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2001 2.5 RS Coupe
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165 Posts
Discussion Starter #1 (Edited)
I'm attempting to tune my friend's built hybrid and noticed a few strange things yesterday.

The car is a 2000 2.5RS with the following:
02 WRX ECU
EJ257 short block with forged internals
EJ20K heads, combustion chambers matched to the 2.5L bore
PE 264 cams
DW 760 cc/min injectors
TD05-16G
FMIC setup from a GD WRX. The piping has been altered a bit to fit the GC engine bay
Tial 44mm EWG
No BOV/BPV - we tried to talk him out of it, but he insisted. It's a rallycross car.

The car is idling poorly, and when it does idle, the manifold pressure is around 14.6 psia. So it's barely pulling any vacuum. On a stock WRX based MAF ROM, it's able to get the AFR to around 14.7. When we switch to the speed density based CarBerry rom, it idles very rich, < 10 AFR. We made the VE table using a utility from the CarBerry forum and the VE table looks reasonable based on previous tunes I've done.

I'm thinking the separate idle control valve on the EJ20K manifold doesn't play well with the 02 WRX ECU, which is designed to use the valve integrated into the throttle body. Even if the IACV is contributing to the problem, I don't understand how the manifold pressure is so high. Do the EJ20K's use a manifold pressure sensor with a different scaling? The fuel trims are removing fuel, and vacuum leaks typically cause a lean condition. Is the lack of a BPV also a contributor? I wouldn't think so because BPV's and EWG's are held closed by a decent amount of spring pressure at idle, so they wouldn't be leaking. The car is drivable off idle with the MAF rom, and the AFR's seem to be where they should be. The EWG also works and the car is able to control to 10 psig of boost which I set in the boost table.

Thoughts? Other things to investigate? Any help is greatly appreciated.

Thanks,
Garrison
 

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331 Posts
How is he running EJ20K heads with EJ205 ecu? Custom cam gear?

The WRX IAC is in the throttle body, so they probably are using that with the correct IAC. The wrx ecu can't operate the 20k iac.
 

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95/99 Brighton STi
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2,945 Posts
:confused: this setup is so strange. Sorry I don't have any real useful advice. Personally, I would probably sell the 20K heads and camshafts for some 205 or 255 heads and matching manifold. Sucks because it's seems like you already have a lot invested. GL
 

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I think you're right about the map sensor. If he has the wrx throttle body then you an use the wrx map, but you probably want something that can read more boost. Like a GM 3 bar or aftermarket. Then you can scale it correctly.
 
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