Lamda Sensor & sports exhaust

[Subversive]

quick query.

I have the PSE fiited to my 2001 boxster S with the valves in permanent sports mode. The car has just gone thru it's UK MOT but the high idle rev emission test is 0.01 outside the tolerated value. My question is should the offical PSE effect this emisssion value when its in permanent sports mode. OR does this not matter and somthing else could be causing the high reading eg. faulty lamda sensor.

I have also de-snorkled the car could this also effect the lamda sensor readings ie the car is now running to rich ?

Anybody had a similar situation with the their local emmision test station with a similar boxster setup ?... :(

[0586slb]

Longer response - :D

If the PSE was connected with the valves working as designed, it would not change a thing. The valves are opened and closed according to roadspeed - not engine speed. I can't remember the exact speeds, but something like 0-35mph is loud, 35-50mph is quiet and then they open up again. All it does is bypass the muffler chamber, so will not have a bearing on the emmissions (being downstream of the Cats).

Again, de-snorkling is well upstream of the MAF sensor, so other than a change of expected intake air temperature this will not have a bearing either.

Usual suspects are the MAF, Lambda probe or an air leak. To diagnose effectively, you need a diagnostic tester to read any DTCs, and to check values like the Long Term Fuel Trim and such. The diagnostic tester will also show if the DME is popping out of Closed Loop Control of the emmissions.

You didn't mention which value was 0.01 outside limits - HC, CO or NOx?

[Subversive]

the value is 1.04 the lambda tolerence on a UK MOT is 0.97- 1.03

not sure if its the HC or CO. I'm taking it down to jz machtech on thursday for a porsche diagnostic test. With this test will they know if its the Maf, lambda, or exhaust leak ? the other thing i did was take the foam off the back of the filter would this make a difference?

[Subversive]

this looks like the sensors as i have had the exhaust checked over for leaks and replaced the air filter still no joy still reading 1.04...;-) Can someone advise if I will need to replace all 4 lambda sensors or the 2 that are pre cat or post cat. At 80 quid each they are quite steep

thanks

[0586slb]

Ad Hoc changing of parts can be expensive. You have to have some form of diagnosis carried out to direct your fault finding. I did not mention in my earlier post that failure of a Catalytic Converter may also exhibit the same symptoms. This is why you should have a robust diagnosis done.

[Paul Fraser]

Had the same problem 1.142/1.098 against a 1.030 pass. A few questions...

My CO/HC were 0.016/000% and 13/6ppm which is virtually nothing, so I assume this means all the fuel is being burned, so what is the lambda value actually showing...?

Secondly, what readings do I need to be able to pull off the OBD-2 serial cable I have. Will I be able to with this OBD reader; if not which one will provide the information. TIA.

[Paul Fraser]

OK, more on this: got my OBD2 reader up and running and found that I can get readouts on the sensor voltages, short and long term fuel trim figures. Can anyone give me advice on what the results mean or where I can find out, thanks.

PS found out some useful info on what the lambda sensor does on Wikipedia.

Edited January 29, 2008 by Paul Fraser

[Paul Fraser]

OK, changed the lambda sensors, checked the air inlets and exhaust for leaks, put some injector cleaner in a fresh tank of petrol, cleaned the MAF and it passed, though only just. So I wonder which one it was.

FYI, changing the lambda sensors was a nightmare. They seemed to be stuck solid, but fortunately my uncle (whose pit I was using) knew a garage owner who is semi-related and we ended up at his on Sunday afternoon watching him repeatedly heat the probes with oxy-acetylene. Three times for the nearside and twice for the off. Once he managed to crack them he left us to it. Still very hard to release them. Not helped by the fact that a 22mm spanner was too loose to turn them and we had to use mole grips (corrosion of the nut I guess). Am going to look for a mini-oxy-acetylene kit as it seems to be the only way to get these really stuck bolts etc. to move.

Will post the OBD2 readings I got off the old and new sensors for other's reference when I get the chance.

PS 0.008% CO, 20ppm HC, Lambda 1.29 Still seems to be running a little lean.

[Tee]

My Boxster failed its MOT so I drove the 50 miles to my local specialist to have it checked out. It was tested the moment I arrived and the readings were perfect!

We put it down to that the cats were not at full working temperature when the vehicle was first checked. In future I will take my cars for a 'spirited drive' before Mot's!!