how does tach usually fail?

Discussion in 'Classic Sea Rays' started by carboncow, Jul 7, 2015.

  1. carboncow

    carboncow Member

    55
    Jul 25, 2014
    Ohio
    1989 340 Sundancer & 2007 Sea Doo Challenge 180
    Mercruiser TbIV 454ci V-drive % Rotax 4stroke 215HP
    Just picked up an 1989 340 Sundancer...passed survey with flying colors. Only items to complain about is a non functionality starboard fuel gauge and a starboard tach that is a bit odd...

    It starts off way "off" from it's true reading and then as (something) warms it slowly becomes more accurate while after an hour it's prob spot on. So something is most likely warming, expanding and giving a better contact or reducing resistance.

    Do the tachs themselves tend to fail or should I be pull it out and cleaning wire connections?

    Shawn
    Ohio
     
  2. julietbravomike

    julietbravomike New Member

    56
    Aug 7, 2014
    Dallas & Lake Texoma
    1989 340 Sundancer &
    2007 Yamaha Waverunner FX140HO
    7.4l Merc MIE's w/Borg Warner 72c V-Drives and Onan 6.5 MCCK
    Hi Shawn, one of mine did the same. These tach's are universal in that they will work with a 4, 6, or 8 cylinder engine. To that end, there is a small knob on the back where you can make the 4, 6 or 8 selection. Those internal connections sometimes get funky. Carefully remove your panel to access the back of the tach - then move that knob back and forth a few times across all selections - after that, make sure it's lined up on 8 and fire it up. Should fix the problem.

    The fuel sender units are accessible through the mid cabin - remove the mattress and they're under a wedge shaped protrusion held in place by a couple screws and tons of silicone. That may be your culprit. You can search here and other places about how to diagnose whether the sender is bad. Get smart about gas fumes before you do this though, it's a serious matter.

    Good luck with the boat, we love ours!
     
  3. carboncow

    carboncow Member

    55
    Jul 25, 2014
    Ohio
    1989 340 Sundancer & 2007 Sea Doo Challenge 180
    Mercruiser TbIV 454ci V-drive % Rotax 4stroke 215HP
    Awesome info!

    How does one access the gauges best on these...I have not studied the boat enough to have figured that out. Access on the back via a hatch/mirror or does the front panel lift up for access.

    Do the fuel senders seem to fail electronically? My Tiara had mechanicals and you had to pull an inspection plate to see your level. I was told these are far more reliability and don't see how the electronics fail unless they get stuck or the electronics at the sender...or is it once again often a gauge thing?
     
  4. julietbravomike

    julietbravomike New Member

    56
    Aug 7, 2014
    Dallas & Lake Texoma
    1989 340 Sundancer &
    2007 Yamaha Waverunner FX140HO
    7.4l Merc MIE's w/Borg Warner 72c V-Drives and Onan 6.5 MCCK
    The panel has several screws (and may have screw covers that you have to pop off with a small flat head screwdriver). The thing is pretty wide and flexible, so you have to just very carefully pull/wiggle/lift/slide it out a bit. All the gauges are attached to it. The compass gets in the way, but I think you can get the panel out far enough to do this by flipping the sun cover over. Just be really careful b/c the panel is flexible, but also fragile.

    I had a sender go bad, the gauge was fine. In the interest of full disclosure, I tested my gauge by very briefly touching the sensor wire to the ground post on the sender - bad idea, b/c the needle slammed past full and got stuck, so I had to disassemble my gauge. I think I bought a universal sender off ebay for probably $20. My original sender float was cork and seemed to be floating fine, but I hear they can disintegrate. The replacement was some type of plastic/composite material.

    Both of your issues are hopefully pretty simple fixes. Best of luck!
     
  5. carboncow

    carboncow Member

    55
    Jul 25, 2014
    Ohio
    1989 340 Sundancer & 2007 Sea Doo Challenge 180
    Mercruiser TbIV 454ci V-drive % Rotax 4stroke 215HP
    Thanks. Found a photo showing the screws on the panel. Should be an easy fix if shifting between the 4/6/8 setting will knock some love back into it.

    Any idea the depth of the fuel tanks? Seems that a sender is dependent on the depth and I'm hoping to order one now and then take it all apart and install and reseal in the same day.
     
  6. julietbravomike

    julietbravomike New Member

    56
    Aug 7, 2014
    Dallas & Lake Texoma
    1989 340 Sundancer &
    2007 Yamaha Waverunner FX140HO
    7.4l Merc MIE's w/Borg Warner 72c V-Drives and Onan 6.5 MCCK
    Search Ebay for this item #: 121432749583

    Moeller Marine Electric Universal Fuel Tank Sending Unit (4" to 27" Deep) - you can adjust the length to match the one you take out.
     
  7. carboncow

    carboncow Member

    55
    Jul 25, 2014
    Ohio
    1989 340 Sundancer & 2007 Sea Doo Challenge 180
    Mercruiser TbIV 454ci V-drive % Rotax 4stroke 215HP
    Ordered! Thx
     
  8. JVM225

    JVM225 Well-Known Member GOLD Sponsor

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    +1 on the fix for the finicky mechanical tach. You'll probably have to do it again every year or so.
     
  9. carboncow

    carboncow Member

    55
    Jul 25, 2014
    Ohio
    1989 340 Sundancer & 2007 Sea Doo Challenge 180
    Mercruiser TbIV 454ci V-drive % Rotax 4stroke 215HP
    Thanks. We ran the boat this weekend prior to me doing the move around the 4/6/8 switch and interesting...just like the owner said it's off when the engines cold and gets accurate as it warms. Within 5 minutes of running the boat it was accurate and stated they way for a 3 hour cruise.

    Will be pulling part this weekend.
     

Share This Page

Show Sidebar