Subaru WRX Forum banner
1 - 5 of 5 Posts

·
Registered User
Joined
·
2,210 Posts
Discussion Starter · #1 ·
So today the WRX was in the dealership to have those two CELs diagnosed. These occurred at 15.5psi (indicated), WOT, uphill, 4th gear. I removed the MBC before taking the vehicle in.

The diagnosis reads

"4325 CODE FOR WASTEGATE A100-009 0.5 KYG-00 TEST AND SECURE HOSE ON W/GATE SOLENOID VALVE AND CLEAR MEMORY ORDERED NEW SOLENOID"

I asked to speak to the technician, and he told me that 'I couldn't see any problems but it looks like the solenoid is sticking, causing an overboost which triggered the boost cut'. Obviously not privy to the knowledge that I am running an MBC, he said they had ordered a new solenoid (I feel kinda bad.. but didn't think it would be smart to set him straight).

Ok.. so now I know I overboosted. With the MBC my gauge shows 15.5psi in 4th, so what the hell - I thought you didn't get boost cut till ~19psi?? Since the gauge is showing 12psi with the computer controlled boost in 4th, I see two possibilities:

1. The gauge could be under reading by about 2psi, so I was actually hitting 17 or 18psi at the time of the CEL. This is a possibility as I am using a short section of heat-proof rubber host to connect the plastic air-line to the NPT t-connector. Maybe this is leaking since I just pushed the plastic hose into the rubber one (doh).

2. Maybe they configure the car to run lower boost in Colorado, and the ECU sensors are more sensitive accordingly. As we only have 91 octane gas, and very thin air, this seems plausible. However I haven't heard anybody else mention this, and I know there are some tweaked WRXes in the Denver area.

What gives ?

-Pace
 

·
Registered
Joined
·
18 Posts
Your gauge is worng. Peak boost on a stock ECU controlled motor is 15.5 PSI. Thats at about 4.5K RPM for only a split second. It then tapers off to around 13~13.5. This is in 3rd gear. So check the peak on your boost gauge. Set your MBC to this peak setting in a 3rd gear WOT run. The boost should stay solid or taper off only a little at this setting (15.5 PSI for me). You will then notice that you will boost higher in 4th and 5th. My gauge reads around 17 PSI. If I up the boost so I am showing 16 ~ 16.5 PSI in 3rd, then I will fuel cut in 5th as it reaches around 18. FYI, the best boost setting on the stock ECU is around 15. When the stock ECU sees too much boost, it pulls timing.
 

·
Registered
Joined
·
554 Posts
When I got my MBC and boost gauge I only installed the boost gauge. I ran around for about 2 weeks with a boost gauge installed and MBC in glove compartment. Why you ask? That way I can get used to reading the gauge out of the corner of my eye, and also watch what factory peak boost read. In my case the gauge would peak at about 14.5 and settle at about 13. So after a little time I learned those spots on the gauge from the corner of my eye. Then I installed the MBC. I have it set at 15 now. It will peak to about 17 and I haven't had any probelms yet, I was very thorough on testing. I had to drive on the levy roads for about 2 hours, you know just to make sure it was right, hehe.

Drive around with no MBC and keep an eye on boost readings for a week or so. Then install the MBC and tune it. It seems to me you may not have known the baseline boost from your car, since they will all be a little different.

Good Luck,
Justin
 

·
Registered User
Joined
·
2,210 Posts
Discussion Starter · #5 · (Edited)
gabedude said:
Your gauge is worng. Peak boost on a stock ECU controlled motor is 15.5 PSI. Thats at about 4.5K RPM for only a split second. It then tapers off to around 13~13.5. This is in 3rd gear. So check the peak on your boost gauge. Set your MBC to this peak setting in a 3rd gear WOT run. The boost should stay solid or taper off only a little at this setting (15.5 PSI for me). You will then notice that you will boost higher in 4th and 5th. My gauge reads around 17 PSI. If I up the boost so I am showing 16 ~ 16.5 PSI in 3rd, then I will fuel cut in 5th as it reaches around 18. FYI, the best boost setting on the stock ECU is around 15. When the stock ECU sees too much boost, it pulls timing.
Many people quote the fuel cut as 19psi and the stock ECU peak boost as 14.5psi. However, I'm guessing these are folks who drive at or near sea level: Several people on I-club have actually stated that my high altitude driving (5500 - 8500ft) is definitely a factor. The lower ambient barometric pressure means that my fuel cut is likely closer to 16psi and my peak boost is lower accordingly... Several other WRX owners in Colorado have said that they experienced the same thing.
 
1 - 5 of 5 Posts
Top