Lambda all over the place

[Valter]

Hello, I have a problem with my Evo 3 with a Link G4X. I've recently rebuilt both the engine and redone the exhaust manifold. The car was working fine two days ago after the engine build, but after I did the manifold, the car initially ran well. However, after some time, the lambda reading went lean and changed lambda values rapidly, and the car began to misfire. I don't know what it could be. I'll do more diagnosing tomorrow, but I'll post a log. I've looked at the log but can't find anything that would cause the lambda to behave like that or would correlate to the lambda.  

 

[Vaughan]

I can see Closed Loop Lambda maxing out, I suspect you have an exhaust leak upstream of the wideband which causes it to read lean and then the CLL tries to correct by adding a bunch of fuel which makes it run badly.

[Valter]

The last manifold had a lot of cracks, and the old manifold and gaskets were leaking, but this new one seems to be good. However, I will check for leaks. But if I had more leaks before, why would the closed-loop lambda be struggling now?

[dx4picco]

if the reading of the lambda sensor is wrong for any reason (air leak, dead or poisoned sensor) then it reads something else than the reality.

it it reads leaner than expected and you have CL lambda enabled, it will naturally put more fuel in. but as you have wrong readings, it's still too lean, and CL continues to adds fuel. until you hit max clamp. if that is high then you engine actually runs very rich in reality even if you have lambda reading lean.

[Valter]

I've found the problem! It was a sparkplug that had cracked. Thanks for the help @Vaughan and @dx4picco much appreciated!