77 f250 400 no spark. i purchased truck , it was delivered . I drove it around the block less than a mile, it ran rough so i changed plugs and wires . next day no spark. icm goes to parts store an test bad. i replace with new motorcraft icm and i get weak spark so i get new coil now no spark . now what

Tony

 

Connect a test light from the TACH TEST (negative) terminal of the coil to clean, unpainted metal on the engine (ground). The coil must remain connected to the horseshoe connector. Crank the engine over from the key, and the light should BLINK. Report your results.

 

light blinks when tested as you ask

 

That's good news; that tells you the ignition module is getting power, the module is getting a trigger signal from the pickup in the distributor, the module is working, the coil has power, and the primary winding of the coil has continuity. The module, pickup, and wiring are good - you're 90% of the way there.

How do the cap and rotor look? Is the distributor-to-coil plug wire properly seated at both ends?

 

Since DuraSpark modules usually fail when they overheat, testing them cold usually shows them to be OK, unless the puppies have burned out.

The three step scenario of a failing DuraSpark ignition module.

1) Module overheats, engine dies. Module cools down, engine restarts almost at once.

2) Module overheats, engine dies. Module cools down, engine restarts in an hour...or so.

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

V8's: Heat radiating from the red hot left exhaust manifold is the mortal enemy of these modules.

Use some washers to space it further away from the left fender inner apron. The more air flow around the little charmer, the better.

The modules used in the 1970's were pure crap, so bad that Ford techs referred to DuraSpark modules as NeverSpark!

1974 is one year only. 1975 is one year only. 1976/79 is the same as long as it's the Blue module.

1976/79 CA vehicles used two others for some applications: Red (1976/79) and Brown (1979).

Above where the wires feed out is a colored plastic square, the EZ way to ID which is which.

 

Cap and rotor are fine , i pulled coil wire off cap to check for spark but none

 

Thanks my is the Blue module and it is new today and motocraft

 

1U2Z-12A199-AA (replaced D6AZ-12A199-A, D8VZ-12A199-A & D9VZ-12A199-A) .. Ignition Module-Blue (Motorcraft DY-893) / Available from Ford.

MSRP: $120.84 // FTE Ford Dealer Parts Dept sponsor PARTSGUYED.COM price: $79.75.
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How about this little charmer, did you replace this too? When it begins to fail, the same scenario applies as the NeverSpark modules.

D4PZ-12A112-A .. Stator aka magnetic pickup coil (Motorcraft DU-1A) / Available from Ford.

MSRP: $86.56 // PARTSGUYED.COM price: $57.13.

Applications: All 1974/79 V8's except 1979 Ford LTD/Mercury Grand Marquis with 351W's and EEC.

 

If I remember correctly, Ford's bulletin to the dealerships was to change the pickup coil to, if the ICM went out. I remember seeing the ICM's oozing black goo out of the back side onto the fender apron.


PS: Mine went bad about two months ago, I was about ten minutes out, and it shut off on me twice. The first restart was normal, but he second one took some coaxing, but the third time it was done, never to be heard from again. Snapped a new one on, and it ran better then ever, even got rid of that small occasional miss I had at idle. The snaps on each side of the plug broke off from being so old and brittle.

 

i think the stator is the last old part left,will the stator cause week spark as it fails?

 

Does a bear **** in the woods? Do birds fly and ducks swim?

 

I look foward to your answers makes it hurt less when i pullout my wallet

I will have an update tomorrow. Thanks all very much

 

I don't understand how the pickup/stator is the problem if your test light is blinking. All the pickup does is send a trigger signal to the module. If the test light blinks, then the module is switching the coil. The only way this can happen is if the module gets the trigger signal from the pickup. The ignition module, not the pickup, controls the dwell. As such, it's not clear to me how the pickup can affect spark intensity. A bad pickup can certainly lead to a no-spark situation, but your last question was whether or not a bad pickup can lead to a weak spark situation. You're saying you have no spark, but if the test light blinks, then the pickup works.

My personal recommendation would be to check the primary and secondary winding resistance of the coil; the dwell from the ignition module and the characteristics of the igntion coil have the most direct effect on spark intensity. But if you're having no spark, and the test light BLINKS, then your attention needs to shift to the secondary ignition circuit, which is the high-voltage coil output, distributor cap, rotor, and plug wires. The blinking test light proves out the primary circuit (pickup and ignition module).

I'm not saying it's impossible that the pickup is faulty; I'm saying I don't understand how it's the culprit given the symptoms and results of your diagnosis thus far. You can do a quick spot check for gross failrue of the pickup by checking the resistance between the ORANGE and PURPLE wires of the pickup; it should be between 400 and 700 ohms. As I said before, however, I can't understand how the pickup can be faulty if the test light blinked. If the pickup was bad, the test light would have stayed ON or OFF as the engine cranked.

Or, there's some level of miscommunication between you, me, and the test setup.

 

If i could talk to you it may help, i will PM my number to you if it's ok

 

Attached is the complete DSII test procedure from the shop manual.