07 4.0 rough start long crank HELP

Mach0ne

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I have a 2007 mustang 4.0L. it was running great then one day I parked it overnight and it wouldn't start at all. Cranks until the battery dies. It has a very slow crank when I first turn the key and only cranks fast when I floor the gas pedal (engine flood mode).

I have luck starting it by flooring the gas with it connected to a jumping vehicle. Then cranking the car with the gas floored until it spins VERY fast, then I let off the gas and it starts up very quick. Once it's running its rough for only a second then it runs completely fine.

I've had the codes scanned and there's nothing wrong with them. Things I've found online to fix were the CHT sensor, but the v6s don't have them. The fuel pump, throttle position sensor, crank position sensor.

I have already replaced the fuel filter, and cleaned the TB.

Any ideas on where to start or how to fix this?? Any help is appreciated
 

wildlifeguy

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I'm not a mechanic, so as with any forum advice, take this for what it is as only a suggestion and tool to help you find the issue. My experience with this engine is only 4 months old, but I by myself have removed it from the car, torn it apart, replaced the heads and all timing components and it is currently running great. My advice is to find someone with a good scanner that knows how to diagnose. You can start throwing parts at it, but will likely spend more money than the diagnosis cost. I guess it could be a sensor, but I would think that it would show a code. Based on your description, it will run fine at all speeds until you shut it off and try again? My amateur first guess is fuel related. Maybe a leaking injector? If you had a scanner that shows misfire count by cylinder, you could see if there is a particular cylinder that is the main culprit. I always like to look at fuel trims when running, it may not apply to your issue, but seems to be a good indicator of what is going on in the engine. Good luck.
 

Mach0ne

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Yes it runs seemingly perfect at all speeds, just has trouble starting no matter how long it's been running. Yesterday I drove it for an hour, parked it, and it still cranked over really slowly, like the battery was dead, but it was at full charge. I will definitely go get a misfire by cylinder check and probably just a diagnosis in general. I scanned it myself using a scanner at my shop, and it read full fuel pressure and all good sensors, but I didn't think to do a misfire check for a bad injector, the car had a Missfire code previously (about a year ago) I changed the plugs and it went away. I'm just not sure with anything since it does for sure sound like a fuel issue, but also has a very very slow crank when the key is first turned
I'm not a mechanic, so as with any forum advice, take this for what it is as only a suggestion and tool to help you find the issue. My experience with this engine is only 4 months old, but I by myself have removed it from the car, torn it apart, replaced the heads and all timing components and it is currently running great. My advice is to find someone with a good scanner that knows how to diagnose. You can start throwing parts at it, but will likely spend more money than the diagnosis cost. I guess it could be a sensor, but I would think that it would show a code. Based on your description, it will run fine at all speeds until you shut it off and try again? My amateur first guess is fuel related. Maybe a leaking injector? If you had a scanner that shows misfire count by cylinder, you could see if there is a particular cylinder that is the main culprit. I always like to look at fuel trims when running, it may not apply to your issue, but seems to be a good indicator of what is going on in the engine. Good luck.
 

Dino Dino Bambino

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You might want to check if any of your injectors are leaking fuel into the cylinders when the engine's off. This might explain why the engine behaves as if it's flooded and only fires up with the gas pedal floored. You also wouldn't get any DTCs.
 

Mach0ne

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Checked the oil for gas smell since if the injector was leaking the gas would pass by the piston rings. No gas smell at all
 

DieHarder

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I usually have the best results by troubleshooting using the manual. Unfortunately, the online manual I used to use is now full of advertising and more and more difficult to follow. Still, if anything below helps you troubleshoot your problem might be worth going thru. Otherwise, I'd say hire a mechanic to get to the bottom of it rather than flail around wasting time.


For non-DTC's issues start here: https://iihs.net/fsm/?d=9&f=Step 2-... Codes (DTCs) Present Symptom Chart Index.pdf

Chart 2: Slow/Hard Start: https://iihs.net/fsm/?d=9&f=Step 3-... Codes (DTCs) Present Symptom Charts.pdf&p=11 and

Chart 3: https://iihs.net/fsm/?d=9&f=Step 3-... Codes (DTCs) Present Symptom Charts.pdf&p=12

Once you narrow down the problem area each of the Pinpoint tests are found here (unfortunately not all are included): https://iihs.net/fsm/?d=11
 

Juice

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Battery charged and cranks slow? Fix that first, it should never crank slow.
May still have other issues, but slow crank is your priority.
 

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