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Old 04-18-2023, 02:02 AM   #1
Krauterz
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Member#: 402498
Join Date: Sep 2014
Default weird MAF scaling/AFR 2002 WRX

Good day everyone.
I have recently purchased a 2002 WRX with a Process West Topmount, CAI and Invidia downpipe.
The car is still running the stock TD04 and 420cc injectors.

I have encountered a strange scenario with the MAF scaling. this is a bit of a long story, so hopefully I can get right to the point.

with the MAF connected, the ECU was dumping way too much fuel in. pulling almost 8:1 AFR on a hard pull, bucked and carried on like a pork chop, and would not idle. Disconnected however, it ran 10.5:1 and pulled hard, and otherwise ran fine apart from running in open loop all the time.

I replaced the MAF and front 02 and the issue remained.

The previous owner had the CAI and top mount installed by a tuner, and apparently had it "tuned". I do not know what their interpretation of "tuned" means however, as the MAF scaling was never changed, only timing was retarded slightly, max wastegate duty cycle was locked to 20% all round, and AFR was set to 11.4-11.8 across the board (fairly high, no?)

With the help from my wideband and some guides on MAF scaling, I was able to scale the MAF to get the AFR's to match pretty closely to the fuel tables, however in order to get it close I had to pull almost 25% from the upper end of the MAF table, scaling down to the lower end to essentially stock values.

I am utterly confused as to why I would have to reduce MAF scaling by such a drastic amount and not increase it by a few % if not leave it stock. I would have thought that using an aftermarket CAI would cause the car to run slightly leaner instead of significantly richer.

Previous owner stated "I was driving home from workfine and all of a sudden there was a big loss of power and it was missfiring"

I have:
Checked for boost leaks/vacuum leaks by blowing into the intake with my mouth sealed around the intake boot, I could feel only a very very slight loss which I attributed to EGR or evap.
Done a smoke test with a soldering iron, jar and oil, found no leaks
Compression tested and bore scoped each cylinder, blew 150ish PSI on all 4 and apart from looking wet from rich AFR, looked fine with cross-hatch still visible.
replaced the MAF
replaced the front 02 sensor
tried the stock ROM to no avail

any suggestions or input would be greatly (greatly) appreciated.

I can post logs and the rom that came with the car on request.

Thanks.
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Last edited by Krauterz; 04-18-2023 at 02:07 AM.
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Old 05-02-2023, 03:14 PM   #2
enduroxt
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Member#: 310796
Join Date: Feb 2012
Location: UT
Vehicle:
05 obxt

Default

What is the condition of your MAF wiring harness? still original? In my case, on two different subies, my AF learned values became way negative due to the MAF wiring harness providing poor ground connection to the MAF. I changed the MAF plug using an iwire kit.
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Old 05-06-2023, 05:29 AM   #3
Krauterz
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Member#: 402498
Join Date: Sep 2014
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Quote:
Originally Posted by enduroxt View Post
What is the condition of your MAF wiring harness? still original? In my case, on two different subies, my AF learned values became way negative due to the MAF wiring harness providing poor ground connection to the MAF. I changed the MAF plug using an iwire kit.
Thanks for the input. Decided to get the car speed density tuned and eliminated r yes he maf entirely.
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