Strangest Problem in the World

03blackvert

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My father has a 2013 Mustang GT that has what I describe as the strangest problem in the world. We've had two dealerships and about 5 techs look at it and no one can diagnose the issue. I'm hoping some of the brains on here can maybe give some ideas, tips, or tricks.

The symptom is simple. Won't start. Put the key in, turn it, and nothing. No noise, no trying to start. The dash comes on as you pass "on" of course, but then moving the key to start does nothing. This happens randomly. It will go 2-3 weeks without doing it, and then it will do it 3 times in a row.

First thought, clutch position sensor. That was replaced a long time ago, the switch on the pedal, no change.

From there, it gets weird. When this happens putting a "jump start pack" on the car will usually (but not always) make it start. Now, the battery tests 100%, and we've checked the voltage with a meter it's right where it should be. But somehow the jump start pack makes the difference.

It also push-starts fine. Push it down a hill, pop the clutch, off it goes. When this happens you can immediately shut it off and restart it with the key normally 100% of the time.

Second thought, dealer found a bunch of codes as if someone had tried to start it with the wrong key. They reprogrammed both keys (at a discounted rate, nice of them) to see if that made any difference. Nope, happened with both keys since that time.

Of course, having left it with the shops a couple of times now it will never happen when it's in their possession and they can troubleshoot while it's doing it. They seem almost as frustrated as we are with the car!

I'm thinking the anti-theft is likely not the culprit or it wouldn't push-start, since I believe that system kills the spark if the keys are right. I'm actually thinking the most likely cause is a bad electronic part in the ignition system, some sort of failing chip or micro-fractured board. This would explain the jump-pack sometimes fixing it, as it puts out more like 13.5v rather than 12.5 the battery sits at, perhaps just enough to goose it to life. I guess it could be a bad ignition switch or something else though.

But what I really need is ideas here. Obviously we could just start replacing things randomly until we find the issue, but some of them like the main computer are $$$$. I don't know if there's things I could probe with an ODB tool when this happens, or test points to hit with a meter, or anything else that would be useful. How would you further troubleshoot this bizzaro problem?
 

clinton2003

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first think i would check is the output for start from the ignition switch. seems like that contact in the switch could be wearing oddly or something. trick is to be testing voltage while its not working. (also testing voltage to make sure there is some when it is starting)

you could set up an led, or test light, so you can test it that way (wire in a led to the start voltage of the ignition switch and mount it in a visible place) then when you try starting, you can see if it comes on when you start. if the led lights up when you have a no crank, then you need to go further down the circuit, if it does not light up with the no crank, then obviously you found the issue and can replace the ignition switch.
 

FJohnny

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The car that the wife and I use to take our dogs to the dog park, a Toyota SUV, does what you describe from time to time. Hitting the lock and then unlock resets something that we assumed was alarm related and the vehicle works after that. Give that a try next time and maybe you'll get lucky as well.

You can also turn the key in the door to lock and then unlock in case there's some issue with the vehicle's receiver unit for your key fob signal.

Won't fix anything but might keep from getting stuck somewhere.
 

MG0h3

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If the jump pack seems to rectify the problem, I’d look for an electrical issue at the batt. Do a voltage drop test during the failure.

What exactly happens when you go to crank?


Sent from my iPhone using svtperformance.com
 

TaraFirma

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If the jump pack seems to rectify the problem, I’d look for an electrical issue at the batt. Do a voltage drop test during the failure.

What exactly happens when you go to crank?


Sent from my iPhone using svtperformance.com

I'm thinking some anomaly in the battery preventing the car from seeing the voltage it needs to start, but enough to turn the car on. See if you can swap batteries with someone to test out this theory so you don't have to buy one unless it turns out that it is the battery.
 

PhoenixM3

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I’m gonna go with starter switch, Alex.... Relay sounds easier to replace, though and probably cheaper.
 

03blackvert

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We check the battery each time it happens. Voltage is good. Shop took it out and ran some sort of a test on it with their tester, showed perfectly good.

It is the behavior that the jump pack fixes it with what seems to be a good battery that makes us all the most confused.

We're going to replace the relay ($5, why not), and also test at the relay location next time. If there's no signal at the relay that narrows it down to switch or PCM, if there is signal at the relay then it must be the relay or starter motor. Someone also sent me a wiring diagram, I see the starter motor has a second integrated relay which I now wonder about.

We'll also try the key in the door, and the lock unlock idea, see if that makes any difference.

Of course I posted this because it happened again. So we push-started (yay for manuals), turned it off and it started right back with the key. It's started 3 times since perfectly as well. So now we're waiting for the next time it does it to run some more tests.
 

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