77 Ford won't start

shinnlinger · December 18, 2016, 03:16:34 PM

Hello,

Hoping for some direction on where to look. I have a 1977 Ford f-150 plow truck with a 351m. It wasn't starting due to a bad solenoid so I replaced it. Now it cranks over fine and begins to fire, but as soon as I stop cranking and let the key drop back from the start position the engine dies right off.

I was thinking perhaps the new solenoid might be defective and shutting off spark after the the start positiion, so I pulled the coil to distributor wire and put a spark tester on it. Even with the key in the off position, if I jump the the solenoid leads with a screwdriver, the coil is hot and will send sparks. I assume this is not normal but figured I would discuss with you all. In the on position the coil is hot also as when it is cranking.

any suggestions? Seems to be pumping fuel ok and ether doesn't make a difference. It will fire and then cease the instant the key comes back from start.

Thanks.

Dave

Don P · December 18, 2016, 03:33:32 PM

The symptoms are the same as a problem I had in the farmers market box truck... late one night, an hour from home, happily empty on the way home. I didn't go as far as you have diagnosing just noticed that when the key came back from crank to run it died. The next morning I replaced the ignition switch and that solved it.

Corley5 · December 18, 2016, 03:42:34 PM

Fords had an ignition control module that would go bad and cause that symptom. I put a couple on the old 77 I had. I had an AMC Eagle that had the same Ford ignition and it failed as well. It's a flat box maybe 4" square that should be on the firewall or maybe on the fender well. There's a pigtail of wires coming out of it.

69bronco · December 18, 2016, 04:11:39 PM

Had a similar issue years ago, second the module. Seems like they called it a tfi? Thick film integrated maybe? Good luck, let us know.

sandhills · December 18, 2016, 05:30:51 PM

I'd start with the module as well, you'll need to know the color of the plug on the pigtail if memory serves me correct, changed mine on my old '79 several times.

shinnlinger · December 18, 2016, 05:53:13 PM

Thanks guys,

Ill look into the module. I thought they were all or nothing as in they die and thats the end of them, but do they slowly die and work intermittently ? I went out and fiddled with it and jumped a positive wire over to the ignition pole, I heard an audible click on the solenoid and it started right up. I assumed disconnecting my jumper would kill the truck but it didn't and now it works as it should. Im wondering if the Chinese unit just needed to work something loose but I also made sure the solenoid was solidly grounded to the fender wall at the same time and that may have been my issue too.

Dave

WV Sawmiller · December 18, 2016, 05:54:43 PM

Not sure if anything similar but I had a similar age Ford p/u years ago that would crank and run but I had to keep it at high idle when stopped or it would die. Was new to the area (Beaufort SC - USMC PISC) at the time and low on cash so scared to death when I took it to a local shop (Dr. Tire as I remember). They checked it and I knew would need a new carb, fuel pump, etc. Turned out was only a loose screw/bolt holding the carb on and they tightened and fixed the problem. Total bill around $3 and I had a new mechanic/shop as long as I was in the area. I'm no mechanic and they could have taken me to the cleaners but treated me fairly and gained a customer and good referrals as long as I was there.

Good luck.

coxy · December 18, 2016, 07:27:07 PM

my dad use to call it the brain

snowstorm · December 19, 2016, 06:30:24 AM

i had a 84 yrs ago. the plastic on the back side of the module came apart. that let the salt in and it would skip and after a while not start.

Ford_man · December 19, 2016, 07:36:16 AM

I have a 78 with a 460, I think that the modual gets too hot. I have been thinking about moving it inside the cab to get it away from the engine heat.

Gearbox · December 19, 2016, 08:44:20 AM

I was thinking that 77 was inside the distributor .

scsmith42 · December 21, 2016, 05:35:42 PM

Dave, ditto the module. They used to be real expensive but I think that they are less than 30 bucks now.

The older ignition systems had two different voltages. For starting, they used a higher power voltage that was fed by the solenoid. For running, a lower voltage circuit was used that was routed through a resistor.

The high voltage encourage easy starting, the lower voltage increased the longevity of the points.

Kbeitz · December 21, 2016, 05:58:37 PM

Quote from: scsmith42 on December 21, 2016, 05:35:42 PM
Dave, ditto the module. They used to be real expensive but I think that they are less than 30 bucks now.

The older ignition systems had two different voltages. For starting, they used a higher power voltage that was fed by the solenoid. For running, a lower voltage circuit was used that was routed through a resistor.

The high voltage encourage easy starting, the lower voltage increased the longevity of the points.

And the voltage change came from the starters solenoid.
It had an extra bolt that would give the coil the full 12 volts.

jwilly3879 · December 21, 2016, 08:53:49 PM

There was a lage plug-in connector on the passenger side of mine that became corroded. Cut the connector out and spliced the wires. Problem solved.

Logger RK · December 22, 2016, 07:32:00 AM

I have a 80's Ford plow truck,and did learn not to disconnect the battery when it's running. I did,and it burned out that box I think that's being discussed. I happened to have a van with the same one. Switched it and started right up.

Czech_Made · December 22, 2016, 07:53:28 AM

Quote from: Corley5 on December 18, 2016, 03:42:34 PM
Fords had an ignition control module that would go bad and cause that symptom. I put a couple on the old 77 I had. I had an AMC Eagle that had the same Ford ignition and it failed as well. It's a flat box maybe 4" square that should be on the firewall or maybe on the fender well. There's a pigtail of wires coming out of it.

Same module in AMC Jeeps, got rid of it too - upgraded to HEI distributor.