Lamda Probes

[Smiffy69]

I have a bit of an intermittent issue where once the engine is warm and I swtich of the car for a few mins then restart it will run for a approx 45 seconds and then the revs drop and it will stall ( not good when trying to get on a ferry). 

After reading various threads on the topic I did some tests and logged some of the parameters through easymap and came up with the following theory.  My question is have I understood how this works correctly and therfore is my thoery valid......

Test 1 ...When you start the car there is a Lamda warm up timer (40 secs) which will cause the ECU to close loop i.e. ignore the sensor and use a default value.  After the warm up timer expires it goes open loop and looks to the Lamda sensor for a reading. During the intial 40 secs the engine idles perfectly as soon as the timer expires it goes all lumpy and stalls. The default lamda target is 1.  My trace shows that when the timer expires the Lamda is reading 0.45.  engine starts to stall (fuel mix being leaned out?) then suddenly lamda jumps to 0.96 it then hunts around 0.6 to 0.96 engine almost stalling each time until it finally gives up and stalls.

Test 2 ....When restarted sraight away the Lamda probe is hunting around 1 +/- and engine run fine even when timer expires.  

Test 3 ... disconnect Lamda (run in closed loop) all runs fine and no problem

Test 4 ..... Reconnect and restarted after approx 5 mins and same results as test 1.

Conclusion - the lamda probe is intermittently reporting whilst it gets up to a proper temperature and is therefore faulty ?

Is that a fair conclusion ? 

if is there a way to repair it (clean it ?) or is a new one required ?

 

[SM25T]

On my k-series it ran really rough when the lambda sensor failed. Unplugging it made the engine run fine. Remove it and get the etched numbers off it and search on eBay.

[simon_h]

Terminology all back to front but yes just stick a new one in first. If that doesn't work then check the wiring to the ecu and the lambda heater.

[Tomiam]

I've just had a slightly different issue, but part of it was that my engine would die when left idiling.  I found there was a ton of corrosion on the connector between lambda sensor and loom.
I cleaned it, engine now runs fine.  
That may / may not help, but thought I'd post my experience.

HTH :)

[Smiffy69]

Thanks everyone for your input (and correcting me on my terminology  )- I shall try a new probe and report back as after further testing I think its a coming up to temprature problem (after ensuring all connections are good and that I get 12volts on the heater circuit)

Another question - whats the best way of mearing the fuel flow through the injectors?  I was using the injection time as a proxy for fuel flow to see how it varied with the Lamda readings to try and make sense of the data.