Car dies after 25-30 minutes of use. Help needed.

Dothang67

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May 9, 2006
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289 1967 Coupe, manual transmission; almost stock.

Here is the problem:

Car starts fine, but after 30 minutes of driving in the city it dies. IIRC, all the times that has done this, I was accelerating, and just before it dies, I feel how it becomes unresponsive on the pedal, and then suddenly shuts off, without stalling. After that, it starts again but it is more probable it will shut off the same way a few blocks later.
The problem can occur earlier (during the first 15mins) if I cruise around 1 or 2pm, when the sun is at its peak.


Things that have been done:

-Gas tank has been changed (I thought maybe sediments would clog the fuel line).
-Fuel pump replaced (This helped solve one of the issues; because before it was changed, the car would not start right away, you would need to leave it cool for an hour or two).
-Changed to electronic ignition (Pertronix Ignitor I and Flamethrower coil).
-I also put a clear fuel filter, and even though sometimes doesn't seems completely full, it always has certain level of fuel.


>PO "rewire" the car, but he just leave a mess under the dash.
>It has an alarm, the module is disconnected, but the wiring is still hooked up.
>I also install a kill-switch, right after the ignition switch, could it be that, that kill-switch overheats and then shuts the engine?

If that is not possible, what would you recommend I look for or replace?

Thanks in advance!
 
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jcode68

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Sounds very possible that your gas tank/cap is not vented properly which prevents the pump from being able to pump fuel to the carb after a period of time. The fact that it is worse around noon when it is warmer is also an indicator. If you have ever "shotgun" a beer can, it's the same principle. once all the available air is gone from the tank, the fuel pump can no longer pump fuel. A tell tale sign is the top of the tank will be dented due to actually being sucked so hard the top of the tank collapses a bit, unless your fuel pump is weak.
 

Dothang67

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I used to have the original cap, but I replaced it for an aftermarket one that needs a key to open, may be thats the culprit?
How exactly does the vent system works in the gas tank?
 

ForceFed70

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I used to have the original cap, but I replaced it for an aftermarket one that needs a key to open, may be thats the culprit?
How exactly does the vent system works in the gas tank?
A one way valve in the cap I believe.


Drain the tank to 1/4 and go for a drive without the cap on... easiest way to test.

I would also suspect the ignition system. Could be that the PO bypassed the ballast resistor/wire. Might want to try a different ignition coil.
 

6Stang7

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Does it start right back up when it dies?

If it was his gas cap though, shouldn't he not be able to re-start the car? I would assume that if back pressure was preventing the pump from pushing fuel, then it wouldn't start up.

What caught my attention is that it happens between 1-2pm, so I'm thinking that made he is having a heat soak issue with his carb.

Does your carb have a spacer? If so, what is it made out of?
 

Dothang67

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I would also suspect the ignition system. Could be that the PO bypassed the ballast resistor/wire. Might want to try a different ignition coil.
I guess I need a morning of patience under the dash to check that out, what would I been looking for?

I did try with different ignition coils, this is the third one.



Does it start right back up when it dies?

If it was his gas cap though, shouldn't he not be able to re-start the car? I would assume that if back pressure was preventing the pump from pushing fuel, then it wouldn't start up.

What caught my attention is that it happens between 1-2pm, so I'm thinking that made he is having a heat soak issue with his carb.

Does your carb have a spacer? If so, what is it made out of?
This last time, I didn't try, since I was at a 'not that safe' neighborhood and didn't want to grab unwanted attention. I did wait about 10minutes and it started fine.

It happens faster around noon, but it also has happened at night, after a half hour trip or so.

Yes, I do have an spacer, and its made out of some kind of black rubber. Whats a heat soak issue?
 

6Stang7

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Well, if your carb get's too hot it can cause vapor lock, or in the case of my car, not starting back up within a certain window of time after the car has been shut off.
 

jcode68

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Is the top of your gas tank dented? I'll bet a paycheck that it's a venting problem, especially since you say you switched gas caps. This happened to a friend's 67 as well. If you get the wrong gas cap, it will not vent properly. He had an aftermarket cap, not sure what model it was spec'd for. The simple fix was he drilled a very small hole in the cap and problem solved.
 

2000GTdriver

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I had a similar issue with a 69 Camaro I used to own. The alarm system was randomly cutting off power to the ignition. I would remove the alarm system and trace down the wiring involving it and the kill switch. When this thing shut the engine off it would also kill power to the starter so it would not even crank over, does yours still crank after it dies?
 

Dothang67

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Is the top of your gas tank dented? I'll bet a paycheck that it's a venting problem, especially since you say you switched gas caps. This happened to a friend's 67 as well. If you get the wrong gas cap, it will not vent properly. He had an aftermarket cap, not sure what model it was spec'd for. The simple fix was he drilled a very small hole in the cap and problem solved.
The new gas tank looks fine, but I also check the old one, and it does looks slightly dented on the top. How small do you recommend the hole to be? 3/32"?


I had a similar issue with a 69 Camaro I used to own. The alarm system was randomly cutting off power to the ignition. I would remove the alarm system and trace down the wiring involving it and the kill switch. When this thing shut the engine off it would also kill power to the starter so it would not even crank over, does yours still crank after it dies?
It does crank, but I have always suspected from the alarm system, thats why I disconnected it, but maybe I need to remove it completely.
 

JonK

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My guess is the Petronix, did you add a resistor inline or did the instructions say to/not to?

I installed the Crane version of electronic ign. and had the same issue, I put a resistor inline not knowing that the Mustangs have a resistor inline from the ign. switch under the dash. So I was basically cutting down the voltage until there wasn't enough to fire off the dist./plugs so the car would just shut off after a period of time. Didn't matter if I was doing a steady 30mph or 75mph just shut off. I'd coast to the side and take the cap off, tap the elec. module, get back in and it would start back up.

I plan to divert around the ign. resistor and run a full 12V out to the coil and put a resistor inline there as i don't trust the 40+yr. old wire resistor.
Jon
 

Dothang67

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Trying to visualize 3/32" drill bit... I'm sure that will be fine. Give it a shot and report back.
I'd drive it around with no gas cap (like ForceFed70 suggested) first before you go and drill a hole in anything.
Didn't worked, I drove without gas cap and it happened again.
Also some of the conditions changed:

-I just drove it around 10mins, around 6pm, and it didn't had arrived operating temp.
-It does crank and starts, but remains about 3 to 5 seconds until it shuts off again.


I check the clear filter and was about less than half of its capacity, I also remove the air filter, check the carb while moving the lever(?) and gasoline did sprayed.


My guess is the Petronix, did you add a resistor inline or did the instructions say to/not to?

I installed the Crane version of electronic ign. and had the same issue, I put a resistor inline not knowing that the Mustangs have a resistor inline from the ign. switch under the dash. So I was basically cutting down the voltage until there wasn't enough to fire off the dist./plugs so the car would just shut off after a period of time. Didn't matter if I was doing a steady 30mph or 75mph just shut off. I'd coast to the side and take the cap off, tap the elec. module, get back in and it would start back up.

I plan to divert around the ign. resistor and run a full 12V out to the coil and put a resistor inline there as i don't trust the 40+yr. old wire resistor.
Jon
The Pertronix was installed after, as an improvement and also to check if the points system wasn't the one causing it, since around here we can't find good quality points.


What other options could I try?
 

horseballz

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Another possibility is a small pinhole/leak in the fuel line from the tank to the fuel pump causing you to suck air. One indicator is the filter not full. Just a thought.
Gene
 

jcode68

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Wow, am surprised it wasn't the gas tank vent issue. It sure sounded like the exact symptoms. Sorry I don't have more suggestions other than what the others have listed. Sounds like you have determined the carb has fuel when this problem occurs, so it is likely a spark/ignition problem.
 

a69stang

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Are you using a micro-fine gas filter, such as a Russell? If so, try changing to a Fram, ugly I know, but the micro filters can trap water and shut off the gas flow just as you discribe. Once the car dies, the fuel drains back into the fuel pump, remixes, the car starts until it happens again. Drove me nuts until I figured it out...changed to the Fram... problem solved. Don't know if this is your specific problem, but worth a try.
 

yeloxr7

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If the Pertronix + wire is connected to the coil + wire, and the coil + terminal is supplied from the resistor wire, the Pertronix is only getting 6-7 volts and this is not enough. The Pertronix unit needs 12 volts to work properly.
 

Dothang67

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Do you guys think maybe an old cable could be overheating during the firsts minutes of operation and then suddenly cutting ignition somehow? if so, which cables should I check?


In the meanwhile, I will recheck the fuel line to see of there is a pinhole that could suck air as horseballz suggested. As for the pertronix, i don't think its the culprit, since it was installed after the car started failing. Im thinking may be I should just recable the whole car, this problem is draining my patience.


Thanks for your inputs. :)
 

RGS0907

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I once had a starter that would short out after the engine got hot & kill the engine & it would start again after a few minutes, I guess after it cooled off. My father suggested that it could be the starter shorting & I thought that he was nuts, but that ended up being the problem.