1966 Mustang dies intermittently

Some of you might remember the 1966 Mustang I bought my wife for her 40th birthday last year. Well, perhaps it's how these things work, but it seems that the car I bought to keep instead of resale is a problem child. We've never really been able to drive and enjoy it because it mysteriously dies at random times. To date I have replaced the following:

coil

condenser

points

plugs

Pertronix ignition system

distributor cap and rotor

plug wires

gas tank

fuel pump

fuel filter

fuel lines

rebuilt carburetor

new ignition switch

What happens is that it will be driving just fine (it always starts instantly), but will just die. No sputtering, no choking like it's running out of gas, but just like we turned the switch off. A few seconds before it happens, the tachometer will start to flutter, then dead. Turning the key off and back on will always restart it. Sometimes it stays running for another 30 minutes, sometimes it dies 5 times in 2 miles. There is exactly ZERO correlation between temperature, speed, time of day, humidity, type of fuel, or what I had for breakfast and the stalling issue.

Today I decided that the tachometer was the problem. It's an aftermarket Rally Pac setup and given some of the workmanship of previous owners, I suspected that the wiring was bogus. It always flutters before the car dies and lately it has taken to parking the needle straight down (at like -500 RPM) rather than at 0 RPM, which is about 8 o'clock on the dial. So I decided to bypass it. I found that they were running power directly from the ignition switch to the tach and then to the (-) side of the coil. Stupidly, I jumped the wires together, bypassing the tach. As soon as I turned the key, I heard a pop under the hood and it no longer runs at all. Despondent, I pushed it into the garage and gave up.

My guess is that I fried the Pertronix unit, so I'll put in points and a condenser and see if I have spark again. But that only puts me back to 0 with the stalling issue--I know it wasn't the Pertronix and I know new points and condenser won't solve it. I'm going to unhook all the tachometer leads and hope for the best.

So I have two real questions:

1. Would having a faulty tach connected to +12V at the ignition and the (-) coil terminal cause the coil to lose power? That is, perhaps a bad ground in the tach could be grounding out the coil?

2. If not, what the HECK is causing the stalling? I'm fresh out of ideas.

Melanie is broken-hearted that she's afraid to drive her Mustang because we've never really gone more than a mile or two in it except for the day we brought it home (when it stalled twice in 400 miles). The car only makes me angry and I'm tempted to just shove it into the back of the shop and forget it exists.

Any thoughts? Sorry about the long post, but I'm desperate. Thanks!

Matt,

I would suggest verifying the reliablity of the 12 volt source going to the coil/ignition system. Either have a seperate wire from that terminal to a VOM in the car while its running and observe what happens when it dies. I suspect ignition switch terminals getting hot and intermittantly making contact (hence when you restart the car you move the switch's internal terminals). Attack this as process of elimination like you've been doing by perhaps providing a reliable voltage source like a temporary seperate key switch from battery to the ignition terminal. Melanie really needs to get back into her Mustang!

I see that you replaced the ignition switch, but that doesn't confirm the wiring from that to the ignition system or the reliablility of the source to the switch.

If you have a battery cutoff switch check that as they can get corrosion at the contact areas which is hard to see. I spent 2 years tracking down an intermittent problem with a vehicle that would not restart after it was up to temperature. Also had another one that would make the vehicle sputter like a coil was bad. <O:p></O:p>

Don't know what you blew but I had a car with very similar symptoms of stopping without warning. When I finally tracked it down, the tach wire going to the distributor had a worn spot in the insulation and it would short out to ground from road vibration or body flex. I disconnected the tach wire at the distributor and it ran fine.

Matt,

I've observed Pertronix unit actually being the problem - I do not mean to condemn their product, but have seen them malfunction, and of course there is nothing you can do with a sealed unit. Once replaced with original-type points-condensor parts, the car ran beautifully.

Worth a shot?? Maybe?

good luck - we want her to enjoy the Mustang, not regret having it.

Is there the possibility of a bad or no ground between block & frame or body? I got a car back from a shop once & the ground wasn't replaced car would die then start right back up. Turned out the ground was going through the shift cable that eventually became inoperable. Reattached the ground strap between block & firewall & problem solved.

Dale

Have you changed or checked the connections at the ballast resistor? (See lead 16A) I would be inclined to hook up a voltmeter at various points along that line and monitor while driving.

http://4.bp.blogspot.com/-RRXxvER1wTs/Taxm5L3DxtI/AAAAAAAABr8/MHFVPrxGBd4/s1600/66MotorWiring.jpg

Ron

a 66 mustang doesn't have a ballast resistor

Have you actually confirmed that the problem is electric and not fuel when the engine dies? I had a small ball of solder come loose in a tank once and it would roll around and block the fuel intake. After the engine shut down and the vacuum released it, it would roll away. Very annoying, hard to find, and changing fuel filters didn't solve it. Ditto for collapsing rubber fuel lines in the system.

These are all very good suggestions to try. In addition, you might look at your gas cap. If a vented cap is required, and your using a non-vented type, that could cause your problem. An easy test would be to just drive around with the gas cap removed and see if the problem recurs. Also, I would install a temporary jumper wire with a ballast resistor and alligator clip at each end between the battery positive post and the positive terminal on the ignition coil. Make sure that the negative coil terminal is the one going to the distributor . Take precaution against this arrangement from shorting out to ground. You'll have to connect and disconnect (from the battery end) to start and stop the motor. Let us know how things turn out. We're all anxious for you to solve this problem.

These are all very good suggestions to try. In addition, you might look at your gas cap. If a vented cap is required, and your using a non-vented type, that could cause your problem. An easy test would be to just drive around with the gas cap removed and see if the problem recurs. Also, I would install a temporary jumper wire with a ballast resistor and alligator clip at each end between the battery positive post and the positive terminal on the ignition coil. Make sure that the negative coil terminal is the one going to the distributor . Take precaution against this arrangement from shorting out to ground. You'll have to connect and disconnect (from the battery end) to start and stop the motor. Let us know how things turn out. We're all anxious for you to solve this problem.

Sorry. It's just the symbol just beneath label 16A is typically referred to a resistor in most schematic diagrams.

Have you checked the main connection at the firewall for corroded connections? Maybe with your Pertronix you could run a straight bypass wire between the ignition switch and coil + to see if it solves the issue.

Thanks for the feedback everyone. I've done a lot of additional work and the car is running again. In addition to the items above, I have done the following:

New engine wiring harness

Replacement Pertronix unit

New feed wire for Pertronix

Several new ground wires for the various systems

Quick-disconnect for the tach wire going to the (-) coil terminal

Once everything was reconnected, the car fired up instantly and idled perfectly. Sadly, it always did that before. Right now it's pouring rain and there's hail on the way, so a test drive won't be possible for a few days. Poking around in there, I discovered that the main firewall connector had intermittent connection to the coil, too. Whether that's because I disconnected it tracing wires and didn't reconnect it properly or because it was failing, I can't say, but the new wiring harness has cured that problem. The resistor wire that drops voltage to the coil checks out, so I don't think it's the culprit. Now that the Pertronix is getting a full 12V, it should be a little happier, but I don't believe it is the cause of the problems, since it did the exact same thing with points in it. But wow, does this thing start FAST now. Half a turn and it's running!

Now that virtually everything even remotely related is replaced, we'll see what happens out on the road. I strongly suspect that it is the tachometer unit itself that is somehow grounding out inside, maybe due to vibration or heat, and when it does, it grounds the coil and the car dies instantly. It always restarts because the tach is reset when you turn off the key. So with the quick disconnect on the tach, I'm going to drive it until it starts to twitch and die, disconnect the tach, and see what happens. It's the only link in the chain that hasn't been replaced or addressed at this point. My next call is a priest for an exorcism.

As for fuel problems, it's definitely electrical. The death is instant--one second driving fine, the next the engine is 100% dead. No sputtering or stalling, just dead. If it was a fuel issue, I think it would stall or struggle to run for a few moments before finally dying. That isn't happening, although I did replace the fuel tank and fuel pump and rebuild the carburetor just in case.

I will keep everyone updated just so someone in the future might find a solution to a similar problem. Thank you for all the feedback!

One more update, just in case anyone needs help with a similar issue in the future. I've been paying a mechanic friend by the hour to chase this problem and he's had the car for the last month. He found a lot of things that made him say, "A ha!" and fixed them, only to have it continue to stall. He was going nuts just like I was. More new items include:

Bad Pertronix unit (replace)

Coil with abnormally high resistance (replace--again)

Ignition switch (this is the third switch, original had a bent pin, first replacement was cracked)

Entire engine wiring harness

Pink ignition resistor wire

Lots of miscellaneous wires throughout the car that looked frayed and/or melted

Tachometer and related wiring

Battery

That's all in addition to all the stuff I had already replaced looking for the issue, like the gas tank and fuel pump. He also adjusted the carburetor again because he thought the float levels were too low. The sucker ran amazingly and more than one person commented that it was the best-running early Mustang they'd ever driven. However, it still was breaking up above 4000 RPM and still stalling at unpredictable times. 95% of the time, great. 5% of the time, dying. And it continued to be vexing because turning the key off and on would start it instantly and it would act as though nothing unusual had happened.

Since the Pertronix is happy on 12V and the voltage drop to the coil is basically to keep the points from burning up (and there are no points anymore) he ran a direct 12V feed to the coil, bypassing the resistor wire just to see what would happen. Yesterday he was driving it home (he's put more than 300 miles on the car testing it trying to get it to act up while he's got equipment hooked to it) and there's smoke coming from the cowl vents. He pulls over and shuts it off and sees that the brown wire coming from the solenoid to the coil which shoots 12V during cranking is starting to melt--that's the smoke. Are you kidding? That should be able to handle 12 volts, right?

The verdict? It appears that the starter solenoid was occasionally hanging up and grounding itself, spiking resistance in the system and causing a voltage drop to around 4-6 volts. That's why cycling the ignition would usually cure it--it was resetting the solenoid and fixing the "sticking" situation temporarily. It's why the problem was so intermittent and so unpredictable. It wasn't sticking enough to kick the starter, just enough to bleed off a lot of excess energy that wasn't getting to the spark plugs and would eventually drop low enough to kill the ignition.

So I've spent about $3500 chasing this problem with new parts and about 40 hours of mechanic time, only to find it was a solenoid that I can get at the local NAPA for $20. The upside is that the car now cackles and snarls like it should, pulls hard to 5000 RPM, doesn't stumble, idles perfectly, and we fixed a lot of stuff that may or may not have been an issue in the future.

I won't be convinced it's fixed until we get some drive time on it, because there have been too many "obvious" fixes that should have solved the problem, but this really has to be it--there's nothing else left to replace. My lovely wife will have her car back on Tuesday, so we'll find out.

Thanks to everyone who helped me out, and I hope this is helpful to someone else in the future.

hello everyone , I have a 1966 mustang 289 2 barrel automatic, and I been having the same problem with it. I been driving it and within miles it just shuts off instantly,I tried to restart it but it just turns like its not getting fuel, I thought it was the carburetor so I had it rebuild by a credible shop in Escondido California, I replaced the distributor cap and wire, the ignition coil aswell. I took it for a drive today and with 10 minutes it just die. there is been a couple of times when it dies when I put it on gear. engine temperature is normal when it happens but after just leaving sitting for a day and try to restart it sometimes it starts and sometimes it doesn't. I touched the ignition when driving for a bit once it dies the coil feels pretty hot, I don't if this is normal, but this issue is driving crazy. first time it happened it shut off like 3 times on my way to work. but once I came to stop sign it completely die. it was bugging down one day so I look at the carburetor and one of the injectors wasn't spraying fuel , after sitting for about 8 hrs I took it back home by playing with both gas and brake pedal this is when I decided to get the carburetor rebuilt, and replace coil and wires and spark plugs. I took it out for a spin I kept it in park for a bit to see if it die nothing happened, so I put it on drive and I drove it or a bit I came to a stop to and put it in park for a bit then I try to put it in drive and it just completely die I tried to restart it, engine turned, but it didn't start so I had to push it back. sorry this post is long, I just don't what's wrong.