McDonald Posted August 21, 2022 Report Share Posted August 21, 2022 My 987.1 failed the MOT as Lamda readings were a little high. On inspection, the exhaust seems fine. Technician says it may be an electrical fault or problem with engine management ( no light showing). What kind of issues might cause this? The car runs very nicely. Quote Link to comment Share on other sites More sharing options...
McDonald Posted August 21, 2022 Author Report Share Posted August 21, 2022 By way of further info:- MOT carried out by Porsche Portsmouth. Fast idle reading was 1.29, second reading 1.23. Engine temperature warm as I'd driven 20+ miles to the test. I run the car exclusively on Esso supreme fuel. The car is already booked into Precision Porsche. I'm curious about a likely electrical fault, are we talking about a sensor? Quote Link to comment Share on other sites More sharing options...
Paul P Posted August 21, 2022 Report Share Posted August 21, 2022 very generic guess but I would say maf or cat(s) on the way out. It could be a sensor but sensors tend read improbable things or stop working rather than read a bit wrong. the specialist should be able to read live values a get a feel for the likelihood of a particular component. Quote Link to comment Share on other sites More sharing options...
McDonald Posted August 21, 2022 Author Report Share Posted August 21, 2022 7 minutes ago, Paul P said: very generic guess but I would say maf or cat(s) on the way out. It could be a sensor but sensors tend read improbable things or stop working rather than read a bit wrong. the specialist should be able to read live values a get a feel for the likelihood of a particular component. Thanks Paul, I always try to prepare myself for visits to the garage. Some considerable expense sounds likely from your analysis.🙁 Quote Link to comment Share on other sites More sharing options...
Paul P Posted August 21, 2022 Report Share Posted August 21, 2022 11 minutes ago, McDonald said: Thanks Paul, I always try to prepare myself for visits to the garage. Some considerable expense sounds likely from your analysis.🙁 Internet guesswork at its best. Depends on what they find good luck. 1 Quote Link to comment Share on other sites More sharing options...
BBB Posted August 21, 2022 Report Share Posted August 21, 2022 High lamda readings are often air leaks, but it would have to be before the sensor. Quote Link to comment Share on other sites More sharing options...
McDonald Posted August 24, 2022 Author Report Share Posted August 24, 2022 On 8/21/2022 at 10:16 PM, BBB said: High lamda readings are often air leaks, but it would have to be before the sensor. Thanks BBB. The tester seemed confident that the system looked ok, hence the electrical suggestions. But perhaps he wasn't making a thorough examination. Porsche offered to charge me two hours labour to investigate. I think my Indie will find it more reasonably. Quote Link to comment Share on other sites More sharing options...
½cwt Posted August 24, 2022 Report Share Posted August 24, 2022 How rusty are the nuts on the 3 stud flanges? These joints can look OK but lose clamping pressure and start to leak a small amount if the studs or nuts corrode too much. 1 Quote Link to comment Share on other sites More sharing options...
And.rs1800 Posted August 24, 2022 Report Share Posted August 24, 2022 On 8/21/2022 at 10:16 PM, BBB said: High lamda readings are often air leaks, but it would have to be before the sensor. I thought that a high lambda reading with the other readings normal means a leak after the lambda sensor. If the other readings are high it indicates a leak before the lambda sensor surely? Quote Link to comment Share on other sites More sharing options...
And.rs1800 Posted August 24, 2022 Report Share Posted August 24, 2022 35 minutes ago, ½cwt said: How rusty are the nuts on the 3 stud flanges? These joints can look OK but lose clamping pressure and start to leak a small amount if the studs or nuts corrode too much. Exactly this. Quote Link to comment Share on other sites More sharing options...
BBB Posted August 24, 2022 Report Share Posted August 24, 2022 46 minutes ago, And.rs1800 said: I thought that a high lambda reading with the other readings normal means a leak after the lambda sensor. If the other readings are high it indicates a leak before the lambda sensor surely? You could be correct, I just can’t see how a sensor can detect a leak that occurs after it has already reported a reading. Quote Link to comment Share on other sites More sharing options...
½cwt Posted August 24, 2022 Report Share Posted August 24, 2022 10 minutes ago, BBB said: You could be correct, I just can’t see how a sensor can detect a leak that occurs after it has already reported a reading. Damned clever these Germans...! The post cat lambda is very close to the joint so back pressure, or lack of, can come into play. The 986 is much more vulnerable to this as the equivalent joint is upstream of the sensor. Quote Link to comment Share on other sites More sharing options...
And.rs1800 Posted August 26, 2022 Report Share Posted August 26, 2022 any updates? Quote Link to comment Share on other sites More sharing options...
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