Truck stalled at highway speeds, wouldn't start again

[haruman]

So this is a weird one. Last Friday, I had been driving for about 25 miles, was about 5 miles from home. I was driving on the highway, doing around ~80mph when the truck started to sputter and lose power. I made my way to closest exit and got all the way down the ramp when it died.

Guy stopped and was nice enough to tow me off the exit ramp into a neighborhood. I got it started again after 20 minutes of fiddling, drove about a mile, died again.

This time I couldn't get it started again at all...

Called State Farm up, they came out and gave me a tow to my house.

Last night, for grins, I decided to try to start it. Fired right up! :shrug:

Any ideas? For reference, I have a Weber carb, and an electric fuel pump.

[SubGothius]

First thing, try changing your fuel filter in case it's getting clogged. The reason it starts up again after sitting a while is that some of the debris can settle back away from the filter media, allowing juuust enough fuel to pass that it starts up and idles okay, maybe even drives a while, before enough debris gets pressed back into the media that it starves again.

If that doesn't resolve it, I've been chasing a similar sporadic issue for a couple years, and have eliminated enough other factors by now that I've got to conclude I must have some sort of chunky debris/deposits drifting around in the tank that occasionally gets sucked up against the fuel intake pipe. Usually I can just shut it off and coast along for a block or so to let the debris drift away from the pipe, then restart and continue on my merry way.

If it keeps dying after a couple rounds of this, I'll make a sharp turn to slosh things around a bit in the tank, and that usually gets it sorted. I've also been filling it up before I get below 1/4 tank lately, which seems to reduce the odds of this happening. Ultimately I'll have to drop the tank and take it to a radiator shop to have it thoroughly cleaned out, maybe apply a sealant if they do that sort of thing or do it myself.

By coincidence, there's a similar story in this month's RockAuto newsletter:


Finally we drained and removed the gas tank, turned it upside down, and out fell a fibrous seal from the cap of a bottle of fuel additive the owner had recently added! Apparently, the seal would float until the gas was low enough that the suction from the fuel pump would suck the seal over the port, shut off the fuel flow and stall the motor. When the suction was relieved, the cap would float back up top until it was sucked back down again. At full tank, it was too far away to be affected by the suction. Once removed the motor ran fine again!

[geezer101]

First place to check is the ignition coil - primarily the ballast resistor. If it wants to run after sitting for 5-10 mins and then dies again, there is a chance the ballast resistor is cracked. You will know if it has failed as it'll be red hot to touch (don't just grab it with your hands - it will definitely burn your fingertips if the ceramic has cracked) I'd probably check the fuel system next for a wiring fault/bad earth and the fuel filter as SubG has recommended. If the pump shuts off due to an intermittent fault, you won't know right away as the carb will have to drain the fuel bowl before starving out.

[haruman]

Ok I'll try those things.

Last night I fired it up, let it run for about 5 minutes, gave it some gas and it died again and wouldn't start up after that. Ugh. Lol

[dash]

when it's dead, throw a cap of gas in the carb. If it fires immediately - fuel feed problem

[haruman]

Just put a cap of gas in the carb, nothing.

Might just run out an get an ignition coil and throw it in there, see what happens.

[haruman]

Mine doesn't have a ballast resistor, btw.

I checked the coil. Primary coil resistance is 3.6 ohms, and secondary resistance is 7.5 K-ohms. Seems out of spec.

[geezer101]

AFAIK it should have a ballast resistor. There is every chance the coil is dead or very weak. It will have a tendency to break down at higher rpm if it's tired so running at constant highway speeds would've been enough to push it til the spark was no longer consistent to burn fuel.

[haruman]

Any idea on the specs on that resistor or where to buy it? I can't seem to find much info

[SubGothius]

Just get this coil; it comes with the resistor and is cheap enough you may as well nab both birds with the one stone:

https://www.ebay.com/itm/381825243549

This thread covers the proper wiring:

http://www.mightyram50.net/vbulletin/showthread.php/8541-Winning-the-battle-vs-the-ballast-resistor-88-g54b-ignition-coil-wiring

[haruman]

I have an '80, that's not the one for me...

[geezer101]

Unless you want to keep the truck year specific OEM, that is the best replacement option. It has a higher output voltage and is more efficient at higher rpm to maintain a consistent burn cycle. That transformer type of ignition coil is the type I would recommend :thumbup:

*Some performance aftermarket coils do not work with the ICM's that are installed in the factory distributors and cause running issues (Accel, MSD etc)

[tortron]

coils are pretty generic
i have used a 1950s lucas one from a brit car on a 2000's honda 50cc scooter

it will work, theres no brains in the truck to know whats there



The main thing is to get either a coil that doesnt need a resistor

or a coil and matching resistor

although some electronic ign systems dont like the resistor ones

[haruman]

Whelp. Put the new coil on. Nothing... :/

[tortron]

still getting spark?

if so, try some ether down the carb.

[geezer101]

The distributor? Maybe the ICM in the distributor has cooked... check for spark as tortron has recommended.

[Giovanni89]

ICM's are pretty notorious for failing with heat like a coil. They'll run fine cold and give it up when the engine is up to temp. Sometimes they will still throw spark but the timing will be wayyyyyy out.

[haruman]

One note, the coil I replaced had a note on it NOT to use a ballast resistor. Interesting.

I have a new distributor cap & rotor coming, the cap had some weird green corrosion where it connects to the coil wire.

I'll check for spark once I put that on.

Fun fun

[geezer101]

Be aware that is the job of the ballast resistor - to prevent everything downstream from getting roasted by full voltage through the coil. It'll boost secondary voltage at the plugs but compromise the life of the coil and the ignition system (ICM/breaker points/plug electrodes) That's why they went to solid state transformer coils. They are capable of producing a stronger, more stable spark.

[haruman]

New cap & rotor did nothing, checked for spark - no spark. New ICM it is I guess.

[xboxrox]

New cap & rotor did nothing, checked for spark - no spark. New ICM it is I guess.

12volts getting to the coil with key in ON position & (eng off) ???

[haruman]

12volts getting to the coil with key in ON position & (eng off) ???

Just checked that, and yes.

[SubGothius]

Then sounds like most likely the ICM. If your new one doesn't come with heatsink compound, AutoZone stocks some:

https://www.autozone.com/miscellaneous-cleaners-and-degreasers/heat-sink-compound/p/wells-heat-sink-compound-1-ea/19189_0_0

After removing the old ICM inside the dizzy, scrape/wipe off any residue of old compound (if there isn't any, that may explain why it failed), apply a thin, even layer across the base of the new ICM, install it, then wipe off any compound that squeezed out of the edge. Don't just use dielectric grease, as that isn't doped with thermally-conductive particles like proper heatsink compound is.

[geezer101]

...or arctic silver from a PC spares shop. It's is the best stuff for installing processor chip heatsinks. Don't go nuts with it.

[haruman]

New ICM came a day early. Put it on, fired right up! Woo.

I'll get some heatsink compound and put that on before I drive it any.

Just glad it started! :))

[geezer101]

Awesome :clap: Are you going to install a coil with a ballast resistor? It would suck having to go through this ordeal again... not saying that the lack of a ballast resistor was the cause of the ICM failure but I think having one in the ignition circuit should be considered.

[haruman]

Yes I will. I'll get that one from eBay.

As of today, new coil, new distributor cap & rotor, new plugs and wires, got thermal paste on the new ICM, everything is as smooth as butter again.

[geezer101]

Nice :grin: OOC are you using the factory tune? If you dial it in you'll gain some performance out of it.

[Giovanni89]

Awesome! At least on my 89, the ICM was wired to the key switch side of the ballast, meaning it see's 12 volts. Hooking it to the 6-9 volt side of the ballast will up the current through the ICM, and I think that's what cooks them. Earlier trucks very well may be different, couldn't hurt to check the wiring diagram.

[haruman]

Anyone have a picture or diagram how that eBay coil is supposed to get wired up? I'm a visual kind of guy...

[SubGothius]

Here's a pic of mine, note I disassembled the mounting bracket and reassembled it with the resistor block on the other side of the coil, as that made for easier wire routing:

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=26921&stc=1

[haruman]

Thanks for the pic, that's super helpful!!!!