Our '76 F250 was running beautifully until a week ago. It would not start, but after about 2 attempts of 15 second cranking, she sprang to life. At first I thought it was a fuel delivery problem. Last time, she would not start at all. Noticed that as I flipped the ignition switch to off, the engine gave a single cough. This is repeatable over and over.
It seemed like the switch was making a quick contact just as I turned it off. So I removed the switch, opened it and cleaned the copper contacts. Stretched the little springs a bit too.
Will go to the truck in about 10 days and try my repair. Any odds my fix will work?

Cheers

Mr. Fixit

 

The "cough" you are hearing is actually dieseling, also called run-on. It is unrelated to the ignition switch. Dieseling occurs when you try to shut the engine off, but hot spots in the combustion chamber act like glow-plugs, and make the engine kick around for a few seconds after shutting off (sometimes it's just one last kick, but I've seen trucks diesel for at least 30 seconds straight - awful sight). Dieseling is caused by high curb idle, low octane fuel, late ignition timing, or a lean fuel mixture. Most often it is caused by a high curb idle. Again, I assure you it is unrelated to the ignition switch.

The no-start situation could be attributed to multiple things and it depends on the scenario. Is this a cold-start or a warm-start? How long does the truck sit for the problem to show up?

 

Thanks for the reply fmc400. This is a cold start problem. Let me mention that this truck sits around on a damp island in the Pacific Northwest and is only run 20 times per year for about 3 miles each trip max. In other words, it rarely fully warms up.
I don't understand how dieseling could cause the 'cough' as the engine is stone cold. My experience with dieseling (we know it as 'running on' up here), is when you are shutting off a warm engine - the glowing carbon deposits act as sparks to keep the engine going for some time, if you let that happen.

 

Checking out the inards on my ignition switch I noticed the contacts didn't
line up with each other all that good. :( And yeah, looked like there was a
chance for something like you are describing to happen in a worst case.

I removed two full sets of contacts from my ignition switch that were not
being used, along with modifying how far the switch turned inside which
made the contacts ride up onto each other farther. Giving the contacts
more "contact wipe" as we called it on the railroad. Before... they would
just "touch" and that was about it. :(

IMO the original switch is a pretty sloppy design. :/ Tough! But with sloppy
alignment etc and not made to be taken apart and repaired either. :/

What happened to me was I was out in the middle of absolute no-where
with no one expecting to hear from me either and the dangged thing acted
like my ignition module was gone. As soon as I let off the starter circuit the
engine would die. :) After what seemed like 20 tries it fired up and ran great! :)

Anyway I drilled it and tapped it for 3(?) 0-80 screws to hold it together,
the zinc tabs were about to give it up after I'd taken it apart a couple times
before and when someone tried to steal the pickup, they pulled it apart too.

I can't remember the specifics but there's something very familiar sounding
about your problem, like...
"yeah I remember it -looked like- something like that could happen"
...sort of thing.

Maybe take yours apart again and figure it out?

Hope this was helpful and didn't waste anyone's time! ;) LOL :)

Alvin in AZ (retired railroad signal ape)
ps- I wasn't in any danger I had plenty of flashlight power :) just 6+miles
from the ranch house on an 18 section ranch in the boot heel of NM and
penned livestock that needed feeding before dark is all. :)
pps- was prob'ly more like 8 tries but "seemed like" much more. LOL :)

 

actually you might want to check your ignition BOX instead of the switch and make sure it's getting power while cranking. The cough you are hearing is it firing one cylinder when you drop out of the crank position into the run position and the inertia of the motor carriers it past the next cylinder firing. if everything is right it MIGHT actually catch and start running.
You cleaning MIGHT work if the switch had a bad contact on the bypass connection for the cranking position but if not start at the box finding eh wire that should be hot during cranking and back track that wire until you get power during cranking. IF you have power at your ignition box while cranking then your problem is the box itself (the fact you get a cough when you let go tells me that after the box and the dist pickup are ok)

 

Hey Alvin, I that sure does sound like signal talk to me. I am a signalman out here in NY for the Long Island Railroad. This definietly sounds like an ignition problem to me, I am having a similar problem but not as severe with my 74 highboy, I am looking into it now, if I find anything interesting I will definietly post.-----Jack

 

Cool! :)
A fellow signal ape! :)
There ain't very many of us you know it? :)

Cool. :)
Anything you figure out is good. :)

My post may be completely off the mark. :/
But sometimes dumb posts are needed to jump start a thread.
Like cutting the first piece out of a cake or something. :)

Alvin in AZ

 

Alvin: I did the same thing as you when reassembling the switch (used 3 small screws to hold the metal switch to its plastic insert). I can get a new switch from Rockauto for about $6 but then would have to put the old key barrel into it. I wasn't able to figure out how to get the key barrel out of the old switch last time...
Great to hear you are in the real railroad world - I have great memories of riding across the continent as a kid. Also, I confess to be a bit of a model railroading buff.

jackndelphine: you mention your Highboy has a similar problem - the first signs of my problem were that just after starting, the key needed to be wiggled for normal function.

Monsterbaby: thanks, I'll take my trusty multimeter with me to check that the "Box" is getting power.

Mr. Fixit

 

OK, I finally got over to see our F250. Plugged in the clean ignition switch and sure enough.... she still will not start. Absolutely no willingness to start even when the starter is turning the engine over fast.
So next time must follow up your suggestion, monsterbaby, I'll take over my multimeter and check that power is getting to the "box" during cranking - forgot to take it this last time!!! I still hope this is a bad contact somewhere due to the high humidity.
Will report back.

 

It might just be the coil, if it had a ballast resistor I would guess that but these are internal aren't they? In the coil? My 77 is anyway..

 

No, it's not.

D7AZ12250A .. Ignition Coil Ballast Resistor Assy (Motorcraft DY237)

49" long / Color coded red with green stripes / 1.30 to 1.40 ohms resistance / #16 gauge WIRE.

Application: All Ford car & trucks: 1973/1986.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D5AZ12029A .. Ignition Coil (Motorcraft DG314)

Application: All 1975/79 Ford cars/trucks with DuraSpark II Ignition (except certain 1977/79 vehicles sold new in CA).

 

Ok thanks wdfp and NumberDummy: I'll look for the "ballast resistor" next time I get over to the (island isolated) truck - will it be attached to the coil or stuck on the firewall? Do I have to disconnect the resistor before measuring its resistance?
My knowledge and understanding of these fancypants electronic ignition systems is poor to fair at best...
First, I have to find the power-in wire for the 'box' and test as monsterbaby recommended - will check my Haynes manual.
Appreciate everyone's help!

 

The ballast resistor is actually a special length of wire. It's manufactured with impurities to make it have some resistance instead of a pure short. What you can do is disconnect the coil, turn the key to run, and measure the resistance between the coil positive and any hot-in-run circuit (idle stop solenoid, ignition module power, etc). This will get you the circuit you need. The resistance will be a little higher with this check, but to isolate just the resistor wire you'd have to somehow measure from the coil positive all the way to under the dash which isn't really easily done.

 

Success! Problem solved. Monsterbaby, I followed your advice and checked the connector to the 'box'. After a bit of a struggle, got the connector apart and found two prongs inside. There was a strange white greasy substance covering the connections which I cleaned off (some kind of ancient dialectric grease?) There was 12 volts at the white wire prong but when reattached, no volts at the wire from the connector to the 'box'. Reopened, then cleaned the prongs carefully, gave them a slight twist with needlenose pliers and reconnected.
She started right up! Yahoo.
I wonder how many other connections are about ready to fail?

Thanks everyone for the advice.

Mr. Fixit

 

Cool one, Mons! :)

Doggonit, that's the way to do it, hunt the electrical trouble down
with your meter -while it's failing- ...then -fix it-! :)

Cheap and easy as that.

Jack (in NY), is that how you do it too? :)

"besides the shovel, the meter is a Signalman's most useful tool ;)"
-Steve Campanelli

Alvin knowed better but didn't follow his own stinkin' advise in AZ