boost spikes and fluctuation - Subaru WRX Forum
 
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#1 Old 09-06-2010, 09:08 PM
 
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boost spikes and fluctuation

So I've seen this issue pop up in threads from time to time and I'm experiencing it bad.

My boost is spiking sometimes as high as .14 MPa (yikes !) and then wavering up and down pretty quickly. It is worst in 4th or 5th gear going WOT at 3K rpm (freeway passing) It does it to a lesser degree in 3rd also. I've seen others with this problem resorting to a new BCS or a manual BC.

Mileage on the car is 170K and I've been running the same PDX tuning maps for 3-4 years. I've been experiencing this problem slightly for a while, but it's gotten progressively worse esp. the last week. That makes me think that something mechanical is gradually failing. It doesn't seem like the BCS would do that. I'm wondering if either the waste gate actuator (diaphragm) or the BPV (spring) could be responsible. Any ideas ?

BTW, I just got back from a 4000 mile road trip so I can't throw much cash at the car right now, and believe I have a spare BCS somewhere to try for troubleshooting purposes. I'll drop that in tomorrow, and yes I checked for vacuum leaks.

Thanks
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#2 Old 09-06-2010, 09:25 PM
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I had this issue a few years back, turned out to be the BCS. So that would definitely be the first thing I tried.

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#3 Old 09-06-2010, 09:28 PM
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but shouldn't you be running about .14 MPa (~20 Psi) anyways?!

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#4 Old 09-06-2010, 09:30 PM
 
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No, I'm mapped for around 16-17 PSI max.
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#5 Old 09-07-2010, 04:33 PM
 
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Problem solved ! I ran some electrical parts cleaner through the BCS (with test connectors, so it was cycling) and the restrictor pill, reset my map and did some 3rd gear "tuning" using some empty on-ramps. Not sure which was gunked up, but it smoothed things out right away. I'm only hitting 14.5 PSI so far, but a little aggressive driving should bring that back up. I like it when I don't have to spend money to fix my car
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#6 Old 09-07-2010, 04:54 PM
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congrats!...glad another bug wagon is healthy!

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Last edited by basco; 09-07-2010 at 04:55 PM. Reason: I Kant Spellz
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#7 Old 09-07-2010, 05:34 PM
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Can you explain your fix a little more.

I'm kinda a n00b with this stuff and I'm having the same issue you are..
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#8 Old 09-07-2010, 05:53 PM
 
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The BCS (boost control solenoid) is on the strut tower, passenger side. It has two vacuum lines running to it and a two prong electrical connector. I took off the vacuum lines, the two 10mm nuts that hold the BCS to the car, and clipped the two green test connectors (under dash, left side) together. Plugging those together puts the car in test mode, which cycles the fans and basically all the sensors etc. when the key is on (don't start it) I sprayed a little electrical parts cleaner into the nipples that the vacuum lines attach to in short bursts a few seconds apart, disconnected the green clips and put it back together.

I also cleaned out the vacuum lines that attach to the turbo, T connector, and waste gate actuator since that is where the restrictor pill lives. I used the same cleaner, sprayed into one end, blew through it and then the other. I put my thumb over the line that T's off so that the cleaner and air blew only where it needed to. Again, put it back together and off I drove.

First though, I used the reset ECU and switch map functions of my access port, just re-entering the stage 2 map I always run. The way you "train" the ECU to hit boost levels correctly (without a dyno) is to run WOT (wide open throttle) in third gear to red line a few times. I use empty on ramps to do this, as redline in third is around 85-90 mph, and you need to be able to hold it at WOT all the way for it to work correctly.

I took the car back out for a few more miles and it's running great
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