Can I trust the stock sensor Lambda on stock engine?

[angrybaconman]

Hello! I will keep this as simple as possible, and yes I've searched the forums to see if someone else has asked this question before. Long story short I have a rebuilt b18b1 that I'm planning to turbo later this year. But for now, its got stock compression, stock cams, sock injectors, stock everything as far as the ECU is concerned. When I rebuilt the engine the stock P75 I have ran it just fine.

I've install my s300, and put the stock P74 base tune on it from smanager. I've done the basic stuff like check rpm limits, TPS, make sure the stock injectors and map sensor are selected properly etc. The engine starts up and runs fine as far as I can tell, however the reported Lambda within SManager says its 0.80 most of the time.

I've waited for the engine to come to full temp, I've revved it up to 3 or 4k a few times and let it fall back down and more often than not it drops to as low as 0.69 and then jumps back to 0.80. Obviously a little rich is far better than a little lean, but that seems pretty rich to me. Should I trim the overall fuel a few percent and get things to around .9 or .95 just to be safe? Or are these stock O2 sensors totally untrustworthy?

I have a AEM wideband, but its not installed yet. I'm planning to put it in at the same time my turbo kit goes in with my new injectors and fuel pump. Then I'll need an actual tune.

[Spunkster]

The stock O2 is a narrowband and cannot accurately read AF ratios. You need a wideband to be able to read this correctly.

[angrybaconman]

so even with the stock engine, and stock tune. I should not trust the narrowband? Or is it fine to assume the engine is healthy on the stock tune right now and ignore the readings its feeding smanager?

Follow up question. If I install my wideband, should I run it on open or closed loop?

[Spunkster]

You should not try to tune based on a narrowband reading as it cannot really measure anything more than stoich under ideal situations, hence the name narrowband.

You really need to use the wideband. Whether you use it in closed or open loop is completely up to you and your tuner.

[DaX]

Narrowband sensors just tell the computer "you're richer than you're supposed to be" or "you're leaner than you're supposed to be." The ideal narrowband signal is an oscillating high/low signal. Wideband sensors tell the computer what the actual AFR is - it gives the computer a numerical value.

I agree - it's up to you whether you run open or closed loop with the wideband. If you run closed loop, the pre-loaded response parameters in the S300 are WAY too slow in my opinion. User TTR posted up some parameters that worked great for me in closed loop. I don't have my tuning laptop in front of me to look, but you can search the forum and find them.

[DaX]

OK, here is how mine is set up for Rate of Change:

Slow: 5 - 5 - 4 - 3
Fast - Rich to Lean: 99 - 99 - 99 - 99
Fast - Lean to Rich: 99 - 99 - 99 - 99