Simple EGR bypass circuit help

Discussion in 'The Projects Forum' started by NFrank89, Oct 18, 2010.

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  1. NFrank89

    Thread Starter New Member

    Oct 18, 2010
    well, it should be... (diagram below)

    i'm creating a device that will replace/emulate the EGR valve lift sensor in my vehicle to effectively bypass the egr system without the check engine light coming on. this sensor reads 420Ω when it is closed and 4.20kΩ when its open.

    the egr control solenoid (top) opens a vacuum line to the the egr valve (bottom) when the ecu grounds pin A11 causing the egr valve to open (4.20k)

    pin D12 is a constant ground that reads the resistance value of the egr valve lift sensor.

    when the ecu grounds A11, pin D12 needs to see 4.2kΩ but when A11 is not grounded pin D12 must read 420Ω

    I am having the hardest time figuring this out. if A11 were 12v instead of ground this would be incredibly simple. i tried wiring this circuit up with a relay but the ecu switches the solenoid off and on so frequently that it's impractical (and annoying) to use a relay.

    so far i've figured that if i use a 420Ω resistor from 12v to D12 the ecu will see the valve as closed. then when A11 grounds i need to somehow introduce a 466Ω resistor in parallel with the 420Ω resistor so D12 can read 4.2kohms and see the valve as open.

    this is where my problem is. i dont know how to use the ground from A11 to power a 466Ω resistor and get D12 to read a total of 4.2kΩ

    the circuit you see in the diagram is as far as i got before i got stuck. can someone please help me figure this out? i imagine this should be relatively simple but i'm no electrical engineer... yet ;)

    Last edited: Oct 18, 2010
  2. jpanhalt


    Jan 18, 2008
    Messing with anti-pollution devices in autos is frowned upon here. John
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    That is the case. Our guidelines do not permit help on this issue:
  4. SgtWookie


    Jul 17, 2007
    You really do need to fix the EGR system so that it works as designed.

    While EGR might initially seem like a dumb idea, it actually is a very good one; it reduces peak temperatures when a cylinder fires, and reduces emissions. It effectively increases the octane rating of the fuel you use.

    If you attempt to bypass it and leave the EGR non-functional, it's likely that you will have engine damage due to pinging/detonation, poor performance, poor fuel economy and high nitrogen oxide emissions.

    I've been working on repairing my vehicle's EGR system for a day or two now. My EGR valve was clogged with carbon; I used a sand blaster to remove it. My spark plugs were all ghost-white, which is an indication of excessive cylinder temperatures; normally they should be a dark brown to a light tan. Fortunately for me, I got to it before black spots started showing up on the ghostly white insulator; that's an indication of molten metal in the cylinder and an expensive repair. I still have a control problem somewhere, but the only solution here is to fix it, or have a knowledgeable mechanic fix it.
    Last edited: Oct 18, 2010
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