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TBI operation information needed

Discussion in 'The Garage' started by burbBoy, Jan 19, 2004.

  1. burbBoy

    burbBoy 1/2 ton status

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    I finnally got my winaldl cable made and tried it out today to find my truck is running in closed loop all the time. What makes the computer jump to open loop? I thought all it relied on was temp. The truck has a 170 deg. t-stat and thats about where the tempature was and it was still in closed loop. Any ideas guys?
     
  2. BurbinOR

    BurbinOR 3/4 ton status

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    Your truck, when cold, starts in OPEN loop, then after the exhaust temp reaches apx 600* it goes into closed loop, which is where you want it. Most FI vehicles have 195* t-stats if I remember right, and operating temps around 200* as read on a scanner. Both my TPIK5 and my current Burb run at or about 200-205* year round. /forums/images/graemlins/cool.gif
     
  3. burbBoy

    burbBoy 1/2 ton status

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    hmm me in all my stupidity got open and closed loop terms backwards! oh well thanks for clearing it for me.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Two things have to happen for the ECM to go into closed loop. Coolant temp must be over 160 degrees F and the O2 sensor must be hot enough to start putting out a signal (around 600 degrees, as BurbinOR said). It can take a long time to get into closed loop while sitting in the driveway idling, especially in cold weather. If you have headers then you'll probably only be able to get it into closed loop operation while driving. They cool off too quickly to keep the O2 sensor hot while idling.

    Closed loop means that the ECM is constantly adjusting the amount of fuel being injected, based on readings from the O2 sensor.

    Open loop means that the ECM is just using lookup tables stored in memory to control the amount of fuel being injected. It has no feedback to rely on in this mode.
     
  5. K5 NUTT

    K5 NUTT 1/2 ton status

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    Unless you run a modified chip in your 7747 ecm...you are going to have nothing but problems with that 170 t-stat....alot of the programming in a stock chip is written around having a 195 stock tstat...some companies run chips that require a cooler tstat...so go back to stock until you decide what you want and how much its going to run you.


    DW
     
  6. fly_n_hi_yukon

    fly_n_hi_yukon Registered Member

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    Don't forget that the ECU goes in to open loop at WOT, regardless of the coolant temp, etc.

    Also, the long heat-up time for the 1 wire O2 is the reason that the newer EFI vehicles have 3 and 4 wire oxy. sensors. If the O2 is taking a long time to heat up, it is possible to convert to a heated 3-wire without too much difficulty. /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif
     

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