Open Loop vs Closed Loop

[kv67ssrs]

Regarding the Open Loop/Close Loop differences during operation: It's my understanding that during Open Loop operation (allow Closed Loop/Learning box NOT checked), the ECU fuels the system based on the Base Fuel Flow Rate table. Correct? Without the allow Learn box being checked, the WBO2 sensor feedback is not figured into the equation and the AFR is not adjusted by the ECU?

Although the WBO2 sensor output is not being able to change the AFR in Open Loop, are the numbers that it produces and that are shown on the Handheld or laptop accurate? And, since they cannot self adjust in Open Loop, they may not mirror what is programmed in the Target A/F Ratio table?

In Closed Loop (box checked), the WBO2 sensor feedback is entered into the equation, and the ECU will add/subtract fuel in an attempt to match the commanded AFR? If the above is correct, what would cause a car to run strong & smooth in Open Loop (box not checked), but not in Closed Loop? While Online, there is a noticeable difference when checking & unchecking the box. Thanks in advance for any replies.

[Danny Cabral]

It's my understanding that during Open Loop operation (allow Closed Loop/Learning box NOT checked), the ECU fuels the system based on the Base Fuel Flow Rate table. Correct?

Yes, the Base Fuel Table and any Modifiers too.

Without the allow Learn box being checked, the WBO2 sensor feedback is not figured into the equation and the AFR is not adjusted by the ECU?

No, the ECU is still in Closed Loop feedback (if Closed Loop is enabled/check marked). The ECU is just not in Learn mode.
Closed Loop (WBO2 sensor feedback) & Learn (self-tuning) are two separate functions. CL must be active for Learn to function.

Although the WBO2 sensor output is not being able to change the AFR in Open Loop, are the numbers that it produces and that are shown on the Handheld or laptop accurate?

Yes, the WBO2 sensor still measures/displays AFR even in Open Loop mode.

And, since they cannot self adjust in Open Loop, they may not mirror what is programmed in the Target A/F Ratio table?

Yes, if the Base Fuel Table is not well tuned.

In Closed Loop (box checked), the WBO2 sensor feedback is entered into the equation, and the ECU will add/subtract fuel in an attempt to match the commanded AFR?

Yes, that's the purpose of the WBO2 sensor and the Target Air/Fuel Ratio table.

If the above is correct, what would cause a car to run strong & smooth in Open Loop (box not checked), but not in Closed Loop?

This means the engine doesn't like your programmed Target Air/Fuel Ratio table. (Provided your WBO2 sensor is in good condition.)

EFI Software Help Information/Instructions:
‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
..This automatically opens the definitions for that specific parameter.
‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen.
http://documents.holley.com/techlibrary_199r10544.pdf (Holley EFI Help/Instructions Overview)

[kv67ssrs]

Thanks Danny. Always appreciate the response.

[Danny Cabral]

You're welcome.

[kv67ssrs]

I thought maybe if I asked questions differently I might pick something up that may help with my year long battle with this car/system. I just don't understand how this EFI system can run perfectly yesterday, and today runs poorly. (With not a single thing changed mechanically or programming, same weather, etc.)

I've replaced the WBO2 sensor TWICE, distributor module, coil, plug wires, battery, tried different ECU, rerouted wiring. All sensors seem to functioning normally.
No exhaust leaks. I swear it's gonna be the end of me or the car!

[ROFCIBC]

I just encountered a similar problem. Terminator system on a Mopar 440 engine in my '72 Road Runner. Been working just fine for a couple of years. Had it in the Learn mode until it met parameters in instruction manual, then turned it off. A problem developed that at random times made the system run "full rich" as it black smokes out the exhaust, rough running, surging RPM, and sometimes just quit. Put Learn to ON, but no change. Checked for exhaust leaks, loose wires, all the obvious stuff. For whatever reason, from whatever sensor (suspect WBO2) gives an erroneous reading of too lean and system responds with a full rich command to compensate. Trying to figure out where to go to determine what each of the parameters that are monitored are.

[Danny Cabral]

The WBO2 sensor is the only sensor that measures air/fuel ratio. However, there are a few faults that can cause it to read a false lean condition, causing the ECU to compensate by adding too much fuel.

The tune (Global File) should not be programmed to allow this to happen. When the engine is tuned & running well, you should decrease the Closed Loop and Learned Compensation Limits % to lock in a good tune. I decreased my Learned Compensation Limits to 2% in the idle area (10% elsewhere). My Closed Loop Compensation Limits are 50% or less at WOT (20% elsewhere). When the Learn Table values stop making significant changes, the ECU is finished self-tuning. You can then Transfer Learning To Base, which then allows you to blend the Fuel Graph so it's smooth.
http://forums.holley.com/showthread....2523#post62523 (Holley EFI Tuning Tips & Information - Read 4th & 5th paragraphs.)
http://forums.holley.com/showthread....7370#post47370 (Holley EFI Closed Loop & Learn Table - Especially posts #2, #6 & #11.)
http://forums.holley.com/showthread....ension-Harness (WBO2 Sensor Information - Read 4th paragraph under "Wideband O2 Sensor Notes".)