Series 5 Fuel Cut Defensor vs Stock Wastegate Control
 

I'm fiddling with another project that will require the removal of fuel cut on my stock '89 turbo II. I have built Paul's FCD for this purpose, but something suddenly struck me.

The factoy S5 cars have electronic wastegate control which is based on manifold pressure delivered by the pressure sensor. The FCD modifies this signal so we don't hit fuel cut. What happens to wastegate control when the FCD flat lines the boost level at 8 psi?

If the turbo is below 8psi then control should be normal

If the turbo is above 8 psi but the FCD fools the computer into thinking it's at a constant 8psi. I believe that the factory wastegate control will go into 'hold' mode at the duty cycle supplied at the moment the FCD takes over the manifold pressure signal.

Because the control system will be trying to lower the boost to the factory 7~8psi allowed limit I suspect this 'hold' signal will be flinging the wastegate wide open thus making it difficult to make more boost unless there is a significant load on the engine (5th gear freeway pulls).

Discconecting the electonic valve will only force wastegate spring regulated boost pressure (about 6psi on my S5).

Anyone have any experience with this?

I got rid of the stock boost controller before I put on the FCD.

you have it backwards though. the boost will be higher, and you will get more creep by leaving it on. because when you are hitting say 10psi. the ecu still only thinks you are making under 8. so the controller will always try to raise boost.

Thanks for the reply Scott, I was hoping you'd see the post.

just ditch the stock controller and get a cheap MBC one for like $30. it's better then the stock one anyways.

That's exactly where I'm headed.

I've only seen Paul Stoaks FCD's for S4 TII's, where did you see the circuitry for the S5's?