has not quit on me when I am driving it so I am thinking it must be on the start side of the ignition. Any help you can give me would be greatly appreciated. I am tired of getting standed at Home Depot!

Thanks

 

You are going to have to do some troubleshooting on this one. I would start checking voltages at certain places to figure out where the problem may be.

The difficulty in troublshooting is it only happens when it's warm. So you are going to have to make special troubleshooting trips to warm it up, or just carry a meter or testlight with you when you go to homedepot, and patiently check some things in the parking lot. One thing though, you are going to have to have help with you.

The first thing I would check is voltage at the coil + terminal. Before you go on a test run, get the wiring prepared so you can probe the + wire of the coil, with a good clean place on the engine block to hook the ground for the meter or testlight.

The next test would be to probe the negative (or "tach") terminal of the coil. Put the probe on the - terminal, and put the negative of the meter or testlight on the clean engine ground.

The coil is the last part of the ignition system besides the sparkplugs and sparkplug wires. What you are looking for is around 12 volts on the positive of the coil when the key is turned to run, and also when the key is in start.

If that is ok, then do the negative coil terminal test. What you should see here is the testlight or voltmeter blink on and off when the engine is cranked.

If you have + voltage at the coil, and the - of the coil voltage is blinking, then you should have spark.

 

I wnet home after work yesterday to do some troubleshooting on my truck. I had to go to the gas station to get some gas in her before I drove it around to get it up to temperature. The gas station is only 3/4 mile down the road. It started right up in the driveway. I shut it off, got some gas and went to start it back up. It turned over but no start until I started letting off the start mode. When I started backing off the key she fired right up. I did put a volt meter on it. Before I left the house I had 12 volts at the coil (+) and some blinking at the coil (-). When I got back home from my drive I did not have anything at the coil. It would not start but it wanted to as I started to turn the key off. This morning I tried to start it and it did the same thing as at the gas station yesterday. I have had this happen before but it never started.
I did change out the ignition switch due to cylinder turning hard and it turns really smooth now. I had this symptom before I changed it out so I don't think it is the "switch". What do you all think? does this give you any new clues as to what my starting problem may be? Does the cylinder have any wiring in it? I have never taken one of those apart.

Thanks,
Eric

 

I would first suspect the module - aluminum box on driver fender. There should be a two wire connector on the module (red wire and white wire). The red wire should have power with key in run and white wire should have power with key in start. If these test okay, get the module tested at a parts store.

Marty

 

Ok, you are close. You have a power problem to the coil. If you want to experiment some more, put the meter on the coil + and watch it while you fiddle with the ignition key. See if you can figure out if you have a possible position problem with the ignition switch. It should have had a alignment pin installed when you got the new one. That pin should be left installed till the lever arm is engaged and the switch is bolted down to the top of the column. Then the pin is pulled.

If that's ok, I woud look at the big plug that plugs into the ignition switch. See if the wiring is ok in that area. Also unplug the plug at the coil and look at the wiring in that area. Follow it up to the firewall and see if you spot any problems.

Just make sure you check the voltage at the coil again when it's messing up. Just to make double sure you are on the right track.

 

I installed teh Ignition switch. I did NOT remove the alignment pin. Would this be the possible problem even though it was happening before I installed a new switch? I will do some more checking with the voltage meter. Will I notice something unusual in the wires if they are going bad? colors of copper or covering?

Thanks,
Eric

 

Yes, you can spot a lot of problems by just visually looking at the wires. Also, you can leave the meter hooked up to the coil wires, and start wiggling the wires around under the hood, under the dash, and also mess around with the ignition switch while watching the meter, to see if you can lose the voltage to the coil.

An intermittent problem like this is not going to be easy to find, so be patient. This is were you pay the big bucks for a service guy to spend a lot of time trying to find the problem.

 

Franklin2-
Tell me more about this pin in the switch. Would it have been pretty noticable when I installed the switch?

 

I figured out what that pin is. It looks kind of zig zaggy. I took it off before I installed the switch. I thought it was just for shipping purposes. I hope my problem is only a adjustment on that switch. That would be nice. I will drop the column and check things out at the switch. Would I check the adjustment by moving the cylinder through its motion?

 

If you can, try to put the pin back in. I forget the diameter, but maybe a straightened out paper clip would work, or a small nail.

Take the switch back off, and then move the switch lever back and forth till the homemade pin slides in. If I remember correctly, this is the "off" position of the switch.

So make sure the keyswitch is in the off position. Leave the pin in the switch, put it on the column, hook the rod into the switch, and then tighten the screws down were the switch naturally wants to rest. After you get the screws tight, pull the pin out of the switch, and it should be aligned.

Be aware also that Fords have a lot of problems with the keyswitch linkage up inside the column. You may find after the switch is correctly aligned, the truck will not crank over. This is a sure sign that part of the linkage is broken farther up inside the column. If that happens, the steering wheel has to come off, and the problem has to be attacked from that direction.

 

I took the switch off but I could not tell where the pin goes in. Does it go in on the same side that the rod does? I tries to align it without the pin, tighten the bolts back up, put everything back together and she fired right up. I took it for a drive, got it warmed up good and then turned it off and let it sit for 10-15 minutes. She turned over but did not want to fire again. I don't know. I did some more voltage tests on it today with a diagram that I can not read to well. Everything in the engine compartment seemed to be in order. I also checked for continuity through the pigtail connectors by the module and the distributor. They all checked OK for that. I tested before I got it warmed up and again after. Everything pretty well matched before and after. Do you have a ignition diagram?

 

It sounds like to me you are changing the Key Tumbler and not the Ignition Switch that is down by the floorboard. I think you have a bad Ignition Switch or Plug that mates to it.

Here is the diagram you asked for.

 

No, I changed out the ignition switch on the column underneath the dash. Thanks for the diagram.

 

It's easy to get lost and go down rabbit trails while troubleshooting. I thought we had it narrowed down to a coil power problem. Get it to the point were it won't start, and check the voltage at the coil +, just to verify this is or is not the problem. If you do not have any voltage at the coil +, there is no use looking at the ignition module, coil, etc. We need to look at the power wiring from the ignition switch to the coil +.

So as of now, we are unsure of the exact problem, so I would do the coil + voltage test when the truck will not start.

 

The coil wiring harness- the coil +/- wires clip into this. How snug should those +/- connectors be in that harness? Since my problem began I have had a little play in there but last night I was checking around there again and the + wire connector came right out of the harness without any effort. I think the clip on the metal connector broke off.

Eric