Question about 1985 Pontiac Firebird

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Closed vs open

Please explain this to me I do not understand what the difference is and can you test them?

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  • robert_c_pol Mar 12, 2009

    Yes, what is the difference between closed loop and open loop?

  • robert_c_pol Mar 15, 2009

    Thank you so much.

  • Curt Downs May 11, 2010

    Robert, when u first start a car, it is open loop, as it warms up, it goes into closed loop, which is when sensors that monitor engine controls and engine conditions take over (like O2 sensors), making adjustments to fuel mixture, etc based on engine temp, engine rpm, etc.


  • Curt Downs May 11, 2010

    More info needed

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Are you talking about closed loop and open loop?

Posted on Mar 11, 2009

  • Clint Smock
    Clint Smock Mar 13, 2009

    When you first start the engine it is in open loop. In open loop the ecm runs on a fuel program that is determined by coolant temp. It ignores the Oxygen sensor. After the engine has warmed up, the temp is above 150 degrees and the oxygen sensor is switching (rich to lean) , then the ecm goes into closed loop. In closed loop the ecm checks the oxygen sensor to see if the engine is running rich or lean and will compensate the fuel mixture accordingly. So if you have a bad oxygen sensor the engine will run fine in open loop and run like **** in closed loop. But if you have a vacuum leak the engine will run like **** in open loop but may run fine in the closed. But if the ecm has a code for o2 or map or tps or coolant temp it will force the ecm to stay in open loop

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