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  1. #1

    96 sl 750 fuel delivery. How to test fuel pressure or crank signal to verify bad pump

    After cleaning and testing all fuel hoses and on/off/res valve, I have very little fuel out of pump. Ski wont start. I've read all about upgrading to the 3 outlet pump and will do. I want to test first so that if I need anything else, I can order it all at once, see this thing didn't run when I bought it the other day. 120 psi compression, cleaned carbs out, all looked amazingly good there. Anyway, I'm wondering if something can cause the crank case pulse signal that actuates the pump, to get weak from bad crank seal or what have you. I have dribbling fuel output, with no pressure if I hold my finger over the nipple and crank it even after a lot of cranking. How can I actually test the pulse signal and or the pump pressure, and what are the specs. I just don't wanna order a pump to find out that I need to remove the crankshaft to replace the seals or some crap. Or are they changeable externally, I mean like with the motor out, but the engine still together, that would be cool. I'm an auto technician with great bas knowledge and testing apparatus. HELP!! Thanks


  2. #2
    BlueFishCrisis's Avatar
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    Just order the pump. You need to upgrade it either way.

    Not sure what the specs are on the pulse from the crank case, but I'm willing to bet that the pump diaphragms are done....

    You can change the crank seals "easily" without tearing down the entire motor, but you will still have to split the case halves. I have replaced crank seals by removing the motor, placing it upside down on the bench, and removing the bottom half of the crank case. This of course means you need to remove the flywheel housing, flywheel, and stator (or at least unbolt).

  3. #3
    Fair enough. Thanks, will do. You're the man! Everyone see that? He's the man now.

  4. #4
    BlueFishCrisis's Avatar
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    You can also check the pulse line to make sure it is clear, and that the pulse fitting is not clogged. You may have left over oil or sludge floating around in the bottom of the crank. You can pull the carbs and intake to get a good look inside the motor to see if there is anything in there.

    If I remember correctly fuel pressure while running is somewhere in the vicinity of 4-6 psi at WOT. Not sure what it would be with just cranking....

  5. #5
    BlueFishCrisis's Avatar
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    Also - verify the year of the ski. Polaris didn't make a 750 in 96. The last 2 digits of the HIN will tell you what you have.

    You may also have blockage inside the fuel tank. Depending on the year, the ski may have lines inside the tank that have mesh screens on the pickups. If these are clogged, you will have limited flow and the pump will have an even more difficult time pulling fuel.
    Last edited by K447; 08-01-2014 at 09:19 AM.

  6. #6
    OK, thanks guys. Been through the tank and lines already, doesn't have lines inside and alls well to the pump. Looks like it's a 95,sorry. I just figured that it would have to be possible for a bad crank seal to keep proper crank case pressure signals or pulse from even being able to be possibly created, causing a pump actuation issue. Guess not? I just despise waiting for a pump when I could be pulling the crank, only to find out that Yeah, I've got a better pump now, but need to start a crank job that I could have already had done...

  7. #7
    BlueFishCrisis's Avatar
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    Unless you just buy crank seals and replace them, you can also do a leak down test. This would require you to remove the exhaust pipe and carbs, and seal all openings with block off plates. Using the pulse fitting, draw 9" of vacuum on the crank case. It should not lose more than 3-4" of vacuum in 10 minutes if I remember correctly...

  8. #8
    Fair enough, Thanks.

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