Hey guys does anyone have any idea what this problem I've been having on my car for a couple of months might be?
Basically the car hits about 5000rpm and cuts power... in the vid I've got my foot flat on the floor and it just stops revving at just over 5000rpm and the boost gauge drops into vacuum. It feels sort of like overboost fuel cut (but doesn't cut power quite as suddenly), but it's only at about 14psi so it shouldn't (Z4 ECU - 15.65psi fuel cut)... not to mention that I've got a one-way valve to the MAP sensor hose so the overboost safety feature should be removed completely. It happens in any gear, even in 1st, where I don't think it'd even be able to get to the overboost by 5000rpm! Any idea what else it might be? Relevant mods are VF34 turbo, Walbro fuel pump and 3" turbo-back exhaust. Also if I lower the boost to about 12psi it'll cut out at about 5500rpm... so the less boost, the later in the rev range it cuts out. This started happening a couple of weeks after installing the 3" exhaust, and about a day or 2 after I put in an oil catch can for the PCV valve (probably coincidence :P). Before that I was running about 16-17psi with no problems.
Spark plugs are new, coil packs are in excellent condition, no boost leaks, no dropped off vacuum hoses or anything. I am stumped! as is everyone else I've asked... One thing I thought it might possibly be is the fact that the new exhaust hasn't got anywhere to plug the EGT sensor, so I just left it unplugged. No check engine lights so I thought it was ok. But I don't think this is the problem. I tried the resistor mod that people do on newer WRXes on it but that didn't change anything.
Any ideas? This is really getting on my nerves now!
SOLVED: Problem was high vacuum from higher boost sucking the soft turbo inlet rubber hose shut and starving the engine of air.