pstickne

When does the ECU switch from Closed Loop to Open Loop?
Is it only at WOT?
If so, what good is a piggyback system at 90% throttle?

If it's trying to maintain stoich at 90% throttle, couldn't that create lean conditions?
How would it be any different then stoich at WOT?

What happens when the DME chip is replaced?
Does using a Guru or LR or Vitessa chip change the parameters at which it changes from Closed to Open and back?

autox951

Vehicles start in open loop until the computer sees the engine at operating temp. and will switch back to open loop at WOT or anytime it sees a sensor having a value way out of range, like say a dead O2 sensor.

pstickne

So--to the point of being redundant--disconnecting the O2 sensor would force the system to be run in Open Loop? (This sounds like it would have other implications...)

Is there an easy way to see if it's in Open or Closed Loop? (I suppose getting a regulating lambda of ~1.0 would imply Closed loop...)

Jake951

You can tell with an A/F monitor (even a narrowband one) whether you're running open loop or closed loop. In closed loop, the A/F ratio will dither (i.e. cycle up and down) around 14.7 (stoichiometric). The dithering will be quite obvious because the A/F never seems to stay steady but that's how the DME works in closed loop. In open loop, the A/F doesn't dither.

TurboTommy

The DME switches to open loop in response to a couple of conditions.
The DME considers it WOT if the throttle plate is opened quickly and/or is opened somewhere around 75% (give or take; but it's not 90%).
Also, if the DME "sees" a certain voltage (which, generally, corresponds to higher air flows) from whatever air flow measuring device you're using, it will also kick over to open loop (it doesn't have to be WOT)

So, therefore under these conditions it wouldn't be stoich.

hally

Running a wb02 gives you a fantastic insight into what state the DME is in. It is also a great tool for detecting problems.

pstickne

Tommy, thanks for the general change-over guidelines. Do you know where can I get more detailed information reguarding the DME/KLR operations?

I have a LMA-1 WB installed but my cars at the shop waiting for the LM-3 to be installed... :-/

How much will the A/F typically "bounce" in closed loop?

Jake951

The actual range of A/F dithering in closed loop is not that large...about 14.4 to 15.0, with an average around 14.7. On a narrowband A/F monitor it's very obvious because the dithering covers most of the scale of the gauge. With a wideband, it's still noticeable as a small amount of fluctuation around stoichiometric.