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  1. #1

    Knock Sensor Ground Issue

    Here's the deal. We have 2 2003 F-12x's, one of them intermittently gives us an FI code and we've been chasing our tails trying to figure out whats wrong.

    So far we have swapped the knock sensor from the bad ski into the good one in hopes that we would get the same issue on the good one. The good ski ran properly and just today we checked the resistence on the plugs that attach to the knock sensors.

    First we checked the Resistence on the Ski without problems. On one of the leads we got a resistence of 0.03 ohms and on the other lead 19.02 ohms

    We did the same test of the malfunctioning ski and got the same results.

    We then did the test on the good ski with the ignition on getting a resistence of 0.03 ohms and no reading on the second lead. We checked the voltage of lead # 2 and saw 4.99m volts

    Did the same test on the bad ski getting 80 ohms of resistence on lead one and the 4.99 volts on lead two.

    We are under the impression that the malfunctioning ski has grounding issues?

    Thoughts opinions?

    If it is in fact grounding issues, where do the leads going to the knock sensor go and where is the ground located?
    Last edited by LAXitives288; 02-09-2008 at 11:41 AM.

  2. #2
    spatera's Avatar
    Join Date
    Jul 2007
    S. Georgia
    Are you assuming it's the knock sensor or did you get the 25 beeps when you pulled the code. Just curious how you narrowed it to this being the problem.

  3. #3
    My dad pulled a code and said it was the knock sensor code and it is also rev limited to 3,500rpms.

    I can only assume he pulled to code properly. It also makes sense that the corresponding wires on both skis have different resistences with the ignition on.

  4. #4
    Bob 1tommygunner1927's Avatar
    Join Date
    Apr 2007
    Houston, Texas
    Quote Originally Posted by LAXitives288 View Post
    My dad pulled a code and said it was the knock sensor code and it is also rev limited to 3,500rpms.

    I can only assume he pulled to code properly. It also makes sense that the corresponding wires on both skis have different resistences with the ignition on.
    I had an ECT sensor go bad on my R12X and it showed the same symtoms as yours. Had it replaced under warranty, problem solved.

  5. #5

    Join Date
    Feb 2008
    Central Florida

    knock knock

    I too am pulling a code 25. (at first I was not waiting 5 secounds to get codes and was getting 7 and 8 flashed) I have talked to 2 dealer service techs and it seems that alot of the times it would be the ECM that was bad. Scares me. I am also swaping knock sensors and hope for it to be the problem. Good luck and I will post my findings.

  6. #6

    Join Date
    Feb 2008
    Central Florida

    Have another goofy knock knock question...

    Does anyone know just how sensitive the knock sensor is? Would it be possible for it to pick up a vibration from an out of ballance impeller, cavitation, or pump bearings that a person may not feel or hear??? I would think not, but the reason I ask is I recently installed a repitched and ballanced Solas into a different housing on my ski. It was a used pump I picked up from a non turbo with 20 hours, I looked it over and changed grease before installing impeller, all seemed fine. Runs quite and feel no vibrations but I have never heard it ping either..... Its a long shot but if the sensor swap does not cure it I will swap my other pump back in for laughs.
    By the way the knock sensor has only 1 blue wire and is mounted to the block under the throttle body of #3 cyl, the airbox needs to be removed to get to it. I found it easier to disconect intercooler enough to move it forward a couple of inches to gain access.

  7. #7
    I build Horsepower
    NitroShark's Avatar
    Join Date
    Jan 2006
    What is the reason you have not followed the service manual procedure I'd like to know with your trouble shooting?


  8. #8

    Join Date
    Feb 2008
    Central Florida
    Nitro, Thanks for getting involved, your experience and advise is truly appreciated. Our Hondas have been pretty much trouble free for almost 300 hours and this is the first time that one has required more than just maintaince. Pump swap was about 10 hours prior and can't imagine they are related. On my last ride I developed an intermitent problem and pulled code 25, knock sensor. I have a full shop at home and although I have yet to tear into a Honda ski this is not my first rodeo.
    I should have mentioned I am trouble shooting per the manual and have checked my connectors, wire for continuity from sensor to ECM and no short to ground. Where I am at now is to install a known good sensor so I swapped it with the one off my wifes 03 F12X. I live in Florida and weather will be good Saturday so I will see which one acts up now, my luck they both will....
    Last edited by fats97car; 02-14-2008 at 01:02 AM. Reason: add data

  9. #9

    Join Date
    Feb 2008
    Central Florida
    Knock sensor was spent, the troubled ski ran perfect and the doaner kicked a code 25. Plugged Macs module back in and made short work of 2 RXPs. They could not belive I was out running them, the dealer convinced them Hondas where slow. The R12X runs 66.8 - 67 mph on GPS running Macs stage 2, wedge and repitched Solas impeller.

  10. #10

    knock sensor ground issue

    New to site. I'll give you the short version. I posted on BUt cannot access at work. But even better i'm part of a bigger family now.
    03 r12x 250hrs ,no mods

    Fi light on ,wont go above 3000 rpms.
    Dealer could not find any problems, or codes on computer.WHAT!
    After my 2hr 15 mile track back to ramp on idle!!!!!
    Out on lake for 3hr- no problems
    Out in ocean a week later. Problem Fi light on
    Followed procedure for code look-up- #25.

    I'll try to do a home job. too much $$$$$ at dealer.

    I got a couple of diagrams! BUttt..

    After much reading-

    _some say remove air box (is that were the air filter sits) or is there a different air box?

    - some say just to back off the intercooler and the thing that sits on top of it!

    What i DO!

    -dOES the sensor have its own grounding wire or is it the main harness that has the wire that i have to check?

    -Anybody have info on what bolts to remove to back off the intercooler ect...

    I'll try to look at the sky on wednesday if i get some help.

    Thanks in advance everybody!

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