Lean startup in SD

[marcink]

Hi,

When I switched to SD for AutoVE tuning I started to observe a strange AFR behaviour after engine startup. Alhough my VE table is within 1% now, after starting the car (cold or hot) the wideband sensor shows about 2 points lean (14.5 versus 12:5 commanded or almost 17 versus 14:7 commanded). This difference gradualy decreases in time and it takes 3 to 5 minutes.

First I thought that it is a "feature" of my wideband sensor - following battery voltage (which is higher after startup - like 15V - and then decreases to 14V) or needing warm up. But that is not the case because when I switched back to non SD tune everything was fine. The actual AFR shown was even richer than commanded AFR - but the difference between them stayed the same while in open loop and they became identical after entering closed loop.

So what am I missing? I cannot just increase these 2 cells in the Main VE table because if I get actual AFR = commanded AFR at startup it will become rich after 3-5 minutes.

So are there any other tables to control that behavior?

And this has nothing to do with the after-start enrichment which is operational for the first 10-20 seconds.

Thanks,
MarcinK

[dfe1]

Sounds like you may need to alter Commanded Air/Fuel in Open Loop (B3605). In theory, you shouldn't have to do this, but don't forget that SD is a back-up mode for the system and may be responsible for some "unexplained" changes. Relative to SD operation, the Custom OS is designed to allow both high and low octane spark tables active. But the system is still seeing a Mass Air Flow sensor DTC, (if it didn't, it wouldn't go into SD mode) it's just not turning on the MIL. Also keep in mind that if you change the VE table to bring AFR back on track in open loop, LTFT will keep it from being excessively rich once the system goes into closed loop.

[bink]

Custom OS? Open Loop or Closed Loop? Stock injectors?
Can you list your mods??
{B4204} Closed Loop Normal Temp Timer - is yours 15-16 seconds??



Cheers,
joel

[bink]

Hi,

First I thought that it is a "feature" of my wideband sensor - following battery voltage (which is higher after startup - like 15V - and then decreases to 14V) or needing warm up. But that is not the case because when I switched back to non SD tune everything was fine. The actual AFR shown was even richer than commanded AFR - but the difference between them stayed the same while in open loop and they became identical after entering closed loop.


Excellent thought - IMHO.

If your injectors aren't stock and your Offset table is stock it might reduce your pw at higher bat volts?

Cheers,
joel

[Delco]

Look at your cranking VE rather than your VE table , it uses this for a period after startup

[curtbriggs]

Look at your cranking VE rather than your VE table , it uses this for a period after startup

What range, roughly, should the cranking tables be?

Is a higher VE Richer?