Car won't start

[Red35thGT]

I hardly ever drive the car, I went and picked it up yesterday from my grandparents garage and Had no issues with it other than the normal cold natured starting. I drove the car back to my house (abotu 17 miles) and the car ran fine. I parked the car, went in the house to take a shower. Came back outside to get in the car and go out, and it wouldn't run. It will start as soon as you hit the key, but then it just dies immediately. The message screen on the car is showing "failsafe engine mode" When I run the DTC, I get P0421 which is Warm Up Catalyst Efficiency Below Threshold (bank1). Anybody have any suggestions on what it may be? I'm thinking maybe Mass Air Meter or Throttle Bodies, but I hate to go spend money on these without knowing if thats what it really is or not.

 

[no_slow_svt]

disconnect the wiring to the maf and see if it runs

 

[Red35thGT]

Tried disconnecting the MAF and it still won't run.

 

[no_slow_svt]

bad gas?

 

[no_slow_svt]

is it back firing or stumbling or anything else.
it just dies?

u checked all your fluid levels right? does that look normal?
it will be very had to internet trouble shoot your car.
give us as much detail as possible.

have you tryed giving it gas on start up?

 

[Red35thGT]

The car starts up just like everything is normal. It idles up immediately like all fuel injected cars do, but when the rpms fall back to idle, it just dies. It does nothing if I press on the gas pedal. first thing I checked was the fluids. They are all where they need to be. I realize that its next to impossible to diagnose over the internet, but I was just wondering if anybody had experienced similar problems or symptoms. I have checked to see if the TB is opening with the ignition on when I press the pedal and it does not. I don't know if the engine has to be running or not to move the blades in the TB, but I guess thats my next issue to investigate. I need to find someone with a 05 or newer mustang to check theirs and tell me. I have a few friends with the DBW/TBW cars, so I'm going to call them and see what they have to say.

I appreciate you guys brainstorming with me. I have checked voltage to the TPS and it is getting voltage, but obviously it doesn't increase or decrease if the TB doesn't open. I'm leaning towards the fact that maybe the drive motor on the TB has failed. I guess if all else fails, I'll load this overpriced, obese, car on a trailor and carry it to the stealership.

 

[03 Whippled Cobra]

Sounds like the TB is the issue. If your blades aren't opening then your engine isn't getting any air and it will starve itself out and die.

Any updates on this?

 

[Red35thGT]

update.....

I tested the tb for voltage and it isn't getting any voltage to it. MAF and TPS are fine, I went to Ford and talked to a few of the service guys and they told me that a bad O2 sesor could cause this. Ford said that there are numerous items that send reference voltage to the TB. Being as the only code that I'm getting on this car is in reference to the Bank one Catalyst sensor they suggested that I unplug it and see if the car would start. They said that these computers are very complex and if one system fails, that it will ignore that sensor and start reading another sensor to get the car to run in "limp" mode. For instance, if the TPS were to go out, the car would realize that it isn't getting signal from the TPS and it would start looking at the MAF to make its decisions on throttle. It will compare the amount of air coming through the MAF and the rpm's and use that to figure out where the throttle position is doing since the TPS has failed.

Anyway, back onto my issue. They suggested unplugging the O2 sensor since its showing a problem with it. Unpluggin it would make the computer use bank 2 sensor to make all the fuel adjustments it needs to. That in turn should make the car run if its just a fouled O2 sensor. Well, I came home and unplugged it, and it still won't start. Needless to say, I'm stumped on this one. They seem to think that its going to be something very simple such as a bad sensor somewhere. On intial start up, the car has signal to the TB, but after the rpms come up, it falls off. On start up, the computer sends the voltage to the sensor to open the TB since none of the sensors are operating to send it. Immediately when the car starts to build rpm's and all the sensors and monotoring systems come alive, the computer kills the signal to the TB and depends on various sensors and meters throughout the car to deliver a reference signal to the TB instead. Obviously, its not getting that reference signal. I can manually open the blades of the TB when someone cranks the car, and it will run as long as I am manually manipulating the throttle. So, I guess my next step is to start finding out what all sends reference signal to the TB and just start testing those. I'm gonna try to do this without getting frustrated and taking it to Ford. I just hate to pay them to do something that I can do myself. The part that makes me mad is that there is usually NOTHING that I can't fix on my cars. It may take me a while, and lots of studying and internet surfing to figure it out, but I always seem to do it. I'm starting to realize that I might have just stumbled across something that I can't do. lol. If I don't get it going soon, I'll just suck up and load it onto a trailor to deliver to Ford.

 

[theHumP]

catylist efficiency below threshold means that your cat may be bad, or something is messed up between the signal of the front and rear 02 sensor on that side, and the ecu thinks your cat is bad. Do you have stock exhaust? Do you have a programmer? Have you messed with anything? If you have a programmer, try turning the rear O2s off.

 

[Red35thGT]

Turns out that the throttle position sensor was bad afterall. It was a simple replacement and simple fix.

 

[SLOW95]

Good to hear man bet your happy.