Car feels like it's "breaking up" at high RPM's

Discussion in '2005+ Mustang GT 4.6L Tech' started by ghunt81, May 9, 2019.

  1. ghunt81

    ghunt81 New parts on old junk! S197 Team Member

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    I've noticed this year since I've been driving the car, at WOT in 3rd/4th gear and high RPM's (like above 4000) it feels like it's breaking up a little, like it's stumbling some.

    I realized I haven't replaced the fuel filter in awhile, I have a new one but haven't had a chance to replace it yet (have stuff for a new fence clogging up the garage atm). I know this could be partly it but it runs great at all other areas of the RPM range.

    When I had Lito revising my tune a few years ago he told me my car was running lean at high RPM's, even after he added fuel to the tune. He messed with it probably 3 times and told me it was still lean, but at that point I was pretty happy with the tune and it was running good so we never revised it beyond that. What would cause that, as well? Anyone else had that problem?
     
  2. 1950StangJump$

    1950StangJump$ forum member

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    People like to point to fuel filters but, in my experience, they are never the culprit unless you have a crazy number of miles on them.

    So, assuming the lean mixture Lito was talking about is the cause would be a good start.

    And, assuming you aren't getting enough fuel . . . I would start with the fuel pump or injectors.

    The other option is that you are getting too much air . . . vacuum leak somewhere that only becomes problematic when the car is under extreme load?

    I'm spitballing . . .
     
  3. Phil1098

    Phil1098 forum member

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    Is it still on the original fuel pump? The 05-06 cars had a TSB on them. My 06 had the issue the TSB called out. I just put a new pump in mine to resolve it. What you're describing isn't what the TSB described, but anything that isn't right with the fuel pump isn't good.
     
  4. ghunt81

    ghunt81 New parts on old junk! S197 Team Member

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    Lito asked if there might be a vacuum leak...but I looked all over and couldn't find any spot where there could possibly be one.

    Good chance it is on the original fuel pump though. Might have to add that to my winter project list.
     
  5. Phil1098

    Phil1098 forum member

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    Takes one minute to find out, unclip the rear seat base and lift the black plug/cover. There is a sticker on top of the pump with a build date.