Ford - This is driving me nuts

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I have a 1979 F150 pickup with 400 engine. It used to start just fine. A few weeks ago, it did not want to start at times and other times started right up. Lately it has gotten worse. Most of the time
it starts when it's cold, but once it's warm, it's a gamble whether it will start again. Eve nshutting it off for a few seconds and it may not restart. The starter spins and is engaging the flywheel, but it just cranks and cranks and will not start. However, here's the odd part. It pops when I release the key from the START position. In other words, it appears it is not getting ignition voltage during cranking, but as soon as put the key to the RUN position, it pops. If I am real lucky, it will start within that moment, but 99% of the time it will not start. So, I have to just keep flipping the key and hoping I can catch a spark as the key is withdrawn.
I replaced the solenoid, thinking there was a fault in it. However, that did not solve the problem.
This is driving me nuts. WTF is causing this?
I should note, it IS getting gas. I can see it squirt into the carb, and have flooded it a few times while trying to start it. The timing chain was replaced one year ago, so that is ok. The carb was rebuilt not too long ago either, and the plugs and wires and cap replaced last spring. I am 99.9% sure it is just not getting a spark. This makes me think of the coil, electronic ignition module, or distributor problem. However, the problem is intermittent, and once started, it runs just fine and has lots of power.
Here's an example. Yesterday I started it 4 times on my driveway, It started fine, so I drove it about 20 miles, stopped for gas, stopped at 3 stores, visited a friend, loaded some hay, and came home. By this time I had started it, and shut it off at least 15 times without any problem. I unloaded the hay, and moved the truck up to my gate. The gate was loose so I had to shut off the truck to get my toolbox key. 5 minutes later, I tried to start the truck and it would not start. After cranking it about 30 times, I finally got it to start upon releasing the key. I drove it to the lower part of the farm to load some lumber that I needed to move. left the engine running, but when I stepped on the gas, the tires slipped on wet grass so I got out and turned the wheels to 4WD. When I got back in, I gunned it, and the engine died. It took me 15 minutes to get it to start again. I took the lumber to the shed and left the engine running while I unloaded the wood. It idled fine for 10 minutes, then suddenly just quit running for no reason. Now I can not get it to start at all, but still get a pop when I release the key. Maybe when it gets totally cold, it will start again, but the problem seems to be getting worse.
Any idea what is causing this? Are there any tests I can do using a 12V test light?
This really is driving me nuts.
PS, I did take the coil plug off and cleaned the contacts (low voltage plug).
Mark
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The module on these can do some pretty wonky things.. When the problem occurs, connect your test light to the coil negative terminal... Key on, the light should be lit... cranking, the light should flash...
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snipped-for-privacy@UNLISTED.com wrote:

This is one of the classic Dura Spark module failure modes. The other is loss of spark when the engine is warm, then spark after cooldown. It's possible that the cause is somewhere else, but my money is on the module.
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Your description of your problem could lead to one of several different causes. Apparently you do not have the proper skills or training to analyze the problem. Why keep changing parts? Take your truck to a competent technician and have him do that for you and correct the problem, WBMA. ;)
mike hunt

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snipped-for-privacy@UNLISTED.com wrote:

Put a volt meter across the battery, if the voltage during cranking drops below 10.5 volts, the ignition module (Duraspark) will shut off.
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The first thing that comes to my mind is a dirty or loose plug on the side of the starter relay/solenoid. I have had to replace more than one of those plugs when they got stretched or corroded. The one on my Jeep is currently soldered to the wire from the key that triggers the solenoid. Sometimes they can be cleaned and carefully squeezed to tighten them. This connection powers the coil and ignition module when the key is in start.
One test is to take a jumper wire from the battery plus to the coil plus and see if it starts consistently that way. Note: It will not shut down until you remove the jumper.
If it still hic ups, then I suspect the connection on the ignition module or the module itself as being bad. 'Usually' when the module dies, it dies, but not always.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
snipped-for-privacy@UNLISTED.com wrote:

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Mike Romain wrote:

Mike, the engine will crank but not start when hot. It's in about the middle of the OP.
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Tom Adkins wrote:

True, but heat from the manifolds still affects the solenoid connection on the fender which gives the symptoms he described. Him saying it tries to start when he drops the key back to run implies something in the 'start' circuit for the ignition is bad.
The module or the connection on the module can be suspect easily too, but if it is only a loose push on plug thing, it is a cheap easy fix. Mine acted like that when hot, then all the time. That solenoid connection is now soldered to the connected trigger wire from the key switch because I didn't have a spare plug when it finally died.
Using the jumper wire to power the coil like I described is an easy test. If it doesn't start right up, look at the module.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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Mike Romain wrote:

Oh, ok, I see what you're after. A problem in the starter bypass circuit. I forgot about that one. Did Dura Spark have that circuit to the starter relay? I don't really remember.
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Yes it did.
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On Sun, 23 Oct 2005 22:34:42 GMT, aarcuda69062

What circuit are you referring to? I got a wiring diagram from AutoZone, but I am not sure what you mean.....
From what I see, there is a resistor inline from the RUN position, and a direct connection in the START position. I dont see any other circuits.
Mark
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snipped-for-privacy@UNLISTED.com wrote:

The by-pass circuit runs from the solenoid "I" terminal to coil positive. When the solenoid is closed as is the case when the starter is engaged, battery + is internally jumpered inside the solenoid to the "I" terminal, this is what feeds the ignition coil during cranking. This is the way it is usually done prior to TFI ignition. The by-pass can also be done via the ignition switch. Go with what the wiring diagram indicates. Either way, you should be able to measure cranking battery volts at the coil positive when cranking the engine.
Another point to check is the ground inside the distributor, of the three wires running to the distributor, one is the ground for the ignition box, it is literally an eyelet screwed to the distributor housing (inside), but it depends on a clean ground all the way thru the housing AND where the distributor contacts the engine block, any corrosion between the distributor housing and the engine block will cause problems also.
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check your coil to distributor plugwire for internal corrosion usually on coil end.
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wrote:

I plan to do the test as you said. I replaced the solenoid yesterday and cleaned all the contacts. However, I was thinking there could be a problem with the ignition switch, so your test will tell. Of course this problem is intermittent, so I have to wait till it starts screwing up again.
Thanks for the tip
Mark
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snipped-for-privacy@UNLISTED.com wrote:

That is the bypass circuit I am talking about. The power from the solenoid goes to the coil and the ignition module when the key is in 'start'.
If the solenoid is firing, the ignition switch has no issues. The power to start the coil comes from the solenoid.
So basically if the jumper works you likely have a bad connection either at the solenoid or ignition module or maybe a ratty crimp connector where the solenoid wire meets the resistor wire about a foot or so from the distributor inside the harness.
On my module itself, the bypass is the white wire with the 'run' power being the red wire on the two pronged plug and the solenoid tag is a blue wire. Don't know how much they varied the colors so that might be useless to you.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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wrote:

OK, I gotcha now. Yes, there is a wire on the "I" terminal on the solenoid, and it has power when I turn the IGN switch on. That's one of the reasons I changed the solenoid as my initial trial repair.
Just curious. Can I safely put a small 12V light bulb across the two coil terminals? Because this problem is intemittant, I thought I could do that and then I can easily know if there is power getting there. I am assuming the light would flash from the module and this would indicate if everything was working or not. I know I can go from the coil POS to an engine ground safely, but I hesitate to go to the coil NEG, since it could possibly harm the module. Anyone know?
Thanks again
Mark
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snipped-for-privacy@UNLISTED.com wrote:

I use a multimeter. You can put alligator clips on it's probes so you can turn the key and see the meter at the same time.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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On Sun, 23 Oct 2005 11:28:43 -0400, NickySantoro

It looks like almost everyone pointed to the module. I am going to go check the battery voltage and connections first. However, if the module is bad, do I specifically need one for this year and the 400 engine, or can I use one from another Ford year and/or engine? I know a guy with about 20 junked Fords in his back 40. There's a good chance he has something that may work, but just how many varieties are them?
Thanks Mark
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Worn brushes in a starter can have those same exact symptoms. You can change the brushes, without changing the starter. Polishing the comm while it's apart will give you added starting power. With a polished comm, that sucker will crank faster than you have ever heard it crank. (been there, done that).
You can confirm by tapping on the starter with a wrench or small hammer while someone is twisting the key.
Hopefully you had already checked for loose connections.
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wrote:

Why would the starter brushes make the engine not fire? The starter is cranking the engine properly, I just am not getting a spark (at times, since the problem is intermittant).
Yes, I checked connections on the starter, replaced solenoid, battery terminal cleaned, checked module plug connectors, and ignition coil terminals. Since I got a spare coil, I intend to substitute that too.
Thanks Mark
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