Dodgy Lambda- which one?

[ChrisPap]

Hi Guys,

I've had a stuttering/stalling and high idle problem lately which I traced at least in part (and thanks to EvoOlli's software) to a failing ECU water temp sensor. The idle would increase to 1500rpm whenever the Temp signal fell from 'hot' to -3 deg.

But while I was into the ECU looking a stuff, I found that the Lambda's and adaptives were out. I'm thinking that Lambda 2 is stuffed, and that's screwing with the adaptives, but I'm not sure what the values should be. Can anyone sanity check me, and tell me what the lambda's are off?

Below is the average of all reading over a run (after the adaptives were reset) and below are the graphs.

Lambda1 Lambda2 Adaptive1 Adaptive2
0.51 0.79 0.64 -4.93

Edited by ChrisPap on Tuesday 13th May 13:30

Edited by ChrisPap on Tuesday 13th May 13:53

[EvoOlli]

A Lambda value of around 0.9-1.0 Volts means rich, a value of 0.2-0.3 Volts means lean mixture. So Lambda2 tells the ECU the mixture is too rich and the ECU then reduces the fuel resulting in a negative adaptive. The mixture never goes to lean which it normally should.

Problem now is to find out: Are the values correct and the fuelling is really too rich or is the Sensor faulty.

I would, in a first attempt, change both Lambda Sensors among each other in the exhaust manifold (don't forget to exchange the plugs too ;-)
If the problem stays on Cylinder 4-6 there's something wrong with the injection. If the problem moves to Cyl123 the Lambda Sensor is faulty and needs to be renewed.

[Tom74TVR]

Hi,

I had about the same issue and had to replace both sensors (about 200 euro's for both) but this meant taking out the entire exhaust so it took some time.

Tom.

[ChrisPap]

Thanks for the suggestion Olli. Looking again at the data it's helpful to see the throttle trace as well. Lambda 2 is clearly staying rich when off throttle, but I wasn't sure if that was normal (and the reason for the pops and bangs), but the more I look, it just looks wrong to me.

[EvoOlli]

Hi Tom,

why did you remove the exhaust ? I changed the Lambdas in situ. Only thing I removed was the battery to get access.

[twinreal]

Have a similar problem and my logs of the lambdas look quite the same:



I changed both lambdas but the problem remained, so i don't think yours are faulty. They switch, so they seem to be ok.
As you can see in the log my adaptives are very different. I guess that's because my first two throttle body spindels are worn and getting false air. A "new" set is waiting to get installed.

Are your pots ok and in sync ?

[EvoOlli]

Sorry, but completely different situation....

[twinreal]

For the problem yes, but for the lambda no.
But i'm out of your exclusive thread again ;-)

[ChrisPap]

OK, so this was yesterday:


And this was just now after Olli's suggestion of swapping the sensors:


I couldn't do any more than run it up in the garage because I didn't have time to put it all back together properly and take it for a drive. But to me it looks like now Bank 1 is giving the dodgy lambda readings, indicating that the lambda is screwy, but Bank 2 still has the leaned out Adaptive. I reset the adaptives, but maybe that just puts it in learn mode and it takes a while to get there?

Any help (or a graph/good data from a healthy car for comparison) appreciated!

Edited by ChrisPap on Wednesday 14th May 14:08

[ChrisPap]

Hi guys,

sadly, the saga continues. I managed to find the correct lambda (o2) sensor, albeit with the wrong wiring, so I had to splice the old cable on. Decided to move the existing good sensor from bank 1 to bank 2, and the two lambdas now look much better and closer, although maybe the older sensor now on bank 2 is starting to feel it's age, or maybe it's being thrown by the adaptives?



So the adaptives still look wrong and still on bank 2. It's trying to lean the mixture on the rear 3 cylinders, though Lambda 2 is still reading higher than 1, and I don't know why. Is this normal? The Adaptives are negative and the pulse with on the rear injectors is less. What is normal? Has anyone seen this before or got any ideas?



and this is the diag screen at idle:



and with some throttle, just manage to capture it when adaptives matched, but you can see injector pulse does not:

[EvoOlli]

Did you reset the adaptives again ? How long did you drive with the new Lambda Sensor to get reliable Adaptive Mappings. Or does it happen as soon as you have reset the adaptives ?

Could you read out the adaptive maps (both banks) and show us the table (You need the old TVR Software for that, sorry).

[ChrisPap]

Hi Ollie,
Yes I reset the adaptives just before I started that log. And then drove for about 4 minutes. I can go for a longer drive tomorrow. But the bank 2 adaptives go negative within seconds after reseting the adaptives. It's starting to make me a bit crazy!

I can send you the data file if you like? I'll have to see if I can get the old software working on Virtual XP machine to save the tables.

[EvoOlli]

Let's try one thing: Unplug Lambda 2 => the ECU get's zero Volt which it should interpet as lean. And then try again after resetting the adaptives. Would be interesting if it still tries to lean out bank 2.

[craigcaf]

You might need to replace the other sensor as well. A lambda sensor does age in the same way as a catalyst. Not only do you have a zirconia oxygen sensing cell, but also there is a catalyst function usually in the form of platinum/cerium oxide. The sensor and catalyst function are poisoned over the long term, particularly by phosphates from the lube additives. This can cause the sensor response rate to reduce which can lead to a bias in the signal. You don't easily see this when both sensors are the same age as they have the same response rate to AFR changes and adaptives will be broadly similar. However here you are comparing a brand new sensor with an aged one, and perhaps unsurprisingly you are seeing a relative drift between the sensors. I'll wager if you replace the other one as well and reset the adaptives, you'll be fine.

If you want to know more google something like "phosphorus poisoning lambda sensor". Also quite a good Wikipedia posting on the subject. [edited for clarity...after too much beer].

Edited by craigcaf on Tuesday 20th May 19:16

[spitfire4v8]

I think you're looking at it from the wrong way ..
your lambda traces are fine, you've got to work out why the adaptives are trimming unevenly ..
either your airflows are out (one bank too high one bank too low) or one of your injectors (or more) is flowing poorly on the bang that's trimming richer ..
either way leave the lambdas alone and look at something more mechanical on the engine ..

[EvoOlli]

A thing you can do too: Do you have an infrared thermometer ? You can measure the temperature of every single exhaust tube to check if one cylinder is not working properly...

[ChrisPap]

Update:

Still not quite perfect but I managed to get a syncrometer (not that easy in this age of fuel injected plenum chambers!) and found that the banks were out (less flow on the rear bank) and now with the lambda and TB balance it's 90% there. Ideally it needs the other lambda doing I think and probably clean the injectors but it's runs a lot nicer now, feels so smooth on power and a nicer throttle response.

Oh, also found that it's not getting 100% throttle. Need to find where the end stop adjustment is....

[twinreal]

94% throttle pot = 100%
The pedal movement stop is at the pedal plate. You know which one when you see it.

Edited by twinreal on Wednesday 11th June 16:01

[ChrisPap]

Thanks twinreal, I'm getting 90% on the pots and the butterflies are visibly not at full open, so will sort out when I can.