O2 Sensor and Open Loop

[betsy325e]

Dear Thirtyanians,

It is my understanding that the O2 sensor is ignored at WOT and motronic goes back to open loop. Is this true? Does the O2 sensor do the same at closed throttle idle? There is a mess of conflicting information on the webs.

Thanks,

J

[arams325]

02 open loop

from what ive read the ecu seems to switch into open loop during wot,also when warming up at idle the ecu is in open loop, once the car is fully warmed up it will maintain closed loop under normal driving conditions

[betsy325e]

I've seen on the webs that it is only once car is warmed up O2 is doing its thing except at WOT whereupon it goes into open loop. I've also seen that once warm the O2 is doing its thing except for closed throttle/idle and WOT.

Does anyone know for sure what the deal is?

[jlevie]

My understanding is...

The DME runs in open loop until the engine temperature is above 140F. From that point until WOT it runs in closed loop and uses data from the O2 sensor o adjust fuel trim. Once at WOT the DME runs in open loop, ignoring the O2 sensor. What constitutes WOT varies by car. On an M20 engine WOT is either the WOT switch in the TPS being closed or an engine speed above 4500rpm, at which point the flap in the AFM is wide open.

Stuff we have done on a dyno seems to agree with this.

[EatsHondas]

My understanding is...

The DME runs in open loop until the engine temperature is above 140F. From that point until WOT it runs in closed loop and uses data from the O2 sensor o adjust fuel trim. Once at WOT the DME runs in open loop, ignoring the O2 sensor. What constitutes WOT varies by car. On an M20 engine WOT is either the WOT switch in the TPS being closed or an engine speed above 4500rpm, at which point the flap in the AFM is wide open.

Stuff we have done on a dyno seems to agree with this.

Okay good. I didn't know about the 140 temp mark and if the 02 sensor was used to make changes at idle.

Additionally, a fritzed TPS can fail to tell the DME that the pedal is to the metal, losing you some amount of power.

[betsy325e]

Jlevie,

Thanks. You're encyclo-goddamn-pedic.

Do you know if this applies to etas, or just the is? I ask because the idle control module obviously doesn't receive any information from the O2 sensor. Perhaps it merely reacts to what the engine is doing based on rpms?

[jlevie]

I can't say much about the ICM as I've never had or done any extensive work on an ETA. But what I have read suggests that it only gets enough inputs to be able to manage idle speed. I would think that would include engine temperature, TPS idle switch, and engine speed. You can probably figure out more about the ICM by looking at the wiring diagrams from http://wedophones.com/BMWManualsLead.htm.

[digger]

When i used to run motronic mine used to idle at stoich, I don’t think this was a coincidence

[Som]

Jim, per our discussion on SpecE30, I thought "open loop" wasn't triggered by the 4500rpm, but, rather, TPS WOT + 4500RPM.

I ask because if strictly 4500RPM would trigger open loop (ie "coolant temp sensor only" operation), then my broken TPS (which had no WOT signal) shouldn't have had any effect after 4500RPM. In fact, though, my motor noticeably bogged down at 4500 at WOT.

I have yet to fix my TPS and re-test, so it's possible something *else* is also broken, so I guess I'll see. But the TPS WOT being broken seemed to explain the issue I was seeing.

Som

[jlevie]

Well that is a situation where I'm not sure what is happening. You are probably right that the WOT maps require the signal from the TPS. But I am pretty sure that the DME stops using AFM data above 4500rpm. It would seem to me that it would then be in a semi-closed loop mode and may use some intermediate map.

[TobyB]

an engine speed above 4500rpm, at which point the flap in the AFM is wide open.

I really need to log my AFM data...

and my car idles at 14.7, too. Idle air is probably not metered-
idle rpm is measured, and the ecu almost certainly looks at
o2 for idle fuel metering... this would explain the hunting that an
air leak causes.

t

[Som]

So, I'm guessing this has been created before, but I wanted to put it together for myself to better understand all the modes of operation. This is a first pass, so I'm sure there's things wrong, so let me know and I can fix it.

This is how I understand it, btw. Obviously it has the "semi open" idea in there, too -- which may or may not be correct.

Hopefully it's fairly self-explanatory, but basically I took the 5 related engine sensors and tried to identify 1) how do these factor in to the DME's map-choosing logic, and 2) which sensors are actually used as inputs in the maps.

For sensors that are "Not used" under certain situations, I put the reason(s) in parentheses afterward.



Probably one thing I see I can clear up already is the last column, as that sort of applies to everything, not just WOT situations. Also, regarding this, I've only seen Scott's (Ranger) mention that there's a degradation of performance after about 205 degrees.

Of particular note here is that, and something that may be contested, is that it seems to me that the AFM is NEVER used as a source of input to dictate a fuel map change. Instead, at 4500 RPM and WOT, the DME ceases to use the actual input and makes assumptions from that point on. That said, it's possible at >4500 RPM the DME will NEVER use the AFM input (regardless of WOT) -- in which case I need to fix the "High RPM w/o WOT" column to *not* use the AFM. Edit: For this same column, I imagine another question would be: is the O2 sensor used at high RPM if there's no WOT signal coming through?

Som

[betsy325e]

Som: CRUSHING it.

[nando]

Just because it's in open loop, doesn't mean O2 trims do not apply. There are short term trims (closed loop) and long term trims (open or closed loop). Long term fuel trims always apply. So even though it ignores short term O2 feedback at WOT, the O2 feedback mechanism still affects WOT fuel delivery.

I believe the SpecE30 guys have confirmed this. I seem to remember Jim talking about having to reset the DME every once in a while because it would go lean (it's always trying to reach the internal lambda targets).

long term fuel trims are stored in volatile memory. short term trims are not, but short term trims are used to determine what gets stored in memory. When you remove power from the DME, this will reset any adaptations (Motronic 1.x doesn't have flash memory like a newer DME).

As far as I know, there aren't any adaptations for ignition, since no version of Motronic 1.x has knock sensors.

ForcedFirebird knows some more about the AFMs function at WOT. I remember him posting that it actually was still used, not completely ignored. but maybe that was only up to 4500rpm..

[digger]

i thought i read about the AFM not being used above 4500rpm in one of the bosch books years ago