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Old 02-02-2004, 08:10 AM   #1
Scooby Newbie
Member#: 39562
Join Date: Jul 2003
Chapter/Region: MAIC
My02 WRX Sedan 5MT
WR blue

Unhappy P0420 and fuel consumption

I have a MY02 WRX with a AF531v3 map switch rom(ecutek).

Ambient Temp 87 F

My cars fuel consumption has increased by 80% recently. My car has a SPT bosal exhaust with a gutted uppipe(full decat). It is throwing a P0420 cel. The car runs fine other than the increase in fuel consumption

I have had it checked for boost/exhaust leaks and there were none.

1. Can the P0420 code be causing this increase in fuel?
2. Is the Ecutek temp compensation causing the increase in fuel consumption becasue of high ambient temps?
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Old 02-02-2004, 09:05 AM   #2
Scooby Specialist
Member#: 48960
Join Date: Nov 2003
Location: Austin
2006 TL


I remember hearing that your car runs in some kind of "safe mode" when you get a CEL thrown, and so yeah I believe it's running rich. I threw a P0420 code for about a couple of days however, I didn't really notice THAT big of a difference. I'm not sure about #2, but I doubt #1 would cause an 80% increase in fuel consumption.
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Old 02-02-2004, 11:29 AM   #3
Citizen Mick
Member#: 27646
Join Date: Oct 2002
Chapter/Region: NWIC
Location: Portland, Oregon
2003 Sleeved 2.5
Oil Dry Sump Goodness


The P0420 cat code will not effect which ecu map you are running. Other codes can, not this one.

Of course your ECU could have seen enough knock that your ignition advance multiplier has dropped below 8 and you are running the safe and rich map.

Do you have delta dash to check the IAM?
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Old 02-02-2004, 06:52 PM   #4
Scooby Specialist
Member#: 14427
Join Date: Jan 2002
Chapter/Region: South East
Location: Cary NC
2002 09 Mazdaspeed 3


I ran with a P0420 for months on end with no problems.

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Old 02-04-2004, 02:55 PM   #5
Uncle Scotty
*** Banned ***
Member#: 16200
Join Date: Mar 2002
OK buy Nates beans


Stuck/sticky injector....???
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Old 02-04-2004, 04:27 PM   #6
Scooby Newbie
Member#: 5094
Join Date: Mar 2001
Location: Gaithersburg, MD, usa
11.96, 1.64, 115mph!


Could it be that you are WOT 80% more than before

Things like this tend to happen when new performance parts are installed

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Old 02-04-2004, 09:40 PM   #7
Rally Performance
Member#: 16588
Join Date: Mar 2002
Location: www.rallyperformance.com
Default Agreed

I agree with Mick. Try an ECU reset, and see if it clears up your problem... if you have Delta Dash, you can download the latest version at www.ecutek.com and can see the advance multiplier. The P0420 code won't cause the car to switch to the hi detonation fuel map, but low advance multipliers might.

You may be having another problem, but see if a reset clears it up.

Rally Performance
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Old 02-15-2004, 07:56 PM   #8
Scooby Specialist
Member#: 20768
Join Date: Jul 2002
Location: Los Angeles, CA
2017 WRX
Charcoal Grey


I noticed the same thing when I threw the PO420. Never had the numbers to prove it, but I noticed that as soon as I threw the code, my gas mileage would suck.

I just figured that the ECU was trying to compensate for the cat innefficiency by running the car rich. Why, I don't know, cause I would think that running rich would have the opposite effect, but, my gas mileage deffinitely sucked when I had the cel.

Got the PDE DP, no more CEL, no more crappy gas mileage.

Problem solved.

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Old 02-17-2004, 05:56 PM   #9
Scooby Newbie
Member#: 51538
Join Date: Dec 2003
Location: philadelphia
1994 impreza


I have high gas consuption too.
1.8 impreza 200 miles with a full tank
please help?
already change air filter and actually the old one had a grissy spot in the middle.
02 sensor maybe but how do I check it?

I like my suby I drive it hard even when it is tainy.
new with subys
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