Hey everyone,

First '77 F150, 400/c6

Problem: Truck would run and drive great but would stall out after about 30 minutes and not start again until things cooled down (usually about 10 minutes of sitting). This pattern would continue.

After some suggestions from you folks here at FTE I changed the distributor pickup coil and the ICM. Thinking that one or both were failing after they warmed up and were preventing startup until they had cooled down.

After getting everything put back together I went to start it up and it did so just fine. I noticed that the high idle was around 1000 which was normal before and it would drop down to about 600-650 after warming up and a push on the accelerator dropped the high idle cam. Only now when I push the accelerator it wants to drop down around 200-300 and sounds like it's about to stall. If I let off the pedal before the engine dies it goes back up to 1000-1100. I can't get it to drop off the high idle and anything other than a quick flick of the pedal nearly stalls it out.

Question, would I need to readjust my idle mixtures, high idle cam, or curb idle after replacing the distributor pickup coil? What about changing those parts would so drastically change the running condition of the engine?

It's not fuel delivery related. In my build up I did new sending units, new rubber hoses, new fuel pump, new fuel filter, carb rebuild and it ran great until it got warm and would stall out. I've never had this issue before.

 

Also when I changed the distributor pickup coil I didn't disconnect my plug wires, I just moved the cap to the side to get in there and pry the reluctor off. I also marked where my rotor and my reluctor roll pin were and put it all back as it was when I disconnected it.

ICM is Motorcraft
Distributor pickup coil is Standard Motor Products.

While the cap was off I brushed off the carbon on the inside as I've done nearly every time I pop the cap. I've rechecked that my vacuum advance linkage arm is still connected to the pickup coil, and that the vacuum advance hose is connected. While working on it I removed the horseshoe to the ignition coil and cleaned the connections and added dielectric grease before reinstalling.

 

I haven't yet changed the ignition coil or the horseshoe harness. As it was explained to me that that wouldn't have caused my intermitant shutdown and having to wait to restart issue initially.

 

It doesn't really matter what aspect of what you messed with did it, your idle dropped so you have to get it back up then find out why it went down in the first place.
Maybe you knocked a stuck advance mechanism loose. Maybe you actually did spin the distributor a little (not as likely, but still possible). Or maybe the high-idle cam was actually stuck for a long time and your messing about under the hood knocked it down one notch too.
OR, do you have an electric idle solenoid? Or anti-dieseling solenoid. Or whatever it was called for your year? If so, maybe the wire came undone, or the unit has finally died and your normal idle can't be achieved until it's fixed or the carb is adjusted to compensate.
If you're not familiar with them, the simplest versions from the later sixties and early seventies were there to set the idle with so that when you turned off the key it kicked the idle down a few hundred aditional rpm so the engine would not run-on. In those cases you set the carburetor idle to say, 500 rpm, then adjust the electric solenoid to the usual 600 or 700 or whatever.
Sorry if you knew that already. And because your idle went all the way down to 300, maybe that's not the problem after all.

Likely it's an ignition timing issue, since you were working on the distributor. But simply adjusting the carburetor initially will get you back to where you need to be to stay running (at least until it heats up if you didn't quite fix it yet) so you can check stuff. Then you can check and readjust things properly once you discover what happened.

After that I would definitely put a timing light on it and readjust the timing if necessary. Then of course you'll have to readjust the carburetor again.

Good luck. It seems common that something gets changed even when you're as careful as you can be to not mess with other stuff.

Paul

 

Thanks Paul. I hooked up the timing light today and noticed it at about 30 degrees advanced while at idle. Only thing I can figure is the two components I changed were going out and in an effort to fix them the previous owner adjusted the timing. The carb is seperate since the first thing I did after buying the truck is rebuild the carb (the truck had sat in a field for 16 years). I initially adjusted the carb after rebuilding to tune the engine and the timing was spot on when I did my restore and it ran great until changing the ICM and the distributor pickup coil. So today I got the distributor adjusted to where I can fire it right up and pushing the gas while idleing doesn't cause it to drop down and stall. It starts and idles at about 1000-1100 until the high idle cam drops, then it sits as before at 650. Thinking all was good I shut the hood and started down the block. While in gear when you push the gas it wants to cut out and buck slightly so I know I'm not 100% there, but its progress to say the least. After getting it back into the driveway I revved it up to about 2500 in Park and it backfired. It has never backfired before, so I think I need to just keep at the distributor adjustments for initial timing and total timing. I'm leaning towards my total timing being off at this point. As it happens during high revs while in idle and slight bog down when pushing the gas while driving. Thankfully I was able to turn around and creep back home without pushing the accelerator.

Who knows what the previous owner did, after buying it I soon discovered that that distributor was 180 degrees out. As in it was set to the exhaust stroke and not the combustion stroke with the #1 cylinder TDC pointing towards the front of the truck and not in the 1 o'clock area as it's supposed to be.