Open loop quick questions - Third Generation F-Body Message Boards

pwdbychevy · 12-18-2008, 10:23 PM

I'm using SAUJP_V4 and I'm running the car in open loop all the time(runs better) with 7730 ECM Speed Density. I have 3 questions:

1. Which tables does the ECM use to calculate fuel when in open loop(non PE mode)?
2. Which tables are used by the ECM when in PE mode?
3. I disabled closed loop by setting enable temp to 151deg c. Do you HAVE to set min and max BLM's at 128 when running open loop? During datalogging the BLMs stay at 128 whether I set them or not.

Thanks guys.

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RednGold86Z · 12-19-2008, 01:50 AM

Just some things to keep aware of (I'm 90% sure on these):

VE is ALWAYS used, except in cranking. It calculates the air flow.

PE has 2 tables, vs ECT and vs RPM. Those are multiplier modifiers to the main VE calculation when TPS is greater than the PE threshold. There's 2 PE thresholds - normal, and hot. Hot thresholds are less than normal, to get cooling from the richer mixture.

There's an open loop table multiplier vs ECT vs MAP, that is a modifier to the VE. It changes the commanded AFR (but it's open loop, so it won't make any actual fuel loop correction to truly achieve it), and makes a corresponding fuel multiplier to theoretically get that AFR. When closed loop, the open loop table has 0 effect, and the commanded AFR is stoich.

I'm not sure with GM stuff if during PE and cold engine, if both tables above are used or not, on top of VE. I'm thinking not - just PE when PE, and just open loop when open loop. If you look at the PE vs ECT table, you can see a strong amount of enrichment at cold engine - if the engine really were given both the enrichment tables, it would be extremely rich.

Changing the stoich AFR has no end result effect when in closed loop, as the corrections INT and BLM will center around whatever the switch point of the O2 sensor is. Open loop probably will be affected. But, some calculations in the xdf and ecu may be set up around the assumption of 14.7 - but I don't know for sure.

Open loop automatically FORCES BLM to >=128 and INT == 128. If you reset your adapt values (disconnect battery), they'll surely stay at 128 if it stays in open loop. PE acts similarly to Open loop with the exception of INT may also be able to be >=128 if it was already >128 when entering PE (I'm not 100% sure if INT locks at the current value if >128 or if it resets to 128).

Good luck!

pwdbychevy · 12-19-2008, 09:00 AM

Quote:

Originally Posted by RednGold86Z

Just some things to keep aware of (I'm 90% sure on these):

VE is ALWAYS used, except in cranking. It calculates the air flow.

PE has 2 tables, vs ECT and vs RPM. Those are multiplier modifiers to the main VE calculation when TPS is greater than the PE threshold. There's 2 PE thresholds - normal, and hot. Hot thresholds are less than normal, to get cooling from the richer mixture.

There's an open loop table multiplier vs ECT vs MAP, that is a modifier to the VE. It changes the commanded AFR (but it's open loop, so it won't make any actual fuel loop correction to truly achieve it), and makes a corresponding fuel multiplier to theoretically get that AFR. When closed loop, the open loop table has 0 effect, and the commanded AFR is stoich.

I'm not sure with GM stuff if during PE and cold engine, if both tables above are used or not, on top of VE. I'm thinking not - just PE when PE, and just open loop when open loop. If you look at the PE vs ECT table, you can see a strong amount of enrichment at cold engine - if the engine really were given both the enrichment tables, it would be extremely rich.

Changing the stoich AFR has no end result effect when in closed loop, as the corrections INT and BLM will center around whatever the switch point of the O2 sensor is. Open loop probably will be affected. But, some calculations in the xdf and ecu may be set up around the assumption of 14.7 - but I don't know for sure.

Open loop automatically FORCES BLM to >=128 and INT == 128. If you reset your adapt values (disconnect battery), they'll surely stay at 128 if it stays in open loop. PE acts similarly to Open loop with the exception of INT may also be able to be >=128 if it was already >128 when entering PE (I'm not 100% sure if INT locks at the current value if >128 or if it resets to 128).

Good luck!

Good information!

Thanks Red.