Automotive Scan Tool PID DIagnostics (Diagnostic Strategies of Modern Automotive Systems Book 6) by Concepcion Mandy

Author:Concepcion, Mandy [Concepcion, Mandy]
Language: eng
Format: epub
Publisher: www.autodiagnosticsandpublishing.com
Published: 2011-05-28T16:00:00+00:00

Fig 6 – This chart shows the relation between EGR flow and fuel trims. In this case, bank 2 EGR ports were clogged causing all the EGR gasses to flow to bank 1, hence the misfire on cylinder # 3 & 1.

Notice the LTFT on bank 1 at 0.00% as compared to 15.00% for bank 2 while pre-loading the engine, indicating the ECM reducing pulsation for bank 1. The excessive EGR flow is causing the ECM to reduce injector pulse (to bank 1), since it interprets the inert exhaust gasses as a rich condition. Bank 2, although clogged, is being overly compensated with a wider injector pulse. This is a normal reaction by the ECM to the high load condition and EGR operation. The difference here is that there are no EGR gasses flowing to bank 2.

Wider inj. pulse to bank 2, due to pre-loading of the engine and EGR compensation. However, there are no EGR gasses present.

Excessive EGR flow can also cause the MAP sensor output voltage to go too high (speed/density) and fool the ECM into sensing a bigger load placed on the engine. This will cause the ECM to increase injector pulse, in order to richen the mixture and compensate for the bigger load.

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