edomund

I have a S4 TII with S-AFC 1 wired off the boost sensor instead of TPS.

I am going to unplug my O2 sensor so it doesn't go into closed loop so the S-AFC controls the mixture at all times (others have done this). I saw in another thread that people were thinking of grounding out the sensor wire once it is unplugged.

Anyone done this yet if so what happened?

thanks
ed

Boost Lee

iTrader: (3)

Why ground out the sensor? Just leave it disconnected.

edomund

When it's just disconnected it seems like it still goes into closed loop because when cruising and you drop below a certain TPS % it goes rich (reading it on a innovative wideband O2). You can watch the S-AFC TPS reading and at 60% or lower it goes to around 12AFR and when cruising above 60 % it is around a good 14.7 AFR

I think it just defaults (with the O2 sensor unplugged) when in closed loop (where the O2 sensor is doing the fuel management) to a lean situation and adds fuel.

How do I get the ECU not to go into closed loop so I can control fuel all the time with the S-AFC?

edomund

Anyone?

NZConvertible

Those people are STUPID! This would alsmost certainly fry something in the ECU.

It doesn't. If it's disconnected the ECU never goes into closed loop. FSM page 4B-22, error code 05, oxygen sensor: "Stops feedback correction"

edomund

Thanks NZ I new you would know

So anyone have any idea why it gets rich like I described above when cruising at low TPS%?

BTW it's not my s-afc settings I tried with everything at 0% correction hi and lo to check.
ed

edomund

I realize it says that in the FSM.
But it still seems like it goes into the closed loop it just doesn't get a signal from the O2 so it "stops feedback correction". It seems like it defaults to a fail safe setting but still goes into closed loop it just doesn't get feedback so it doesn't correct the fuel accordingly.

It goes rich right at the same spot the ecu goes into closed loop.

Has anyone had a problem with the their AFR going rich at light load cruising situations under 60-70% throttle on the S4 TPS?

NZConvertible

No O2 sensor = no closed loop. By definition it's not physically possible. Feedback correction is just another way of saying closed loop.

I drove around with no O2 sensor for months and did not have the problem you describe.

Why not just plug it back in and leave it working the way it's supposed to? I'm not sure what you're trying to achieve.

HAILERS

If you ever watched a wideband on a fully hot car, driving down the hwy at say sixty and just barely let off the gas the afr WILL go richer by about a point. Example: it reads 14.2 afr and you just BARELY let up on the throttle. Now it will read approx 13.2 afr or a bit richer if you will. Happens each and every time I go downhill.

And It is not fuel cut as when you let off the throttle almost all the way. Others have seen this. It's just a anticipation mode in my opinion, so when you step back on the gas it won't buck.

I don't remember if my 02 is connected up or not when I do that. I'd guess it does it both ways.

One of the best ways to see when closed loop happens is to rig a single LED to the green check connector in the engine bay and run it to your cabin. When in closed loop the light will pulse on/off, on/off. It's a direct reading off the ECU. I believe it's the two center sockets in the green check connector on a series four that do that function. Gotta be driving for sure.

Syonyk

HAILERS - I was under the impression the momentary richness/leanness on throttle change was due to the lag in the O2 sensor (and the reason we can't use an O2 sensor at WOT/high throttle settings). I don't think it's an anticipation mode or anything, I think it's just the way things work. If you're running with the O2 sensor, and airflow drops slightly (but not enough to kick out of closed loop mode), the fuel will remain the same, and it will go rich for a second or so until the O2 sensor catches up & corrects. Same thing with adding airflow - it goes lean for a second until it catches up.

If the O2 sensor is disconnected, it won't go into closed loop/feedback mode. Period. There's no way for it to do it.

However, the ECU still does some funky things with the fuel delivery in open loop mode. :-/

I also can't see how grounding the O2 sensor wire would cause any trouble. It's an input to the ECU, not an output - the O2 sensor creates a voltage, and it's read by the ECU. It's a high impedance input, for that matter. With the car off or running full lean, the wire is functionally grounded anyway.

That said, I don't see a need to ground the O2 sensor wire. Leaving it floating works just fine.

-=Russ=-

HAILERS

It does it with the 02 disconnected. I just checked. NEXT time I'll take the Palm with me sooooooooooo I can help people relate to this. Next time I'll look at the tps percentage AND the boost/vacuum reading on the Palm before and after just barely letting off the throttle (whereupon the afr will go approx a full 1afr richer.

edomund

Mine does the same thing as Hailers is saying except it stays rich until I get the throttle above 70% again. If I'm under a certain % it is rich (almost 2 AFR richer). If I keep it under 70% throttle cruising it will be rich while cruising.

I can't understand why the ECU would make fuel richer at less thottle in a cruising situation.