Hello i am searching forum but cant find anything relevant about testing front o2 sensor.
I dont have cell codes but car has rough idle and STFT1 is -5% or lower. When STFT1 goes lower it nearly stalls then STFT1 jumps up and it fires up again then again STFT1 starts to fall and it goes like this in cycles.
I fear i have very lean mixture on idle and it will kill the engine. Also exhaust is stinky. Not like unburnt fuel but instead i dont know what to compare it to. Car has no smoke and healthy CAT. Car has modified intake and exhaust ports on side walls. The exhaust ports are larger than on 6 port.

 

The ECU regularly runs diagnostics on the O2 sensor, it does its own testing. You can confirm the mixture by looking at the spark plugs, but I would bet the fuel trims are doing their job and keeping your mixture in a safe range.

Something is either causing too much fuel to be delivered, or restricting air to the engine. How is LTFT? Was the car tuned for the enlarged ports?

Can't comment on the smell if you can't describe it.

 

So, you've modified the intake and exhaust ports and now you have an awful lope?

 

No it havent been tuned. I just need this engine to last untill technicall/emision test are done then it is going out.
Its a fresh built engine so it needs to run for little bit till it gets proper compression.
I just want to be sure it wont get destroyed by idling on wrong mixture.

 

If it was me, I would pull and read the plugs to ascertain the mixture. However the actual problems sound like a combination of untuned porting, engine not broken in yet, potentially mistakes during engine installation (some people have put secondary injectors in primary positions, for example).

How reliable is the rebuilder who worked on this?

 

I built the engine. I did like 20 engines already.
Injectors are ok doublechecked by wire colors.
But back to base question is there a way how to check front o2 sensor?

I will pull the plugs. But i am running premix and it was only idling until now so they will be black as ash.

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Like I said, the ECU tests the oxygen sensor and pops codes if anything. O2 sensors don't fail by providing an offset reading, they fail by being slow to respond to mixture changes or providing an erratic signal when mixture is stable. The ECU looks for both of those conditions.

You're welcome to try changing the sensor, but it's not the sensor.

Also mixture at idle is far less important than under load. The worst thing that happens is the engine stalls.

​​​​​​For a fresh rebuild you shouldn't let it idle. Drive it, vary the rpm range. That will help it wear in and if you still have problems you can treat them accordingly.

You built 20 rotaries or 20 other engines?

 

2 + 2 = 5

 

For very large values of "2".