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Old 04-15-2015, 02:27 AM   #1
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Lambda high - No fault codes

Just broken the 986 out of winter store, having been parked up due to the steering blowing a line. Replaced the rack and the coffin arms, alignment done, just went for the annual inspection and the lambda reading is 1.034 - pass is .97- 1.030

so it's running a tad lean !

my first suspicion was an O2 sensor, however, there are no fault codes thrown. at all.
Also there is a slight misfire at 3000 RPM.

I've run MAF cleaner through the ilet, cleaned the K&N filter and just about to check plugs. Also the fuel in it has been in there since November.

AOS was replaced max 3,000 miles ago

Anyone have any thoughts ?
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Last edited by Bruce Wayne; 04-16-2015 at 08:22 AM.
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Old 04-15-2015, 05:16 AM   #2
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Disconnect the MAF and check Lambda. This will tell you if it's MAF. Also, check Lamba for both banks.
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Old 04-15-2015, 07:42 AM   #3
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'Also the fuel in it has been in there since November.'

Did you put in fuel stabilizer before storage? Either way I'd burn through the tank and see what the readings are with fresh fuel. Who knows what happens to all those hydrocarbons over the winter and how they effect all those sensors.

Nice avatar pic BTW.
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Old 04-15-2015, 10:29 AM   #4
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Interestingly, the readings i have are as follows:

Short Term Fuel Trim Bank 1 - Average 2.64

Short Term Fuel Trim Bank 2 - Average 3.56

Long term on both are the same values


O2 Sensors

Bank 1 sensor 1
Output Voltage 0.115v - Average 0.39

Short Term Fuel trim Average 2.86

Bank 2 Sensor 1
Output Voltage 0.705v - Average 0.41

Short Term Fuel Trim Average 3.33



What i'm interpreting from this is that the Bank 1 Sensor Voltage seems down and is causing a the fuel trim to lean off. But then I'm kind of fixated on O2 Sensors at the moment having just had to replace on the range rovers !!

Any alternative theories greatly appreciated.


PS re the avatar
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Old 04-15-2015, 10:52 AM   #5
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Could be a vacuum leak, bad fuel pressure/volume.
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Old 04-16-2015, 03:19 AM   #6
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Ok, having run a couple more tests..

the live reading at 3,400 rpm shows an Air Flow Rate of 0.75g/s.

Disconnected the battery for an hour

the live reading at 3,400 rpm shows an Air Flow Rate of 1.0g/s.

If i compare that to the other 3.2 boxster (tip) it shows an Air Low rate of 18.25 g/s at 3,400 RPM

The O2 sensors are within range, so this is leading me to think an issue with the mass of air reading at the air flow rate.


MAF ?
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Old 04-23-2015, 09:43 AM   #7
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So having changed the MAF, i now get proper Air Flow readings.. no longer 1.0 across the board and at any RPM.

Took the exhaust out today, the elbow joints were blowing slightly, so used heat proof aluminium tape to provide a good seal to the end joints and wound the sleeve clamps up tight..

Bingo.. Lambda dropped from reading 1.034 / 1.041 down to 1.01 Mot passed.

Nb. I noticed from the annual MOT data that i have done a total of 7,000 miles since 2011 !
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