So after getting my project truck on the road just in the past few weeks yesterday I took it into town to do some running around for about three hours. Nice hot day and my cooling system worked great with a lot of stop and go. I was heading home just cruising about 40mph and it quit like someone turned the key off. Turns over great just no spark. Had to get a tow home after standing on the side of the road in 80 degree heat for 90 minutes. It fired right up this morning after cooling off. The new coil? Hot module?

My 68 has a 351W with a Duraspark II ignition set up. The distributor is original to the motor (which had 80k miles) and checked out okay so I didn't replace it. The blue grommet ignition module is new, a Motorcraft unit. It's shimmed up off the inner fender for air circulation. Plan was to have a spare because I've had them quit before but I hadn't gotten one yet. I did just change out the original coil a few days ago. Also, interestingly I had done a compression test the other day and pulled the coil wire to turn it over. I happened to come across an old thread this morning that said not to do that if you have Duraspark. ??


What's the best way to test the module? Do coils quit intermittently? Now I'm not sure how safe it is to drive.

 

For the kudos everyone gives a Duraspark...why is it they die so often and you need to carry a spare?

I know the new Napa version I installed in my '89 died a quick death. Luckily it was in the driveway idling when it quit. Fortunately a friend had given me an extra original Motorcraft version that I installed. I swore up and down I am going to put a points distributor in it if it dies again.

Neighbor has an 1980 pickup that he called me the other day on testing a duraspark module and such as it quit on him. I couldn't tell him the specifics on how because I've been lucky enough to only have had one of these in my life.

 

You mentioned replacing the coil. Which coil did you put on it? Ford had a specific coil for that system. Part number D5AZ12029A. I am assuming that's why they gave it those slide on terminals in that horse shoe shaped retainer. I don't know if it had specific resistance values in it for the ignition module to work with.
Fire it back up and cruise around the block until it stalls. Bring a gallon of water with you. Once it dies pop the hood and carefully feel the ignition module. If it's really hot the module is bad. Cool it back down with the water. It should fire back up soon if not right away.

 

The new coil is a NOS Motorcraft 2-DG314. black with a blue top that fits the horseshoe connector. Stamped "347 Made in USA. For use with external resistor". I have an ceramic external resistor 0.8 OHM.

 

That's the correct Motorcraft short number. Curious I don't remember any blue top. You might check the ground in the Dizzy below. Also feel the magnetic pickup on the stator. The blue part in the bottom pic. If it moves around some it is bad. A tiny,tiny bit is OK. Maybe even check all connections in the plugs in the system. Dizzy and Module. If they are clean put some silicone dielectric grease on them to weatherproof.

 

I'm thinking of replacing the Duraspark II dizzy. It's the only original part left from the 79 LTD I got the 351W motor from. Tag on it says:
48
D9SE
12127
AA
9E01
I wonder if I should replace it with the same spec or if there is another year/model spec that is better. Maybe an HO truck?

 

Checking on Rockauto the part numbers are the same for 2 barrel 351w and the HO as well. I also just noticed my original dizzy has a dual diaphram vacuum advance which is not good. Summit has Davis Unified recurved Duraspark distributors for $265. In the end I found a guy on Ebay (Vintage-torque) who is custom recurving a brand new one to my engine specs for $200 and free shipping.

 

That tag fit 79 LTD and T-Bird 351W. Except California emissions. The 79 LTD was the 1st year for new body style and a lighter car. If you buy a reman or rebuilt Dizzy they are a crap shoot anyways as far as it's timing curve springs go. Yes, you can recurve one yourself but I vote for aiming at a 351W Dizzy in a heavier vehicle like a Bump. So I looked some up for a 79 Econoline 351W. I came up with 6 possibilities but none around anymore NOS. One of them was part number D8AZ12127C. This fit some Econolines and the 78 LTD BIG car. I don't have a L/M slide where I am at the moment but it prolly fit Marquis also.

 

The go-to part around here for your problems is a Pertronix unit. These things are almost bulletproof.
If I had your problem, I would buy a cheapo rebuilt stock distributor for the new bearings and plate-support bushings, gut out the points and install a Pertronix.
Mine have been going for 30+ years.

Semper Fi

 

Be sure you have a good ground on the Ignition module (duraspark box)
The earliest versions of the box had a separate ground wire in the harness. (3 pin power connector) Later ones used the modules chassis for the ground.


If you are getting a high resistance ground it will fry the box eventually or cause it to stop working, as under hood temps increase the resistance in the ground connection to the point to where it will stop working when it cools off and resistance drops it will work again, a high resistance ground will eventually crater the box.


You can add a separate ground wire to one of the hold down bolts. It may help solve the problem. Also some NOALOX (not Copper Kote or Copper Sheild) on the mounting surfaces/bolts will help insure a good connection to ground and keep the bolts from seizing in .

 

I've got it mounted with 1/4" spacers and serrated washers but I'll add a ground wire and some Permatex antiseize just to be sure.


Today I drove it around the neighborhood and then left it idling at home for 1/2 an hour and it never quit.

 

Don't use pematex anti-seize it is not really that electrically conductive.
Use either NOALOX (available at home depot) for Aluminum or Kopr-Sheild (not Copper Kote) for steel an CU connections. Kopr Sheild can be had at any Electrical supply.


It is a myth that the Permatex / Loctite Copper anti seize will enhance electrical connections it does not. It is a thread Anti Seize compound.


NOALOX is specially formulated to use with AL connections and really is the best Anti seize on the market bar none. It is just not for use on high heat applications.


Thomas & Betts CP8-TB Kopr-Shield? Joint Compound With Brush; 8 oz Can, Copper - Crescent Electric Supply Company




Ideal NOALOX 4 oz. Anti-Oxidant Compound-30-026 - The Home Depot

 

Matthew has a point Uni. Most times when there are electrical gremlins there is a ground at fault. (pin intended) Looks like that brass colored loop in my pic above of the stator is to ground the Module. Note this in the above schematic. A darn good engine ground would help this. But I like his idea of a ground for the module's body. More grounds can never hurt.

 

So I was thinking the problem was probably with the magnetic pick up in the distributor. The distributor was the only original component from the 79 LTD that donated the 351w so I decided to replace the whole thing. I looked at a Davis Unified recurved dizzy that was $265 through Summit. I ended up getting a new recurved unit from an Ebay seller (Vintage-Torque) for $200. Very knowledgeable and friendly guy. So I installed the new dizzy a couple of days ago. I got my timing light set up and grabbed the vacuum module to give it a slight turn and the truck died. What the heck! After some sleuthing I figured out I had a broken wire going into the wiring harness side of the plug. The wire looked fine on the outside. All I had to do was hold the plug firm and wiggle the wiring harness and the truck would stumble or die. Today I went to the wreckers and got a plug, spliced it on and all is well.

 

Cool. Glad to hear you smashed that gremlin like a fly.