Engine Engine Stalls with AC on 2007 Mustang GT 4.6L

WildFire07

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Jul 9, 2019
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I am having a weird issue on my 07 Mustang GT, 4.6L, 5 Speed. In first gear the car stutters and tries to stall with AC on. I have changed the fuel filter twice, the sending unit works when it wants. The malfunction of the sending unit does not correspond with the fuel issue. I started to notice some hesitation in 1st without the AC on. I am going to change the filter one more time, but I am suspecting the fuel pump. Regulator is good according to OBD reader.
 
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WildFire07

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No Fault codes. Just dies. Throttle body is new and the Stang was doing it before the change. Brenspeed tune didn't make any difference neither.
 

Onesick99GT

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Nov 20, 2018
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@WildFire07 Any high pitched whistling noise coming from under the hood? Does it buck at all under throttle. When did the issue start? How long has it been doing it for. Interior dash have any issues like RPMS bouncing, speedometer not working, odometer not displaying, ect ect. Did you load a tune on there? replace any parts recently. I need to know all of this to better assist.
 

WildFire07

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Jul 9, 2019
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@WildFire07 Any high pitched whistling noise coming from under the hood? Does it buck at all under throttle. When did the issue start? How long has it been doing it for. Interior dash have any issues like RPMS bouncing, speedometer not working, odometer not displaying, ect ect. Did you load a tune on there? replace any parts recently. I need to know all of this to better assist.
No High pitched whistling, No bucking with the exemption of the Mutha Thumpers, Gauges are fine, Have gotten Bren speed to rewrite program to see if that was the issue. As far as parts, changed the throttle body and had the control box under the hood replaced and reprogrammed by Ford. The problem was there before any of that. Changed fuel filters, changing fuel pump this weekend.
 

Onesick99GT

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Nov 20, 2018
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Did you adjust your throttle body and go through the procedure of calibrating it. Less air means it will stall under load. More load you need more air. If the throttle plate is completely closed your IAC is probably struggling to give your motor enough air to combust.
 

Onesick99GT

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Nov 20, 2018
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You cant buy a throttle body slap it on there and expect it to run like the factory installed one. A tune wont fix it either. It take air, fuel and spark to properly make a car run. The PCM makes necessary adjustments to hold idle under load but if the car is not right mechanically, like a throttle body being completely closed the pcm might not be able to have enough adjustment to compensate for it. Make sense!
 

WildFire07

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Jul 9, 2019
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Did you adjust your throttle body and go through the procedure of calibrating it. Less air means it will stall under load. More load you need more air. If the throttle plate is completely closed your IAC is probably struggling to give your motor enough air to combust.
It was stalling before I put the new throttle body on
 

WildFire07

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Jul 9, 2019
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You cant buy a throttle body slap it on there and expect it to run like the factory installed one. A tune wont fix it either. It take air, fuel and spark to properly make a car run. The PCM makes necessary adjustments to hold idle under load but if the car is not right mechanically, like a throttle body being completely closed the pcm might not be able to have enough adjustment to compensate for it. Make sense!
It would make sense if the car was acting different before i put another Ford Throttle body on and get procedures from Ford performace on what to do.
 

Onesick99GT

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Ok that's good were ruling stuff out. I had a similar issue with my gt that was stalling under load, like turning a corner in first gear coming to low rpms in 1st, and second gear. It also idled extremely low at start sometimes stalling. Have you had your battery tested and alternator tested? I would rule both of those out.
 

Onesick99GT

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Nov 20, 2018
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When turning on your ac it draws current which would pull power and put load on your car potentially stalling it. Could be a bad battery or even a failing alternator. Check your ground connections on your battery terminals. I had one of my ground terminals crack and didn't realize it until I put a wrench on the nut lossened it up and noticed it was half broke under inspection. My car would randomly stall. Sometimes it would just dim the headlights because the connection wasn't good.
 

WildFire07

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Jul 9, 2019
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When turning on your ac it draws current which would pull power and put load on your car potentially stalling it. Could be a bad battery or even a failing alternator. Check your ground connections on your battery terminals. I had one of my ground terminals crack and didn't realize it until I put a wrench on the nut lossened it up and noticed it was half broke under inspection. My car would randomly stall. Sometimes it would just dim the headlights because the connection wasn't good.
I have checked these things with a meter and gauges, as well as obd reader. Grounds are a pain, but i learned my lesson when one worked loose and blew the battery up on my wife's car. The stuttering is happening without AC on as well. Also at very high speed, fuel pressure has a serious drop during these moments according to OBD reader. I am going to try a fuel pump that I lucked up on for $50 with a one year warranty.
 

Onesick99GT

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Nov 20, 2018
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It does sound like a failing fuel pump. I've had the same thing happen on a ford ranger of mine years ago. When I would hit the gas peddle it would stutter, hesitate then continue to go. Replacing the fuel pump will probably fix it. Make sure to replace the fuel filter at the same time.
 

WildFire07

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Jul 9, 2019
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It does sound like a failing fuel pump. I've had the same thing happen on a ford ranger of mine years ago. When I would hit the gas peddle it would stutter, hesitate then continue to go. Replacing the fuel pump will probably fix it. Make sure to replace the fuel filter at the same time.
Before everyone goes the Junkyard keeps saying something about a booster pump. What are they talking about?
 

Onesick99GT

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Nov 20, 2018
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You can technically increase your current fuel pumps output by using a booster pump. Its like a turbo for a car. Increases the pressure. No need for you to get one unless your pushing crazy numbers and needing that extra fuel pressure. Like 800 horses and your current fuel pump isn't cutting it. So people buy a booster pump to increase the pressure to the fuel injectors. Make sense!
 

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