Runs 15 minutes then dies and won't start

[davids2toys]

Now that I am looking at the fuel system lines I am a little concerned even though I never had a problem until this. Could be the ethanol in the gas. My fuel log and lines are not protect at all by the Turkey pan. See pics

[rnkjr]

Chat GPT: Most Probable Causes (ranked)
1. MSD 6AL box failing when hot
Why this fits perfectly:

Car runs normally until fully heat-soaked (15–20 minutes).

Engine dies instantly, as if key was turned off — classic MSD box shutdown symptom.

After cooling 20–45 minutes it restarts immediately.

Numerous coils tried → no change.

Pickup tests OK cold and hot.

Grounds check OK.

Ignition switch replaced with no improvement.

Important detail:

MSD boxes often fail only when hot, and about 70% of the time they still pass the "paper clip test" when tested immediately after failure, especially if they are in the shade or starting to cool.

Even when they pass the paper clip test, the internal capacitors or the switching transistor can break down under heat + load.

2. Magnetic pickup intermittent when hot (despite 674 Ω)

Even though resistance is correct (MSD wants 500–700 Ω), failing pickups often:

test perfect cold,

test perfect immediately after a shutdown,

but fail only under thermal expansion + vibration.

This can produce the “dies instantly at a stop sign” symptom.

Testing tip:
Check AC voltage output while cranking during a hot no-start. You should see 0.3–1.0 volts AC.
If it drops to 0–0.1, the pickup is dying even if resistance is normal.

3. Heat-soak failure of the coil trigger signal path

You already tried multiple coils — that strongly suggests the coil is not the problem, but the trigger path TO the coil might be intermittent.

This includes:

MSD box to coil wire (heavy red + heavy orange)

MSD box ground path

Small red wire (switched 12V) heat drop / intermittent open

Loose spade connectors at the box

A small-red-wire voltage drop is a known MSD shutdown cause.

[NROTOXIN]

Check AC output....

[davids2toys]

Originally Posted by rnkjr

Chat GPT: Most Probable Causes (ranked)
1. MSD 6AL box failing when hot
Why this fits perfectly:

Car runs normally until fully heat-soaked (15–20 minutes).

Engine dies instantly, as if key was turned off — classic MSD box shutdown symptom.

After cooling 20–45 minutes it restarts immediately.

Numerous coils tried → no change.

Pickup tests OK cold and hot.

Grounds check OK.

Ignition switch replaced with no improvement.

Important detail:

MSD boxes often fail only when hot, and about 70% of the time they still pass the "paper clip test" when tested immediately after failure, especially if they are in the shade or starting to cool.

Even when they pass the paper clip test, the internal capacitors or the switching transistor can break down under heat + load.

2. Magnetic pickup intermittent when hot (despite 674 Ω)

Even though resistance is correct (MSD wants 500–700 Ω), failing pickups often:

test perfect cold,

test perfect immediately after a shutdown,

but fail only under thermal expansion + vibration.

This can produce the “dies instantly at a stop sign” symptom.

Testing tip:
Check AC voltage output while cranking during a hot no-start. You should see 0.3–1.0 volts AC.
If it drops to 0–0.1, the pickup is dying even if resistance is normal.

3. Heat-soak failure of the coil trigger signal path

You already tried multiple coils — that strongly suggests the coil is not the problem, but the trigger path TO the coil might be intermittent.

This includes:

MSD box to coil wire (heavy red + heavy orange)

MSD box ground path

Small red wire (switched 12V) heat drop / intermittent open

Loose spade connectors at the box

A small-red-wire voltage drop is a known MSD shutdown cause.

Well the first part of this certainly sounds like my issue. The pickup was put in a few years ago but has had hardly any use. Also looks perfect. When I called MSD the assured me if it passed the paper clip test it is DEFINATELY not the box!
So how do I do this AC voltage test? Where am I doing this test? What is the voltage drop/ heat drop at the small red wire, I don't understand. So what am I looking for at all the other locations you listed. I only have one spade terminal (yellow wire), it is on tightly

[Whodeeny]

I believe I had a failure similar to what you are experiencing. The car would start and run for a few minutes then die. I couldn't get it restarted immediately. If I waited until the next day it would restart then the same thing would happen. I initially thought the fuel filter was plugging up or I had bad gas. Finally it started, died then I couldn't get it restarted at all. I had it towed to a shop that works with restorations and special interest cars. They diagnosed a failed MSD box. A new box was installed and now the car starts and runs fine. HERE IS THE KICKER - I SENT THE BOX TO MSD FOR REPAIR. THEY CHECKED IT TOLD ME THERE IS NOTHING WRONG WITH IT. I will try the old MSD box again on the car in the spring when I am home again.
BD

[jts359]

Have you taken the air cleaner off and moved the throttle to see if gas is spraying out of the accelerator pump jet ? On my Supercharged Studebaker there is a tee in the fuel line and fitting with a .047 hole in it which sends fuel back to the tank thru another line , This helps to eliminate vapor lock , Ed

[davids2toys]

Originally Posted by jts359

Have you taken the air cleaner off and moved the throttle to see if gas is spraying out of the accelerator pump jet ? On my Supercharged Studebaker there is a tee in the fuel line and fitting with a .047 hole in it which sends fuel back to the tank thru another line , This helps to eliminate vapor lock , Ed

Yes I have. Did you read all the pages in this thread?
Wouldn't that return hole cause a decrease in fuel pressure?

[Tom Wells]

David,

I understand winter problems...

That's why I'm in FL now ;-)

When spring arrives, see what happens - I'm still very curious - non-alcohol gas wasn't available when I fought that problem.

Tom

[davids2toys]

Originally Posted by Tom Wells

David,

I understand winter problems...

That's why I'm in FL now ;-)

When spring arrives, see what happens - I'm still very curious - non-alcohol gas wasn't available when I fought that problem.

Tom

we will see, I do not think that is the problem though

[jts359]

Originally Posted by davids2toys

Yes I have. Did you read all the pages in this thread?
Wouldn't that return hole cause a decrease in fuel pressure?

Its only .042 and i found no issues with starvation , And if your using a Afb type of carb fuel pressure should be no more than 5lbs. And sorry i missed that part of your saga , good luck , Ed

[davids2toys]

No pics! I am getting an error message but not telling me what to do. So frustrating

[davids2toys]

Different browser attempt,
This worked but still one of the pics failed

[davids2toys]

One more showing the log

[davids2toys]

Deleted

[rnkjr]

I hope you noticed, my prior post was a Chat GPT response to your first post. With that being said, here is the Chat GPT response to your 11:51PM post: 1. How to do the AC voltage test on the distributor pickup

Your MSD distributor has a magnetic pickup, which produces a small AC signal that tells the MSD box when to fire the coil.

Where to test:
Unplug the two-wire magnetic pickup connector going into the MSD box.
It’s the violet and green wires.

How to test:

Set your multimeter to AC volts (not DC).

Put the meter leads on the violet and green wires.

Have someone crank the engine.

What you should see:

0.3 to 1.0 volts AC while cranking = pickup is good

0.0 to 0.2 volts AC = pickup is failing even if the ohms reading was normal

Heat can kill the signal even though resistance checks fine — that’s why this test matters.

2. What “voltage drop at the small red wire” means

The MSD 6AL has two power feeds:

Big Red = main battery power

Small Red = switched ignition power (what wakes the MSD box up)

If the small red wire loses voltage when hot, the MSD shuts off instantly, just like turning off the key.

Where to test:
Back-probe the small red wire at the MSD 6AL box (the small plug).

How to test:

Set meter to DC volts.

Put black lead to a good ground.

Touch red lead to the small red wire.

Check reading while cranking during the hot no-start.

What you should see:

11.5–12.5 volts = normal

Anything 10.5 volts or lower = MSD won’t fire

Voltage jumping, flickering, or dropping sharply = bad ignition feed or switch connector

This is a very common cause of random MSD shutdowns.

3. What to look for at the other connections
A. Big Red (main power)

Should have 12–12.6V key ON and 10.5+ volts while cranking.

B. Big Black (ground)

Should be bolted to clean metal, preferably the engine block or battery ground.
If in doubt, run a jumper cable temporarily from the MSD ground to the battery negative and see if the problem disappears.

C. Orange & Black at the Coil

You don’t need to measure voltage here yet — just confirm the connectors are tight and not corroded.

D. Yellow spade connector

If you only have one yellow spade, that’s normally the tach output.
If it’s tight, leave it alone — it doesn’t affect starting unless it’s grounding out.

The real goal of these tests

You already replaced coils, ignition switch, checked grounds, and the pickup ohms fine. The next step is to catch the system in the act when it’s hot and refusing to start.

One of these readings will be wrong only during the failure window, and that will tell you whether it’s:

the pickup signal disappearing

the small red ignition feed dropping voltage

or the MSD box itself breaking down from heat

[davids2toys]

Originally Posted by rnkjr

I hope you noticed, my prior post was a Chat GPT response to your first post. With that being said, here is the Chat GPT response to your 11:51PM post: 1. How to do the AC voltage test on the distributor pickup

Your MSD distributor has a magnetic pickup, which produces a small AC signal that tells the MSD box when to fire the coil.

Where to test:
Unplug the two-wire magnetic pickup connector going into the MSD box.
It’s the violet and green wires.

How to test:

Set your multimeter to AC volts (not DC).

Put the meter leads on the violet and green wires.

Have someone crank the engine.

What you should see:

0.3 to 1.0 volts AC while cranking = pickup is good

0.0 to 0.2 volts AC = pickup is failing even if the ohms reading was normal

Heat can kill the signal even though resistance checks fine — that’s why this test matters.

2. What “voltage drop at the small red wire” means

The MSD 6AL has two power feeds:

Big Red = main battery power

Small Red = switched ignition power (what wakes the MSD box up)

If the small red wire loses voltage when hot, the MSD shuts off instantly, just like turning off the key.

Where to test:
Back-probe the small red wire at the MSD 6AL box (the small plug).

How to test:

Set meter to DC volts.

Put black lead to a good ground.

Touch red lead to the small red wire.

Check reading while cranking during the hot no-start.

What you should see:

11.5–12.5 volts = normal

Anything 10.5 volts or lower = MSD won’t fire

Voltage jumping, flickering, or dropping sharply = bad ignition feed or switch connector

This is a very common cause of random MSD shutdowns.

3. What to look for at the other connections
A. Big Red (main power)

Should have 12–12.6V key ON and 10.5+ volts while cranking.

B. Big Black (ground)

Should be bolted to clean metal, preferably the engine block or battery ground.
If in doubt, run a jumper cable temporarily from the MSD ground to the battery negative and see if the problem disappears.

C. Orange & Black at the Coil

You don’t need to measure voltage here yet — just confirm the connectors are tight and not corroded.

D. Yellow spade connector

If you only have one yellow spade, that’s normally the tach output.
If it’s tight, leave it alone — it doesn’t affect starting unless it’s grounding out.

The real goal of these tests

You already replaced coils, ignition switch, checked grounds, and the pickup ohms fine. The next step is to catch the system in the act when it’s hot and refusing to start.

One of these readings will be wrong only during the failure window, and that will tell you whether it’s:

the pickup signal disappearing

the small red ignition feed dropping voltage

or the MSD box itself breaking down from heat

Wow, great explanation...THANKS. real busy at the moment and going away twice before the end of the month. I will try to get to some of this if I can. also, one thing I forgot to mention, My MSD box is in the cockpit, not the engine compartment so the heat soak in the engine bay should not be a factor affecting the box directly

[scott cooper]

I have been involved in a similar issue and we found a bad circuit breaker close to the fuel pump, small silver rectangle breaker that turned out to be bad, would be fine for a few minutes then would shut down and with no volts going to the pump car shut down, just a suggestion, thought for sure it was a bad fuel pump but not the case

[strictlypersonl]

Scott's idea is worth checking.
When the circuit breaker trips, everything should be dead. Easy to confirm when the fuel gauge doesn't respond to the ignition switch "on". Signal lights won't work either.

Circuit breaker bad: you can temporarily connect its wires together.

[davids2toys]

Originally Posted by strictlypersonl

Scott's idea is worth checking.
When the circuit breaker trips, everything should be dead. Easy to confirm when the fuel gauge doesn't respond to the ignition switch "on". Signal lights won't work either.

Circuit breaker bad: you can temporarily connect its wires together.

Scott and Bob: I have a mechanical fuel pump

[Tom Wells]

David,

Happy New Year!

Did you get the chance to try the no-alcohol fuel?

Tom