How to detect faulty cylinder in an engine

Discussion in 'The Projects Forum' started by Teena123, Feb 17, 2013.

  1. Teena123

    Thread Starter Member

    Nov 22, 2012
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    Hello i was just wondering if there is anyone out there who could have an idea on a circuit that can used to determine faulty cylinder in a Car engine? Any suggestions?
     
  2. #12

    Expert

    Nov 30, 2010
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    Watch the spark voltages on a scope. The cylinder with low compression will fire at a much lower voltage.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Are you trying to solve a problem on one vehicle, or are you trying to develop a product which will diagnose the problem?
     
  4. cork_ie

    Member

    Oct 8, 2011
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    The best diagnostic method available to detect any type of cylinder fault is to measure the rotational speed of the engine from cylinder to cylinder.
    This can be determined by examining the waveform from the crankshaft position sensor and the relative rotational speed. If you wish to determine which cylinder is weakest you can use a signal from one injector to use as reference point. That is the theory and it works well.

    If you want to be very innovative and develop something genuinely new, then I would suggest a pulse counter which can utilise the pulse signal from the crankshaft position sensor and determine the time taken for each cylinder to go from TDC to BDC on the power stroke for each cylinder, then output the data as relative power contributed by each cylinder. Bear in mind that you will also have to consider how crank sensor determines TDC - missing pulse or otherwise.
     
  5. #12

    Expert

    Nov 30, 2010
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    That seems a lot more complicated than going to a garage and watching the scope for low spark voltages!
    But I guess that's what the world is coming to now that microprocessors can be had for $1 or $2. Someday soon, my car will not quit beeping because it has a burned exhaust valve or a bad spark plug.

    Here's my offer: You keep making things that beep and I'll keep stuffing electricians putty in the beepers.:D

    Just don't program it to shut off the ECU when a spark plug wire arcs in the early morning dew:eek:
     
    Last edited: Feb 17, 2013
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  6. cork_ie

    Member

    Oct 8, 2011
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    It is, but more accurate too. Besides diesel engines can also be monitored this way.
    A weak mixture , due to a faulty injector or air leak will actually require a higher spark voltage,
    If you just want to monitor relative compression the easiest of all is to monitor starting current while cranking engine.
     
  7. Teena123

    Thread Starter Member

    Nov 22, 2012
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    Okay i think i understand a way to go about this, i could use a 555 timer as pulse counter to determine a missing pulse which should show a weak cylinder right.
     
  8. #12

    Expert

    Nov 30, 2010
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    Not quite. First, a low spark voltage is not, "missing" and second, corkie is talking about small changes in velocity.
     
  9. Teena123

    Thread Starter Member

    Nov 22, 2012
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    What circuit would you suggest i use??
     
  10. Duane P Wetick

    Active Member

    Apr 23, 2009
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    There is probably no better diagnostic tool for a piston engine than a compression tester.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
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  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Need a few clarifications.

    Faulty Cylinder is defined as:????

    Is this test to be run while the car is driving, or while in a shop and fixing it?
     
  12. Teena123

    Thread Starter Member

    Nov 22, 2012
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    Someone please i need help!!!
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Most of the common methods of finding a bad cylinder have been listed.

    You haven't answered any of the questions, so what is left to say?
     
  14. Teena123

    Thread Starter Member

    Nov 22, 2012
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    Oh i'm sorry didn't see the comments above, well lemme explain everything. I am using a piezo transducer to detect vibrations produced by a car engine, after that now i also want to detect a faulty cylinder in the same car engine while driving.
     
  15. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    As I suggested in one of the other threads you started on this topic, "My suggestion is for you to post a schematic of what you have built. Otherwise, there is no way for anyone to suggest anything sensible."
    [​IMG]
     
  16. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It seems that you have started seven different threads all associated with this same subject, and have received over 60 replies, and you are not satisfied. In all of this, you have never provided any evidence of your own efforts. If you really want help, post the schematic of what you have built. Or are you expecting someone here to do all the work?
     
  17. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Knock sensors are already built into modern cars.

    Many of the other parameters are as well.

    Is this a homework assignment? What do you know about/worked with, and what sort of test equipment do you have?

    A piezo sensor will detect knocking, which is undesirable. It won't detect low compression, which cylinder is firing, not to mention it will get extremely hot and fail to function after vibration. Have you considered these issues in your project?
     
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