jbossolo

Hi gents, quick question-
Last WE at COTA (Chin), running down back straight, 4th-5th, WOT, car all of a sudden loses all boost. Goes from 1.2-1.3bar to 0.3bar max. No warning lights at all. Car felt like it went into a "limp mode". It did go into PSM a couple of times during that run, as it was pretty damp, but nothing major.
My mech checks it, no loose hoses, absolutely zero boost leaks, no codes.
He thinks it might be the n75 boost control solenoid valve.
Any ideas/suggestions?
BTW, car has an EMW 1.2bar tune and a SpeedTech X-flow exhaust.
Thanks!

jbossolo

I think I should add that the previous day the alternator gave out, panel lit up like a X-mas tree. My mech found a Bosch OEM unit (on a Saturday at 4 PM!) and did a quick swap at the track. Car ran fine during Chin's "happy hour" session right after that, nearly 45 mins uninterruptedly, no issues at all.

993GT

assume you mean UMW tune? so probably not an issue there, but worth asking UMW..
sounds like a stuck N75... also, did your tech check the wastegate flaps by hand for free movement? what turbos are you running?

jeanmarcboilard

If your N75 valve failed you should still be making boost up to your wastegate spring pressure which should be around 0.7 bar. Since there's no leaks or codes, you might have a wastegate stuck open or broken wastegate rod. That would result in barely any boost being made and no codes being thrown.

Atrox

Went through this, Mine was a potentiometer issue with the throttle body. Before I swapped tb's I would do the e gas reset and it would boost fine. Could also be a MAF issue. Like you I would be going fine, floor it and nothing .2-.3 boost max.

SteveMFr

As a former tech and shop manager (in a previous life), I can only suggest you check around everything that was done to replace the alternator first. When a car has an issue shortly after having work done, 99 times out of 100 it is related to the prior work. There are coincidences but they are rare.