legacycentral bbs

Long story short, I have a 93 wagon which is mostly stock except for a Cobb DP and stock STI catback. It's had a very noticeable lack of power which felt ignition-timing related to me. Every once in a great while I'll get a miss so bad it pops though the intake. I have an SSM2, so I looked at MAP, ignition timing, knock correction, and knock signal. Under heavy load but not WOT, I was seeing just over 10 psi, 10-15 degrees advance (sometimes less), -4, and OFF. The knock sensor was an original gray connector with several cracks. It wasn't setting a code but I replaced it anyways with an Intermotor. I've had great luck with their stuff on other cars so I figured why not. I cleaned the MAF also (again.) Didn't change anything.

It just so happens that I have a 93 SS auto which runs GREAT but the trans is basically shot. So I looked at the same data and found the max boost is 7.7 psi, the timing advance is 25ish degrees, and -1 knock correction. This car runs perfect and pulls smooth and would easily outrun the wagon. So I swapped the BCS/pressure sensor/switching solenoid tree, and MAF, and guess what? The wagon runs awesome now! The MAF signal looked the same on both cars, so that's probably not it.

When/if I ever get enough free time again, I am going swap individual parts back over and figure out the root cause. Just FYI, the FSM says the max target boost should be 7.35 psi. My thinking is that at 10 pounds, its not necessarily seeing actual knock but instead going into an almost "fail-safe" part of the map. I have a gauge to monitor injector duty cycles but didn't do that in this case.

If you have any other ideas feel free to share. I've spent hours on here searching and didn't find anything that I hadn't already tried.

Jim

Jim,

Thanks for the feedback. It's possible that the added boost was causing the ECU to go into a limp or reduced power mode.

Stock target boost on a US turbo Legacy is 8.9psi.
The 7.35psi referenced in the FSM is the wastegate actuator spring pressure.

I'd guess your Pressure Exchange Solenoid or MAP Sensor was bad.

Hey let me know if that is the solution because I have almost the exact problem you were having.

Oldandslow wrote:Hey let me know if that is the solution because I have almost the exact problem you were having.

I read your other thread, I'm having the exact same issue but the only code I'm throwing is 45. I put 12V across the solenoid that switches between boost and manifold pressure and it clicks, I replaced the map sensor, all the vacuum lines are new and the correct I.D. After all 3 items have been checked out, I'm stumped. I'm on the rob 440 tune, I should be making about 16 PSI, but the boost gauge I connected between the turbo outlet and the MAP sensor only showed right at about 10 PSI before bucking and backfiring. So I guess my point is, I did what he did (albeit different code) and it didn't fix my issue.


Sidenote, I don't remember if you've tried disconnecting your MAF, but mine runs much better with the MAF disconnected. Still doesn't see more than 10 PSI and anything over 10% throttle causes the backfire but it drives around town ok. Does yours do the same with the MAF connected? I thought that would point to the MAF being bad but I only have code 45 and I checked the part number and it's the correct MAF.

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I have not tried disconnecting the maf. I'm having pretty much the same issue. I don't have a boost gauge though so idk how much boost I'm pushing, its a stock tune though.

Oldandslow wrote:I have not tried disconnecting the maf. I'm having pretty much the same issue. I don't have a boost gauge though so idk how much boost I'm pushing, its a stock tune though.

That's what's frustrating is that everyone has the same symptom, but there's no common mods between any of us. I'm on an EJ20G with mods and a tune, while you are on a stock engine with mods, and the OP for this thread has a tune and a stock engine with mods. Makes it hard to pinpoint if it's one issue that we all share, or if there's lots of ways to make OBD1 Turbu Subaru's behave this way.

Reporting back. Car is still running great. Haven't had time to switch things over individually to pinpoint the exact cause though. Fuel economy still sucks.