First of all hello everyone, newbie here.

About the truck:
1977 F250 Supercab Ranger XLT 4x4 w/ 351M & C6

Problem:
Truck starts and then after 4min 20-50 sec, timed it multiple times, it will cut out. Doesn't matter if its sitting or driving, like Old Faithful it will just cut off. Once that has happened it will drive great all day until the next morning. Gets fuel without issue.

Background:
Replaced ICM (Blue Grommet)
Replaced Distro cap and rotor
Replaced Distro pickup
Traced all ignition wires (All good)
Replaced starter solenoid
Replaced voltage regulator

Any help is greatly appreciated

 

Well, we all need to fart and some coffee before we get going, no? Hahaha

A cold starting issue, it seems.....'77 351M......Motorcraft 2150 carb? Have you made sure the choke (automatic or manual) is working right?

All your vacuum lines in good shape - no cracks, still pliable lines, and all connected to where they should be?

 

Edelbrock performer carb (500CFM) w/ same intake. Choke is manual.

Vacuum hoses are good. (Engine block to tranny, Carb to brake booster, PCV to Carb and Carb metered to distro vac advance)

 

Used to have a Triumph which had a similar problem... after 15 minutes on the highway
(regardless of how warmed up it was before you started driving fast) it would start to overheat. Pull off, let it cool 15 minutes, and you could then drive a hundred until you got tired of it. Replaced the thermostat twice... never did figure it out (before some idiot ran a stop sign in front of me and totalled both cars)

 

....And your manual choke is working fine? No binding/slipping issues when you pull to the fully opened position? Have you looked/checked the choke when in the full closed/full open position? I'm not trying to be a wise apple here, just want to make sure we're good on the choke.

Your vacuum line for the vac advance is hooked to ported, you say. Ok, that's the little nipple on the carb's right (passenger) side, yes? So, all your EGR stuff is gone, too?

 

Manual choke is working fine. I always allow it to cut off on me before I drive it. After about 2-3 min I will open up the choke to bring the idle down to normal (~700 RPM). After I can get it started again, typically 10 min or so, it drives without issue no matter how many times I cut the engine off. Next morning same routine.

Yes passenger side, and yes no EGR.

 

Are you confusing the manual choke - operates by a pull/push **** & wire from inside the truck, to the carb, with an automatic? When cold, an automatic closes by a punch on the gas pedal and opens (a few minutes later) when warm, by another blip on the throttle.
I'm a bit confused here as to what you have. Sorry..............

 

Yes I have a push pull ****. Pull to cold start and push in once it is warmed up.

 

Have you tried pushing it in just a little at a time until she runs good?

Pushing the choke in a bit at a time, I mean.............

 

She runs great until I hit 4min 20 seconds and then she dies. then she wont start for approx 10 min. It seems electrical to me, but is weird because it will only do it during the initial startup ie; once a day.

 

Yeah, that's strange...I would say you have a bad brain box (It's happened before - new stuff is junk) 'cause it's showing that kind of attitude. But, since you said it only happens once, then it's good all day, that's the poser.

Is it a Motorcraft brain box? Can you have the old one (or both old and new) checked out at your local parts store?

 

Roger its FOMOCO blue grommet. Same thing was happening with old ICM.

 

Well, the only thing I can say is I think you're right about an electrical problem, (even though I still think it's choke adjustment related). Maybe re-check the wires at the connections and to/from the ICM. Maybe there's an intermittent short to ground that only shows its ugly head after 4 min 20 sec. Do you have the brain box mounted on the fenderwell such that some air flows under it (washers)? Heat is a killer for these guys.

How about the wiring to the DSII, inside the distributor? No cracks or lose wiring connections? The plate moves ok?

Some one on here has more stuff on the ball about this than me....

 

Tryin' to think outta the box here, so hang with me a second;

Do you always activate the manual choke for the first starting sequence each day? If so, I was pondering whether your plugs are getting fouled out during the initial warm up.

Easy enough to check. Next time it dies, pull some plugs and see how sooted and or wet they are. Might have to lean out the choke some, clean plugs, check plug gaps, check heat range of plugs. You have a little modification to the fuel delivery and intake that can be contributing to the issue if the rest of the electronics are still set up for the stock two barrel and iron intake.

Your comment about being able to start it again after about ten minutes is what got me headed in this direction. I seen similar issues with chebbys in the past.

 

Thanks hdgapeach! So I pulled the plugs after it cut out this morning and they were a bit wet. So I checked spark, yellow! which got me to checking the coil. Since I have had a couple of dentsides I know to always carry a few items in the toolbox ie; a new coil. Replaced the coil and checked spark, beautiful blue! Installed everything and WHAMO!! purring like a kitten. Just goes to show that even though its new does not mean its good.