Acceleration Enrichment Mode - (Jim) Yeah, that's definitely for racing my neighbor's car. Not really Jim...

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Acceleration enrichment mode is used in the event of a heavy engine load or hard acceleration condition called for by the driver. The ECM enriches the A/F mixture ratio to as much as 10.0:1, sacrificing fuel economy and emissions in order to maximize engine torque. This is allowed by government regulation, since hard acceleration is sometimes needed to maneuver the vehicle safely, therefore, it becomes a safety issue. The ECM enters this mode mainly by reading the throttle opening rate from the TPS. Some systems use a W.O.T. switch that activates the fuel enrichment mode. In most modern vehicles, however, the ECM simply reads the lowest TPS voltage as 0.0 % of throttle opening. A W.O.T. event, then, is considered when the TPS signal voltage reaches a certain level in a set period of time. The fact that the system is accelerating (fuel enrichment) does not necessarily mean that the system is in open loop. Most OBD II systems can still maintain fuel control even under hard acceleration conditions except W.O.T. During this mode, the ECM also uses other sensors such as the MAP/MAF and engine RPM signal, however, the TPS is still the main input for throttle rate of opening to the ECM. A faulty TPS signal can enable this mode and actually create a driveability complaint of flooding and engine stalling during heavy acceleration. The actual process of fuel enrichment is achieved through a combination of wider injector pulses and what is called asynchronous fuel injection pulses. During asynchronous injection, the ECM adds a series of extra injector pulses to the cylinder combustion event, so that instead of keeping the injector open for an unusually long time it simply adds a couple of extra pulses in between injection events. This will have the effect of enriching the mixture, while the ECM keeps a somewhat better A/F control.


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