MR_Q

Hey,

I did a quick search and didnt see anything, so sorry if its there and I missed it.

I have an 05 GT manual all stock with around 65K on it.

It occasionally has a really bad stumble. It happens when Im driving on the highway at around 65MPH, then downshift to pass. The car will just hit a wall. Its like it stalls for a second (or less) then just picks up and goes like nothing happened.

At first I thought that it was just the traction control coming on as it felt very similar to that. Whats strange is that it only does it from a cruise and if it does it once, you have to let it cruise steadily again for a few minutes before it will do it again. It doesnt seem to matter if you shift down or not, at 65 in 5th if you steadily roll into the throttle it will still do it, though not as bad. Its almost like the car gets relaxed and is surprised when you ask it to go faster, but then wakes up and is happy to oblige.

Whats odd is that you can go WOT from a stop all the way up through all gears and it will run just fine. It MAY be a little down on power but that could just be in my head. City driving is fine.

There is no check engine light and gas mileage is the same as always. I cleaned the throttle body with no change. Plugs have not been done. Its my next step, but Im nervous about it.

The only other issue Ive had with it is once when driving the car randomly decided it had to idle at 2200RPM, even after shutting it off and restarting it. I fixed it by recalibrating the pedal (Push gas down for 10 seconds, hold there for 2 etc) and it hasn't done it since. Not sure if the problems are related or not.

Any suggestions would be appreciated.

wcgman

I recall reading somewhere about how this can happen and it had something to do with fuel system...like a known problem but no real fix? I don't want to take a guess but hopefully my comment will trigger someone else's memory who does recall what it was.

zt'sgt

Do a search for TSB 06-9-9. It was regarding a bad design on the factory fuel pumps in 05-06 that allowed air bubbles to form at the pump intake during prolonged cruising. I had it done a few years ago on my 06 GT, while it was still under warranty, after experiencing hesitation after a long cruise. They installed a new pump with a revised design and no more issue. Only thing that seems odd is that it just started happening to you now. Still, worth looking into.

adj86

+1

Mine did it right after I got mine in 05 a couple times, but then magically disappeared. Hasn't happend after that. Kinda weird, but just thought I would add.

MR_Q

That sounds like whats happening with me. Sounds expensive. Maybe Ill get lucky and it will go away too. I am in no mood (or place) to pay for that. I am assuming that it just has a single pump in the tank. Ive pulled the pump in my 86 Bronco without much trouble but that has a lot more room to work under than my mustang. I may do some experimenting and see if it does it less/more depending on how much gas is in the tank. Worth a try. Could changing the fuel filter help maybe? I wont have to worry about it for a few more months anyway as Its still winter time

The ironic thing it that what finally convinced me that I needed a new car (This car) was that my old car was stumbling on acceleration.... I later found out that it needed a new fuel pump

Lifter583

My 06 GT did the same thing...progressively got worse...had a new fuel pump installed (after warranty was out of course) all continues to be fine since...

zt'sgt

I don't think the fuel level in the tank really matters with this isssue. It's not that the fuel pump is weak but that the design of the the pump inlet tends to allow a build up of air bubbles when the car cruises for a while. When you get on the gas hard, after cruise, the pump sucks in the air.
As far as replacement of the pump goes, I'm pretty sure you access the pump by removing the lower part of the back seat. So labor cost might not be too bad. Like I said, mine was within the warranty period so I didn't pay.

Nuke

It's the fuel pump. Read the TSB. I bought a used '06 and it stumbled on hard acceleration after steady-state cruising. After the fuel pump was replaced per the TSB, it was fine.

Also be aware that having the TCS on and going WOT will occassionally cause a momentary (and embarassing) loss of power similar to the fuel pump issue.

robs

My 06 does this too. Don't annoy me enough to spend cash on a new fuel pump. Will only do it after 50 or so miles of interstate..

SpartaPerformance

I agree it seems to be the fuel pump issue.