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Thread: CX500TC stumbles bucks then dies, will not stay running, literally tried everything.

  1. #21
    jak
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    Senior Member jak's Avatar
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    spraying WD-40 or gas will do nothing to a pressurised intake system remember the turbo is pressurising the intake it will blow pressure out not draw it in like A naturally aspirated engine
    1980 cx500custom. dirt tacker 1978 engine

  2. #22
    Senior Member Pim205GTI's Avatar
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    Quote Originally Posted by jak View Post
    spraying WD-40 or gas will do nothing to a pressurised intake system remember the turbo is pressurising the intake it will blow pressure out not draw it in like A naturally aspirated engine
    It is a little more complicated then that.

    At idle it will create a vacuum in the manifold, just like a naturally aspirated engine. This because the Turbine doesn't spool up yet.
    So if there is a leak at idle it will run on the lean side.

    When the Turbo kicks in it will create a boost pressure above atmospheric in the manifold. A leak will then create a too rich mixture.

    So if you have a manifold leak with the Turbo the fuel mixture will be all over the place.
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  3. #23
    Senior Member johnste1960's Avatar
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    I know you check the fuel pressure however I can't help but going back to an issue I had with my 98 ram pick up. Which I bought brand-newI bought Brand new. The vehicle had all kinds of issues with it. All intermittent. it would die leaving stranded on the road, then Itwould immediately start up and start running good again when I had it on cruise control it would take off at high-speed then it would slow down. The heat would automatically go up to the defrosted down to the floor. I had it into the dealer numerous times and they could never duplicate the problem or find the issue I actually got to the point where I was in invoking the lemon law. Dodge actually sent an expert out from the factory and even they could not find the problem just when I was about to go to court, it was just about that time where the truck completely died would not go anymore and left me stranded on the highway out in the middle of nowhere. On the highway out in the middle of nowhere I had the vehicle towed in to the closest Chrysler dealer and with the hard fail they were able to isolate the problem to a bad fuel pump. so anytime I get problems like this I highly suspect the fuel pump even if things are looking good when you check it. Looking back everything made sense because as the fuel pressure was changing the vacuum in the engine was changing it was affecting the cruise control it was affecting the fan Vance him all the symptoms that I was having . Once they replace the fuel pump that I never had an issue with the vehicle and it was actually one of the more reliable vehicles I had on after that. You might want to try putting in a new fuel pump
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  5. #24
    Senior Member abecedarian's Avatar
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    Constant "36-38 psi " could be a problem.
    When on boost, pressure should increase almost at 1:1 ratio, as in say the manifold pressure is 10 PSI boost, fuel pressure should be 10 PSI above idle pressure.

    Ed brings up a good point about the fuel pump too.
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  6. #25
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    Quote Originally Posted by abecedarian View Post
    Constant "36-38 psi " could be a problem.
    When on boost, pressure should increase almost at 1:1 ratio, as in say the manifold pressure is 10 PSI boost, fuel pressure should be 10 PSI above idle pressure.

    Ed brings up a good point about the fuel pump too.
    Remember guys the excess fuel dumps back into the tank. The fuel regulator controls the pressure. Also if you look in the book, the fuel pressure has a very narrow range of fluctuation across the rpm range.

  7. #26
    Senior Member Pim205GTI's Avatar
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    Quote Originally Posted by Nunzio View Post
    Remember guys the excess fuel dumps back into the tank. The fuel regulator controls the pressure. Also if you look in the book, the fuel pressure has a very narrow range of fluctuation across the rpm range.
    Abecedarian is right. The absolute fuel pressure rises along with the manifold pressure, see picture :



    The fuel pressure topside is connected with the manifold and keeps the pressure difference between the fuel and the manifold constant.

    The pressure difference should be around 36 psi ( 2.55 Bar ).

    So if the boost rises to say 10 psi the absolute fuel pressure should be 46 psi

    Quote Originally Posted by Nunzio View Post
    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.
    So this is not good
    Last edited by Pim205GTI; 11-20-2016 at 09:12 AM.
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  8. #27
    Senior Member Old Okie's Avatar
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    At the risk of showing my ignorance, I cannot make the connection between the fuel pressure and the boost pressure.
    Seems like if the boost changed the fuel pressure the boost would have to blow back through the injectors????
    The boost goes in the intake pipes and the fuel goes through the injectors and I can not see them interacting.
    What am I missing here???
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  9. #28
    Senior Member Pim205GTI's Avatar
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    Quote Originally Posted by Old Okie View Post
    At the risk of showing my ignorance, I cannot make the connection between the fuel pressure and the boost pressure.
    When the manufactures started with boosted fuel injection the faced the following problem. The pressure difference between the fuel going in and the room it is injected into ( manifold) controls the flow. So if boost starts to build up the flow through the injectors will decreased. If then boost reaches a point when it's higher then the fuel pressure the flow wil reverse. Because flow through an injector is not linear to the pressure difference it was easier to control the pressure difference and keep that steady resulting in a constant flow.



    So this is our fuel regulator. There is a diaphragm in the middle. On the lower side the fuel pressure pushing upwards and on the manifold air pressure and spring pushing it down.
    So if the manifold pressure rises, the fuel has to push harder to lift the diaphragm to escape. Harder to push = higher fuel pressure.
    So you see the fuel and air pressure are balanced.
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  10. #29
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    he fuel pressure topside is connected with the manifold and keeps the pressure difference between the fuel and the manifold constant.

    The pressure difference should be around 36 psi ( 2.55 Bar ).

    So if the boost rises to say 10 psi the absolute fuel pressure should be 46 psi
    According to the Turbocharger / Computerized Fuel Injection Manual, fuel pressure is maintained at 36 psi, that's why its a balance system. the manifold pressure allows fuel pressure to dump when its high and the spring regulates that when it's low. It says the fuel pressure won't exceed 36 PSI. See here in the manual.

    Name:  Cx500 Fuel Regulator Pic.jpg
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    Last edited by Nunzio; 11-20-2016 at 03:00 PM.

  11. #30
    Senior Member edinlr's Avatar
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    Two thoughts here. Is there any chance that you have some garbage in the fuel lines of the fuel rail? Even good fuel pressure and rebuilt injectors won't work if they are not getting good flow. On the other track, what is the bike doing when it dies? Does the ignition go dead, lights etc., that would sound electric and I would still go back to the ignition switch going south or the kill switch on the right handlebar. Usually you can tell by the feel if the throttle goes mushy and it feels like it is running out of gas, (or on an old bike when it stumbled when you went on reserve) or if it dies suddenly like someone hit the kill switch. I would also check all of your grounds and pull them off and make sure they are clean and that the connectors are very solid.
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