Stumped by random start/no-start runs/dies

[Jason72Bronco]

Here is generally my issue: a truck that will start and run perfectly, and then sometimes will die without warning and then will crank but not start....followed by starting and running later on. (This post is detailed because I like to put up front as much detail as possible to cut down on back-and-forth questions on things already done!)

Subject: 1972, 302, 3spd. Many new parts over last year and truck has been reliably starting and running perfectly until now. Driven at least weekly. No rats chewing on anything that I know of. (B4 and now pics attached)

Fuel: New tanks and lines. Fuel pump working when running and when cranked. Recent fuel filter, clear gas through filter. Holley 4160 carb. Yesterday I checked and cleaned needles and seats, float levels and accelerator pump. When it is running, fuel flow is perfect. I don't think this is a fuel issue, as it runs perfectly when running and does not stumble or miss or stutter when it dies. It just dies instantly...more on that.

Ignition: Mallory Unilite ignition, Mallory Promaster coil, wires and plugs all less than a year old. Perfectly timed, and when running has perfect spark, no missing, steady idle and acceleration, all confirmed with timing gun.

Starting/Charging: Starter working fine. Solenoid and voltage regulator less than year old. Good battery fully charged reading 12.5v. Good alternator reading 13.8v when actuated. New battery cables, extra ground strap from engine to body. Inspected most grounds with multimeter, and all clean and good.

Possible question mark: Ignition (key) switch. It seems to work fine, but I have not pulled it and cleaned it. It turns on and off and doesn't short out or do anything funny when you jiggle it around. Plus, I'm not touching anything near it when the truck dies. I still get good voltage readings at various locations when turned to "on" position, even during a non-start episode.

Biggest unkown: Almost 50 year old wiring and connectors between all of the above systems! Yesterday I cleaned a few of the main connections with electric contact cleaner (Deoxit) and Q-tips just in case.

So, like I said the truck has been starting and running great since I did alot of work over the last year. Runs so good that I don't hesitate to hop in and take it anywhere, day or night, hot or cold. But one day this week I went to work, and when I came out to go home it cranked and cranked and no start. I fiddled and looked around as much as I could with no tools. Went back inside for ten minutes to call a ride, came back out and started right up as usual. And yes, it has a half tank of gas.

Drove around the block a few times to make sure things were ok before I hit the road home, pulled into a parking lot to look around under the hood while still running, and got back in to go home, still running and idling fine at 180 degrees (normal) water temp. Just sitting there about to leave, and it dies. Won't start again. Decided to get a tow so I didn't just run the battery down trying to crank. Of course, once it was delivered to my driveway it started right up. I let it warm up and began checking things while it was running, and it died when I wasn't touching anything.

Rinse and repeat this scenario several times over the last few days. When it dies it may be going down the road, it may be with me just standing in front of the running engine bay scratching my head, and it dies. When it does die it is sudden, like someone pulled the coil wire. No hesitation.

I was thinking coil issue. I bench tested the coil and Ohms are within specs (.7 Ohm and 12,500 Ohm). I even grabbed my old coil (that still worked when I replaced it) and swapped it out. No change.
Now this next test is odd to me, and I know that voltage at the coil can be odd since it is one big transformer. With key in "on" position and not running, wire going to coil (disconnected from coil) is 12v. When connected to coil, (+) terminal reads 4v. When it is running and all wires connected, voltage at coil (+) is around 9v. Again, I know voltage readings at the coil terminals can be funky but is this normal? Reading at the brown wire on the starter solenoid is same. When key is "on" around 4v, when running, its around 9v.

Based on issues I've had with other old cars, I suspected a possible ground issue. So, I added a ground strap from the engine to the body, and all ground connections I could fine were great. Plus, it dies whether it is moving and jiggling around or just sitting still in the driveway, so I don't suspect just a loose connection.

Also, I substituted in a coil wire, looked around under the distributor cap and rotor for anything odd or broken. No change to condition.

I tend to use the word "random" sparingly, because there is almost always a reason for everything. But this issue does not seem to be related to moving, not moving, temperature hot or cold, sits overnight or sits for a few minutes. I'm in a good mood or not. So far its just random.

So any help in what to test/do next is greatly appreciated in advance. (Of course, as with any intermittent issue like this, I won't know when I can do a test when it is running, and when I can do tests when it is not! It's up to the truck.)
And no it is not for sale. Yet.

Jason

 

[surfer-b]

It sounds if though somthing is getting hot an needs to cool, I have had coils do that, run great then just quite, let them cool an they will work again, I hav also had the brain box on the side of the fender with Ford duraspark ignitions do the same.yes on the voltage readings at coil that Is normal there is a resistor wire in the system that lowers V so as not to burn up coil, however the system you have does it reguire a full 12v if so that could be the problem. If that system needs 12v all the time then use the coil wire to trigger a relay to get full voltage to the coil

 

[crankman]

Had something close to that happening on my 76 found the 3 prong quick connect off the distributor was dried out and the male spades were working loose. Might check that

 

[MonsterBIlly]

I have had similar, ine timenit was the fuel pump. When it dies and then wont start, remove the fuel line from the carb and crank briefly. If the fuel pump is bad it will not pump during cranking and this will indicate whether or not it is the pump.
Another test, take off the air filter when it dies, look into the carb and see if it squirts fuel while pumping the throttle kever with your hand. If no fuel from the squirters, you know this is the problem. If fuel does squirt, then you can rule out fuel issues.

Another thing. Sometimes disteibutor caps can get tiny hairline cracks which you cannot see. They can load with carbon and short out the spark. When this happens you may get the exact problems you are having. Do you have an extra diatribitor cap you can swap onto it. If not, ot may be possible to look at the cap while cranking in the dark, with a helper, and look for arching.

Abovenit is mentioned that your ignotion system may need 12v all the time. Factory wiring as mentioned, sends 12v to coil at cranking inly, then 9v while running. Make sure your mallory ignition is getting the voltage it needs.
If you can list the part nber for your ignition parts i will look it ip and see if i can see anything. Just because it ran well for a while doesnt mean it wan correct.

 

[Jason72Bronco]

Thanks guys, here is the update:

I'm 99.9% sure it is not fuel related. Fuel pump works when cranked, I can visually see fuel squirt in the carb venturi when I pump the throttle linkage. Everytime I check the carb bowl levels, they have fuel. Even with a bad pump, the carb would work until the bowls emptied, correct?

I do not believe it is heat related. Sometimes it starts cold, sometimes not. When it does start and run for a period of a few minutes, the temps get up to normal (190 degrees) and it still will die, and won't restart. Again, not heat/cool dependent.

Also, when it does start, sometimes it will run for a few minutes and it will let me check around on things, blip the throttle, drive, etc. Sometimes it only runs for about 20 seconds.

My coil is a new Mallory Promaster Classic Series #29440. Attached to its (+) post is the pink/reddish resistance wire coming from the ignition switch, which reads 12v when key is turned to "start." This coil can accept the resisted voltage of this Ford as specified in the manual. https://documents.holley.com/frm34163_29440.pdf. Further, this is the same wire from the ignition switch that has fed a coil on this truck for decades. (The prior coil was also a Mallory Promaster connected the same way...the only reason I replaced it was because it was at least 30 years old.)

The coil is feeding a Mallory Unilte electronic distributor (#3755101) with a Mallory specified connector (#29349). Inspection under the cap and the rotor show no signs of cracking or arcing.

Today:
I had some suspicions about the wiring job by a PO from the coil to the Suntune tach mounted on the steering column. The wiring job was an amateur job at best, but it had worked for decades. In any event, I removed all of that bad wiring to eliminate that as a possilble issue, and to sleep better at night. No change. (Tip: If you are installing aftermarket accessories on your Bronco, please AT LEAST use red wire for positive and black for negative. Your subsequent owners will either thank you or curse you based on your wiring skills today.)

I replaced the ignition solenoid. No change. (After changing it, it started. False hope, it died not too long after that.)

I added another ground from (-) strap to the bolt grounding the voltage regulator. Nada.

I decided to go old school, and I fabbed up a remote switch to actuate the starter solenoid. I pulled a plug, reattached the plug wire and held the plug end against a ground. Turned ignition to start position, and used the remote to actuate the starter solenoid. Crank, crank..no spark. Several tries. No spark. (I'm guessing when I finish typing this I will go back out to the garage and it will start and spark!)

Anyway, still stumped. Next, I guess I will pull the key/ignition switch and check all of that, although by using the remote starter I would think that eliminated the ignition switch as an issue. And keep checking more old wiring and connections.

Finally, a question if you know: on the wiring diagram it shows a violet wire attached to Ignition/key switch that is activated only when key is turned to "start". This wire goes to a "Dual Brake Warning Sw." After the switch it connects (somewhere) to the green/red wire that eventually goes to the voltage regulator....and is also connected at the ignition switch at the same place as the pink wire that goes to the coil! So, other than at the ignition switch, where does this purple wire route? I'm curious, because since it does actually connect up with the VR wire and the coil wire, it's possible that some kind of short/ground in the purple wire is my problem. I can find it, but any advice on a head start would be appreciated.

Also, any other thoughts...I'm all ears.

 

[gr8scott]

Try attaching a jumper wire from battery + to coil + and see if it stays running.

 

[AC932]

That purple wire should run down to the brake distribution block, where it goes to a switch that connects the brake warning light on your dash to ground when more fluid flows to the font/back than normal (I'm pretty sure it's ground side switched?). When you turn your ignition to start, it should light up as a test, then turn off.

These switches nearly always ended up stuck closed and so many unplugged them to turn the light off. That meant they were technically shorted to ground anyway. When I got around to re-wiring mine, it was broken in that way as well.

That was a really long way of saying that a short to ground on the purple wire shouldn't be the cause of your issue.

 

[Mike Bryan]

I too had duraspark issues, truck would run great, then for no reason, would die. Turned out my unwrapped header were generating too much under hood heat, note the bronco hood sits tight to engine bay. I moved my duraspark to inside the cab, and no more problems.

 

[Jason72Bronco]

Thanks for the replies. I will check these tomorrow.

I've already tried with an extra 12v(+) wire to the (+) terminal on coil to try and start it, but not to see if it would run if I just use the jumper. (First I have to find it in the "right mood" to run so I can try it.)

The purple wire was just a thought, since it does eventually come to join the others. But, I think you are right, the switch looks to be a ground-based switch on the diagram.

Finally, I've experienced a variety of heat soak issues with proximity to headers on other vehicles (mostly starters too close and need a heat shield), so I know that can be an issue. However, my mystery problem crops up whether the engine is cold or fully hot. Also, my coil is pretty far from the headers, and I'm doing most of this testing with the hood open and its 60 degrees outside. I wish it was that simple.

I'm waiting for one of you to suggest a bad sending "eye" on the electronic distributor. Actually, I'm dreading that, because it would mean replacing the whole distributor. As far as I can tell the "eye" is not serviceable separate from the whole distributor. It looks fine, but something may be up with the circuitry. I don't really know how to test it.

Thanks, Jason

 

[Broncobowsher]

It sounds like you are on the right track.
Couple more things I will put out/ask.

When it is running and dies, is it a sputter and die or instant death?
Do you have a tach? When it is running, does it read anything while cranking the engine? What I want to know is if when things are good will the tach read anything? You might have to do something like a flooded start when not flooded to get the engine to crank but not start to check.
Why do I want to know this? so when it is in it's mood look at the tach and if it now doesn't read (and it did when it was happy) you know you are looking at an ignition problem.

Here is one from the boat people. Unhook the tach at the coil when it is in a bad mood. The tach could be grounding out the ignition.

 

[knack]

I had what sounds like the same symptoms going on for a long time. Very random & hard to troubleshoot. Turned out to be a bad wire between the ballast resistor(doesn't sound like you're using one) and the coil. Wire passed enough current to operate a volt-ohmmeter, but would sometimes create an open circuit and not power the coil. Finally, the wire degraded enough to fail completely and I was able to figure out the problem. If I bent the wire harness a bit it the truck would run, bend it back and it would die.
Might be worth a jumper wire for a while just to see what happens.

 

[Boss Hugg]

Without reading all the previous responses, I'll add in that when it dies/does not fire up, pull a spark wire and observe the spark/no spark while trying to start the engine. If no spark, you know it's ignition.

And BTW, I've seen enough people have trouble with aftermarket ignitions that I just don't trust these high dollar systems like MSD and Mallory. I guess they have to be worth something, but all too often I see them causing unnecessary problems. I ran a Pertronix ignitor 2 module in my OEM distributor and the only problem I had with it is when I left the battery charger hooked up (on high) and the ign switch on over night. I was doing a new "EZ wiring" universal harness and I only got to work on the thing every now and then, but I'd go out in the shop and smell electrical fire. I was afraid my "shouse" was trying to burn down for several days before I traced the smell to the reason the engine wouldn't crank.... I may have posted pics here before.

But I digress! Good luck with the diagnosis.

 

[Jason72Bronco]

Thank you for all of the responses. After a ton of testing and thinking, I did finally find the problem:

Short Answer: Bad Mallory Unilite Distributor (six months old)

Longer Answer, if you care to learn:
Quickly, some replies, yes my tach was working when it was running, both in the vehicle and with timing gun. I'm not using a ballast, I'm relying upon the stock pink/reddish resistance wire from the ignition switch to the coil (more on that later.) As previously mentioned, I ruled out any fuel issue a while back.

After my last post I decided to take Gr8Scott's advice about jumping to the coil and expand on it. More and more I was suspecting a short of some kind somewhere in the wiring system that I could not replicate. I wanted to completely eliminate the entire wiring system on the truck and work backward from there to find the culprit.

So, I removed the starter "S" wire and ignition"I" wires from the starter solenoid. I removed the alternator wire as well. So, all that is left on the solenoid are the cable from the battery on one side, and a cable to the starter on the other. I then removed the stock resistance starter wire from the ignition switch at the (+) terminal on coil.

Then, I fabbed up a "self-contained" start/run switch. I ran a wire from battery (+) to an on/off switch that then ran 2 wires, one to the (+) terminal of the coil and one to the "I" terminal of the starter solenoid. In effect, this switch will replicate having key in the "run" position.

I also ran a wire from the battery (+) to a momentary on/off switch, then to the "S" terminal of the starter solenoid. This replicates the "start" position of the ignition switch.

The coil to distributor connections stayed as normal.

This setup would allow me to start and run the vehicle with zero of the wiring in the truck. No wires to voltage regulator, alternator, horn,...nothing. (and yes, I know that it will be running only off the battery while I do this.)

Truck would not fire. Pulled spark plug, no spark. Changed coil, no spark.
Down to one last thing: something at the distributor. The unit is six months old, and everything looks fine. But I pulled the distributor, put the old one in, and she fired right up. Ran for a while under my setup, everything fine. Removed my setup and hooked everything back up to the way it was before all of this began (except for the distributor) and took a ride around for 30 minutes. Ran perfect, and I hadn't even re-checked the timing yet. Let it sit overnight, fired right up and ran.

Over the years I have had my share of "new" parts be bad off-the-shelf, from master cylinders to alternators. But I guess I can add this distributor to the list. It lasted six months. The 30+ year old one of the exact same model that I took off the shelf, dusted it off, and swapped back in is still churning.

I researched this distributor unit, and apparently it is very sensitive to having either a ballast resistor or a resistance wire. I have always used the resistance wire, but maybe it is not "resisting" enough. (Not sure how to measure the correct resistance on my MM) It could just be a bad distributor unit, but I don't won't to install a new one if there is someone I'm doing that caused it.

So, question if you know. Would it be okay to add a ballast resistor on the wire from the ignition to coil (+), even though it is already a resistance wire? (This electron math exceeds my knowledge.)

Thanks again for the responses.
Jason

 

[jagbucket]

There is a inline spark tester that is an easy way to check when in no start mode.

 

[Mike Bryan]

Second the thought about boat guys, as I am one of those. My correct craft Ski Nautique would be running great, then just die for no reason. New distributor, plug wires, plugs, nothing helped. It would always die while we were out,and needed to be towed in. Well, after checking every ground, and everything else, come to find out it was my wire from the tach grounding in the dash plug. I undid the tach wire from the coil, and presto, runs great. I just bypassed the plug with a new wire. All is good. I would rather the rods be hanging out the side of the block than deal with this kind of stuff. At least I’ll know what’s wrong.

 

[DirtDonk]

...So, question if you know. Would it be okay to add a ballast resistor on the wire from the ignition to coil (+), even though it is already a resistance wire? (This electron math exceeds my knowledge.)

Kind'a makes your brain hurt sometimes, eh? I know it does mine!
In theory it's possible to do what you ask, but you'd want to know the total resistance, which I think is just adding the two values together. As opposed to doing some tricky-math. But I could be wrong.

But if your wire is even remotely near what it used to be, a new regular ballast resistor would probably be too much additional resistance. Bringing your voltage much farther down than would be called for.
I think 'bowsher or Viperwolf or Steve83 (as well as many others) will know what to do in this case.
It might come down to you replacing the resistor wire with a regular wire before running it through a ballast resistor.

Do you have a link to the current Mallory instructions? I always found them very vague (to me at least) on whether the Unilite with a particular coil needed a resistor or not. I used to think it depended on the coil used, and the Unilite could handle the higher voltage at that point. But years of Unilite failures have left me doubting.

Paul

 

[Skytrooper15]

If it is still running with the old mallory distributor I wouldn't do anything else to your Bronco and if you add another resistor inline with the stock one it will drop the voltage more if not too much.Hope this helps.

 

[DirtDonk]

Oh, to what I was saying about resistance, you would do well to measure both the resistance of your existing resistor wire, and the voltage that is reaching the coil.

Is your Unilite utilizing the same power lead directly from the coil?
With the old unit it place and the engine running for a few minutes, measure voltage at the wire and see what you find.

Paul

 

[Seventee]

I had a similar issue years ago. The culprit ended up being the "Extra Performance" Duraspark II ignition module I got from Ford Racing. It was manufactured by MSD. %)

After that maddening experience, I decided to just say no to aftermarket ignitions. Although I've heard much better things about Mallory.

 

[DirtDonk]

Very interesting. I had (still have actually) that same module and it worked great for awhile until I swapped it out for an MSD Timing Control version.
But it worked great while I had it. Sorry you ended up with a bad one. You're certainly not alone though, regarding the relatively sad state of aftermarket stuff!

Probably more stories of bad Mallory stuff though, even than the "dreaded" MSD stuff.%)
I've been lucky with both (and with Pertronix too) so far.

Paul