As the subject says, I've got a bone stock '04 WRX wagon with 12000 miles with a factory boost guage installed. No hose mods installed, etc. When I stay on the throttle, I can see the needle on the guage fluctuate back and forth between an indicated .07 and .1 (why they couldn't install a guage that read in PSI is beyond me). I also feel the car slacking off and picking back up when the guage's needle is dancing. I friend who was rallying with me on Saturday noticed it before I had a chance to mention it to him, so it's not just me. A few thousand miles ago, the Subaru service manager told me that there was nothing wrong or a CEL would come on. Has anyone else experienced this phenomenon, and if so, what is the common cure? I'm reluctant to go with a MBC until the warranty is out. Is there something I can point to and show the service manager to get the engine to be able to hold boost? It's my first turbo car, so I'm a neophyte to the various idiosyncracies.
Thanks,
Myron

 

Bad gas....ECU pulling timing, maybe....

 

Is it going back and forth, or just falling? On a stock car, the boost should peak at .1 mPa (14.5 psi) near 4500-5000 rpm and then taper off to about .7 mpa (12 psi) at redline. If it is actually fluctuating back and forth, then you either have a bad ECU or it is pulling timing for some reason (bad gas, cold weather, etc. are reasons why).

 

I use any of several name brand fuels when I fill up the tank (Amoco, Sunoco, Shell), all are 93 octane, and I've noticed that it doesn't seem to depend on the ambient temperature. It's most prevalent in 4th and 5th gears at or near WOT as the revs increase. Thanks for the ideas so far, and I hope to hear more about it.

 

Shell sucks. Amoco= Phillips 66 right? If so, stick to that, it's the same as Union 76 I believe, which has been dyno proven to be the best brand on the west coast.

If you are getting boost fluctuation at or near WOT then something is definitely wrong. Find out if anyone near you has Delta Dash or an OBDII scanner. Hook everything up, then go drive and reproduce the problem. If you see the car pulling timing when boost drops, then Subaru owes you a fix of some sort. Even better, log the following parameters if possible: RPM, MAP, TPS, engine load, ignition timing, knock correction, learned ignition timing, and knock signal. Use a very short interval and record only during the WOT moments.
Also, if you have no mods, which it sounds like you don't, see if someone with the same year and transmission WRX (has to be the same year, but the part numbers on the ECU don't have to match) and see if you get the same problem with theirs.

 

As a mater of fact, as I was coming home from an autoX yesterday I was trying a few things. If I go to WOT from about 3K rpm, I'll see the fluctuations, but if I go part throttle until the boost holds at ~.05Mpa on the guage, then slowly feed in throttle, I don't notice the fluctuation being so prevalent. Sadly, I still have no definitive answer.

 

Its just boost that's fluctuating? Are your RPMs fluctuating too? What's going on with the tach during these times?

jason

 

I've typically just watched the boost guage, but it's something I can feel in the seat of my pants when it happens. The fluctuations I'm seeing happen rapidly, but I'll see if the tach can pick them up the next time I experiment.