CX500TC stumbles bucks then dies, will not stay running, literally tried everything.
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  1. #1
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    CX500TC stumbles bucks then dies, will not stay running, literally tried everything.

    Okay so I bought this bike and it ran wonderful for about 900 miles. Pete has been working with me to try and figure this issue out. I had noticed a couple hick ups one day on a ride, thought it was nothing. Took it for a long ride and about 200 miles in it started to skip, bog and cut out. I was able to get it home, but only after it completely died on me several times on the way home. It was cutting out then would pick up and run for a while. Also felt like the boost was gone.

    Oh and this is a pretty decent example of a CX500TC, only 11,790 miles on it.
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    The bike starts up runs and ides fine.
    Warms up from a 2k fast idle then settles to 1000 rpm once warm.

    Things I have checked:
    1. Valve clearances were the first thing I looked at. I had some very tight valves and adjusted them. Found noise coming from valve train and was concerned, so I pulled the motor found a cam follower spring broken. I replaced that and reassembled the engine, replaced the gaskets, mechanical seal, checked the pickups and all looked great. No rust whatsoever. Completely replaced all gaskets for turbo and exhaust with copper, annealed the gaskets and used copper paste on all joints. Nothing leaks.
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    2. Then checked compression, each cylinder is at 145-150 each time I tested. Did 3 times each cylinder
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    3. Checked cylinder leak down. Both cylinders were less than 5 - 6%.
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    4. Checked the turbo with a gauge and it builds 9-10 psi, also disconnected the waste gate and tested the valve it moves the correct amount with 18-20 psi applied.
    a. turbo rotates freely and has minimal axial play
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    5. Checked all sensors lines for leaks, and found none. As a precaution I changed all vacuum lines.

    6. Checked all sensors with inline splitter/jumper as per the troubleshooting manual using vacuum/pressure and volt/ohm meter. All are dead on and in spec.
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    a. Also swapped each sensor with known good ones no change.
    b. Checked the throttle sensor and in spec. Checked sensor adjustment and it is .67 per spec
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    c. checked thermostat temp sensor and all in spec. .30 ohms fully warmed. Also used a potentiometer to adjust the resistance and it would swap from fast idle to normal idle as I regulated it.
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    d. Did not check MAF sensor yet Made sure the orifice is in the line and it is.
    e. swapped ECU with known good one with no help
    f. swapped CDI unit did not not help.

    7. Checked pickups with ohm meter and all withing spec, in fact on the low side (ohms) of of spec in manual.

    8. Checked fuel pressure key on not running (38-40 psi), while running, (34-36 psi). Left connected and rode bike while cutting out and dying, 36-38 psi and never dropped.
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    9. ECU does not throw any codes when the bike is sputtering and dying. Fuel light never comes on signifying an issue.

    10. Checked the voltage while running, output is 14.67 +/- .40 volts

    11. Swapped RH injector with new rebuilt one and no help. Then swapped the removed RH for the LH side, no help still sputters and dies.

    12. Gave up and drank lots of beer as I'm stumped.
    Last edited by Nunzio; 07-04-2016 at 07:56 PM.

  2. #2
    Senior Member Pim205GTI's Avatar
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    Quote Originally Posted by Nunzio View Post
    Oh and this is a pretty decent example of a CX500TC
    I think that is an understatement

    Back to your predicament,

    - exchange the wire-harness ?
    - exchange the ignition coils ?
    Last edited by Pim205GTI; 07-05-2016 at 03:19 AM.
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  3. #3
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    Very nice

    Check the resistor connector for the coils.

    If the connections move that cuts the ignition

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  5. #4
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    Quote Originally Posted by Pim205GTI View Post
    I think that is an understatement

    Back to your predicament,

    - exchange the wire-harness ? RE: I had the bike stripped to the frame, inspected the harness, there was nothing chaffing or signs of wear. Also when all the tests were being done this checks the wiring integrity
    - exchange the ignition coils ? RE: I checked them per the manual and all in spec, also checked them when they were hot still good. Not saying it couldn't be a coil. I will need a good known set to swap and check
    Was thinking of getting some Dyna single fires (green) but they don't look like a good fit for where the plug wired exit.

  6. #5
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    Quote Originally Posted by SPTOQ View Post
    Very nice

    Check the resistor connector for the coils.

    If the connections move that cuts the ignition RE: Connections are good, there is not a check for this in the manual. There is not a resistance measurement. Also there is three wires and it looks to be a dual resister. Meaning one for each coil individually
    Anyone have the resistance measurement for the resister?

  7. #6
    Senior Member Pim205GTI's Avatar
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    Quote Originally Posted by Nunzio View Post
    - exchange the wire-harness ? RE: I had the bike stripped to the frame, inspected the harness, there was nothing chaffing or signs of wear. Also when all the tests were being done this checks the wiring integrity
    Your intermitted / irregular problem sounds like an electric gremlin.

    I would still find another wire harness or when the problems start try to wiggle the harness at all connector points , I realize that this would be a little hard will driving

    There is a small wire harness between the ignition coils and the CDI unit, start there...
    Last edited by Pim205GTI; 07-06-2016 at 06:42 AM.
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  8. #7
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    I don't suppose that you tried taking the covers off of the spark plug caps to see if the caps are bad and arcing into the well.
    Or, unscrew and inspect the stuff inside the spark plug cap to see if the works are all crapped up?

  9. #8
    Senior Member MobileAZN's Avatar
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    1980 Honda CX500 Custom (In a pile of parts, current project)
    1981 Suzuki GN400CR (Cafe Racer, current ride)
    1976 Honda CB125S1 (Full original restoration. Sold her and miss it. Every. Single. Day.)

  10. #9
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    Quote Originally Posted by timothy_d View Post
    I don't suppose that you tried taking the covers off of the spark plug caps to see if the caps are bad and arcing into the well.
    Or, unscrew and inspect the stuff inside the spark plug cap to see if the works are all crapped up?
    Yes. I replaced the plug wires as a precaution, I also removed the resister in the cap with brass rod, as I'm using IRRIDIUM plugs.

  11. #10
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    Okay, so let's look at the symptoms again.
    This bike has, if I recall correctly, multiple fuel filters. Replace or clean all of them.
    After fuel, you are down to electrical.
    What are things that can fail when they get warm or hot?
    Now cross reference those things against issues that throw codes, eliminate those items.
    Whatever is left is a good starting point.

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