davenew

I drive around for awhile with a max boost of 6 psi. A few minutes later I hit the throttle and have full boost again! A few peddle presses later it's back at 6 psi max. WTF? I thought once the ecu cut boost it would remain cut until the fault code is erased. Is that true? I'm thinking of driving around while logging throttle angle w/vag to see what's really going on.
thanks

PSmalls::DoggieStyle

That's limp mode, not throttle cut.

davenew

ahh, I'm not familiar with that term

PSmalls::DoggieStyle

Also, log block 115 just to see "actual" (TCD capped boost) vs requested. TCD was made to work with X chip boost curve, but you may need something higher for APR stage 3 to reduce the negative boost deviation. If it's not the part throttle issue anymore, that's my best guess. It's not a super hard fix, just need to pull Piggie's arm and see if he'll make you a special TCD.

davenew

I did have a boost code but I'll run out again and see exactly what it is. thanks

PSmalls::DoggieStyle

Here's a quick example of negative boost deviation:

I tried running XR on my car with MBC in parallel and a TCD. TCD is set to ~.95 bar peak capped boost level and XR requested 1.3-1.4 bar in low RPMs. WIth this .35-.45 bar deviation, I threw a negative boost deviation code and went into limp mode. This is a very common code with TCD+XR, but you won't go into limp mode with MBC only....just get the code.

GIAC chips are known as being more "open" to deviations than other code. APR may only allow a .2 bar deviation, for example. I suggest you log block 115 and go from there.

davenew

I just ran out there. Here's my fault codes:
2 Faults Found:
16955 - Brake Switch (F): Implausible Signal
P0571 - 35-00 - -

17963 - Charge Pressure: Maximum Limit Exceeded
P1555 - 35-10 - - - Intermittent

The first one is caused by my EDL defeat switch

PSmalls::DoggieStyle

However, that'll just make you spool-up slow and still have a slow car.

If I were you, I'd just get A box GIAC K03 software and give it a try. You don't have to change any of your hardware. You'll need to tweak some, but it should be pretty easy. RS4 sensor reads lower than S4 sensor so you may have to add quite a bit of fuel, but I'm not positive. If there was any hardware change I'd suggest, it would be using S4 MAF sensor. Then again, I'm not totally familiar with tweaking homebrew using RS4 injectors so I'm sure you'd still be fine with RS4 sensor.

That's just my 2 cents. People have tried getting MBC/EBC to work on APR stage 3 before and came up empty. There was a local car here slow as molasses with APR stage 3, then he tried MBC and ran into your same issues, then went to a GIAC setup and is one of the fastest S4s I've ever seen and/or heard of.

davenew

I didn't realize people have tried it (and failed) with apr..

PSmalls::DoggieStyle

Sorry, I thought you knew.