When it rains it pours! I've been working out the bugs on my 75 F100 over my past few months of ownership, every time I think I have things all squared away another gremlin rears its ugly head.

Yesterday on the way home my truck just up and died, the engine completely cut out, I coasted over to the road side and confirmed i had fuel delivery, then I checked for spark and there was none.

After 45min of trying to start I called a tow truck, shortly after I was home I decided to try and start the truck, to my surprise the engine fired right up! (I wish I had waited a little while longer and saved myself the $85 tow fee) lesson learned.

Today I checked the coil and stator assembly as per instructions I found on here, both were in spec, at least while cold, maybe the readings would be different if checked at operating temp?

I have no way of checking the ignition module, at least none that I'm aware of. Against my better judgment I took the truck out today and drove around for 1hr, I surely expected it to die again but to my delight it never did. I'm not sure how to rationalize this.

What's the best way to proceed, short of just throwing parts at the truck. Is it possible this episode was just a fluke, or is it an indication of things to come?

From the research I've done on here the module, coil, or stator are the most likely offenders when the engine just cuts out (ign. switch was replaced a few months ago).

 

I'd double check the ignition wiring and its integrity. I always carry a spare ICM (my old Motorcraft which barfed its gooey insulation) but am running on a newer, Wells branded ICM.


Intermittent electrical issues are troublesome to diagnose. In the Navy we had a weapons systems computer that worked fine for about six hours but went haywire after that. After weeks of troubleshooting, we discovered a hairline crack on a circuit board which, after heating up, warped and started processing intermittent signals and code. But cool it down and it worked fine. Funny how a simple $250 circuit board could degrade the mission capabilities of a $40 million aircraft (P3 Orion, Update II - circa 1985)

 

I had a similar incident happen. Was towed home. After a while it stared up again. I drove it around and it happened again. I waited a bit the second time and it started right up. I changed the fuel filter and it solved the problem.

 

Well, the engine on my 75 F100 cut out on me again this morning! only this time I had my trusty DVM at the ready because I wanted to test the parameters of both the stator and coil while the ignition was in a failed state.

Testing proved both were well within spec, so to my thinking this pretty much narrows it down to a failing ignition module. No problem, it's an easy quick swap out for a new module, or so I thought.

After I let me engine cool for an hour I go to Napa and buy a module, I install it right in the parking lot, the truck won't start! They give me another module to try and the truck still won't start!

They guy tells me something else must be wrong with the ignition, so I proceed to plug in my old module and the truck fires right up! He gives me a baffled look and we go inside to check he gave me the right module, He did. We even tried a third module.... again, no start!

The only difference I noticed in modules was my module has 7-wires, the replacement modules had 6-wires and included this disclaimer "Ford design changes have eliminated the blue wire from the three-terminal plug. This module contains six wires and will replace earlier applications. No modifications are required".

What the heck is going on here, it obviously doesn't work in my application! Has anyone run into this before, if so, what did you do? Where can I buy a module that works? Frustrated!

 

I found a NOS Motorcraft module online and was hoping someone could tell me if it will work for my application.

The number stamped on the online module is D5AE-12A199-A3D (6-wires)

The number stamped on my module is D5AE-12A199-A1A (7-wires)

Both modules have a green grommet, the only visual difference is the eliminated blue wire, as I noted in my previous post.

After the Napa fiasco I'm a bit hesitant to pull the trigger without any confirmation this module will work me.

 

Using NPD's catalog for reference, "D5AE-12A199-A3D" isn't an ID number that is used on these trucks.

 

Hmm, that's odd. They emailed me a photo and it's clearly stamped "A3D".

 

I'm sure that is what it stamped.

All I'm saying is that NPD's list of ID numbers, like 25 of them, doesn't show an "-A3D" as being applicable to these trucks through 1979.

NPD's 80-96 catalog doesn't list an A3D either.

 

I understand, I appreciate your research on this!

What research I've done is telling me the modules with green grommets were used in '75 only, and this module does have a D5 prefix. So in 'theory' it should work, no?

Throw in the whole blue wire elimination thing into the mix and things just grow more confusing.

 

Yes, in theory.

I got my replacement ICM (for the black grommet, -AA suffix Motorcraft) from Rockauto. What arrived is an Airtex/Wells with an instruction/note sheet citing the change in 1976 that Ford went to a six-wire setup and that the enclosed ICM with six wires would be compatible. It works fine. The original Motorcraft is now the onboard spare because cleaning up its leaky goop was a total hassle... twice I have had to clean it up.

Anyways, I think the PN or cross referenced aftermarket PN is more important than the grommet color.

 

Did you replace a 7-wire module with a 6-wire module, or was your old module already a 6-wire?

All the parts stores around me only carry 6-wire modules (with the design change note included) none have worked for me.

I'm hesitant to buy a 6-wire module online that I can't try first, obviously.

I did find a 7-wire module on ebay last night, it's a 'KEM' branded module, NOS and made in the USA. For $20 I just took the chance and bought it.

If the KEM works out then my old Motorcraft will become my 'behind the seat' spare. It's good for about an hours drive until it overheats, enough to get home in an emergency.

To my knowledge it's the original Motorcraft module, 40yrs of service isn't too shabby! try getting that with todays cheaply made auto parts.

Anyone familiar with KEM auto parts, are they well made parts?

 

The module can do strange things at times (it's an electronic device). Heat is its enemy. Sometime you can revive it by pouring cold water on it. I always carry a spare. Once one failed in the AZ desert for me. Having a spare helped a lot. Mine is a '76 and uses a "blue" module. O'Reilly sells them with a lifetime warranty, so you only have to pay for it once even if you have to have the frustration of the down time.

 

I've got my fingers crossed for this ebay module. I should know Thursday!

 

This happened to me about a year ago. My voltage regulator was shorted out. It drained the battery while running and off. Let it sit for a half hour and it would start back up. For the hell of it I left it plugged in overnight to see how much it would drain. To my surprise I went out in the morning and the top half of the battery blew off. Previous owner had cobbed up the wires to run a different alternator which shorted out the regulator.

 

The KEM module from ebay arrived today! I noticed it's pleasantly 'hefty', much like my original Motorcraft module, all the modules I handled from the parts stores were noticeably very light, I'm not sure what this means, if anything, but I did take note.

I also took note of the backing, or filling material. It's a very hard semi-clear epoxy like material, you can actually see the circuitry underneath, much like the original Motorcraft module. All the parts stores modules I handled were filled with some sort of black rubbery 'goop' that looked like it might melt if overheated.

I will plug in the new module when I get home tonight. Fingers crossed!