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2000 gmc yukon xl 6.0l nose dives in overdrive

Josh Cease

By Josh Cease
in Ask A GM Technician

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Josh Cease New Member

Josh Cease

Posted
Posted

I have a 2000 gmc yukon xl 6.0l 4x4 with 238,000 miles but motor was rebuilt 50,000 miles ago just started acting up and it runs smooth and I was cursing doing about 60 and gave it gas and as soon as it hits overdrive its nose dives and loses  power and  It doesn't feel like it's the transmission it acts like either the CPU  or throttle body just goes stupid but you can left off the pedal and press the pedal back down and it drives fine ??? Just acts up when trying to pass or putting pedal to floor ? I've done a tune up and all I dont know what else it could be ? 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

There are two things to look at, fuel pressure and catalytic converters.  A plugged fuel filter will behave this way, and if you don't know when it was last changed, now is as good a time as any to replace it.  

 

A plugged catalytic converter will also behave this way.  You may find the exhaust is quieter than you remember.  Depending on how plugged up it is, flooring the gas pedal in park may cause the engine to simply not go past 2 or 3k rpm.  Do not hold the pedal down any longer than a second or two.  If it is plugged you will see it right away.  If you park your truck next to a wall on the passenger side, rolling down the passenger side window will allow you to hear the exhaust sound while doing this.  If the converter is plugged it will have a hissing sound, almost like compressed air.  If you put a fuel pressure gauge on the fuel rail and if the filter is plugged, the fuel pressure will drop off noticeably. 

Josh Cease New Member

Josh Cease

Posted
  • Author
Posted

The cats were taken off completely new exhaust from front to back  and the fuel filter was changed about a week ago its it weird how it does it .when its does it the pedal pulls away from my foot and sticks and loses power but if you tap the pedal again it will start driving normal again until you try to accelerate 

 

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Make sure there's no mouse motel in the airbox, or in any of the intake hose to the throttle body. Make sure the MAF isn't all coked up with crap, especially if running an air filter that requires oil, like a K&N.

 

If that checks out, you'll need a fuel pressure gauge next. Need to know the fuel pressure running, and on a snap-throttle. If pressure dips on a snap, you need a pump.

 

You could also have a throttle body issue going on there. Pedal should never stick.

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