open loop fuel & O2 sensors

[auspeed]

Hi,
I have been playing with an e38 for highway economy. I have set the coolant temp to 200 in the closed loop table to try keep it in
open loop and lean our the mixture. THe o2 sensors still appear to be switching when cruising on the highway is this normal when the car is in open loop?

Does anyone know where the instant fuel usage is calculated from on the instrument cluster..

[swingtan]

Have you actually checked to see the fuelling mode to confirm you are in OL?

To ensure OL mode is held, you need to set the following.

{B1502}: Set to above normal operating temperature.
{B1504}: Set to above normal operating temperature.

You also need to clear the LTFT's using the BIDI controls or resetting the ECM. LTFT's are applied in both OL and CL fuelling modes so not clearing them will cause errors in setting the airflow. As for the the O2's "switching", are you looking at the O2 voltages or the actual STFT data? Assuming your fuelling is correct, the O2 voltages can still oscillate, however the STFT data should read "0".

Finally, the Gen IV motor runs most efficiently at the stoichiometric ratio of the fuel. When I was testing, lean cruise made little to no difference when compared to correctly tunes CL fuelling. The testing was done by checking the average fuel usage on the trip computer after the same 600km trip was run in both modes.

As for the cluster, I believe it's calculated from the ECM injector data data (Injector flow rate, IBPW, etc.)

[auspeed]

ok so {B1504} was still at stock values so that is obviously letting get into closed loop? {1502} was maxed out

Were looking at the O2 sensor voltages and they were still oscillating..... I normally use STFT but the owner is remote & was using what data he supplied me.

Appreciate your feedback with stoich being your most effective result. Its getting 12l/100km on pretty flat roads with 3.45 diff gears & baby cam in SD mode which is too high i reckon...

[swingtan]

You need to average economy readings over a decent range. Glancing at an instantaneous reading on the dash means nothing.

Get the STFT and the LTFT data to confirm no corrections are being made.

Over the 600KM trips I tested on, I did 8.9l/100KM in a manual VZ L76, 220/224 cam 3.46:1 diff gears.

[statesman]

When I was testing, lean cruise made little to no difference when compared to correctly tunes CL fuelling.

What method did you use to optimize the lean cruise tables?

[swingtan]

I used a CAX for the "Max lean limit" table which is not normally defined in my OS. This controls how lean the ECM will go from stoich and as lean cruise is not used in the stock OS, it's set to "1" so the ECM will never command leaner than stoich.

If you have the table defined, you can use B0148 to control lean cruise.

If you don't have it, then you can set B3671 to be lean BUT you need to address pretty much every other fuelling table to compensate for the leaner than stoich setting. This includes PE tables and the load fuelling tables.

Simon.

[auspeed]

ok got some feedback...... maxing out {B1504} & {1502} did switch off closed loop and the sftf's as directed.
Running the car quite lean in open loop did not appear to change the economy at all... When the car was running in closed loop and pulling +18 SFTF seemed to give the best result.... Correcting the trims to a closer +9 made the economy even worst..
Not sure if I'm looking for savings that are not there but a VF with baby cam & 3.46 gears should be able to get better than a 11l/100km on flat highway roads....