# Lambda disconnected how this affect engine and operation



## RARCGTI (Nov 27, 2004)

Hi 

Since i bought mi rabbit GTI the oxigen sensor connected to the headers is being disconnected and the car works vey very good ,it has a neuspeed throat with the fuel enrichment switch connected but i dont know if it works becasue if you push this nothing happened ,i read about the lambda operation and i understood that controls the ideal air fuel ratio ,if the lambda is disconnected how can affect the engine? is it necessary to be connected if its running very good? if i change a new sensor will the performance reduce?

REGARDS


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## WaterWheels (Aug 14, 2005)

RARCGTI said:


> . . . if the lambda is disconnected how can affect the engine? is it necessary to be connected if its running very good? if i change a new sensor will the performance reduce?


Don't really know or understand just how people came to the idea that the Lambda sender (O2 sensor) causes a reduction in any kind of performance. I mean really, think of all the vehicles running around with one or two of these sensors and how much power they make. You don't hear anyone with some of these high end vehicles asking if they will get more performance by deleting the sensor now do ya? Your older car is really no different. That "enrichment" switch on the throttle is to remove the Lambda system from the mix when under full throttle driving (going open loop as it is said). It does not by-pass or really delete the system, but rather send a fixed duty cycle to the frequency valve to enrich the mixture some. 

Is it nessary to keep it connected, the Lambda system? No, CIS began life without having it, CIS basic, and it was one of the first items added to help with emissions. But I think if you really decide to delete the system then remove it altogether so than if something fails it does not effect the running of the engine. Remember, with the sensor disconnected the system is sending a fixed signal to the frequency valve and if the box fails or some of it's wiring it could cut fuel or make things richer suddenly. You are not really running CIS basic right now but more like downgraded CIS Lambda, the electronics are still in play. Right now the mixture is set (adjusted) to the fixed frequency valve, not completely mechanical/hydraulic as with basic.

I would suggest repairing the system, if it needs fixing, and tuning it to the complete working Lambda system. It will help save some gas while driving normal and still provide enrichment when you stomp on the pedal too.


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## RARCGTI (Nov 27, 2004)

Thank you very much for the explanation ,i will check the system because yes my rabbit burn to much fuel 

REGARDS


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## Mtjade2010 (Dec 2, 2010)

The Lambda sensor is basically an oxygen sensor. It feedbacks a signal (a DC voltage between 0 - 0.9 volt) to the ECU, which controls the frequency valve to regulate the fuel system pressure to adjust air/fuel mixture. It's a close feedback loop for the purchase of emission control. If you sensor is disconnected the feedback loop becomes open there is no control any more. So if your air/fuel mixture is rich your gas mileage suffers and your CO, HC emission all go up. 

I believe the PO disconnect it to make adjustment to increase air/fuel mixture ratio to boot power. When the air/fuel mixture is at 14.7:1 the emission level is at the optimal. But the engine performance suffers a little. The engine performance is at the best when it is around 12:1. At this mixture level the emission will be very very bad though. 

You can restore it back to what it should be again. Just connect a digital volt meter to the disconnected lead of the Lambda sensor and adjust the mixture screw at the AFR until the voltage reading is around 0.45 volt. Well, it will not stay at 0.45 volt. It is likely it will be near 0 (lean) or near 0.9 volt (rich). Just adjust the mixture adjustment screw to a point where it is about to cause the sensor voltage to flip from rich to lean or lean to rich. That's the base point of the mixture adjustment. At that point you can reconnect the sensor to the system and let the ECU to keep the mixture ratio at bay. You will find that your gas mileage is back to much more reasonable level and your emission will be clean. Performance wise it will be as good as it should be. Unless you race a lot you won't feel the performance difference.


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## dkfackler (Feb 8, 2010)

Even better is connect a dwell meter to the blue wire in the test connector and adjust the mixture screw until you get the Bentley-recommended reading.

Check with Bentley for additional procedures-- like disconnecting the crankcase breather hose, ensuring timing is correct, idle speed is within spec, all electrical consumers are 'off', etc. 

Sometimes you get into a circular situation with CO setting/idle speed, but be persistent and you'll figure it out.

In any event, if the voltmeter or dwell meter readings are rock-steady and don't fluctuate, the sensor is toast and you need to replace it.


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