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2007 gt acceleration problem

40K views 82 replies 10 participants last post by  ski48 
#1 ·
So a couple days ago after filling up gas at the pump, I tried accelerating around 50% throttle and my car did this thing where it like had absolutely no power then lurched forward..So obviously I let off the gas. And as days go on it keeps getting worse.

Now if I try to accelerate at all it pretty much does this, or it basically just has no power at all and the rpms stay at whatever they were originally.

The weird thing is, if I just drive normal without accelerating very hard everything is fine, and the car still idles great.

If I put the car in neutral and rev up the engine it usually will rev up fine, but sometimes it still does the loss of power thing mentioned above.

So, is my car misfiring? I don't hear any weird noises like you usually would with a misfire.
Is my throttle position sensor bad so the engine is getting mixed signals?
Bad coils, what?! Lol.

One other weird thing, if I'm in way higher of a gear then I need to be, like let's say 5th gear when I should be in 3rd..If I put the pedal to the floor it doesn't do anything weird..

Some things you may want to know:
2007 mustang GT manual
51k miles. 😎
Cold air intake
62mm dual throttle body
Xcalibrator2 tuned(need a newer one)
Running 93 octane.

I believe that is about the only engine related mods.

I don't believe coils/plugs have ever been changed.

I did clean the throttle body/maf sensor about 3 months ago.

Let me know what you guys and gals think, thank you very much! 😊

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#2 ·
sounds like a fuel delivery issue. I would start by replacing the fuel filter. its under a plastic cover under the drivers side, about under the front seat. some need a ford fuel line tool, some are said to use the plastic push on clips like the PVC hoses on the intake to valve cover. my 05' needed the fuel line tool. replace that and report back. after that, you can check fuel pressure at the fuel pressure regulator on the drivers side fuel rail. you might be able to hook up your Xcal and check some parameters. if after the fuel filter replacement, your results are the same, id look at your TB. is it an aftermarket like BBK? good luck
 
#4 ·
IMHO I believe it's the throttle body. I've seen people on forums having all kinds of weird issues and when they switch back to the stock throttle body, everything gets fixed. The only throttle bodies these cars work well with are the stock ones and the Ford Racing/Gt500 throttle body. I understand this might be difficult for you as your car is tuned and I'm not sure if you have the stock parts/tuner on you. It also could very well be a fuel delivery issue like the guy above me mentioned as that's something I thought could be the issue as well. While reading your post, I was wondering if you had an aftermarket throttle body until I saw you did at the bottom of your post.
 
#6 ·
Could this possibly be an Evap system issue? If the tank was overfilled and excess fuel went in to the evap system could this cause these symptoms? Or perhaps a leaky fuel cap. Just not bad enough to cause the CEL to come on yet? I only ask since the issue seems to have happened after refueling.

A while back I was cruisin' about 75mph on the interstate when all of a sudden the engine lost power and then surged a bit and then leveled out. It was almost as if I hit the rev limiter. The CEL light came on. When I made it home I pulled the code which indicated an evap issue. First suggestion was to check the fuel cap, which I did by loosening and then firmly re-tightening it. I had refueled a few days prior so I probably didn't snug it down all the way. Hasn't happened again.
 
#8 ·
Alright guys, I changed the fuel filter. Nothing but clean gas came out of the old one. Car still has problems under acceleration.

I think it would have to be fuel related though since the car runs fine when just cruising or slowly accelerating. Since it has problems during acceleration it makes sense that it isn't receiving enough fuel, correct?

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#9 ·
I would find a way to monitor the fuel pressure since that seems to be the issue and there are no codes coming up. I have read that this issue will arise while driving at a constant highway speed for some distance then the need to accelerate like to pass a vehicle, and the car will hesitate and stumble just long enough to notice then accelerate like nothing was wrong. this issue from what ive read is caused by cavitation or air bubbles around the intake of the fuel pump caused by the vibration of the pump and the gas not moving or in a static state from the constant speed of the car. I have experienced this a few times with my car and just wrote it up to that, but this was at highway speed (80mph on cruise for a while). I'm not sure if the ECM monitors fuel pressure or not. you may have to get a manual gauge. ive been thinking about getting a Bluetooth OBD2 reader and getting the Torque? app. that may help you if you don't have a handheld programmer/tuner to plug in and data log. sorry for the long winded answer. good luck
 
#10 ·
Thank you for your reply!
It is all the time though, not just after cruising for a bit. Pretty much anytime I try to accelerate quickly, from stop, cruising then accelerating or any other time it bogs down like nothing is happening. Could still be what you were saying though.
From what I saw their isn't a place to put a guage into the fuel line, no hookups at all on the fuel rails. Kind of lame really. Oh well.
I do have a handheld tuner, I'll have to see if I can check the fuel pressure with that.

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#11 ·
The first thing I'd suspect from what you've written is bad gasoline. Gas stations find that premium fuel is seldom used by their customers. That station at which you pump gas could have contaminated fuel in it's premium fuel tank. Best to find out the wholesale supplier of fuel for that station, call them, ask them to check the tanks at that station and report back to you.

Other simple things I'd do...throttle body cleaner, MAF sensor cleaner. Either might be the fix, and both cheap to do.
 

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#14 ·
Nevermind, still have the problem! 😔 Lol.

So the latest update:

Tonight, I was going down 95 and once I got up to 80 their was an obvious loss of power, like the engine was struggling to maintain that speed. So I dropped it down to 75 and put cruise control on.

About 30 minutes in, the traction light started coming on and off, then stayed on, and the abs light came on. About 30 seconds later all the dash lights started flickering and long story short I was stranded on the side of the road, and pretty sure I had either a bad battery or alternator.

My buddy came with a battery, we hooked it up, and it started right up.
So, I probably did have a bad battery, and I was excited at first because I thought maybe that was the problem all along. But it isn't, the car still does the weird accelerating thing. I checked the battery with the voltmeter while the car was running and the alternator appears to be working fine.

So, my latest ideas as to what may be wrong, let me know what you guys think!

1. I'm assuming that the alternator is now controlled by the ECU like most modern cars. Is it possible that the ECU is making the alternator do crazy things and causing problems? I had an aerostar once and the ECU had the alternator putting out 18 volts! So, just thinking maybe something similar could be happening that is affecting the rest of the electrical system?

2. Does the car have ignition modules and coils or just coils? Maybe I have a bad coil, ignition module, or spark plug(s). If it were one of these, I don't think it could be completely bad since the car still idles and cruises fine, but maybe there's just a weak spark somewhere due to a failing part?

3. Low fuel pressure. I'm starting to think the problem is more of an electrical thing, but I still will try and look into the fuel pressure. Bad fuel pressure would definitely explain an acceleration problem.

Lastly, I think I may be getting a little bit worse gas mileage, and it seems like the problem more often occurs around 4k rpms and higher. When the problem surfaces, if I didn't push the clutch in and tried to just keep accelerating, basically nothing would happen. I have to push the clutch in, wait a second for the problem to "disappear" then slowly accelerate up to the desired speed.

The problem is not always the loss of power then lurching forward feeling like I said earlier. Now it is more of just like a no power feeling when it occurs during slow acceleration. I don't know what to refer to it as.

I know this is a long post, but thank you very much for those of you trying to help, I really appreciate it! 😊

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#15 ·
With the symptoms you've given and all I've read here on this subject, I'd give the alternator a hard look.
Go to the 2005-2010GT tech home page and click on the search bar. Type in "bad alternator ".
 
#17 ·
If the diodes are starting to go out in the alternator it will allow excessive ripple in the current and cause all sorts of havoc in the electronics.
 
#19 ·
Sooo, brand new battery, brand new alternator. Still has the acceleration problem. : /

I never get any fault codes/check engine lights.

I do have a tune on my car with a handheld tuner. It wouldn't have the check engine light disabled would it?

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#21 ·
Bad fuel pump, problem fixed !
Lot of money for one week. [emoji854]
Anything else want to break?! Lol.

Just kidding, thanks again for the help fellas!


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How'd you finally get it diagnosed?
This thread was like throwing darts. There sure were a whole lot of, "I'm pretty sure it's.." Bad throttle body...


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#23 ·
You guys are probably sick of me saying this, but there's still more to the problem..

The car definitely works a lot better than before, but there's still definitely an issue.

Now the car still accelerates pretty normal but once it gets to 4k-5k rpms..Nothing. the engine just sounds like nothing is happening at all. Sometimes you get lucky and it will keep going but not usually.

Do you guys think something could have happened with the tune? I reflashed it, but I don't know what else it could be.

There's only one fuel pump correct? I noticed there was two access points under the rear seats. But I only went into the drivers side one.

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#26 ·
Okay, here's two quick videos but you get the idea, let me know if you need any other kind of video.

First video is in 4th gear and I held down the gas pedal for a couple seconds after the problem popped up. I'm actually surprised how good the sound is in the video compared to in person. Also the noise that sounds like I let off the gas at the end..I still had the gas held down. I didn't let off the gas until like half a second before the video ended.



This video is in first gear accelerating quickly. I let off the gas when the problem popped up.



Thanks again!
 
#29 ·
On another note. Does the car have one or two fuel pumps?

I know it has a saddle tank, but is there a fuel pump under both rear seats? I changed the fuel pump assembly under the driver's side. Could I have changed the wrong one? Assuming there is one under the passengers side too of course.

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#31 ·
It sounds like a misfire. Have you checked/changed the plugs lately? Do you have stock or aftermarket coil packs? Since it seems to be cutting out above 3k RPM, check your cam position sensors. I recently did a complete timing gear maintenance and about 6wks later it felt like I was getting a mis-fire but wasn't getting a CEL or codes. Checked all the plugs and swapped in all my stock coil packs with no change. I then decided to go back over all the connectors that I had to undo for the timing gear maintenance and found the driver side plug wasn't pushed all the way in. Pushed it til it clicked. Problem gone. You did say the old alternator tested bad. It is possible that it was allowing excessive ripple in the current that can weaken or even destroy other electronics.
 
#32 ·
To my knowledge the plugs and coils are all the original still. I could start pulling those and checking them. I just never swapped them because of the whole spark plug snapping thing, lol.

Assuming the connectors look good on the cam sensors. How can I check them and know they're working properly?

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#33 ·
the reason I asked about the same rpm range in different gears and you said same in any gear. I'm thinking you have a dead spot in your gas pedal. its not to much of a stretch and easy to check. our cars are drive by wire (I'm sure you know that) so the gas pedal sends a signal to the TB motor on how much to open. if there is a dead spot, the TB loses signal and or closes somewhat. before digging into the pedal itself, open your hood, remove your intake and find a mirror with a stand or have some one hold it. have the mirror positioned so you can see the TB blades from the drivers seat under the opened hood. turn the key to on but don't start. slowly press the gas pedal all the way down and watch the blades as you do, go slow. you know your car and know where about the issue starts, watch the blades about that point. report back. if you need to dig into the gas pedal, its fairly easy. let us know what you find, good luck.
 
#35 ·
I tried to slowly accelerate passed the problem and see if it gets better, but it didn't, basically stayed the same until redline. Not sure if that is normal with having a dead spot.

If I do have a dead spot where the throttle body is not performing properly what is most likely the problem? The TPS or the motor in the throttle body?

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#36 ·
Well, so I thought of something. The problem existed before and after the new fuel pump was installed. So I took a step back, and put a guage back on the quick disconnect on the fuel rail.
Even at idle and even during reving the engine, the guage was inconsistent. It didn't stay at one value and go up and down. It was kind of all over the place.

So I'm thinking it's definitely something fuel related. What about the fuel pressure sensor? Is their a way to test it to see if it's working properly?

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#37 ·
it could be the signal sender (gas pedal) or the signal receiver (TB motor). you could take the TB off I suppose but a mirror is much easier. all these things are related to the operation of the motor. you give it gas, pedal tells TB to open, more air comes in, ECM reads MAF and demands more fuel and IIRC the fuel rails are fed via the fuel pump and the fuel pressure regulator that is operated via vacuum, adds fuel to the injectors. if something is telling the ECM and MAF that less air is coming in, then the ECM regulates that and vacuum goes down and less fuel to the injectors. good luck
 
#38 ·
...and the fuel pressure regulator that is operated via vacuum, adds fuel to the injectors. if something is telling the ECM and MAF that less air is coming in, then the ECM regulates that and vacuum goes down and less fuel to the injectors.
FWIW, an S197 GT does not have a vacuum operated fuel pressure regulator. The ECM varies the speed of the fuel pump based on sensor signal inputs, and that varies the fuel pressure.
 
#39 ·
Start by eliminating the easiest things first. Check/change your plugs and inspect the coils. Here are some really good videos for changing the plugs:
 
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