O2 sensor - Page 1 - Porsche General - PistonHeads UK

Well, 02 or Lambda sensors are used to gauge the amount of unburnt oxygen in the exhaust fumes (I think?) and therefore show the ECU what kind of fuel/air mixture the engine is burning (ie too rich, too lean). Lambdas only kick in after the cats have warmed up and the engine is warm, and then they go 'open loop' and start to regulate mixture. If too rich, they will lean back the mixture, if too lean they'll enrich it. They are important on cat cars because unburnt fuel (ie too rich) will destroy a cat. They also help you get decent fuel economy by providing optimum mixture at all functioning times. Lambdas can alter the fuelling many times a second, and a malfunctioning one is often the reason for a hunting idle... they may tell the engine to run rich (revs rise) then kick in the other way and lean the mix (revs fall) then enrich again and the process repeats... If you disconnect a lambda, engines will normally go into a default setting, running rich to prevent detonation caused by a lean mixture. Therefore, if suddenly you only get 10mpg instead of 15mpg, this could be a malfunctioning lambda. They are wear items in my opinion, and need replacing every 3 years or so. So yes, you can disconnect them, but unless you tell the ECU, they may just go to a default setting and cause over-rich running. Cheers Domster PS All the above is just how I understand it, and I'm not very technically minded, so it may all be bollocks. Someone like Colin/NineMeister will be able to talk for England on 02 intricacies... >> Edited by domster on Thursday 31st October 10:10

Cheers Dom, all as expected but, specifically, how does it interact with CIS and is it normal to use it when you have a cat bypass????

Err, what is CIS? I am being You can keep your lambda with a cat bypass, it will help keep the mixture at the correct levels.

Is CIS the pre-Motronic injection setup as used on the 911SCs?

CIS is the fuel injection used by the 3.3 turbo. It is a mechanical based injection system. Given that it has no ECU how does it regulate the fueling???

D'oh. CIS or Continuous Injection System is a bad term to pick as it covers both K-Jetronic (semi-mechanical) and early Motronic (electrical) systems. For the record, K-Jet is fitted to the late 2.4T, all 2.7 & 2.7S, 3.0 Carrera, 3.0SC, 930 3.0 and 930 3.3. Oops, and the 924 & 924 Turbo, sorry wetheads. Now, the system on the 965 Turbo is still K-Jet but has an additional electronic controller in the form of a frequency valve that regulates control pressure (and hence mixture) and I think that it is known as KE-Jetronic (don't correct me if I'm wrong, I don't need to know). Anyway, the reason for KE is to allow for accurate mixture control, basically to run it within the range for successful Cat operation. Dom is spot on that it is the Lambda sensor that measures the mixture in the exhaust and sends a voltage signal back to the "brain" to then action a change; this process provides continuous measurement and adjustment of the mixture. Normally the system only works at low and part throttle because the standard sensors are only "narrow band", in other words are accurate only around stoichiometric (ideal) mixture, typically from La 0.95 to 1.05, if ideal is 1.0. For motorsport applications you need to run with wide band lambda (0.75 to 1.1). Maximum power is usually achieved at La 0.90-0.94 on a normally aspirated engine and La 0.85-0.88 on a turbo and you risk damage to the engine if you run it lean flat out. Don't panic though as standard control systems do not operate in this region, you rely on the chip mapping or the basic adjustment in the case of K-Jet. Proper motorsport La sensors are usually heated and fully temperature compensated and are now using a 5 wire LSU or NTK sensor. Our Motec PLM stand alone measurement system uses the LSU sensor and will record mixture from almost cold, is accurate to .001 and has a range from La 0.7 to 32.0, but at £1000 a time I don't think I'll have many takers just to see what is going on in the exhaust when you're driving. It is ideal though for mapping and adjusting K-Jet/carbs on the road. Finally, Lambda sensors will last for up to 5000 hours (5 yrs +) or more depending on the quality of fuel used, but the system will detect them as faulty if they do fail. So DO NOT go out and replace perfectly good sensors unless they are diagnosed correctly as duff, OK? All you will do is waste £150 and risk damage to the exhaust getting them out. >> Edited by ninemeister on Thursday 31st October 11:20

My reason for asking is that I mentioned to a mechanic that I had a cat bypass and he started waxing on about my O2 sensor and whether it had been removed. If it has been removed is this a problem?

Only that the engine may run rich at idle and light load, so keep it in as it does no harm and saves fuel. Actually, if you look at lambda response, the mixture will oscilate from rich to lean in order to "cycle" the cat up to temp and help to keep it clean, so in theory running without could have it perfect and not cycling. But don't be fooled, if the adjustment is a fraction out the lambda will beat it every time. If you have one leave it in. If you haven't, don't worry.

What exactly does it do on a T2 and what happens if you disconnect it???