Hi everyone. I have a 1975 F-100 longbed with a small block and a C-6, plus Holley 600, and Holley pump, headers ,etc.This engine and trans were transplanted from another Ford vehicle by a previous owner. I am assuming from the C-6 and the ample torque and overall power exhibited that it is a 351w., and perhaps from the early eighties.
The ignition system is electronic, but I do not know which. It might be a duraspark?
It has a distributor cap which looks like an older "points" cap. Inside it has an 8 tooth "rotor" and a fairly small ignition module with a bright metal roughly rectangular magnet assembly with a blue plastic " reluctor? " , and outside vacuum advance which is plugged.
The problem I am having is ignition related. I am usually a logical troubleshooter, but this has me stumped.The truck will shut-off suddenly, just like the key is turned off, once it stops it is very hard to restart. The ignition will not fire while cranking, until you let go of the key. If the ignition is off and I use my remote starter the ignition fires normally, but no start, with the key in the run position there is no spark when using the remote starter. If one ,ahem, grasps a plug wire the spark seems quite ample The non-starting, and shut off is getting worse and more frequent, I am now afraid to leave my driveway. LOL.
I have googled this problem and it seems common, but with variations, to several Ford products. This seems to be the best informed and most sensible forum so I joined .
Perhaps you can point me in the right direction.

Thanks! Rich

 

Follow the wires leaving the distributor, and you should run into a silver box. This is the ignition module. I would replace it. Even if it's not the problem, it's good to have one under the seat as a spare.

 

Welcome to FTE

1974/75: "Old style" V8 dizzy cap used with DuraSpark electronic ignition.

The ignition module is mounted on the left (drivers side) inner fender apron, just in front of the firewall.

Note: The module used in 1974 is 1974 only // The module used in 1975 is 1975 only.

D4AZ-12A199-C .. 1974 Igniton Module (Motorcraft DY-157B) / Marked: D4AE-12A199-A1A or A1D or A2C or A2D.

Fits all: 1974 I-6, V6 & V8 Passenger Cars, Trucks, Bronco's and Econolines.
-------------------------------------------------------------------------
D5AZ-12A199-C .. 1975 Ignition Module (Motorcraft DY-166B) / Marked: D5AE-12A199-A1A or A1B or A1D or A2A or A2B or A2C or A2D.

Fits all: 1975 I-4, I-6, V6 & V8 Passenger Cars, Trucks, Bronco's & Econolines.
---------------------------------------------------------------------------
D4PZ-12A112-A .. Stator aka Magnetic Pickup Coil-mounts inside dizzy (Motorcraft DU-1A)

Fits all: 1974/79 V8 Passenger Cars, Trucks, Bronco's and Econolines except 1979 LTD/Mercury Grand Marquis 351W with EEC.
So what else is new!? This has been a common problem associated with these two ignition modules since day one. **

The three step scenario of a failing DuraSpark ignition module:

1) Module overheats, engine dies. Module cools down, engine re-starts in minutes.

2) Module overheats, engine dies. Module cools down, engine re-starts in an hour...or so.

3) Sooner or later, usually sooner, the module overheats, burns out! Now the engine will not restart.

Since the little darlin' only fails when it overheats, taking it to an autoparts store to be tested...usually doesn't work, unless it has failed altogether.

When replacing the module, uses some washers to space it further away from the fender apron.

Heat radiating from the red hot left exhaust manifold is the mortal enemy of DuraSpark ignition modules, so the more airflow around the little darlin' the better.

** These two early ignition modules were so un-reliable, that Ford techs referred to them as Never/Spark!

 

Thank You "Franklin2" and "Number Dummy" ! You hit the nail right on the head, especially Number Dummy's 3 step description of the fail sequence. I am used to GM electronic modules that die all at once or maybe give you one restart when cooled off.
This however reminds me of mid 1970s British electronic ignitions, a slow but fatal decline starting with a shut off and then a 20 minute cool down before running about 50 more minutes, this might keep up for a couple of weeks. Those Brit electronic engineers were always a nerdy twisted lot, they apprenticed under Lucas electric ( the Prince of darkness) ! Apparently some must have gone to work for Fords
Thanks again, you have set me on a more positive path.
Rich.

Additional info! OK, after a nice afternoon with the local parts houses I couldn't get a Motorcraft ignition module for a '75, and the Ford dealer didn't have it. A few "use any year as long as the plugs fit" answers didn't generate much confidence. Didn't want a Chinese made unit either.
So. I did the HEI mod From "RRiggs of gofastforless.com" Followed his instructions to the "T". Got a nice fat Heatsink and fan working. The truck seems happy with it, I just need to tidy up the wiring next week. We will see how reliable that is.