Bronco stalling on highway and won’t restart.

[rbwamsley]

Looking for some help on where to start with my issue, as it has left me stranded on the highway three times. Two times, my bronco has died while driving at 60mph (90 degrees plus outside). The other was pulling into park (70ish degrees out). After that, the truck will not start for a long while (20-40min).

I’m not sure where to start looking or what could cause it. Any help would be appreciated.

302 with a Petronix HEI correction: DUI HEI

 

[gnpenning]

First thing to check for is spark. Start at the spark plug and work your way back. Carry a old spark plug and a multi meter. Generally electrical if it fails hot but works after cooling down. Check and test.

Do not throw parts at it

Since you said it just quit, I don't it's fuel related but it's a quick easy check looking down it to the carb and operating the throttle. Look for a squirt of fuel.

 

[rbwamsley]

Thanks for the help. I like the idea of the old spark plug.

 

[Bitch'nBronco]

I had a similar condition, it wound up being the coil. Mine also failed during the summer months, it would die and then work again after an hour or two. Solid advice from @gnpenning

 

[73azbronco]

how old are all the electrical ignition parts, coil, wires plugs, ignition relay, anything in the dizzy?

Possible vapor lock, what is fuel pressure? I'm not betting on it though.

 

[rbwamsley]

how old are all the electrical ignition parts, coil, wires plugs, ignition relay, anything in the dizzy?

Possible vapor lock, what is fuel pressure? I'm not betting on it though.

Plugs and wires are roughly 7yrs old. Everything else is unknown, but over 10 years.

 

[DirtDonk]

Just to be clear here, when you say it won’t start, does the starter still crank the engine and it just doesn’t fire up? Or does it not even crank when you turn the key?

If it turns out to be a no-spark condition, carry some water with you and when it happens, pour water over the coil and let it cool down for a couple of minutes to see if that helps.
But even before it happens again, you should be checking for reliable voltage at different places. Is it sitting dead now? Or will it fire up like normal?

What year is your bronco?
What ignition does it have? I see you said Pertronix, so does that make it a 73 or older bronco? Or did you change out Dura Spark for Pertronix?
Is it original Wiring?
Seven years is a long time for some components, but a bad plug wire or two won’t kill the engine going 60 miles an hour. Doesn’t help things, of course! But they wouldn’t be working by themselves. It can certainly make the coil work harder and hotter though.
And Pertronix Ignitors work very well, but can also fail as well. Just like anything else.
If there are any splices in the electrical wires to the ignition components, I would closely inspect them, or maybe even replace them.
Any water getting down into a butt splice and causing corrosion, can cause this intermittent dying and no start.
Had that happen myself. Positive wire to the coil head corroded about 6 inches away in the harness.

 

[rbwamsley]

Just to be clear here, when you say it won’t start, does the starter still crank the engine and it just doesn’t fire up? Or does it not even crank when you turn the key?

It does not fire up. Cranks just fine though.

If it turns out to be a no-spark condition, carry some water with you and when it happens, pour water over the coil and let it cool down for a couple of minutes to see if that helps.
But even before it happens again, you should be checking for reliable voltage at different places. Is it sitting dead now? Or will it fire up like normal?

It's an HEI setup, so just pour the water over the dizzy? Correction from above I have a DUI HEI. What places should I be looking for reliable voltage?

It will start now.

What year is your bronco?

'74

What ignition does it have? I see you said Pertronix, so does that make it a 73 or older bronco? Or did you change out Dura Spark for Pertronix?
Is it original Wiring?

Correction from my original post. I have a D.U.I. HEI not a Petronix. Sorry about that. Yes, original wiring.

 

[DirtDonk]

Good to know. Big difference!
First thing I would do would be to grab an extra high-quality ignition module. Not the cheapest thing you can find just because it has a lifetime warranty, but probably the most expensive one you can find.
Maybe even one from Pertronix or DUI.

Second, or maybe even first instead, verify where power is coming from for the distributor.
If your left side (ignition, or “I” maybe?) wire on the distributor, cap is going to the stock red with green stripe wire, that could be the source of your problem.
The HEI setup is meant to run on a full 12V and not the lower voltage coming through that wire.
Different ways of achieving this, but probably best and easiest is to use a relay.
Without a relay, the HEI could put more strain on that particular wire from the ignition switch. This could be the cause of your intermittent working as the wire heats up naturally, but heats up even more due to the higher demand of the HEI.
I don’t know what the current ratings are for HEI versus standard ignition, but I have heard that it’s more.

So, a few more details, please.
But to answer your previous question, yes, as long as you don’t go crazy, pour water over the top of the distributor.
Obviously, you don’t want water getting inside, but anything that can more quickly cool the coil area would help narrow down a solution.

 

[hsach]

Definitely check spark, but also check your fuel pump. Not sure if you have electric or manual. These symptoms also point to a weak/dying fuel pump. I just changed one on my '78 bronco last weekend, 3rd or 4th in recent years. I switched from a Carter to a Delphi to see if that lasts longer. A dead pump is easy to diagnose, a weak one is a pain in the ass, especially in the summer heat and elevation, if that affects you. I use ethanol free gas only now, have all new fuel lines from tank to carb, new tank and sending unit, and I still see modern mechanical fuel pumps fail. Reading DirtDonks reply above, I would do all of what he is suggesting, but I would also change out the fuel pump if you can. Very easy job if it is a mechanical setup. Good luck!

 

[rbwamsley]

Definitely check spark, but also check your fuel pump. Not sure if you have electric or manual. These symptoms also point to a weak/dying fuel pump. I just changed one on my '78 bronco last weekend, 3rd or 4th in recent years. I switched from a Carter to a Delphi to see if that lasts longer. A dead pump is easy to diagnose, a weak one is a pain in the ass, especially in the summer heat and elevation, if that affects you. I use ethanol free gas only now, have all new fuel lines from tank to carb, new tank and sending unit, and I still see modern mechanical fuel pumps fail. Reading DirtDonks reply above, I would do all of what he is suggesting, but I would also change out the fuel pump if you can. Very easy job if it is a mechanical setup. Good luck!

I still have a manual fuel pump. I replaced it roughly a year ago.

 

[DirtDonk]

I still have a manual fuel pump. I replaced it roughly a year ago.

Believe it or not, that’s actually bad news.
Bad, because new pumps tend to be crappier than old pumps.
Bad too, because we tend to drive our Broncos a lot less than we used to. And an almost guaranteed early death of a fuel pump is to not drive very often.
Are you able to drive your bronco often, maybe even as a daily driver? Or does it have to sit for weeks at a time?

 

[73azbronco]

what is your fuel pressure?

 

[nvrstuk]

Everybody has great Q's and troubleshooting tips...

Just need some more answers!

OP, let us know if you get it going!

 

[rbwamsley]

Just to be clear here, when you say it won’t start, does the starter still crank the engine and it just doesn’t fire up? Or does it not even crank when you turn the key?

If it turns out to be a no-spark condition, carry some water with you and when it happens, pour water over the coil and let it cool down for a couple of minutes to see if that helps.
But even before it happens again, you should be checking for reliable voltage at different places. Is it sitting dead now? Or will it fire up like normal?

What year is your bronco?
What ignition does it have? I see you said Pertronix, so does that make it a 73 or older bronco? Or did you change out Dura Spark for Pertronix?
Is it original Wiring?
Seven years is a long time for some components, but a bad plug wire or two won’t kill the engine going 60 miles an hour. Doesn’t help things, of course! But they wouldn’t be working by themselves. It can certainly make the coil work harder and hotter though.
And Pertronix Ignitors work very well, but can also fail as well. Just like anything else.
If there are any splices in the electrical wires to the ignition components, I would closely inspect them, or maybe even replace them.
Any water getting down into a butt splice and causing corrosion, can cause this intermittent dying and no start.
Had that happen myself. Positive wire to the coil head corroded about 6 inches away in the harness.

what is your fuel pressure?

Unfortunately, I don’t have a fuel pressure gauge. I should probably get one.

 

[rbwamsley]

Would a low almost bad battery cause this to happen? I took mine into get checked because it wasn’t cranking as well as it used to. Turns out it was pretty much done, so I picked up a replacement.

 

[rbwamsley]

@DirtDonk it looks like my current setup is using a relay like you mentioned, however it looks sort of janky. There are two wires coming from what I think is a relay. One goes into the DUI HEI, the other connects to a wire that goes into the harness. I took a video.

https://imgur.com/a/zFNYWcy

 

[rbwamsley]

Unfortunately, I don’t have a fuel pressure gauge. I should probably get one.

Just ordered a fuel pressure gauge.

 

[DirtDonk]

“Would a battery dying cause this?“

No, not normally.
The battery isn’t what’s running the vehicle. The alternator is. The battery is a storage device, so it lets you crank the engine with the starter to get things moving. Once the engine is running and the charging system is activated, the alternator is recharging the battery of course, but also running the rest of the system while it’s at it.
Since the alternator puts out about 14 1/2 V to the battery’s 12.6 or so, the alternator wins.
So if your battery completely died in one instant while driving down the freeway, you might not notice it until you try to start at the next time.
It should not kill a running engine.

 

[DirtDonk]

Thanks for the video. Couldn’t see every detail, but it certainly looked like there’s some questionable connections at the distributor.
You could even start the engine, and carefully wiggle those wires to see if anything changes. Just be careful of spinning fans and belts and other things!

Couldn’t really see the details on the relay because it was at the bottom of the screen and covered by some IMGUR words that I could not get rid of.
A lot of the connections look to have been made awhile back, and are not sealed, so could easily have corrosion or loose contacts at this point.
Even the battery cables look a little older. Have you cleaned and checked both ends of all three of the large cables to make sure that they’re clean and tight?