Lack of Boost

[gwbartlett]

When I took my 05 GT out for the first time this spring I noted a lack of boost and obviously lack of performance. The gauge shows 10 psi upon initial power application and then drops to less than 5. The car has 25,000 miles and has the FRPP performance upgrade. It is now at my Ford dealer and shows no codes. The Master Tech working on it (he has maintained it from new) wonders if the upgrade affects the MAF reading and injector pulse reading. The MAF reading is 148 hertz/13.01psi where typically it would be 154-156/14.0-14.8psi.

Also at 2,500 rpm with no load it seems to be running slightly rough.

Any thoughts would be appreciated.

-GWB

 

[freeflyer]

Check the bypass valve.

 

[paul b]

Check for blockage before throttle body, bad air filter or collapsed air inlet?

 

[Wwabbit]

mouse nest in intake filter

 

[DakotaGT]

Check the bypass valve.

+1

 

[gwbartlett]

The bypass solenoid was replaced. No blockage and the air filter had been replaced.

 

[freeflyer]

The supercharger is geared to the engine. If the belt is not slipping then the air is going somewhere. If there are no leaks in the intake manifold, no excess crankcase pressure and no excess coolant pressure then I'd say your bypass valve is staying open. Or the new pulley is slipping on the supercharger snout shaft.

Have you verified with a analog boost gauge what psi your seeing in the intake? If not start there and check the above mentioned items.

 

[Black GT]

Check the bypass valve.

Plus 3. I had same problem with my Whipple 05. The bypass valve was stuck open. Just opened and closed it by hand and it started to work fine. Happens when you don't drive for awhile. But, if you replaced the bypass, then might be something else.

 

[gwbartlett]

It is as if the bypass solenoid is getting a signal to open to avoid full boost. The MAF values that I mentioned in my original post?

 

[freeflyer]

Maf values are going to be different because of the tune.

 

[Wwabbit]

old or bad gas?

 

[gwbartlett]

It looks like the vacuum controlled bypass valve had a failed diaphragm. Thanks Rich at the GT Guys!!