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How does ECM know a fuel injector periodically fails?

Discussion in 'Technical Chat' started by JoeSchmuck, Aug 2, 2009.

  1. Aug 2, 2009 at 7:58 AM
    #1
    JoeSchmuck

    JoeSchmuck [OP] Well-Known Member

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    This is a technical chat item as I'm trying to collecting some data for a project, no failure actually exists (yet):rolleyes:

    My question is how does the ECM know if a single fuel injector is periodically not working.

    I suspect if you disconnect a fuel injector that the ECM would recognize there is no load (11.6 to 12.4 ohms nominal). If this is true, how many consecutive failures would cause it to be registered as a problem or would it toss the fail light on a single open line cycle? Of course this is under the assumption that the line is tested only during operation of the fuel injector, not constantly monitored which very well could be the case.

    If there is a different way the failure of a fuel injector is detected for a single cylinder, I'd love the hear it.

    Thanks,
    Joe
     
  2. Aug 2, 2009 at 8:11 AM
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    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    Im not sure how, exactly, the ECU detects the fail. Im guessing it senses the load, or resistance, as you mentioned. If it happens one time, the ECU will record the issue, but not trigger a CEL until it happens a few more times.
     
  3. Aug 2, 2009 at 8:54 AM
    #3
    JoeSchmuck

    JoeSchmuck [OP] Well-Known Member

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    Yes, I believe it will record the event and not toss the CEL until a certain threshold (count overall or count per engine run cycle) is met and I'm curious what those sensing specs are. I just don't know if it looks for a load continually or just during a request to operate the injector. The latter would be best for my little project. Now to find a solid state relay that can handle 5 amps and cycle at 300 Hz that doesn't cost an arm and a leg.
     
  4. Sep 25, 2009 at 6:40 AM
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    98tacoma27

    98tacoma27 :POOPCORN: Staff Member

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  5. Sep 25, 2009 at 7:29 AM
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    lookylookitzadam

    lookylookitzadam Retrofit Club!

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    My best guess would be by measuring resistance. Most cars use this method for other components as well
     
  6. Sep 26, 2009 at 5:54 AM
    #6
    JoeSchmuck

    JoeSchmuck [OP] Well-Known Member

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    Thanks for the link. This is of course for recording a misfire, normally the lack of a spark but it was interesting to read that the misfire appears to be initiated by crankshaft rotational speed variations not only due to the unburned fuel or hydrocarbons. "The camshaft position sensor is used to identify misfiring cylinders and the crankshaft position sensor is used to measure variations in the crankshaft rotation speed. The misfire counter increments when crankshaft rotation speed variations exceed threshold values." So this will also be a key item to ensure is addressed.

    I will be disconnecting one of the fuel injectors and placing a 10K resistor across the two pins in the harness in an effort to fool the ECM into thinking the fuel injector is still there. I will work my way towards 100 ohms but will stop at the highest value which the ECM recognized the fuel injector as being present. I am hoping a 1K resistor is as low as I have to go.

    After that we will have to see if the misfire is actually recorded. My plan is to turn off fuel injectors in a rotational pattern only for predetermined requirements such as load on the engine and engine speed. Heavy load disables the circuit or a bypass switch of course.

    I'm doing this because of the minimal heavy use on my truck and fuel costs and most important, I need a new project to keep me busy. I don't that even if I'm successfull in fooling the engine that I will save fuel. I quite possibly could end up using more over normal driving.

    Now time to find a high speed high power (400Hz 10AMP) SPDT electronic relay that doesn't cost me a ton of money since I'll need 6 of them for the final prototype.

    Thanks for the info,
    Joe
     
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