Hi Lambda Reading

[meldrewlives]

I'm a frequent reader but infrequent poster on this forum so here goes.

Recently had my 993 Targa MOT'd and the Lambda reading was at the very upper limit i.e. reading of 1.03 cf 0.97Min and 1.03Max.

If I understand correctly this is a reading of unburned oxygen in the exhaust? Can't see anything obvious e.g. hole in the exhaust and wondered if anybody had a view on likely cause? Have to admit the recent post about MAF sensor failures made me wonder whether it could be related to something like that.

It's due a service in a couple of months so I'll get it looked at then unless anybody thinks it's more urgent.

Edited to say: Oops that subject should be High Lambda

>> Edited by meldrewlives on Monday 9th January 12:52

[domster]

If the car runs fine with no misfiring then don't panic. It's a mixture thing, the lambdas compensate for the fuelling/ignition anomalies of your individual engine. If it's running lean/rich beyond what a lambda can compensate for, then yes, something more serious may be wrong in your engine and you may get misfires/detonation whatever. But remember, lambdas can play up and need replacing... I wouldn't treat what it says as gospel.

Don't panic and maybe ask the question next service, unless it starts running like a dog.

[Rocket123]

Once my 993 failed the emissions test with a reading of 1.075. However when I pointed out to the morons operating the machinery that they had the wrong year of manufacture, they re-ran the test and it passed. I think they changed the MOT test procedure for emissions for cars manufactured after 1st January 1996, hence the difference.

Anyway the point being that was 4 years ago, and my car still runs fine.

Rocket

[meldrewlives]

Thanks guys - it seems to run fine; get a little 'driveline shunt' at very low revs when traffic crawling in first and I come off the accelerator but that's all.

Rocket - your point made me look back over previous MOTs. I've had the car since new and up to 2000 the Lambda min/max was 0.95-1.05. Then for some reason it changes to the ones I quoted in my original post. I'll ask the garage whether they used the right standards next time I pass there.

[elfer]

I was thinking the same last week. My 993 went through its MOT on Friday, also with 1.03. I checked my history file and found it was 1.03 last year too (at a diffferent testing station). Three years ago though it was 1.018, on it's TUeV test at Zuffenhausen.

So it's testing leaner than it did in Germany. OK I thought, either a) I've a small air leak that's got no worse in the last 12 months, b) 1.03 is normal for a 993 and the German equipment was mis-calibrated, c) UK fuel causes it to run leaner or d) the car wasn't properly warmed up for the UK tests. My money was on answer d.

Any idea what your Targa got last year?

I also get that slight drive line shunt in low speed traffic....

[domster]

What's the mileage?

If it is a bit rough at idle etc. and mileage is 100k plus then maybe the injectors are worn and 'dribbling' at idle. I suppose this could cause the lambda values to fluctuate as they try to prevent hunting.

Not sure, but don't fret if car drives OK through the range. If lambdas fail the ECU will run a rich default map, so it won't run dangerously lean. A little driveline shunt could just be the mapping, especially if at slight throttle openings.

[elfer]

I realise you're asking meldrewlives but mine's done 65k

The slight driveline shunt i get is a low throttle, low speed snatchiness. (Say I'm trying to hold 30mph in 3rd with a constant, small throttle opening. If I ever-so gently reduce throttle pressure ever-so-ever-so slightly it's as if I've abrubtly lifted off completely.) Mapping makes sense. Thank you.

[meldrewlives]

Domster - mileage is 54,000 so more likely mapping than injectors I think. Elfer - at the previous MOT the Lambda was 1.012 so it's apparently running leaner now than previously. Don't know whether the fact that it's on Optimax now and probably wasn't back then makes any difference, don't think it should. I too wondered whether it was properly warmed up for the test. It'll all get sorted at the next service anyway.