I have a '74 F250 with 460 and breakerless ignition system(computer module). When cold it starts and runs fine. After it comes up to temp it dies and refuses to restart. I had a battery problem a couple of months back...replaced battery and alternator. Then I discovered that after driving the truck and killing the engine, it often would not restart. I replaced the voltage regulator, and later the starter relay/solenoid. It is still misbehaving and I have now replaced the coil, ignition switch, key switch, put on new spark plug and coil wires. Have checked battery cables and burnished ground. I have now opened up wiring harnesses and all wires look good and they are still pliable. I have swapped out the module for one on my shelf with no change but have no confidence in it. Wife has gone to town (40 miles) to get new module, any avail repair parts for distributor, and a fuse link. The problem seems to be heat related but I cannot find out who the culprit is. Any suggestions?

 

Is it cranking but just not starting, or just nothing when you turn the key?
What fuel supply do you have? Carb? what kind?

 

Thanks for the reply.
Its cranking but just not starting. 4 Barrell carb. Dont remember what brand and computer is not in the shop but I will check and reply if brand matters.
Problem does not seem to be a fuel prob (tho I have been wrong a few dozen times on this prob) but appears to be electrical.
When this condition occurs, sometimes there is a transient surge of voltage at the start as switch is turned there, and then it quits, but bumps again as switch is returned to off.

 

The attribute of the switch having a "power surge" at some point, has it done that before and after you replaced them?
Can key be held at the contact (power surge) point? and does that make a difference?

Check all wiring that you can get to, especially ALL grounding connections - including battery cables.

When you've been replacing these various parts, have you always disconnected the battery?
If not (big shame on you), you may be redoing a lot you've already done.
If you did, great.

It is not uncommon at all for control modules to be bad out of the box.

Just to check, MAKE SURE KEY IS OFF- removed is even better- look down into carb then 'give it some gas' at the linkage. Is the fuel flowing?

 

Leeburch1,
There could be several causes to the problem you described. However, you may find that a purposely-planned systematic approach to isolating the problem will be a more cost effective solution than component replacement. Here is something you might want to try:

First, if the engine is cranking at sufficient speed to start the engine, you can usually rule out the battery, starter, alternator, voltage regulator, and starter solenoid. These items are part of the starting and charging system. The problem you described sounds like an engine electrical (spark) problem, a fuel delivery problem, or more remote, timing issue.

The best way to isolate the cause of this problem is to start testing as soon as the problem occurs. Try removing the wire from a spark plug. Then, insert a Philips screwdriver into the wire’s spark plug connector. While holding the screwdriver close, about 1/16” from something grounded, have someone crank the engine. If you see a spark, the electrical system is probably not the problem. While performing this test, make sure you are holding the plastic handle of the screwdriver; the secondary winding of the spark coil can put out well over 35,000 volts. Since the current is low, this voltage is not likely to harm you. However, it will make you reluctant to repeat the same mistake twice. The auto parts store near you most likely sells a spark tester that will perform the same function. These devices are cheap and easy to use. Most look like a spark plug with a clip welded on the side.

Again, if you see a healthy spark check for a fuel delivery problem by removing the air cleaner, and while looking down the throat of the carburetor, actuate the accelerator. This in turn will actuate the accelerator pump, spraying gas into the carb. If no gas, verify this is the problem by dumping a small amount, approx. 2 oz of gas down the carb, and crank away. If the engine starts then shuts off again you're on your way to resolving this mystery. Check the fuel filters and fuel pump. Also don’t forget to check the filter in the tank, which believe it or not, could very well be the problem.

If you perform the spark test and don’t see a spark, place one lead of a voltmeter on the hot side of the coil, and the other to ground. You should read 12 volts. If so, your ignition switch is fine, and the trouble is most likely in the control module. If you don’t see 12 volts, then the problem is in the primary wiring of the truck form the ignition switch to the coil.

Since this memo is long running, get back to me after you perform these test, and let me know the results. From there I can help you home in on your problem without spending a ton of cash.

Happy hunting,
John 24255

 

Thanks guys; I have done most of what you suggested.
This afternoon I replaced the Stator, and lo and behold; the truck starts and restarts after heating. So far it looks like a fix....but I will let you know if it isn't. I have made all changes one step at a time rather than scattershooting at it. If it stays fixed, I will believe the stator was the problem all along.

 

Thanks for keeping us up to date. Many users never get back with the solution to the problem.

 

leeburch1,
I'm having the same exact problem in a '77 F-100 302ci. I've replaced the solenoid, coil, ignition switch, ignition module, and am prepared to change the magnetic pickup. I've let it run until it dies (mine will die if it is run long enough to get that hot) then it won't restart, then I start testing. I've pulled a spark plug wire and grounded a spark plug, and turned it over. I get no spark. But when I turn the key to off after turning it over, it'll spark. Also when I used a multimeter to test the coil, I get 12 volts when the wires are not connected to the coil, but it drops to somewhere around 6 when the wires are on the coil. You said the stator solved the problem. I hope it did. Does it sound like I have the same problem, If I change my stator will this be my solution. If so please let me know, I've been flabberghasted for about 2 1/2 weeks now.

 

JC,
This is an interesting piece off information. As we know, the rise and drop of a magnetic field in the coil induces an extremely high volatage output which results in a spark to the plugs. When the stator pick up fails, there is no signal to the coil to break the ground, so the coil just stays charged and no voltage is induced. By turning off the igniton, you are killing the energy source to the coil and thereby, collapsing the field. This causes the coil to fire. I had never tested this but theorictically, this makes total sense.
SCIENCE!
KingFisher

 

That is exactly correct. (Sometimes when just cranking the no-start engine and you release the key in frustration, you might feel the engine act as if its trying to start, so you crank again, and when you release the key from the crank postion it again tries to start. That's your clue that the magnetic pickup assembly within the distributor has failed - ususally heat related.)

You can check the magnetic pickup coil by unpluging it from the harness just outside the distributor and placing an ohmmeter across the pins of the purple and orange wires: If the reading is infinite, the coil is shorted open, if the reading is 0 ohms, the coil is shorted closed. I can't find my spec for a good pickup, but IIRC, its in the 800 to 900 ohm range. Does someone have this spec handy???

 

Okay. Great I've diagnosed my problem (Hopefully!!). Now for the repair. To remove the pickup... Will I have to disassemble my entire distributor? I've been looking at it for a while, and that's why I haven't changed it yet. I'm not quite sure how to change this piece. If it can be done w/o removing my entire distributor, please tell me.
Thanks.

 

1. Remove distributor cap, rotor, and adaptor. Disconnect dist harness plug.

2. Using two big screwdrivers, pry up the armature assembly. (Don't lose the tiny roll pin that clocks the armature to the shaft ;-)

3. Remove the wire retainer from the groove in the hub of the base plate.

4. Remove the ground screw that holds the ground strap (where the wires come through the dist wall.)

5. Lift up on the wires and grommet to remove them from the dist wall.

6. Remove the tiny c-clip that attaches the vacuum advance rod to the stator plate.

7. Lift the vacuum advance rod off the post and rotate the stator assembly so that the post is not under the vacuum advance rod.

8. Lift the stator (aka pickup) assembly from the distributor.

9. Install new stator assembly in reverse order ;-)
(Don't lose the tiny rollpin or the small c-clip!)

 

LOL I dropped the rollpin while replacing the pick-up and lemme tell you, the man who invented the magnet on a stick is a savoir. Replacing the pickup is an easy thing to do. The stator might hard to get off though since Im sure it hasnt been removed before. I used a small gear puller to get it off, so dont be discouraged if you cant seem to get it off.

 

Thanks for the help fellas. I got the the pickup off with relatively no problem, replaced it, and it seemed to do the trick! Hopefully that's the last of my ignition worries (since now all the parts are new!).

 

Sorry it took me so long to catch your post but I dont do internet often. The guys took you down the right road. Glad you got it fixed. My old truck is still purring; except that it doesn't seem to charge properly. I am probably killing another battery. But I'm running. Like you, my parts are all new now but I think the Stator is the one that fixed it. Good luck.