More fun new problems... borked MAF? Suggestions welcomed

scooterforever · 11-09-2006, 07:27 PM

Edit: All better. Details in post #3.

Just started loosing power on WOT pulls tonight. No CELs other than a hidden P1094 for TGV delete (hidden via Street Tuner).

On successive short WOT bursts I felt noticeable power loss. AFR started dropping, 10.6... 10.5... when I saw a 9.6 I stopped testing. RPMs are strong, no transmission slippage (ATF is accurrately filled now, thank goodness), and boost readings are fine. EGTs are low, call it around 1,400, but I don't have a peak & hold gauge, so it's hard to tell for sure.

So... does it sound like I have a dead MAF? Car idles fine. No CELs other than the tumbler valve. Could a dead MAF start reading too high voltage? Which would then cause my injectors to add too much fuel??? Just brainstorming.

Thanks in advance.

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ride5000 · 11-10-2006, 08:47 AM

it sounds like a boost leak. can you pressure test the induction tract?

best way to test a mafs is to swap with a known good one from a buddy.

scooterforever · 11-11-2006, 04:10 PM

Thanks for the suggestion, Ken. The problem solved -- it was either the MAF or the O2 sensor or both, but it's all better: I just pulled 4.78 MAF volts on a highway pull. I'm back!!!!!!

Details

At the suggestion of Crazymikie, I logged my AF learning + AF correction versus MAF voltage at low speeds, and they were all over the place. Mikie's conclusion was a bad MAF or O2 sensor or both, so... given that I have already sunk a fair amount into this new platform (and the idea of washing my cylinders sickens me), I figured I'd swap out the 4.5 year old 76k mile sensors and start fresh. Village Subaru in Acton helped me out and gave me really competitive pricing on a new O2 and MAF sensor, plus they were the only dealer within 100 miles to have both in stock. Props to Village Subaru!!!

This morning I swapped the MAF and the O2 sensor. Started up the car, let it idle, and sure enough the AF correction dropped once warmed up. Once warm, I changed my oil for good measure (didn't smell gas in it... but figured I'd start from scratch with fresh oil).

Test drive showed the car to be immediately responsive, back to it's old state of enjoyment. 4.78 MAF volts... feels ooo so good.

11-09-2006, 07:27 PM	#1
scooterforever Scooby Specialist Member#: 55011 Join Date: Feb 2004 Location: New England Vehicle: 2002	More fun new problems... borked MAF? Suggestions welcomed Edit: All better. Details in post #3. Just started loosing power on WOT pulls tonight. No CELs other than a hidden P1094 for TGV delete (hidden via Street Tuner). On successive short WOT bursts I felt noticeable power loss. AFR started dropping, 10.6... 10.5... when I saw a 9.6 I stopped testing. RPMs are strong, no transmission slippage (ATF is accurrately filled now, thank goodness), and boost readings are fine. EGTs are low, call it around 1,400, but I don't have a peak & hold gauge, so it's hard to tell for sure. So... does it sound like I have a dead MAF? Car idles fine. No CELs other than the tumbler valve. Could a dead MAF start reading too high voltage? Which would then cause my injectors to add too much fuel??? Just brainstorming. Thanks in advance. * Registered users of the site do not see these ads. Last edited by scooterforever; 11-11-2006 at 04:12 PM.

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11-10-2006, 08:47 AM	#2
ride5000 Scooby Guru Member#: 32792 Join Date: Feb 2003 Chapter/Region: NESIC Location: lincoln, ri Vehicle: 2003 GGA MBP 12.9 / 105+	it sounds like a boost leak. can you pressure test the induction tract? best way to test a mafs is to swap with a known good one from a buddy.

11-11-2006, 04:10 PM	#3
scooterforever Scooby Specialist Member#: 55011 Join Date: Feb 2004 Location: New England Vehicle: 2002	Thanks for the suggestion, Ken. The problem solved -- it was either the MAF or the O2 sensor or both, but it's all better: I just pulled 4.78 MAF volts on a highway pull. I'm back!!!!!! Details At the suggestion of Crazymikie, I logged my AF learning + AF correction versus MAF voltage at low speeds, and they were all over the place. Mikie's conclusion was a bad MAF or O2 sensor or both, so... given that I have already sunk a fair amount into this new platform (and the idea of washing my cylinders sickens me), I figured I'd swap out the 4.5 year old 76k mile sensors and start fresh. Village Subaru in Acton helped me out and gave me really competitive pricing on a new O2 and MAF sensor, plus they were the only dealer within 100 miles to have both in stock. Props to Village Subaru!!! This morning I swapped the MAF and the O2 sensor. Started up the car, let it idle, and sure enough the AF correction dropped once warmed up. Once warm, I changed my oil for good measure (didn't smell gas in it... but figured I'd start from scratch with fresh oil). Test drive showed the car to be immediately responsive, back to it's old state of enjoyment. 4.78 MAF volts... feels ooo so good.