Hondata

I have a 2003 Honda S2000 with Kpro4 #42646 and I'm using version 4.2.5 (tried 4.2.3 also).
Modifications that might matter some is ITB's, 500cc injectors, no IACV, wideband sensor is PLX SM-AFR with DM-6 gauge (wired to DI0).
The problem I have is that every time I switch to External wideband for closed loop my AFR at idle (haven't tried driving it) just keeps rising until full lean causing the engine to almost stall.
I try catch the rpm's by using a little throttle and the AFR goes down again but then keeps climbing up again.
I can see short term fuel trim goes negative and pulls out fuel but I cant understand why?

If I change to stock Narrowband sensor for closed loop everything works just like it should and AFR is very close to 14.7 at idle.
I have attached a log using that as well, obviously kalibration is changed but only the closed loop sensor selection.

Does the AF reading in your datalog match what the display for the wideband says?

Yes it matches exactly.

It sounds like it needs to be tuned so that the short term trim stays close to 0.

I have tuned the idle tables and they are not that far out, either way it works perfectly with OEM narrowband and AFR stays very close to 14.7.
When I switch to the wideband sensor it looks like the closed loop regulation is inverted.
How can I get short term fuel trims reading -20% when the AFR reads fully lean?
I was really hoping I wouldn't need to wire in the analog signal as well but I'm not sure if there is anything else that could be wrong.
Thanks for your support by the way.

We will be testing this tomorrow on a vehicle with the wideband connected to the digital input.

That's great, I'm looking forward to hear about your findings.

We tested this in a vehicle with a digital PLX input, using closed loop running from the PLX, with both PRB and PRB calibrations. Everything looks ok. I also used your calibration (with altered fuel & MAP settings) and closed loop was ok as well.
I would also then check the fuel injector dead times, as they seem low. Then run open loop and check that the lambda changes in a logical way. eg if it is running 15:1 AFR, add 10% fuel and check that the AFR changes to 14:1.
How are you getting a good MAP signal with ITBs? It seems close to stock.

Just did a quick test run it seems to work now!
Since this is technically my front sensor (S2000) I'm guessing it somehow disrupts the wideband input.
Very glad it was such an easy fix :)
Now I was just wondering if my oem front sensor will be damaged if I keep it installed while being disabled?

The injector dead times is directly from Bosch and I hope they are correct.
And yes the MAP signal is really nice and stable for an ITB setup, it's because I'm using a very clever vacuum block from urgedesigns.com

Now I was just wondering if my oem front sensor will be damaged if I keep it installed while being disabled?

Possibly. They are easily damaged by water condensation, and without the heater it may be a problem.