Franklinstower
Samba Member
Joined: September 21, 2006
Posts: 1896
Location: PNW
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 Posted: Wed Jun 07, 2023 7:32 pm Post subject: Re: designing a fresh air intake subie 2.5 |
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| 11BC2 wrote: |
OK.
The MAF has to be in the same size tube/hose/ducting as the OEM Subaru ducting.
If it is, have you checked smoke tested the intake for leaks?
If no leaks, and fuel pressure is good(can't remember the last time I changed a Subaru FPR), I'd suggest a new DENSO MAF and AFR.
Post pictures of your setup. |
Now that I think about it more, this could be an issue. Not using stock or similar inlet air sizes could alter air velocity through the MAF causing fuel trim when it isn't necessarily required... Lots going on with fuel trim inputs, but I agree, the more sophisticated the ecu and mapping, a slight change such as an intake change could cause issues down the road.... Although the Ecu should "learn" the changes and adapt the maps. Hmmm 
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'89 Westy - EJ25/22 Frank 4.44 5mt
'75 Miami Blue Sunroof FI Standard Bug |
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11BC2
Samba Member
Joined: August 27, 2017
Posts: 495
Location: Cool, California
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| Posted: Thu Jun 08, 2023 12:58 pm Post subject: Re: designing a fresh air intake subie 2.5 |
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| Franklinstower wrote: |
Now that I think about it more, this could be an issue. Not using stock or similar inlet air sizes could alter air velocity through the MAF causing fuel trim when it isn't necessarily required... Lots going on with fuel trim inputs, but I agree, the more sophisticated the ecu and mapping, a slight change such as an intake change could cause issues down the road.... Although the Ecu should "learn" the changes and adapt the maps. Hmmm |
I have used and designed several MAF housings for Subaru turbo engines, and the I.D. of the tube where the MAF measures the airflow must OEM diameter to the MAF that is used.
Also, the location of the MAF is critical; no bends before/after the MAF location, about the same distance from the engine as stock.
Turbo and N/A engines use different p/n MAFs, and between the the various years/models, the turbo MAF housing inner diameters are different, even though the same MAF is used. Subaru simply has different MAF tables.
Yes, the ECM can "learn" to a certain extent, a small vacuum leak (FPR reference hose removed) is large enough of a leak to set a P0171 code. |
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