2015 GT PP Hard Starting Issue

Hey everyone,

This is my first post on this site, but I have been a long time member of AFM.

I just recently picked up a 2015 GT Performance Pack 6-Speed with 14K miles on it. So far I've owned one of every generation after the Fox Body. A 1996, 2002, 2006, 2011, and now my S550. So as you can probably tell, I love Mustangs, but this new one has some issues that I've been trying to deal with.

When the car is cold, or been sitting for a few hours, it almost doesn't want to start. I get in, hit the start button, listen for the fuel pump to prime, push the clutch in, hit the start button again, and it cranks for 8-10 or more seconds before starting, then stumbles in idle like it's going to die, then jumps up to 1600-1800 RPM until it idles down.

I keep the car in the garage and its only been around 40 or 50 degrees outside. This also happens when I drive the car to work, after about 3-4 hours later I'll go to leave for lunch and the exact same scenario happens. After that first start, the car will start immediately without the least hesitation every time until it sits for a few hours again and cools off again.

No matter how many times I hit the start button, push in the clutch, etc, before hitting the button to fire up it will do this when starting the first time.

So the car is still under factory warranty, I took it to Ford and they had the car for over 5 hours one day and "could never recreate the problem" basically meaning they didn't check anything since they didn't experience it first hand.

I'd like to attach a video of it happening while trying to start it in my garage, but I don't have any video sharing sites to upload to and embed the link. I may put it on YouTube later just to get it posted here. The CEL is on, but it's due to the Intake Air Temp Sensor (P0113) going bad, which Ford is replacing under warranty. I recheck it everyday to just make sure no other codes have popped up until they get the new sensor installed.

To me it seems like a fuel issue, but I have no way to recreate it after driving to the dealership unless I leave my car over night.

A side note, sometimes in my garage after it just starts and has it's little fit I feel like I can smell fuel, even more so than my last 2011 5.0L which was catless with GT500 mufflers and dyno-tuned making almost 420RWHP.

Any suggestions?

I don't ever push the button twice. I get in, push the clutch, then start it. Never had a single problem like you're having. Maybe that sequence of button/clutch/button again is what's causing it? Have you tried not doing that?

AlyourPal said:

I don't ever push the button twice. I get in, push the clutch, then start it. Never had a single problem like you're having. Maybe that sequence of button/clutch/button again is what's causing it? Have you tried not doing that?

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Yep, unfortunately I've tried it with every combination of button presses. My thought process was that if it was letting the fuel drain back from the rails into the tank that priming the system first would improve the issue. No dice though!

Yeah I don't think that should be a concern with a modern fuel injected engine. I'd focus on air charge (air filter cleanliness, MAF sensor, throttle body not sticking or defective, vacuum leaks from your intake manifold). But that's just a hunch. Weird it's not throwing any codes.

sounds like the crank position sensor is failing to me but that should throw a code I would think

Any codes? Should fire up with in a second or so.

I haven't had any issues with starting, but often get the smell of fuel upon start up in the cold weather. I always thought it was due to needing the cats to warm up before they start working properly.

As promised, here is the video on Youtube.



Also, no codes besides the previously mentioned P0113 which I will attach a picture of as well.

What is strange to me is that it only happens after sitting for awhile. I started the car last night with the same issue on start up, drove for 30ish minutes, parked it for an hour or more while I went in a business, came back out and it was completely fine just like always after the initial start up. It seems to only occur after sitting 3+ hours.

Normally I do all my own trouble shooting and repair, but with it still be under factory warranty from Ford I want them to fix it before they say I did something to void the warranty, but anything you all suggest is something I can mention to them when I take it back in to get the air temp sensor replace.

I would look in the fuel arena as it's cranking just fine for battery power

Are you running E85? My car does it once in a while when running E85 during the winter. Now that temps have been in the 30's, it has started to take longer to start but that is expected with E85 during cold days. When I run 91, it starts right up during the coldest days.
Try cleaning the sensor that is throwing the code with MAF cleaner spray. Also, clean out the MAF sensor. Previous owner might have ranned a cold air intake with an oiled filter and might have gotten carried away with the oil.

Thanks for the replies everyone.

The car is 100% stock running normal pump gas.

Ford already has the air inlet temp sensor ordered, so I'll just let them replace that since warranty covered it. But I'll pull the MAF and spray it just to be on the safe side!

VinnAY said:

I would look in the fuel arena as it's cranking just fine for battery power

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VinnAY can you elaborate a little more on what you're meaning?

I'm thinking your hunch about fuel drain-back is correct, and here's why:

The logic that governs that fuel priming with the engine not running will only run the lift pump for a few seconds (~3-5 seconds). This is to make sure the system pressure doesn't exceed any design specifications (too high of fuel pressure can damage PRVs in the lift pump assembly and near the rail). This logic assumes minimal to no drain-back. If you are sending more fuel backwards than expected when the car is off, you would definitely experience the hard cranking shown in your video, and that cranking will keep going until the fuel system is filled and pressurized adequately.

I would suggest asking the dealership to take a look at whatever check valves are in the fuel system. I'm not intimately familiar with where they are, but there should be a couple in there that they could look at.

jbird60 said:

I'm thinking your hunch about fuel drain-back is correct, and here's why:

The logic that governs that fuel priming with the engine not running will only run the lift pump for a few seconds (~3-5 seconds). This is to make sure the system pressure doesn't exceed any design specifications (too high of fuel pressure can damage PRVs in the lift pump assembly and near the rail). This logic assumes minimal to no drain-back. If you are sending more fuel backwards than expected when the car is off, you would definitely experience the hard cranking shown in your video, and that cranking will keep going until the fuel system is filled and pressurized adequately.

I would suggest asking the dealership to take a look at whatever check valves are in the fuel system. I'm not intimately familiar with where they are, but there should be a couple in there that they could look at.

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jbird60, this was my thinking with hitting the button a few times before startup, but it appears it only primes the system for a very short amount of time and doesn't do it everytime you hit the button without your foot on the clutch.

I had this issue once on a Jeep Wrangler and it ended up being the fuel pressure regulator. I think it had a check-valve that had failed letting gas drain back into the tank.

My dilemma now is that Ford swears up and down they can never get the problem to replicate and that my video(s) (I have several showing different scenarios) aren't good enough for them to start testing anything. :tsk:

Either a sensor, weak fuel pump, or your fuel pressure regulator is going. Next time you get in your car when it's been sitting for awhile, press the ignition button, but don't start the car. Listen and see if the fuel pump primes or not. Try starting and seeing if that helps. If no help, do this process twice before starting and see if it helps. Trying to narrow it down can be hard.

Ebm said:

Either a sensor, weak fuel pump, or your fuel pressure regulator is going. Next time you get in your car when it's been sitting for awhile, press the ignition button, but don't start the car. Listen and see if the fuel pump primes or not. Try starting and seeing if that helps. If no help, do this process twice before starting and see if it helps. Trying to narrow it down can be hard.

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Ebm, thanks for the reply.

I have actually tried that with no luck. I get it, hit the button, hear the pump prime for 2-3 seconds, it goes off, hit the button again and I never hear the pump prime again no matter how many times I hit the button or push the clutch to the floor.

I experience no cutout issues while driving, even at WOT, so I'm not thinking weak fuel pump because it sounds strong when priming.

I would think a sensor would throw a code, but is there any you can suggest taking a look at?

Fuel pressure regulator or some check valve is what I'm thinking, because I have no fuel leakage or any other issues after the first start. So I'm still under the impression that the fuel is draining back into the tank, then when I hit the button and prime the system it's not giving it enough fuel since it had all drained back instead of staying at the rails/injectors.

Has anyone heard of any fuel pressure regulator issues on S550s?