Thread: EGR valve advice
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Old Sep 6, 2014 | 10:51 PM
  #26  
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AlanFowler
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Default Some Info from another site
Still not resolved this issue of how to prevent an eml light when blanking the EGR on a Euro 4 but found the following quotation on another site from 2012. He seems to be thinking along the same line that I was but this thread did not seem to come to a definite conclusion either.



"When the egr opens and under certain circumstances (I suspect maybe on the overrun at particular revs) the ECU expects the MAF sensor to show a drop in air flow. This is because some exhaust gas is now flowing through the EGR so there is a corresponding reduction of fresh air drawn flowing past the MAF sensor. This drop in airflow should manifest itself to the ECU by a drop in MAF output voltage (picture with colour codes based on my vehicle posted elsewhere).

With the EGR blanked there is no reduced airflow across the MAF but the engine knows the EGR valve is open because of the position sensor on the EGR itself. The answer is to introduce a voltage drop from the MAF when the EGR is open. This could be done by using a couple of op amps in a fairly simple circuit. But it may also be possible to make it even simpler by driving a small relay from the vacuum solenoid and using that to introduce a volt drop".
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