Closed Loop - Wait a minute, I told you to be more open to my feelings not closed minded like that. Wait honey, it's not that!...

Loop is referred in auto technology as the relationship between ECM sensor and back to ECM, forming a circle or loop. Closed loop means that the ECM is in control and evaluating the O2 sensor at all times for feedback - hence the name feedback loop....

 

THEORY OF OPERATION

(for more information please refer to the Cranking Enrichment Mode blog)

• Closed-loop mode – is activated by the ECM only after the engine has warmed-up, the system is already in open loop, there are no other main sensor failures and the O2 sensor signal has started switching (sufficiently warm). In late model vehicles, the ECM tries to put the A/F control in close-loop as soon as possible to reduced excessive emissions and get the catalytic converter working. It is imperative that the A/F mixture be at stoichiometry (14.7:1) for the catalytic converter to function properly. The fuel control system spends most of its time in closed-loop mode, and as mentioned before, it puts a great deal of control in the O2 sensor being able to cycle or cross the 450mV mark. With that being said, the system could be in closed-loop and not be operating properly. Closed-loop simply means that the ECM is using the O2 sensor signal as a feedback. The closed-loop mode is notorious for masking all kinds of A/F related problems. The first thing that should be done to verify a 100 % fully operational closed-loop system is to check the O2 sensor cycling for correct amplitude and frequency. A case in point to this is an O2 sensor that is biased lean or rich. In such a case, the ECM will wrongly adjust the mixture according to O2 sensor signal and as a result create an excessive amount of emissions. Such problems are impossible to be detected by the ECM, since there is no other air/fuel feedback circuit. It is also important to understand that the ECM should be in control (closed-loop) throughout most of the throttle opening range except at W.O.T. and deceleration. At this point the ECM enters fuel-enrichment or enleanment mode for the duration of the W.O.T./deceleration event and controls the A/F mixture form comparing the TPS and MAP/MAF signals to a look-up table.

NOTE:  A subroutine is a specific part of a computer program that performs a certain function. Computer programmers can simply write instruction that follow the format—” If this condition is such, then do that”. This can also be said in the following way—”If the ECT value is cold, then go to the Warm-up Enrichment Mode subroutine”. Once the microprocessor goes to this subroutine, it will follow an extensive list if directions dealing with the engine operation during the warm-up period.

NOTE: During closed-loop, the ECM makes its combustion analysis from measurements taken by all the various sensors. Once these readings are analyzed, the injector base pulse plus any adaptive correction are used and stored in RAM/KAM memory. As the vehicle is driven, these corrective or adaptive injection pulse map is stored in memory throughout the entire engine operational range and used for any successive A/F adjustments. The adaptive memory operation is therefore responsible for adapting the A/F control to engine wear, aging and minor fuel problems. Its departure from base injection can be seen by studying the fuel trims. The further away the system deviates from base injection the greater the fuel trim correction seen at the scan tool fuel trims PID. The fuel trims PID is simply a base-injection deviation value of the comparison made by the ECM of adaptive correction to base injection. The greater the deviation from base injection, the greater the fuel trim value. The adaptive RAM/KAM memory is always erased when the battery is disconnected. When this happens, new fuel trim adaptive corrections have to be learned by the ECM.

 

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