Author Topic: O2 sensor downswing/upswing/decay  (Read 1231 times)

Offline Alexiskayak_7

  • Members
  • *****
  • Posts: 625
O2 sensor downswing/upswing/decay
« on: June 26, 2012, 06:43:20 pm »
Can anyone explain me what these maps do?
I am trying to understand how you can tune them for fuel economy.

Offline Andy

  • Traders
  • *****
  • Posts: 1495
Re: O2 sensor downswing/upswing/decay
« Reply #1 on: June 26, 2012, 06:47:11 pm »
For which ECU?

Offline Alexiskayak_7

  • Members
  • *****
  • Posts: 625
Re: O2 sensor downswing/upswing/decay
« Reply #2 on: June 26, 2012, 07:07:46 pm »
For G40s digi I ECU.

Offline Andy

  • Traders
  • *****
  • Posts: 1495
Re: O2 sensor downswing/upswing/decay
« Reply #3 on: June 26, 2012, 09:48:59 pm »
The ECU is always aiming for 14.7:1 AFR in closed-loop, I'm not 100% sure, but this *might* be in the source code rather than a calibratable map - certainly it's not a map address I'm aware of.

The upswing/downswing maps define the correction limits (correction of fuelling up/down respectively) of the closed-loop lambda control. Without these limits you can face two problems:
a) Instability - the corrections the software make constantly over or under-shoots the target 14.7:1 AFR, so wobbles all over the place.
b) Dangerous lean AFRs on lambda failure - a faulty lambda means incorrectly applied fuelling corrections. Thus you need to limit the amount of correction that can be applied, so to avoid running so rich the sump fills with fuel or so lean it melts the engine, when the lambda's failed.

I think the decay dictates where the ECU transitions from closed to open-loop control, as at higher rpm and loads it's not in closed-loop - even if the WOT switch is not active.

Offline Andy

  • Traders
  • *****
  • Posts: 1495
Re: O2 sensor downswing/upswing/decay
« Reply #4 on: June 26, 2012, 10:05:22 pm »
If you want to tune for economy, I'd start off by checking that your base fuel map has sensible enough numbers in it for the lambda closed-loop control to be able to achieve 14.7:1 at cruise.

With this done, you have two options to take things further:
1. Run leaner than 14.7:1 in closed-loop
2. Extend the region of closed-loop operation

To achieve #1 I'm not quite sure what is required. You could possibly lean out the base fuel map beyond 14.7:1 AFR (tune with the lambda unplugged to achieve this) and then limit the upswing and downswing so that the lambda can't even richen things up enough to achieve 14.7:1 AFR.

For #2 you can possibly experiment with the decay map. Or more simply lean the base fuel map at higher loads/rpm.

Offline Alexiskayak_7

  • Members
  • *****
  • Posts: 625
Re: O2 sensor downswing/upswing/decay
« Reply #5 on: June 27, 2012, 12:58:50 am »
If you want to tune for economy, I'd start off by checking that your base fuel map has sensible enough numbers in it for the lambda closed-loop control to be able to achieve 14.7:1 at cruise.

With this done, you have two options to take things further:
1. Run leaner than 14.7:1 in closed-loop
2. Extend the region of closed-loop operation

To achieve #1 I'm not quite sure what is required. You could possibly lean out the base fuel map beyond 14.7:1 AFR (tune with the lambda unplugged to achieve this) and then limit the upswing and downswing so that the lambda can't even richen things up enough to achieve 14.7:1 AFR.

For #2 you can possibly experiment with the decay map. Or more simply lean the base fuel map at higher loads/rpm.

Can you post a picture how should i limit the upswing and downswing maps? Also, about the decay map, i am going to set it to 3 at higher rpm.Can you post a picture of a tweaked decay map too?
Andy, do you use grautec's adapter for live trace?