First I want to say hello, just joined and looking for some info/experience for my truck and this seemed to be the place to go.

I have a 1981 F250 that has a 7.5 foot Western plow. I just use it for plowing; not a road vehicle. Lately, it has been stalling after I plow for a while when it gets hot and it will not restart; seems to lose spark as it won't fire on starting fluid.

It has a 351M engine. It is not overheating; I have a manual temp gauge and it runs 190 degrees. Thinking ignition issues I have already done a coil, plugs, wires, cap, rotor, and bought new connectors and re-wired the duraspark system. All these things made it run better and needed to be done. I thought I had it fixed as it ran fine for a couple times plowing then last time I plowed it did the same thing; died when hot so I towed it back to its spot with my tractor and left it. Went out today (two days later) after it sat in -30 weather and it fired right up and ran great.

From what I have read the last weak link may be the actual duraspark box. I am just wondering if this sounds like it could be a duraspark box issue or if I need to look elsewhere in the wiring or distributor? It has the blue duraspark box

I really want to get this truck running well again. Even though its rough I love it because it pushes snow like an animal and even being manual choke it will always start; even after weeks in the negative temps.

Sorry the post was so long; just wanted to give the full story. Thanks for any help.

 

Welcome CPG. What you describe sounds pretty typical for a bad Duraspark box (module).

 

I assume it restarts fine once it cools back down? If so, yes, it is almost certainly the Duraspark module. One of the early signs of impending failure is that the module fails when warm. Get a quality replacement module, and you should be back plowing reliably in no time.

EDIT: Something just occurred to me - since you have a plow on the truck, do you have any additional equipment that has been installed on top of the module? I've seen pictures of snowplow installations that have gear added on top of that driver's-side fender that interferes with airflow around the module. Your current module is bad now regardless, but you'll want to be aware of potential airflow problems when you replace it.

 

Welcome to the forum, cpg!

Take the Duraspark box to your favorite auto parts store and they can test it. However, sometimes the failure which you have experienced is difficult to test for since it occurs once everything gets hot. It is not an uncommon sign of oncoming failure, though.

Do you know someone else with a Duraspark system so that you could temporarily swap the boxes?

If you do decide to replace the unit, be aware that forum members have reported poor results with the cheap "off shore" units available. Most recommend Motorcraft and quite a few members routinely pick up units at the junk yards very reasonably.

Once sorted out, the Duraspark system is durable. Your box may be quite old.

 

There is no added plow stuff around the box, the solenoid is on the other inner fender.

Also, every time it has done this it has restarted fine later once the truck is completely cooled down.

My box has the original duraspark sticker so my guess is that it is the now 33 year old original. I have found a few boxes that will work on Rock Auto for cheap but they seem to be the generic brands so as you said probably not great quality. I will check my local salvage yard but if I can't find one would I get the Motorcraft brand from a Ford dealer or do other parts stores carry them?

Thanks for all the help and the warm welcome. Glad I joined!

 

Just had a thread on here somewhere today of a guy that has installed like three new ICM boxes. All failed new. One he had tested at the Napa store he bought it at
and it was bad out of the box. Buy Ford Motorcraft only. Even if made in Mexico.

Try this to test yours: When it has sat and is cool and ya are sure it will start
than heat it up with like a hair dryer. It may start but not run as long as normal,
but my guess it wont start at all. As for having it tested it will be cold at the store
and prolly test good. Take a hair dryer with ya and then test it there hot. It
will most likely fail and hopefully the parts cluck will know to test the next one
that comes in by first heating it.
Go to a junk yard and grab a couple that have the same color plastic plug as yours.
A blue one is prolly what you have if it has lasted 33 years. Then Buy A Motorcraft Box
and nothing else.

And welcome to FTE. It's the Best

 

I'm having good luck with a NAPA (Echlin) branded module.
Been a few years, and the cranking retard function DOES work properly.

That said, I keep a spare (known good) box under the seat for when this one fails.

 

I have had more good luck with Echlin (sp) than bad I admit. Maybe a better
quality Chitcom I guess.

 

I too, have had good luck with my Napa Echlin box.....

 

Thanks for the info. I see my NAPA has one in stock for like $50 versus my Ford dealership who has to order it and wants like $125 for one. Figure even if it lasts a while it will be fine as its just my plow truck; not my daily driver. Looks like I will be paying my local NAPA a visit. Not surprising as that is where I usually get my parts since their parts seem to be some of the best quality aftermarkets.

 

Let us know how this works out for you, I'm trying to figure out a similar problem with one of my 70's F-250s.

 

Well the box was definitely the issue. I was looking at the wrong one and NAPA didn't have mine in stock so I went to Advance Auto and got a BWD module since there was some wet snow in the forecast. Plowed today for about an hour with the new module then the truck started missing and died then wouldn't start (same as before). Felt the module and it was really hot. Plugged the old one in that was sitting in my cold garage and it fired right up and ran okay to finish up and park.

In the end the box was definitely the issue and my Echlin box will be in tomorrow. I returned the BWD and got my money back and I really wouldn't recommend them. I know I was warned about some aftermarkets but I hoped it would last longer than an hour; at least until I got my Echlin. If you are having similar problems this may very well be your issue.

 

I wonder if the same thing is going to happen with an Echlin box because there is a wiring problem someplace causing the modules to fail.

 

That is a possibility. I will try the better box and see if it works. If not I will be looking for issues somewhere in the wiring though hopefully I don't have any as I made a whole new wiring harness for the box, distributor, and coil.

 

This has me wondering about the recurring failure of your Duraspark II module.
Was your coil also "really hot" when the ignition failed?

I'm asking because the coil should be getting power in 'run' through a length of resistor wire built into the harness.
(1.2 ohms 20W is ideal IIRC)

With the coil properly connected and the key in run, what voltage do you see between coil hot terminal and ground?

There seems to be much history of people having ignition failures when the transistors in the module are asked to switch the higher voltages present while the engine is running.

So, I guess I'm asking if your new harness incorporates a resistor or not?