Closed loop issue

Discussion in 'Technical Department' started by williet87, May 17, 2017.

  1. williet87

    williet87 New Member

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    Hopefully someone can help me. I just put in a 350 performance crate engine in my 98 z71 and as soon as we got it cranked it's had closed loop problems. I've had it checked for vacuum leaks already. Here's a list of new parts.
    Pcm
    Upper intake
    02 sensors
    Distrubuter
    Plugs
    Knock sensor
    Ignition control module
    Crankshaft position sensor
    Engine coolant temp sensor
    Radiator
    Map sensor
    Fuel injectors
    Fuel pump and I know I'm forgetting some. I can't figure it out. Runs good until it hits closed loop. If I unplug a is sensor and keep it in open loop it runs fine. Any suggestions would be nice


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  2. williet87

    williet87 New Member

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    Sorry, typo. If I unplug a 02 sensor it runs fine.

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  3. idrivea2005sierra

    idrivea2005sierra New Member

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    If you unplug the O2 sensor and the engine runs fine I would immediate suspect the O2 sensor is bad. If not bad, at least not sending the correct signals. Do you have a tool to read the ECU? You should be able to watch the O2 readings and see if they are bouncing around correctly. I would start with an OBD read and see what's happening.
     
  4. williet87

    williet87 New Member

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    I don't have one. I just put the new 02 sensors on last night and the only difference is it will go into closed loop faster than before.

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  5. idrivea2005sierra

    idrivea2005sierra New Member

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    Your first offensive move here is to understand what the computer is thinking. You need to find a buddy with a reading and logging software. Not just a code clearing unit; it needs to data log the PIDs. Once you have that we can look into the fuel logic causing your issues.

    Did you replace the temperature sender? If the computer doesn't know the engine is at temp it will use a "warm up" fuel map which is richer than it should be. Regardless of closed loop. Again though, the OBD reader can tell use what temp the computer is seeing.
     
  6. williet87

    williet87 New Member

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    I found a 20 year chevy tech that's gonna take a look at it and run a diagnostic test on it. Hopefully I will find something out in the next week

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  7. williet87

    williet87 New Member

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    Yes I did put a new engine coolant temp sensor on it as well.

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  8. mitchell0715

    mitchell0715 GMFS Member

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    excuse my ignorance, but is there a thermostat on that engine?
     
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  9. williet87

    williet87 New Member

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    Yes it is. I installed a brand new one during the engine swap.

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  10. mitchell0715

    mitchell0715 GMFS Member

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    possible it was bad when new? sounds like a thermostat problem is the only reason i mentioned it... but im no expert
     
  11. williet87

    williet87 New Member

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    I've bought many new bad parts lol. Wouldn't be suprised

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  12. mitchell0715

    mitchell0715 GMFS Member

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    i think its an easy part to get to, so maybe itll be worth a try. had one fail a few years back caused the same problem on my 00 5.3. kept it in closed loop and overheated

    anyone know how to check that they're working? i mean besides the obvious, it open at hot temps..maybe pull the sensor put it in a pot of hot water?

    also if theres air in the system, it might cause it not to open
     

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