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Old 04-30-2020, 01:32 AM   #7
Scooby Newbie
Member#: 461463
Join Date: Jan 2017
Chapter/Region: BAIC
Location: San Francisco, CA
2004 WRX wagon


Hey everyone, thanks for the help so far. I've tracked down two problems so far, based on the advice here:

1. I have a custom boost gauge that taps into the electrical output of the MAP sensor. My boost gauge was limiting the output of the MAP sensor to 3.3V, which equates to 8 PSI. I figured this out by boost leak testing the intake up to 15 PSI, and watching the boost value on the ECU and my boost gauge. Both were stuck at 8 PSI, but as soon as I unplugged my gauge, the ECU boost reading jumped up to 15 PSI. Entirely my fault there.

2. After fixing the problem with the boost gauge, I was still only getting 8 PSI while driving around. I then pulled the vacuum hose off the WG actuator nipple, and with careful throttle control, got the boost up to 14 PSI. Bam! The factory boost control solenoid was bad, as you guys said. It seemed to be working when I manually tested it with compressed air, but I guess it was sticking open when the ECU pulses it quickly.

Per Unabomber's and Blaze13rex's suggestions, I am replacing both the factory BCS and the MAF. The car is at 150k miles, so you are definitely correct that the MAF probably needs replacing too.

I have replaced most of the vacuum lines by this point (they were either split or rock-hard and not sealing properly), but I will take your advice and replace the last few too.

Thanks everyone for the help
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