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Old 12-24-2014, 07:57 AM   #1
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MAF puzzle

A few years ago I got an MAF CEL on my 2000 986S, so I replaced the original 124 MAF with the updated 125.01. I took the car to a shop who said they could do the ECU update. After that, the car ran fine, no CEL.... but when I dynoed the car, it showed a lean condition, around 16:1, at idle and part throttle. Under full throttle it richened up.
I've been using Durametric to try to figure things out. With a new 125.01 MAF, both O2 sensors read 0.09 volts and the MAF shows 18-20KG at idle. Under throttle, the O2 sensors may bump up to 0.2, but not much higher. Looks pretty lean to me.
I tied the 124 MAF for kicks. It also reads 10-20KG, but the O2 sensors read 0.8 at idle (looks rich to me), then drop to nothing under revs...and the engine stumbles.

Anybody else seen this?
The O2 sensors have about 25K on them and the car has a Sotronic reflash.
I've tried unhooking the MAF altogether and MAF reads 0, the O2 sensors read 0.05 and drop when revved, no stumble in the revs, runs great.
From what I understand, at 14.7:1, the O2 sensors should read 0.45
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Old 12-24-2014, 08:58 AM   #2
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Headers?

Different than stock paper filter?

Trying to learn more about the car before commenting
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Old 12-24-2014, 09:13 AM   #3
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is that absolute volts or deviation from lambda?
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Old 12-24-2014, 09:28 AM   #4
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The reading is absolute volts.
The car has headers, 100 cel cats, Borla Muffler, 75mm TB. Here's the airfilter setup (stock MAF housing) w/AEM Dryflow, brand new.
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Old 12-29-2014, 03:46 AM   #5
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Nothing? No experience out there with fuel trim problems and the MAF update?
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Old 12-29-2014, 08:28 AM   #6
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all I can suggest is that, if afrs are that far off then you should be getting a cel. if o2 sensor is broken then you should be getting a cel. can you read out your ltft and stft? they should be pretty high if you are that far off lambda. that's why I think that you are not seeing absolute values but rather deviation from lamda - makes a lot more sense that way ...

Last edited by The Radium King; 12-29-2014 at 09:27 AM. Reason: bad greek.
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Old 02-13-2015, 02:49 PM   #7
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MAF issue solved

I used my Durametric software and with a bit of advice from a local mechanic was able to solve my MAF issue.
Waaaaay back in '07 I had a MAF CEL, so I decided to update from the original 124 MAF to the 125.01 MAF. I haad an Indy do the ECU update, but they said something odd had happened but they couldn't explain. Hmmm... Nevertheless, the car ran with the new 125.01 MAF and my CEL was gone.
a year or so later, on a dyno test, they said I was running lean. Hmmm....
Chased the problem for a while, but no CELS so no worries, right?? not really.
I posed the problem to a different local mechanic, and he said he thought I had an MAF issue. OK. So I pulled the 125.01 from the car and put my old 124 in (I dont throw anything away). At idle, my O2 sensors showed 0.85.... rich, but a long way from the lean 0.045. But the car wouldn't drive. On acceleration, the car stumbled and coughed. Bad MAF. I looked at the MAF in my '99 996 and sure enough it was also a 124. I put it into the Boxster and holy **************** the car runs great. Great drivability, great numbers. I used Dash Command to monitor the 02 sensors while I drove around a bit, and they happily bounced between 0.2 and 0.8. Right where I want them. I put that MAF back into the 996 where it belongs and found another 124 on eBay. That went in, and the car is running better than ever. Off the line it is ON, and the mid range is much better than before. O2 numbers are right where I want them. I'll be scheduling another dyno test soon to see exactly where I am.
Bottom line. If you've got an older car and are updating from a 124 MAF to 125.01, make sure they do the ECU right. Or stick with he 124.
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