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Discussion Starter #1
My STi has pulled the Too Lean CEL twice now at idle. The code takes a good week to appear after I clear it. Dave, Steve, anyone what are your thoughts? Maybe I need the fuel pump upgrade like you Dave. Just a word of warning to all the STi guys wanting to use this turbo.
 

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A fuel pump upgrade is definately in order. Pumps can move much more fuel than they are rated for when really pushed, but it wears them out quickly. A larger pump really never hurts unless you go completely overkill.
 

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Possibly Injectors,the Best Thing To Do Is Find A Shop With A Exhaust Gas Analyser
 

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Discussion Starter #4
Ya, I was thinking fuel pump then dyno run. I wonder how my car could be so different then Steve's? Sure am glad I didn't go with the 20g now. Dave does your fuel pump work ok on the OEM ECU? Which one did you go with? What is it rated at? I appreciate the help guys.
 

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fuel trims

Something is pushing your fuel trims to full rich trying to get to stoich under closed loop.
I would look to see if you have an intake leak between the MAF and the turbo, maybe a hose that is cracked or popped off or loose.

If that is not the cause then your not delivering enough fuel, ie fuel pressure is low or something similar.

Larry
 

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Discussion Starter #7
It's very strange to me that the CEL appears at idle and not under boost. To me if the STi is going to be lean its going to be lean under boost and not idle. As far as I know I have no leaks.
 

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If you have a good scan tool you can recall what is called freeze frame data. This shows you the exact engine conditions that were happening when the CEL was set. It is possible that the code is getting set under boost but the light won't come on until idle.
 

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Larry hit the nail on the head IMHO. The ECU doesn't monitor AFRs at WOT to inidicate a lean CEL. When I tested out the APS CAI I got consistent "system/car running lean" CELs. I took the intake off and the CELs stopped.

I would suggest the following:
-Replace your aftermarket intake with the factory intake.
-check to make sure you didn't possibly tear the turbo inlet tube when installing the 18G? A little unmetered air either via the non-stock intake or a possible leak/tear could cause this CEL.
 

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Newer subies actually do monitor the A/F R at WOT. Hence the factory 5 wire 02 sensor. It's how they get away with such silly power levels out of the STi's with them still easily passing smog. Aftermarket intakes really screw with some of the caculations the ECU makes... I didn't realize you were on an aftermarket intake... if you are, get rid of it. I personally wouldn't really hazard a guess as to what's going on until I saw a freeze frame.
 

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analog_909 said:
Newer subies actually do monitor the A/F R at WOT. Hence the factory 5 wire 02 sensor.
I am sorry I was a bit unclear. I wasn't saying suby's don't monitor afrs during WOT but they don't seem to care about them NEARLY as much as when they are in closed loop operation. IE: If they did you would see CELS with UTEC/piggyback tuned cars when the af goes from high 9.x:1-low 10.x:1 afr (Stock) to anywhere from 10.5-12.5:1 depending on the tune and fuel used.

I have also heard the accuracy of the stock quasi-wideband goes down as EGBP in the exhaust manifold goes up when under WOT. Don't know if there is any credence to that argument ... but it falls inline with aftermarket wideband sensor locations being suggested to be placed after the turbo (where EGB pressures are much lower).
 

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Lean/Rich codes are set when the actual AFR isn't within what the ECU is mapped for. They get set when the ECU is trying to maintain a certain AFR, but for whatever reason can't. Like a plugged injector will set a lean code because the ECU thinks it's delivering X amount of fuel but in reality is delivering much less. UTEC tuned cars and the like alter the factory fuel/ignition maps, so the monitors will be comparing actual AFR's with what is in the new map. It's not like there are 2 separate maps in there, one that the ECU looks at to determine how much fuel the car needs, and the other one to see how much fuel should be getting delivered for purposes of setting CEL's. Working within the factory parameters like that is really the genius behind reflashing.
 

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analog_909 said:
Lean/Rich codes are set when the actual AFR isn't within what the ECU is mapped for. They get set when the ECU is trying to maintain a certain AFR, but for whatever reason can't. Like a plugged injector will set a lean code because the ECU thinks it's delivering X amount of fuel but in reality is delivering much less. UTEC tuned cars and the like alter the factory fuel/ignition maps, so the monitors will be comparing actual AFR's with what is in the new map. It's not like there are 2 separate maps in there, one that the ECU looks at to determine how much fuel the car needs, and the other one to see how much fuel should be getting delivered for purposes of setting CEL's. Working within the factory parameters like that is really the genius behind reflashing.
Sorry yes you are correct... I shouldn't try to think when I first wake up [heh]. But typically this checking/CEL will occur when the ECU is in closed loop from my experience.

Would you say that the ECU usually only checks for afrs in closed loop (light throttle) and not so much in open loop (WOT)? I ask becuase when I first put on the 20G I was going lean from 6000-7000 at WOT (like 2 full points leaner than stock afrs 12.0:1 compared to 10.0:1) and the ECU never seemed to care. This was a case in which I was on the stock ECU with no piggybacks of any kind.
 

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Closed loop and open loop simply refers to when the ECU is factoring in corrections from the 02 sensor. I really don't know too much about the logic on suby ECU's, but my guess is once the car is warmed up, the thing never goes into open loop. This is the whole reason for them putting a wideband in the car in the first place, to comply with smog/emissions standards. The reason normal cars go into open loop under WOT is that standard O2 sensors are really only good between about 13.5:1 -> and about 15.5:1. Under WOT or very heavy decel. the ECU ignores the 02 sensor (goes into open loop) because the motor will be operating outside what the 02 sensor will be able to see.
 

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STi_This said:
My STi has pulled the Too Lean CEL twice now at idle. The code takes a good week to appear after I clear it. Dave, Steve, anyone what are your thoughts? Maybe I need the fuel pump upgrade like you Dave. Just a word of warning to all the STi guys wanting to use this turbo.
The only CEL I've ever got was for hitting fuel cut when I was boosting more than 17psi, the FCD fixed that. Since then I've never had a CEL, a good 10k miles, 6k on the 18G. Like others have said it must be a vacuum leak of some kind or your intake (I run the stock air box with K&N & ram-air).
 

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I got another $5. People need to sell intakes for subies with a big yellow sticker on them that says "DO NOT INSTALL WITHOUT A REFLASH"
 

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Discussion Starter #19 (Edited)
I'll pull the Bltz SUS off and see if that is the culprit. Man, I really didn't want to get rid of it. Thanks for all the information guys.

Here are my performance mods:

TD05-18G Turbo – Flows 600 CFM
BPM GT 3” Catless Race Exhaust
Blitz SUS Intake System
Apexi AVC-R Boost Controller
Pace Fuel Cut Defender
 

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Discussion Starter #20
Why would I be pulling a "too lean" code with the 18g when I never didn't with the VF-39? I've had the Blitz SUS on both turbo's. Sucks, I really like this intake and don't want to go back to a factory airbox. I'll probably dyno with the SUS on to see what numbers I pull before I pull it.
 
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