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Hello,

 

I hope that somebody can give me some advice about the following:

 

Mine car (shelby GT 2007 Automatic) has some trouble with cold start up.

It cranks but has trouble to start at once.

 

When the motor is hot there is no issue.

 

We replaced battery and spark plugs.

And the PCM tells that the fuel pressure is OK.

 

The PCM gives measurement of an AAT ( air ambient temperature) sensor.

What is its function?

 

it gives -20C

 

Maybe i am searching the wrong way.

So any help is much appreciated.

 

Kind regards,

 

Marc (from the Netherlands)

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Marc, if your AAT sensor is reading -20C when the temperature is not actually that cold, that could be your issue. It causes an incorrect calculation in the computer for the air/fuel ratios. If i remember right, the sensor is part of the MAF (Mass Air Flow) sensor. I would check your wiring to be sure of no damage, if it's ok then i would probably start with replacing that sensor.

 

Hope that helps and keep us informed if it fixes it or not.

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Marc, if your AAT sensor is reading -20C when the temperature is not actually that cold, that could be your issue. It causes an incorrect calculation in the computer for the air/fuel ratios. If i remember right, the sensor is part of the MAF (Mass Air Flow) sensor. I would check your wiring to be sure of no damage, if it's ok then i would probably start with replacing that sensor.

 

Hope that helps and keep us informed if it fixes it or not.

 

-20C is showing a disconnected sensor or open circuit (possible bad sensor). That's the coldest temp the ambient temp sensor is able to sense.

 

 

Phill

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If my memory serves, when there is an open circuit or a temp sensor is unplugged, it will read as -40 degrees. I could be wrong, but my 13 years of ford technician experience is telling me that is right. Either way, check the wiring first before replacing the sensor.

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If my memory serves, when there is an open circuit or a temp sensor is unplugged, it will read as -40 degrees.

 

I was thinking that's what -20C is but I could be off a decimal point.

 

I'm 'old school' and don't do metric so well!

 

 

 

Phill

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I spoke with the ford racing tech hotline, they said it is the stock sensor that comes in any mustang gt for '07. I didn't get a part number, but i hope that will help enough to get you in the right direction.

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Hi all,

 

We are still searching for a solution for the problem:

 

If the car is standing for longer than a couple of hours it has the following issue:

 

When starting it cranks, but has trouble to start.

You can smell the fuel at the back of the car.

But no error codes in display.

 

When it has started and I leave it for maybe a hour standing still without starting it has no trouble starting.

 

Next week the garage will do a fuel pressure test.

But maybe you can help me with some advice about this issue?

 

Kind regards,

 

Marc

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Hi all,

 

We are still searching for a solution for the problem:

 

If the car is standing for longer than a couple of hours it has the following issue:

 

When starting it cranks, but has trouble to start.

You can smell the fuel at the back of the car.

But no error codes in display.

 

When it has started and I leave it for maybe a hour standing still without starting it has no trouble starting.

 

Next week the garage will do a fuel pressure test.

But maybe you can help me with some advice about this issue?

 

Kind regards,

 

Marc

 

These are classic symptoms of a leaking fuel injector or leaking fuel injectors.

 

Connect a fuel pressure gauge to the fuel rail, charge the rail and then shut it down. It should HOLD pressure (*easily* for the hour you note).

 

If the pressure leaks down (over the same hour), you have a leaking or multiple leaking fuel injectors.

 

Get yourself a can of Chevron Techron/Techroline and run it through a full tank of gas. If that doesn't help, have a professional fuel injector cleaning performed. If that doesn't STOP it, diagnose which injector/s is/are leaking and replace it/them.

 

 

 

Phill

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Hi,

 

We did the test.

 

And pressure was not going down in 6 hours we tested it.

 

When it we crank it the pressure is 400kpa. That's OK right?

 

So we can eliminate: fuel pomp, fuel injectors.

 

I have no error codes.

But when we hook it up to scanner we see some misfires.

 

Cold start is still not doing well.

smell like fuel at the back.

 

So you would say to much fuel or no sparks.

 

Any advice would be great!

 

 

Marc

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Hi,

 

We did the test.

 

And pressure was not going down in 6 hours we tested it.

 

When it we crank it the pressure is 400kpa. That's OK right?

 

So we can eliminate: fuel pomp, fuel injectors.

 

I have no error codes.

But when we hook it up to scanner we see some misfires.

 

Cold start is still not doing well.

smell like fuel at the back.

 

So you would say to much fuel or no sparks.

 

Any advice would be great!

 

 

Marc

 

Misfires could be from a bad coil pack or plug, I would switch the coil packs on the cylinders that were misfiring and see if they misfire moves to the cylinder it was changed to. if it does then your prob is the coil pack, if not then it could be a plug, or worse it could be the computer going bad and not sending the signal to fire on that cylinder randomly. I had the cpu go bad on a older ford with the 4.6 and it did something along the same lines. It was very old though.

 

The fuel smell from the misfires sounds about right. It'll build up and and that's your outcome. You smell it in the back cause it's working it's way through the exhaust, that is very bad for the cats.

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Misfires could be from a bad coil pack or plug, I would switch the coil packs on the cylinders that were misfiring and see if they misfire moves to the cylinder it was changed to. if it does then your prob is the coil pack, if not then it could be a plug, or worse it could be the computer going bad and not sending the signal to fire on that cylinder randomly. I had the cpu go bad on a older ford with the 4.6 and it did something along the same lines. It was very old though.

 

The fuel smell from the misfires sounds about right. It'll build up and and that's your outcome. You smell it in the back cause it's working it's way through the exhaust, that is very bad for the cats.

 

Yeah, I agree with all of the above. The raw fuel in Cats isn't bad though, it's the result of the raw fuel in built up in the CAT/s. Heat. Which really shouldn't be a problem if your misfire goes away once it's started.

 

Does it (go away)?

 

What is 400kpa in PSI? I'm not a metric guy, give it to me in SAE. The fact that it doesn't bleed down does tell me your injectors are good AND your fuel pump check valve is good.

 

The raw fuel smell out of the exhaust indicates a excess of fuel but you'll get the same thing with a lack of spark. Are you getting (good) spark under CRANKING???

 

 

Phill

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  • 2 weeks later...

 

Yeah, I agree with all of the above. The raw fuel in Cats isn't bad though, it's the result of the raw fuel in built up in the CAT/s. Heat. Which really shouldn't be a problem if your misfire goes away once it's started.

 

Does it (go away)?

 

What is 400kpa in PSI? I'm not a metric guy, give it to me in SAE. The fact that it doesn't bleed down does tell me your injectors are good AND your fuel pump check valve is good.

 

The raw fuel smell out of the exhaust indicates a excess of fuel but you'll get the same thing with a lack of spark. Are you getting (good) spark under CRANKING???

 

 

Phill

 

Hi Phill,

 

400kpa = 58.0150951 Psi

 

We have swapped the following for a new replacement:

 

-Fuel pressure transmitter on fuel rail

-MAF sensor

 

The AAT temperature is OK now.

But still having hard cold starts with a lot of gas using.

Back is smelling from gas.

 

So it must be in the sparks right?

Only i find it strange when the car is standing a couple of hours it will start with a loud growl.

And when it is standing for more than 6 hours it sound like it is flooded.

 

Again any advice is really appreciated!!

 

Kind regards,

 

Marc

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Hi all,

 

 

Do any of you know which sensor are involved in the cold start procedure?

 

Because it looks that the PCM is getting the wrong readings and thinks it needs more fuel.

So we are searching in the sensor section.

 

Any thoughts?

 

 

Marc

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Hi all,

 

 

Do any of you know which sensor are involved in the cold start procedure?

 

Because it looks that the PCM is getting the wrong readings and thinks it needs more fuel.

So we are searching in the sensor section.

 

Any thoughts?

 

 

Marc

#1: Engine Temperature Coolent Sensor (ECT). Am in my cell phone while out of town, can't be of more help for now.

 

Phill

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  • 2 weeks later...

OK thanks!

 

Could it lose a tune?

 

marc

 

Not unless someone over wrote/reprogrammed the tune with a programmer, usually a handheld device. Not sure who is working on your car (garage/dealer) but someone who doesn't have knowledge of these vehicles could easily unknowingly overwrite the tune trying to fix something. It probably wouldn't run with the stock mustang tune though, so I wouldn't guess that is the issue, It would be way more than the Ambient air temperature sensor issue.

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Not unless someone over wrote/reprogrammed the tune with a programmer, usually a handheld device. Not sure who is working on your car (garage/dealer) but someone who doesn't have knowledge of these vehicles could easily unknowingly overwrite the tune trying to fix something. It probably wouldn't run with the stock mustang tune though, so I wouldn't guess that is the issue, It would be way more than the Ambient air temperature sensor issue.

 

Thanks My Blue haven!

 

I think we got something here.

I will check if i can find a tuner in the Netherlands.

 

Have a nice day!

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  • 4 weeks later...

Hi all,

 

Please excuse me for the late reply.

But i had be sure that we find the solution.

 

It looks like it was the battery.

I placed a new battery and some amplifiers for the audio upgrade at the same time.

The battery is upgraded van 50 ah to 90 ah.

 

I drive short trips to the office and back.

So in this time the battery never gets even close to full.

 

So the starter motor isn't getting enough power.

And the motor is turning normal at this moment.

there for getting to much fuel.

 

So a bigger alternator would be the solution for this.

 

Thank you all for helping!!

I really appreciated the effort you made by replying me.

 

Have Great day!!

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