Boost drop problem

[luke2152]

Problem here is likely mechanical but want to bounce ideas around anyway. Car in question is my mx5 powered kit car with subaru wrx turbo. Had it running well last year and made a few changes to it over the winter. Namely switched ms2 to ms3 and removed the intercooler to experiment with just using water/meth injection. So issues could be related to this or to just sitting idle for a few months or completely unrelated.

Basically runs great pulls like a train builds plenty of boost (but not enough to trigger overboost fuel cut or rev limiter) and then the boost drops abruptly to 0 or slightly above and stays there til I get off the throttle and back on it. Then situation repeats. The boost drop is abrupt - almost like an artificial limiter which makes me question myself that I haven't put some wrong settings in when setting up ms3.

Boost control is just stock wrx wastegate pressure with no solanoid or manual controller. My gut feeling is that the wastegate is operating as normal until it opens and then sticking open until I get right off the throttle. However I tested it with a bike pump on the actuator and it seems to work just fine moving smoothly and not sticking anywhere although situation could be different with lots of heat and gas flow.

Anyway attached is an msq and datalog. Datalog is of doing a few 5th gear pulls on the motorway.

[Matt Cramer]

Can you get a more complete log? I'm guessing that was an SD card log, and it doesn't have very many fields. But boost dropping by 75 kPa in 0.2 seconds makes me wonder if there's a leak somewhere, or a blow off valve that's misbehaving.

[luke2152]

I will get a complete log for you soon. I'm currently running no BOV and had a good look for boost leaks - none obvious so i should probably rig up a pressure test. Also thinking maybe wire wastegate shut and test it like that but set a sensible overboost fuel cut first.