04stangman

Hi guys i need some help diagnosing an issuse that just started today. I have a 2009 shelby gt500. She only has 20,000 miles on her and i put everyone on her, she has always ran strong. This morning i decide to play with another stang on the freeway. I down shift to 4th gear...hit the gas and my car seems like it lags, my rpms raise about 2500 up about 5000 then my supercharger kicks in and the car speeds up. Now after i come home i tried to disconnect the battery and reset the system and it didnt do anything. I checked all the lines i could.... and i looked the whole engine over. I cant find a thing.... my check engine light isnt on.. the car seems to run ok until i press the gas pedel to engage the supercharger.... now my rpms raise, the supercharger makes the winding sound then the engine rpms go down and i cant accelerate very fast. ;( you guys have ideas i might be able to look at? Sorry about my spelling, i typed all this on my phone.

1slow67

How is the belt? The only thing I can think of is maybe the belt is slipping.

Hopefully a mod will move this into the S197 section so you can get some better answers.

GT500Steve

I am assuming that the car is making full boost on the gauge, correct? If so, I would guess it is probably the clutch slipping.

04stangman

I checked the belt, its clean free of grease and tight. The guage reads a few pounds, but it seems like right when i press the gas the supercharger spools up the rpms raise and i loose power?

GT500Steve

I am assuming your car is stock.

If you are not getting a check engine light on the dash and there is no other obvious issues (loose connection at air filter or TB, etc) I would say it is one of two issues.

#1. Boost bypass valve for supercharger- There is a valve that limits the amount of boost and if that malfunctions it can cause the car to make almost no boost at all, causing very sluggish acceleration. If the car is making full boost (9 psi stock, 12-13 psi with a pulley) you can rule out this option.

#2. Clutch - If the car is making boost, and the rpms are coming up, but its not going anywhere... sounds like a clutch issue. There was a TSB on the 07-09 cars, and you might be able to get a dealer to install the upgraded clutch assembly at no cost to you. The best way to test this is to get on the highway, put the car in 5th gear about 60-65 mph, and floor it. Watch the boost gauge and the rpms... if they are both going up but the car isn't accelerating then this is your problem.

Those are the first 2 things that come to mind, especially without it throwing a trouble code.

04stangman

Thanks for all that advice...

LilRoush

I vote clutch starting to go.
And instead of racing illegally on the street, take it to the track.

04stangman

Ford says it is the clutch, $2800.00 for a new updated clutch. Oh, and i dont race my car anywhere fyi.

LilRoush

Same thing.... just not smart.