Runs 15 minutes then dies and won't start

[davids2toys]

Hi guys, it has been awhile. A couple of more surgeries kept me away for awhile. I have a MSD 6AL box and MSD dist.It has a magnetic pickup in the dist which failed way before this problem. It was replaced and has been fine.This new problem started 3 years ago. Pulled into a cruise night and the car just shut off like it ran out of gas. We all did a bunch of trouble shooting and a cobra friend had a brand new coil. Installed the coil, started up and drove it home. I thought it was the answer, WRONG! The following weekend drove it to a party at a friends house. Ran fine for the 1/2 hour ride and then died in his driveway. installed another new coil but it would not start. We parked it in his garage. I came back the following day to screw with it. i had installed a MSD noise capacitor before this problem started so I unwired it and joined the wires together. Still no start. I called my Roadside assistance and had it flat-bedded back to my house. During some trouble shooting it seemed like the ignition switch was questionable so I changed it out. Started it up a few times and thought all was good. Then I had 2 more surgeries which took me out of commission for about 2 years. So a month ago I got it ready to go for the maiden voyage. It ran great! So 15 minutes into the ride I puled up to a stop sign and it just shuts off. Tried to start it back up, no luck. Had fuel at the carb, so I sat on the side of the road for 45 minutes. I figured it might be the coil and might start after it cooled down. It started right up and I raced home before it died again. I have been testing and inspecting everything and it was passing with flying colors. Cap , rotor, Pick up in dist was very clean and tested fine at 674 ohms. Did the paper clip trick to test the box and it was fine. Check all my grounds, fine. I gave up and thought maybe simulate the shutoff / no start condition and then do the same tests while it was hot and not starting after it shut off. Today I ran it in my driveway. It started and ran just fine. After about 20 minutes it just died. Tried to start it, nothing but spinning. Immediately did all the tests again. everything tested good. Also while cranking it had 6 lbs fuel pressure so that would eliminate vapor lock. I let it sit for about 30 minutes tried to start it, fired right up!!! I'm stumped. You guys have any ideas???

[mrmustang]

I'd say either the 6AL box is starting to fail, or your fuel pump.
Do you have an electric or mechanical fuel pump?




Bill S

[strictlypersonl]

The other possibility is a failing ignition switch. Check the voltage at the MSD.

[PeteF]

I had similar symptoms years ago on ERA2041. It turned out to be the fuel pump. Upon disassembly, I found that the diaphragm valve was a press fit, and would sometimes pop out of its seat and lose fuel pressure momentarily, and the engine would die. Sometimes it would restart and sometimes it wouldn't. A new pump solved the problem.

[davids2toys]

Bill,I have a mechanical fuel pump and it is reading 6 lbs even when it is on the side of the road not starting.While it is cranking over, I was looking right at the Gage.
I also tested the box while in the stalled no start condition. The MSD tech told me if I am getting the spark using the paper clip test, it is not the box.

[davids2toys]

Bob, the switch is new. Where and how are you suggesting I check the Voltage at the MSD

[davids2toys]

That is interesting Pete, I never heard of that. I always thought the fuel pump worked or did not work. I do have a new one on the shelf. It is weird because it has only done this under no load, car hardly moving or stopped. I suppose if nothing else works I may just change it the hell of it

[Ron61]

David,

You have tried about every test but it still sounds like a heat related electrical problem to me. Have you tried pulling a plug wire when it won't start and then turning it over and watching to see if you are getting a good spark to the plug. Mine will arch about 1/2 inch or more so make sure you don't have you fingers at the end of the plug wire when you do this.

[Grubby]

Coil is going bad.

John

[PeteF]

If you saw good fuel pressure while cranking, then the pump should be good. The coil sounds like the next possible culprit.

[PeteF]

But, rereading your first post, you have changed the coil twice already. I'm out of ideas now

[twobjshelbys]

Coil or wires and connections coukd be heat sensitive. Remove andcre-seat all of them.

[Tom Wells]

David,

I had a similar problem with a 557.

It was caused by fuel boiling in the float bowls of the Holley carb.

The boiling point of today's substance we laughingly call gasoline is so low that my bowl vents looked like Old Faithful. I proved this by removing the hood scoop and the air filter and watching it do exactly that at low speeds. The fuel would geyser up, make a u-turn and go straight into the intake. Instant shutoff.

Highway cruising was fine but in low speed traffic it shut down as if the key was turned off. No coughing, no sputtering, just running fine one second and dead silent the next...

I spent nearly two years trying to fix that (and spare you the details LOL) before switching to Holley EFI - problem solved!

Picture the pressure in the float bowls at zero psig and the EFI at 43 psig. That big pressure difference prevents today's fuel from vaporizing at typical underhood temperatures.

The temperature required for evaporation of today's fuel is probably 50 or so degrees lower (I knew the number but time has swallowed it) than it was 40 years ago when carbs were king.

Another thing to think about, yes?

Tom