SD vs Open Loop

[superls1]

I have not seen much on this, and yes I have tried search on several forums. I have been playing with my new WB and working on my VE table. I expect to plug my MAF back in after complete. I was just trying a few things out today for curiosity.

What is the difference between SD and Open Loop besides the MAF? I guess, what commands the A/F in Open loop when not in PE? Does the VE table below 4k rpm, and MAF above 4k rpm rule still apply in Open Loop?

Would this not be an easier tune for the strip? i.e. something that could be flashed to not worry about LTFT's etc.

Just curious. I didn't have enough time to play with all the variables tonight, so I thought I might ask before doing much more.

[Black02SS]

When in open loop, the AFR is commanded by the EQ Ratio When In Open Loop Table (B3601). This can be displayed either as a multiplier or actual AFR. (Change the settings by pressing alt-enter).

This table is the back up table if there is a fault with the o2's forcing it into open loop.

SD is when you tune the car without a MAF, while Open Loop is running the car without relying on the oxygen sensors. You can force the car into open loop by changing the Closed Loop Enable Temp Table (B4205) to something that the car won't reach, ie. 258* F. This will force the car to rely on the VE table for its fueling along with the PE Table.

I tune the car in open loop with PE disabled. I change my MAP values in B3601 from 75kPa to 1.13(12.96) and dial that in first. Then after you get the entire VE table dialed in, you can re-enable closed loop, re-enable PE mode, and fine tune it if needed. If you decide on hooking the MAF back up, you will need to make sure it is calibrated correctly to reflect the new values in the VE table.

[superls1]

You can force the car into open loop by changing the Closed Loop Enable Temp Table (B4205) to something that the car won't reach, ie. 258* F.

That is what I did.



When in open loop, the AFR is commanded by the EQ Ratio When In Open Loop Table (B3601). ... This will force the car to rely on the VE table for its fueling along with the PE Table.

This is where I am a little confused. I thought my VE was close, but I seemed to be running lean particularly compared to the Open Loop Table. So, I was wondering if the VE was used in Open Loop for anything other than sanity checking the airflow? Maybe my VE is just not as close as I thought.

I had read on another board that under 4k RPM, the PCM relied heavily on VE tables for air calculation. However, above that the PCM relied mostly on MAF, but it still used the VE calculations for comparing airflow measured by the MAF. I assumed this was mostly in reference to Closed Loop operation, and that anything over 4k RPM would most likely be Open Loop PE anyway.

While working on my VE table, I had disabled PE. Since I thought I was close, I had lowered those values back to where I wanted them. So, I could have been hitting PE some yesterday, but that would mean I was really lean. Most of my observations were in the 2-3k RPM range, and my PE vs RPM table is ~12.9 in that range.

[Black02SS]

As it may not be right, this is how I tune.

Change all values in the Open Loop Multiplier table from 122* F(MAP15kPa-75kPa) to 1.00, this sets the commanded AFR to 14.63. Then Make sure that from 85kPa-105kPa you have 1.13(12.96). Hit all the cells that you can with nice easy throttle transitions populating as many as possible. Do this until your ve table is dialed in to where you want it. Ultimately, you want to see a actual afr of what the car is commanding. Then you can go back and re-enable PE.

[superls1]

I tune the car in open loop with PE disabled. I change my MAP values in B3601 from 75kPa to 1.13(12.96) and dial that in first.

When you say Open Loop, are you meaning SD with MAF unplugged or fail frequency set to 0? I noticed that after raising the Closed Loop enable temp, I never saw any LTFT's other than 0, and fuel trim learn was always "Off".

Also, do you mean you commanded 12.96 from 75kPa and below?

[superls1]

You were posting while I was writing. Thanks for the info.

[Black02SS]

Anytime. That is what we are here for.

[superls1]

When you did your VE tuning, did you unplug your MAF or set the fail frequency to 0?

[Black02SS]

Both. I have done both. Currently it is set to 0.