Question for you learned folks - what happens when you unplug the lambda sensor on an Exige?
How will the car run? Reason I ask is a stuttering problem at low load and low revs has finally been determined as a dodgy lambda sensor.
A new one was fitted but it seems this new sensor is faulty as it with it disconnected, no stuttering at all, nada, zilch.
It seems to run fine as in no stuttering and crisp low down but definitely feels low on power with the lambda disconnected. I am of course going to get another asap but interested to know what will the engine management be doing with no signal being received from the lambda? I guess I should mention the car is without a cat too.
I have posted on this myself. My s1 ran like a mule, so much so I fitted an Emerald and verniers, which was not set to use the lambda sensor and it was fine. I then found my lambda probe was faulty and fitted a new one and thought I would try the OEM ecu, result, fixed. Runs a bit better than the emerald but is down on mid range power (seat of pants dyno).
A fully broken ( or disconnected) lambda probe should cause the check engine light to come on and the ecu to run the engine in a limp home mode (power down, running rich) A faulty sensor will just confuse the software and it could run like a mule. The probe is upstream of the Cat (I think from memory) so the ecu will not detect a decat.
Winthatt, oh my goodness so you had the exact same issue as me, I wish I had known earlier on! It turned out to be just that, a faulty lambda.
SeanB thanks for the input too!
Perhaps a library of running faults and fixes could be compiled? I would happily help out collating the information if that’s something that folks would be interested in. Perhaps it does exist already and I just haven’t found it? I’m quite new to Exige ownership so on the learning curve…
It has been truly epic getting to this point and I can say that on behalf of the garage too. They were suggesting going down the Emerald route too but I really didn’t feel that was the solution. But you know what, this was a lambda sensor that had been replaced by the garage as part of rectifying a running rich issue yet it turned out it was this lambda that was at fault. Understandably it wasn’t first on the list to be looked at as the cause of the stuttering at 2000rpm.
Has the vacuum pipework & associated T-pieces, etc been checked for breaks, perished tubing and so on?
Also how was the lambda fault detected? Just that sometimes - depending on exhaust, etc - there can be issues when emissions testing because of air being pulled in.
tlracer - Ah yes I neglected to mention the suspected lambda sensor was identified when yet again the car started stuttering and I should have mentioned the symptom was fairly consistently there after the car went into a stupidly high idle that took ages to settle down. It would idle around 2000rpm+ before settling and then sure enough drive off and the stutter would be there.
So the last time this happened - plugged into the ECU to check readings and everything looked normal apart from one fuel trim reading which was static and not moving as would be expected. This was the indicator that the lambda was perhaps stuck/faulty/not doing its thing.
Well folks unfortunately the kangarooring stutter has reappeared after running faultlessly on a big long drive on thursday. Yesterday it started nicely, ran great for a few minutes to the petrol station then started the spluttering again.
There’s a noticeable stink of petrol too. Really quite unpleasant. This is really weird. A replacement lambda and it ran great. Now its doing the same thing again.
It has been parked outside whilst raining heavily. Perhaps water in the plug holes? It had an advanced rain cover system in place tho comprising a towel and bin bag.
The garage suggested it could be the ecu burning out the lambda. I’m not sure what this means or how that can happen. Does the lambda not send a voltage varying between 0 and 1v according to oxygen content in the mixture?
I took a look at the S1 Exige wiring diagrams and to my surprise the Exige has a 4 wire lambda probe (I think a k-series Elise is one or two). I am not clear which wire is which from the ECU but two will be the heater and two will be the input and output from the sensor itself. Therefore, it is possible for the ecu to damage the sensor (I would think) but still unlikely.The heater could burn out which would make it slow to start or the sensor could be shorted. I would think the problem is more likely to be in the wiring harness than the ECU itself. I saw someone was selling a 170bhp S1 Exige ECU, which may be worth a try.
I would have thought any good auto-electrician could check it, there is nothing special on the Exige, it is simple (cheap).
Thanks guys, I’ll take a look at the voltages to the lambda to see what’s going on. Then HT leads and ecu to see how that affects the warm running - all this only occurs once the coolant temp is at 66 degrees and above…
The ecu probably ignores the lambda sensor below 66 Degrees and runs open loop. I do not know that for a fact Brit s normal to run open loop during warm up (one older Efi systems).