Mot emissions fail

Too lean. Not sure which side probe went in, or whether tester tried both. Engine passed in this spec last year after rebuild etc. Thoughts? Mot tester queries whether it may be an air leak in exhaust, which is newish (before last year's Mot) stainless manifolds and 200 cell cars. And knackard re-welded several times PSE rear boxes........... Car runs lovely, idles fine. No fault codes....... Cheers James

Can't see it being a leak in the exhaust as the fumes leak out, not suck air in. Was at tickover or at higher revs that it failed on?

Ive struggled for several years with emissions , ive changed most things and still no better , but always seem to scrape thro in the end

Hi Alex, Hmmm, yeah thought the same. The sheet seems to indicate the speed between 800 and 1500. So idle as opposed to 2000 rpm. No running issues at hot or cold that I can detect from driver's seat. Lambda sensors probably quite elderly. All manifold and Cat bolts tight. Some very small blows from various bits around boxes and pipe join to the Cat pipe. May have to actually take it to a Porsche indy!!! Not done that for a couple of years..... Cheers BHZ661 - that's what I want to avoid if at all possible. I'll pull a spark plug or two and see what they look like may be. Cheers

If its around tickover I'd suggest maybe your MAF is giving an incorrect reading.

Maf should read approx 16 kg/hr .. with a voltage of 1 volt engine not running .. approx 1.27 volts running ... over 1.1 volts ignition on and the maf needs replacing . 200 cells and you need to get them stinking hot to get a pass .. it might be just that . Not sure if you have post cat sensors but i'm afraid that yes a crack or a leak will allow air to enter the exhaust and cause an incorrect reading .. normally on post cat lambdas and its a cause of an eml light on .. not always obvious shall we say . You also have a possible inlet manifold air leak .. faulty lambda sensors .. i could go on .. It's a case of looking for fault codes or looking at actual values for the different sensors and trying to figure it out . Im afraid im not allowed to borrow a tester other wise i would have EDIT .. Just to point out an eml light on is normally to do with save the planet stuff and not an actual running fault . Common to have an eml light on and no obvious running problems .. manufactures are more concerned with saving the planet than the car .. that's current legislation though so they have no choice . Im certainly not going to argue that this is a bad thing though .. just pointing out a how it works

Uh oh! Could be in for a long haul then! Will test MAF first. To summarise: Engine off, ignition on. Should be 1 volt. Anything over 1.1 and it's shot. Engine on. 1.27 volts should be seen. Which pins of the four should I be looking at Iain? By the scrapes on the tailpipes. Probe has been up both pipes, which indicates an overall problem rather than a leak in the exhaust I feel, but then if both silencers are toast, maybe not. Only have pre cat lambda's. Looked for codes, none displayed. Cheers

Just realised that doesn't work as I can't get to the pins with the connector connected to feed it! Cleaned it with tihnners. If the engine runs and idles, if I disconnect the MAF, should the engine change speed etc if it's working? If nothing changes can I safety assume it's not working?

Pin 5, you may be able to get a paperclip or suchlike onto the connection with it still plugged in, that`s what I normally do at work :thumb: