Ongoing 8.1 Issue Still Unresolved

Discussion in 'General Discussion' started by copb8tx, Dec 6, 2017.

  1. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    I'm still fighting an issue with my port 8.1L engine where it 'pops' under heavy load or at 3500+ RPM's. You could almost describe it as a very very light backfire maybe. But's a rapid pop-pop-pop sound.

    It's been discussed here: http://clubsearay.com/index.php?threads/8-1-power-issue.84318/page-5 however it was somewhat buried in a long thread and I didn't want to keep adding to the OP thread so I'm starting my own.

    In a nutshell, I've replaced plugs, wires, fuel filters, oil (not related) and now the fuel injectors. The engine idles and runs flawlessly up to the point of the problem. No smoke of any kind. They engine has 400 very well maintained hours on it.

    So now what could be failing? I was thinking possible the one of the individual coil packs. Does that make sense? If so, how can I find which one it is? They are very expensive at almost $800 for a set of 8.

    What other components should I be considering? A friend mentioned the Throttle Position Sensor but I'm not sure how that would cause the is issue. Or could it?

    If I don't get a clear path then I'm going to have to have my marina look at it and quite frankly I have very little faith in their capabilities.
     
  2. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    Start with removing the valve covers and checking for a broken valve spring.
    If the springs all look ok , try pushing down on each rocker, they should NOT move by hand pressure.
    Next a leakdown test and compression test
     
  3. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    [​IMG]
     
  4. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    Would a good leakdown and compression check eliminate the valve spring issue? If so, would these tests be easier to do than removing the valve covers?
     
  5. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    couple of simple tests, pull the sparkplugs and examine them pure white is a water ingestion problem, taste the tips, salty is water ingestion/reversion.
     
  6. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    sometimes the popping is due to a valve not seating or "floating " at high rpm`s because of a broken spring. GM engines use a inner and outer spring setup. Leakdown and compression test will indicate any problem with a valve suck as a burned seat or damaged intake valve face or seat.
    Another quick test is to see if all the valve stems / rocker arms are all the same height. Pressed in studs have a habit of pulling out and loosening the hyd lifter preload, "a soft valve"
    Do you need the manual?
     
  7. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    I pulled the old plugs and examined them to see if they were chalky, oily or in any way different. They all looked as you'd expect them to and they all looked pretty close to the same as each other. No since of any water related issues. They were then replaced with the new ones.
     
  8. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    Yeah, I'll need a manual if I decide to get this deep into the motor. I may get past my pay-grade here pretty soon though. How complicated is it to pull the valve covers off with all the other stuff mounted above the motor? Is this a 1,2...8 hour job?
     
  9. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    sent a link in pvt message? see post 2 and post 8
     
  10. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    [​IMG]
    [​IMG]
     
  11. Little Ducky

    Little Ducky Active Member

    513
    Jun 5, 2017
    Chattanooga TN/Dickson TN
    1998 SeaRay 290 Sundancer
    Twin 5.0L w/Alpha 1 drives
    Popping sounds like a timing issue.

    Lets hope it's nothing internal.

    Cam position sensor could be the issue.

    For cars they are not pricey to replace but have no clue for a boat motor.
     
  12. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    Got it. Thank you very much.

    Was it just for the electrical service manual or did I miss a mechanical as well?
     
  13. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    both are there 30 mechanical and 33 electrical
     
  14. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    By my untrained ear it sounds like some sort of ignition issue. The engine runs up on plane at 3400 rpms completely smoothly without noise.

    Can coil packs have a current draw issue that would manifest itself this way?
     
  15. copb8tx

    copb8tx Active Member SILVER Sponsor

    Jan 26, 2008
    Lake Texoma, TX
    2005 420 Sundancer
    T-8.1S Horizons
    Thanks. I'll go back and be more thorough.
     
  16. Little Ducky

    Little Ducky Active Member

    513
    Jun 5, 2017
    Chattanooga TN/Dickson TN
    1998 SeaRay 290 Sundancer
    Twin 5.0L w/Alpha 1 drives
    Like a car ..... newer boats have a computer that can be read/downloaded. Has anything been logged? I bet if there is a miss fire it would show up and indicate which cylinder(s) or faulty sensor.
     
  17. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    a weak ignition coil can fire a spark plug fine at lower engine rpm's but not supply enough spark at higher engine rpm's to properly fire the plug thus causing a mis-fire.....

    my bet is on a weak ignition coil.....

    good luck....

    cliff
     
  18. M Prod

    M Prod Active Member SILVER Sponsor GOLD Sponsor

    146
    Oct 6, 2017
    North Vancouver, BC
    2005 340 Sundancer
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine C80
    8.1 Horizons /V Drives
    This sounds very similar to what happened on my last boat. Engine would run flawlessly, then after getting it up to cruise it would start 'coughing'. It was intermittent at first (every 5-10 minutes or so) and then got more and more frequent. I also noticed a power loss as it would be very difficult to get up on plane with more than 4 people aboard (this was a Bayliner 245 with a 5.0). I did everything you did to no avail, and then finally had a compression test done. No compression in #7 cylinder and #8 was low. Turns out it was a bad valve intake. I ended up having to have both heads replaced. It ran flawlessly since then up until I sold it. I highly recommend having a compression test done. It will let you know if the problem really is internal, or something more minor.
     
  19. beeker

    beeker New Member

    14
    Nov 21, 2016
    Ok.
    03 185 sport
    4.3 v6 190 hp. Alpha one
    Is popping noise rapid,loud and coming from intake ?If you do decide to pull valve covers to ck valve springs and valve stem heights,turn engine over and visually see that all valves fully open.If you have flat cam at an exhaust valve ,pressure that would normally exit out exhaust will exit thru intake and create rapid popping noise thru intake
     
  20. Espos4

    Espos4 Member

    199
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Lots of good info there, but Before you get too deep into this, I would swap all 8 coils from one motor to the other. Label them with a sharpie or paint pen to keep things organized.

    See if the popping moves to the other motor.

    Also closely inspect the wire harness connectors that go to the coils, look for damaged, corroded, or loose crimps.
     

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