7 UP Mustang

My Mustang manual only goes up to 1992, so I cannot check for your year Mustang. I am wondering if it uses a fuel pump regulator, and if you checked the pressure at that point. Also my 90 LX uses a throttle position sensor that tells the computer where the throttle is setting. It sounds like a fuel issue to me. Good luck and hope it is fixed soon.

JC316

I think Crankshaft position sensor. Backfiring usually indicates that the timing is out of whack, especially on a cold car where the gas has no heat source like a hot catalytic converter to ignite it. I had this happen with a geo metro, I changed the oil pan gasket and it wouldn't start, but when it did, it was backfiring through the intake and exhaust, and would run extremely rough. Turned out that the added thickness from the pan gasket caused the sensor to have too much gap and fire at the wrong times. Also, showed no check engine light.

ezking

Heh you guys are thinking exactly what has been going through my mind the past week.

basically my thoughts now are

Fuel pressure
I know its not the fuel pump, but it could be the pressure regulator on the rails, although slim the car should run for longer then a 1second spike to 2k rpms, but still a slight possibility

Air
IAC is what im gonna focus on tomorrow, IAC can explain everything that has happened so far, and would do so without throwing any codes.

PCM
This would also explain it, although this is the last possible route I wanna take.

I've eliminated electrical arcing, or wire problems. It cant be a failing sensor or the car would tell me that a sensors signal is off. I know the PCM is scanning because my OBDII scanner tells me the IM? or w/e codes that are ready and the ones that arent, and the check engine light comes on when you turn the key to on, and everything else acts normal.

A lot of people have pointed to a failing crankshaft position sensor, but I can arc the spark plugs, when your crank position sensor fails to send a signal, the coil packs WILL NOT generate any spark at all, trust me I have tested this ;P

A lot of people have also said camshaft position sensor, but if this sensor sent anything out of normal back to the PCM it would throw a DTC code, even if it was just interference, from something else. Unless the PCM itself was bad, but I dont see how it could fail at just that and still function 100% at doing all the other functions of the car.

So tomorrow im gonna replace the IAC, clean up the TB n plenum a bit, and replace the plugs. I had this engine half torn down 8 months ago, and with 1 coil pack hooked up we accidently turned the key to start and the damn thing ran. It has compression and there are no signs of mechanical interference. This has to be by far one of the most resilient engines I have ever worked on.

IAC can explain everything that has happened soo far, and I have it sitting in my room next to me atm, its pretty gnarly in there, im not 100% on how these ones work though as this is my first time taking one a part, well see if the car reacts any differently tomorrow with a new one.



Thank you, thank you, thank you, for all the information and suggestions, anymore are completely welcome, especially anyone who has had a similar problem. I've never been this stumped before, kind of a reality check eh?

disposablehero27

try fuel filter, easy and cheap, i had an air bubble or something in mine, thing would start, but run rough and shut off pretty quick, the more you started it, the least amount of time it ran, until it ran no more. popped the filter off, looked at it, drained, put back in, ran like new. worth a shot, easy and cheap.