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Old 09-25-2001, 11:42 PM   #1
WRXXX
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Default Intake throwing a CEL?!?! HELP!!

OK, just installed my APC-Cobb intake system today. After driving around for a while, came back home. Headed back out to get something to eat when i noticed the Check Engine Light on. The only thing that could possibly cause this would be the MAF correct? Anybody have this hapen to them? If so what did you do to correct the problem? If not, anybdy have any suggestions?


Thanks
Geof
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Old 09-26-2001, 02:09 AM   #2
jmott
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yes someone else had this happen to them.

the cobb site says "we dont reccomend buying this without a unichip bla bla bla"

they mean it.
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Old 09-26-2001, 04:23 AM   #3
subywan-kenobi
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Did you do an ECU reset?? Were you careful with the MAF?? Extremely careful??

I also had a flashing CEL 3 times that went away almost immediately with my Blitz for the first 2 days, but I contribute it to the ECU still learning because I get it every time I reset the ECU for the first tank of gas, but once the ECU learns completely, I don't ever get CEL. I don't know what to tell ya, but I wouldn't be too worried about it.

Mike S.
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Old 09-26-2001, 07:06 AM   #4
Imprezd
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I garuantee you guys are detonating and not paying attention.

Anybody need a Knocklink?
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Old 09-26-2001, 08:29 AM   #5
Scottie
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Unlike a lot of the earlier MAFs used on Subarus, the Denso unit used on the WRX does not have its own housing. Instead it mounts to the filter box. If you mount it to to something else, like the APS intake, you could throw off its readings for a couple of reasons.

Despite its name, Mass Air Flow sensor, it is actually the mass velocity not the mass flow that the sensor is measuring (this, of course, is assuming we're talking about some type hot wire or hot film sensor). The mass flow part comes from the fact that the air is flowing through a fix cross-sectional area of know flow characteristics. Basically, the faster and/or denser the air moving over the heated element is, the greater the cooling affect on the heated element. It is the relationship between mass velocity and cooling that drives the operation of such sensors. If you mount the sensing unit into a housing of a different cross-sectional area or one where the velocity profile is different, then you're going to get screwed up readings.

For a given flow rate, the velocity will be slower for a larger cross-section than a smaller one. Thus, if you put the mass air flow sensing unit into a housing with a larger cross-sectional area, the velocity of the air will be slower for any given flow rate. Meaning it will indicate a lower flow rate than is actually entering the engine and you'll likely run lean. Closed-loop operation may be able to correct for this, but the ECU may still post a flag.

Another issue is the screen that is typically up stream of the sensing unit. The Bosch hot film unit used in North American MY99 2.5RS had one. I haven't looked inside my WRX's intake system yet, does anyone know if the stock WRX Filter box has such a screen? In anycase, the screens are used to purposely cause "micro" turbulance. This turbulance results in a more even velocity profile through the cross-section. Without such a screen, it is possible that you could have laminar flow at the lower flow rates and turbulent flow at the higher flow rates. With the change from laminar to turbulent flow comes both changes in the velocity profile and the cooling coefficient.

Last edited by Scottie; 09-26-2001 at 01:38 PM.
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Old 09-26-2001, 09:12 AM   #6
JenisonWRX
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Take a number

Talked about it HERE and HERE

I'm still getting CELs. I have a lambda link on the way. I don't get CELs all the time...however the CEL is thrown (I'll have to re-read this to verify) if 3 consecutive car runs throw the error. Then the CEL is lit.

My ignition advance (what I suspect) is really high (40 @ 3k). Which if I'm detonating...would be lower because the ecu would retard the timing.

Be careful...the car got so bad over time that it was not even drivable. I have not driven it much since ... it does drive and man does she pull hard ... but the fact remains .. we are running lean.
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Old 09-26-2001, 11:01 AM   #7
Imprezd
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I have known this for some time now... Just someone else who experiences the same...
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Old 09-26-2001, 12:14 PM   #8
Scottie
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The first thing I would do for a Check Engine Light is pull the code. This would at least give you an indication as to what might be wrong.
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Old 09-26-2001, 12:29 PM   #9
WRXXX
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Well, I reset the ECU last night and started the car up.... no CEL, so stopped and started the car about 15 times.... no CEL... Drove around for about 2 hours... No CEL... Hopefully the problem is fixed... Will let you know if i run into anymore problems. Thanks for all of the advice guys.


Geof
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Old 09-27-2001, 11:33 AM   #10
WRXXX
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CEL came back on again yesterday when i started the car up, so immediately, i called Trey who said that it is a problem with the WRX, that the airflow has changed, causing the MAF to read higher, throwing the CEL. Said that his Unichip system would correct this problem. Set up an appointment to install the Unichip Tuesday Oct. 9th.
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Old 09-27-2001, 11:38 AM   #11
Imprezd
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sweet...
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Old 09-27-2001, 12:49 PM   #12
Scottie
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"......causing the MAF to read higher......"???????

JenisonWRX mentioned that he pulled the code "Mixture too Lean". If the MAF was reading higher, it would send more fuel than needed (Rich), not less.
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