Thursday 13 July 2017

Lambda Senor Rewire

For a long time now it has been intermittent and I had the same symptoms with 3 different sensors so the next suspect was the wiring.    So I stripped it all out and it wasn't good.    

From where the 4 wires (2 x heater, earth and signal) exited the loom near the alternator they had just been bundled together with insulating tape, all red, and sent down to the sensor.   What should happen is the signal wire and it's earth should be screened cable to avoid interference from the alternator and ignition.  So out it all came, carefully labelled

I reused the 2 heater wires and made proper plug connections at the end so I can swap Lambda Sensors just by plugging and unplugging.   Then I used some 2-core screened cable to go from just by the loom down to the sensor, again using proper plugs.
Started the engine (She has been on axle stands for 3 days), plugged in the laptop and watched.   And no-one was more surprised than me when everything started working properly.   So dropped her off the stands and took her out for a run.    She went beautifully all the way to Colsterworth and back, very crisp and responsive, so I was very confident.  However, when I checked the data I found this:

She she was working fine until the 9 min point then there was a catastrophic failure.    But the reason I hadn't noticed was that the ECU had seen there was a problem and switched me into Limp Home mode.    So that was disappointing,

But at this stage I suddenly realised there was a nasty burning smell from somewhere and when I took the bonnet off the reason was obvious.   Smoke was pouring off the exhaust.   And this was the cause.

Although I had carefully routed the wires away from the exhaust pipe on initial assembly, when I had finished underneath there was a lot of wire hanging down so I had pushed it upwards to secure with a cable tie.    That must have pushed the signal wire against the exhaust pipe.   Luckily I bought 2M of cable and used only half of it, so it will be a simple job tomorrow to replace the wire.

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