OSUjustin313

I am about to give up. I have a 1999 ford mustang V8 GT that keeps randomly shutting off. It will be a mile, sometimes 30, sometimes 50, but it always does it. Here's the story and a few tips about going to the dealership.

I noticed my car did not lock properly one day: it would beep twice instead of once. then, the dome lights would not turn off, so I had to switch them into the center position to trip them. I didn't think anything of it, but then my A/C and heater stopped working. Next, the car started stalling when I hit the brakes. After, that , it would inermittently hesitate. Then, eventually, got to a point where it would backfire once in a while and hesitate and die. It would start right back up at first but, over time, would only crank but not catch. I took it to the dealership in Columbus, OH who told me it was the IAC and they cleaned the induction system. I was very skeptical. I picked it up and drove it around a little, but it put out a code for IAC (it never actually had a code before, which is why I was skeptical). I took it to a friend and mustang enthusiast. On the way there (after 30 miles), the car put out a code for IAC, injectors not firing, and fuel pump. After checking the schematic, I noticed the CCRM may be bad: I replaced it for $50 but that has not fixed the issue...took it back out on the road to troubleshoot and the ignition cut out again and the anti theft prevented it from starting back up...had to wait a while and limp it home. This has been going on for 3 months now, and I do not know if it is the ECM, CPU, anti-theft, wiring, harness, coil pack, or whatever else....any help would be appreciated.

wmfateam

Do you know anyone who works at a ford dealer who can scan your car with a ford scan tool system? That's where I would start. Generic scanners can only read so much.

MustangVixenGT

Could be electronics shorting due to water leaks.

Or is the control box that controls the electronic ignition is overheating. This will cause a car to just randomly shut off cause of well outside temp differences have them check that.

Fryguy22

Sounds like an electrical issue. Take a good look at your harness and control box.

BMWiduch

You have an electrical issue my friend. Your problem is going to be somewhere between the computer leading up to your engine harness... It sounds like you have a wire that might be grounding out on the body or could just be burned out. I would definitely recommend taking it to a Ford Specialty Shop such as Crown Ford. I know down here in Tennessee, when ever we get electrical problems, we test every last wire that fits the problem, we hook it up to a computer scanner, and we also do a complete update to your PCM.

OSUjustin313

thank you for the feedback on everything. It is very appreciated...

I'm hesitant to take it to the dealership because they ripped me off big time last time I went there...they claimed it was caused by the induction system and tried to charge $400 to clean it.
Right now, I have it parked at a friends who is looking into the wiring: He thinks its the security system sending signals to shut off: But, it is intriguing to note that this problem seems to be heat related: when its warm or when the car heats up, thats when I have the first signs of trouble. I also cannot keep pouring money into this car...This issue alone has already cost me around $1,000.

Either way, I will take a look at the wiring harness and re-check the grounds and the rest of the electrical system...first time I did, it was dark out so a good chance I missed something. Thanks again guys.

MustangVixenGT

Right there when you said heat related, makes me think electronic control box. My 72 Mustang had that issue when its box was going bad. It would overheat and just shut off, I am pretty sure its not your security system. It's just going to get worse and worse till the box completely fries.

Stevo86

The "electronic control box" that made your '72 run is not even remotely similar to the ignition system on a '99 just so you know.

OP as far as your issue goes, it could be PATS related but that is usually a crank no start kinda situation. I could also hazard a guess at the crankshaft sensor intermittently not working. You really could use some freeze frame data from when it happens to compare the crank signal and cam signal right before it shuts off.

However, your host of other electrical issues could lead to the junction box (maybe the fuse panel under the dash but probably not) under the hood. It's possible you have some seriously bad grounds in there.

If you know someone who can disable PATS with their handheld tuner you can also have them do that to their car and swap in their known good PCM to see if that fixes it.

Electrical issues can be frustrating for sure, good luck man.

MustangVixenGT

My 72 hard all electronic with and msd system not exactly the same but it was not stock with relays if thats what you were thinking. So yeah it did have an electronic control box...

Stevo86

Your MSD box simply turned a points system into a points system with multiple spark discharge (hence MSD) and provided a hotter spark. In other words it fired the spark plugs more than once per ignition cycle and did so with more voltage. It probably also provided a rev limiter for a vehicle that otherwise wouldn't have had one. It may have even had the capability to electronically advance the timing after base timing was set.

However, you still had a distributor that was ultimately responsible for completing the ignition circuit and firing the single ignition coil by providing a path to ground (the spark plug). In a modern car with a distributorless coil on plug ignition system the PCM provides all the brains of the operation. It fires the individual coils by interrupting the ground side of the coil circuit.

So yes it did have an "electronic control box" but the fact that both ignition systems had electric components is about where the similarities end. Check out howstuffworks.com and learn how some of the newer stuff works. That website is awesome.