Tuesday, 30 May 2017

Lambda Sensor (contd)

Spent a lot of today looking at the lambda sensor.   First thing to do was rebuild the exhaust pipe so the sensor could be changed in-situ without having to take the exhaust off.

So now it is facing the ground, still angled a bit to give room for the heat guard to go back on.   And the 4-way block added to allow easy switching of sensors.  And as I am relatively convinced the present sensor has been 'poisoned' by the emissions from the supposedly sensor-safe exhaust paste I used to seal the joints I decided to just use an exhaust bandage and two half pipes clamped over it to seal the joint.

Next was to try the spare sensor I had in the drawer that came with my spare 'MOT' exhaust pipe (that pipe is presently fitted with a brand new sensor) .   This was not as simple as it sounds.   Most manufacturers have standardised on white for the 2 heater wires (doesn't matter which way around they go), grey for the sensor signal and black for earth.  As you can see from the picture, this sensor came with black/black/blue/white.   A search for a wiring diagram confirmed that the heater was black/black, but if it had come from a Honda then the blue was signal and white was earth, but if it came from a Toyota then it was the other way around.   And I wasn't overly confident anyway as the previous owner had said he ran it for a long time not even wired in.

So first attempt was using the Honda system with blue as the signal.   A quick 5 min run around the houses and all I got was a flatline.  So for the second attempt I switched the wires and did the same run and the result was still a flat line.   So either I still have the wiring wrong or the sensor is shot.  I suspect the latter.

So for the third attempt I took the brand new sensor from the MOT exhaust and wired that in.  Same run and this time I saw the system go into closed loop very quickly and it stayed locked on for the whole trip.   

MEMSAnalyser confirmed the behaviour, that it switched in after 45 seconds.
So I now know that the sensor from the drawer is probably shot.    And now having had the chance to drive under the 2 systems, open loop and closed loop, back-to-back I can tell that the closed loop run was much better then the open loop one.    While the car drove perfectly well with a dead sensor, with a working sensor she is so much sharper and crisper and and much more positive acceleration.   So I would prefer not to drive without a sensor (even though I did it quite happily for the first 2 years)

I am a bit wary about using my brand new one, as I would prefer to keep that one for MOTs.   On the other hand the 'official' sensor runs to about £60.   So before shelling out for another one I am going to try 2 experiments:

1.  I am soaking the old one in petrol overnight as apparently that might clean off any impurities.

2.  I will get a cheap one (£7) off E-Bay and see how it works.

So we'll see how I get one with those.


  1. Are you sure vertical is good? - I'm not sure how critical it is but my new sensor advocated max 60º from vertical to prevent condensation damaging the sensor.

  2. Good point. When I figure out the final solution I will change it so it points up about 15 deg from the vertical. Need to redesign my heat shield.