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  1. #1

    MSX140 fuel pressure woes

    Last fall the center cylinder on my MSX140 engine burned up, the spark plug had disintegrated, I attributed the failure to the plug. Over the winter I rebuilt the center cylinder, did the fuel pump mod, and put it all back together. It started right up.

    Figured I should check the fuel pressure before dunking it in the lake. Ran up to the auto parts store and borrowed the gauge -- 0 PSI. Not believing the gauge, I did the same at a 2nd auto parts store. 0 PSI.

    Ok, must be a problem with my reworked pump. I pulled the pump yesterday, and just now, ran it in a bucket of mineral spirits with a loop and a brand new pressure gauge -- lo and behold, 26 PSI. Did the same with a 2nd pump, 30 PSI. So both pumps are good.

    At this point I can only suspect an injector failure --- anyone have experience with this? How to troubleshoot the individual injectors? Obviously I suspect the center injector -- it must be dumping fuel wide open into the cylinder. Anyone seen this failure? Help needed.... Thanks..... radio-active

  2. #2
    Msxslayer's Avatar
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    Maybe check see this ther is voltage at that injector

  3. #3
    Maybe pull the plug and spin it? It wouldnt be running on all three if that injector was leaking bad enough to have zero psi.

    When you say loop, you mean you are taking the whole module, putting in your bucket, making a loop between in and out with the gauge? Are you certain the lines are in the injectors correctly and you are testing the pressure side of the injectors? Not trying to insult you just covering bases. By mod you mean tapping the module plastic and installing a brass fitting right?

  4. #4
    On the MSX140 the entire loop sits at the regulator pressure -- in fact the test port is in the return leg. Yes I do mean tapping the plastic and inserting the brass fitting.

    I appreciate the suggestions -- keep 'em coming. I'm not 100% certain it was running on all 3, I just ran it long enough to check the pressure.

    I think the next step might be to totally bypass each injector, one at a time, all while monitoring pressure. I'm not reinstalling the fuel pump assembly until I'm certain what component is at fault.

  5. #5
    martincom's Avatar
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    Plugged/restricted fuel line would be my guess. Did you remove the valve core from the Schrader valve--in the event it is not opening?

  6. #6
    ^^^ he makes a good point. The Schrader valve could be jacked up.

  7. #7
    Moderator HiPeRcO's Avatar
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    Indeed it's often the case that the Schrader valve sits too low to be pressed down sufficiently. Just remove it for the test (but don't forget to put it back in )

  8. #8
    I'm going to feel really stupid if it was just the shrader valve. I spent a 1/2 day pulling the pump again.

    I'd like to convert the small shrader valve permanently to the larger, more standard style. Any help finding a 1/4" barbed T with the larger shrader test port?

  9. #9
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by radio-active View Post
    I'm going to feel really stupid if it was just the shrader valve. I spent a 1/2 day pulling the pump again.

    I'd like to convert the small shrader valve permanently to the larger, more standard style. Any help finding a 1/4" barbed T with the larger shrader test port?
    How often do you expect to be checking fuel pressure?

    Unscrewing the Schrader valve core before doing a fuel pump pressure test takes maybe 30 seconds.

  10. #10
    I'm paranoid about fuel pressure! I'm tempted to install some sort of indicator or gauge.

    Good news is I just located the correct fuel gauge and a quality adapter, here at work. In fact it was among the tools recovered from a Polaris PWC/snow dealer that went out of business.


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