Closed loop fueling

[picasso]

Hi,

while on the dyno configuring the VVT I experienced that the closed loop fueling hit the maximum enrichment level set (15%) and then after a few seconds disabled the closed loop fueling with the result the AFR went lean.

Is this a normal behaviour or is it possible to configure the closed loop to continue at maximum enrichment even if it doesn't reach the AFR aim value?

Another question, is it possible to configure closed loop fueling to be active only in parts of the engine load / MAP axis? ie. turn it of at WOT.

[David Ferguson]

Have you looked at the parameters under "Fuel Closed Loop" (either using the worksheet typically found in M1 Tune->Engine Systems->Fuel Closed Loop, or by using one of the All Calibrate worksheets)?

The parameter "Fuel Closed Loop Fault Delay" controls how long a trim limit will be maintained before a sensor limit fault is set. So set this to a really large value if you want it to run at the trim limit for a really long time.

Or, change your "Fuel Closed Loop Trim Maximum or Minimum" to a larger value so it doesn't hit the trim limit default.

You have some control over when the closed loop is active, using Coolant Temperature Threshold, and the various "Activate xxx" parameters. But none will allow deactivation only at WOT (only below).

Now the behavior I have described is found the the GP and most firmware packages, but it's possible for a firmware package to be built with different behavior, so be sure to tell us what firmware package you are using.

Also, all of this information is available in the M1 Help topics for the firmware -- start with searching for "Fuel Closed Loop", then read all the help in the hierarchy below that.

[picasso]

Thanks for your reply.
Yes, found the parameter "Fuel Closed Loop Fault Delay" and is was set to 10s, so now I know why tis happened.

Regarding the possibility to disable closed loop fuelling at WOT, I found a way around that by setting up a table with 0 trim at WOT, instead of the one cell set at 15% for the whole load/rpm range.

Another question regarding "Fuel Closed Loop Period" and the calculated value of Exhaust Mass Flow. I assume this value is calculated as a total for the engine. The actual engine here is a V with two lambda sensors.
I assume the actual mass flow for each cylinder bank is then half of the total. To what extent will this influence the
Fuel Closed Loop Period time to be used. Is there a rule of thumb of which values to use or how to set this up correctly?

[David Ferguson]

Yes, Exhaust Mass Flow is calculated for the entire engine, but the transport delay (ie, Fuel Closed Loop Period) is directly related to this value, so it's a good axis for the Period table.

To determine the values for the Period table - make sure closed loop fueling isn't active (temperature or throttle thresholds are handy) and operate the engine on the Exhaust Mass Flow Breakpoints (or at any fixed RPM and change the table breakpoints to match), and change the Fuel Mixture Aim by 5-10% (wait lambda to respond and stabilize), and back. Examine the data to determine the time between when the Fuel Mixture Aim changed, and the actual lambda reached the target value (or at least became stable). Change to a different RPM and repeat. You will quickly see the trend and can adjust values in the table. Now enable close loop fueling, and enjoy fueing that should reach and stay on your targets, even if the tune and/or compensations aren't perfect yet.