270 Sundancer 1999 7.4MPI low rpm WOT

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by StefanFL, Aug 14, 2019.

  1. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    Hi I recently purchased boat from title and it was doing 27-30mph (depending on trim) at 3200rpm WOT, It did run very strong up to 3200 and pained without the problem with 2 person a aboard ( 3/4 gas/freshwater tank).

    On my last trip on the way back to marina I experienced some misfire, and other electrons started jittering (like tachometer/other electrical gauges we randomly jumping around).
    I suspected bad cables, so I order cables/distributor cap/rotor and spark plugs.

    Meanwhile I wait for parts I am trying to investigated problem with 3200rpm wot and if it's somehow connected with ignition issue, and my findings are following.

    My model year came only with B2 or B3 drives (gear ration 1:2.0 and 2.2) (prop 21-23p),
    however according to the prop model and pitch my drive is B1 (unknown gear ratio)
    Prop is 14.5 diameter with 17 pitch SS (QS5052X)

    Pitch is much smaller then original and that's main reason I believe drive is swapped as with 1:2.0 gear ratio engine would go too high on WOT.
    I am unable to estimate gear ratio in my drive.
    I know with B1 it could be 1.36, 1.5 or 1.65.

    Is any of these gear ration going to work with my boat by just swapping prop if needed?
    I believe if gear is 1.36 I stand no chance, so I hope it's either 1.5 or 1.65.

    Is there any way to figure our gear ratio? maybe if I can locate serial number of drive?

    In case ratio is 1.5 or 1.65, should i get full WOT with my current prop?
     
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Take care of your misfire 1st and see how it goes. You could remove your drive and rotate the prop shaft 1 revolution and count the revs on the input shaft to determine ratio
     
  3. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    I received all parts, will go after work to replace everything and test it.

    Thank you for advice for rotating the prob.
    She is in wet slip and I will have to rent a trailer to pull her out of water and take the drive out.
    Just trying to find out if there is a way to figure gear ratio while in water, so I can get new drive or prop and replace it once I pull her out.
     
  4. Wanderer 290

    Wanderer 290 Member

    83
    Jul 1, 2019
    01 sea ray 290 sundancer
    Twin 5.7 b3’s
    You can avoid pulling drive by shutting down the engine in forward gear then rotating the engine at the crankshaft pulley bolt 1 complete revolution with a breaker bar and socket while another person observed the prop. Pulling the spark plugs would lighten the effort to turn the crank.
    Or start the engine on the trailer with muffs to supply cooling water and use a mechanical tack on the prop and compare the engine and prop rpms.
     
  5. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    Great idea for pulling plugs and turn crankshaft.
    I will probably try this method even if everything works fine after tuneup, just to know gear ratio for future.
    Thanks!
     
  6. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    Update. Just finished changing:
    1.Spark plugs
    2.cables
    3.distributor and rotor
    4.coil
    Unfortunately i forgot keys and house is 1h drive, so I pulled dash and started it using alligator cables :)
    Didn't want to drive like that through, so will test drive tommorow.
    I tried to rev it, and it seems to hit limiter in neutral around 3400rpm.( I'm not sure on what rpm this engine have neutral limiter.

    There is one strange thing I will upload the pictures of distributor when I get home.
    According to service manual first contact on port side closer to engine should be Cylinder #1 , on old distributor everything was shifted by 1 to right.

    When i followed manual engine didn't want to start, so i shifted back to how it was and it start really quick (0.5sec).

    Possible issue 2 is that on port side around Cylinder #7 i can see some oil, seems like leaky valve cover gasket, hope this cannot affect oil pressure.
     
  7. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    According to service manual green dot on picture below should be #1 and go clockwise 1-8-4-3-6-5-7-2.
    I tried this and engine didn't start.

    on old distributor #1 was on red dot, so i shifted everything and it started right away.

    Does this make sense?
    Is it possible that someone before shifted whole distributor?
    Should i take it apart, position #1 to tdc and reposition distributor or it doesn't matter if running well?
     

    Attached Files:

  8. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    The position doesn't matter as long as the wires go to the correct cylinder and timed . You should check your timing.
     
    techmitch likes this.
  9. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    I went for a test drive and issue is still there.
    Engine start immediately now ( it was taking few seconds before), and seems to pull stronger, but wot is still the same 3200-3300 range.

    I have tried to run with disconnected knock sensors, to eliminate possible of faulty knock retard the timing, same situation.

    Unfortunately i don't have timing light to check if it's advancing, so will have to buy or borrow tommorow.

    I found some suggestion that ignition module under distributor cap could do this without throwing code.

    I dont have rinda to check ecm, but tested that my beeper is working by disconnecting water temp sensor and it was beeping.

    https://www.youtube.com/playlist?list=PL8aoAN7vpA7hUIJ1tq5MqhWZN_hUtxnAl

    I have fuel flow gauge and it was reading 24gph on full wot. 3/4 throttle (still same rpm as last 1/4 does not affect engine speed, it get louder)
    17-18gph

    Thanks for all advices will try to source timing light tommorow.
     
  10. StefanFL

    StefanFL New Member

    7
    Aug 14, 2019
    Atlanta, GA
    270 Sundancer 1999
    7.4MPI Bravo (gen VI)
    Update.
    cleared codes from ecm, and with trim up engine did go all the way to 4000rpm.

    ecm is just repeating code 12 and there are no other codes.

    Engine did cut off few times, like die completely for a sec and then wakes up immediately. (strange)

    Tried to WOT it multiple times, did between 3400-3600, 4000onces but trim was up too much.
    Jumps out on plane around 3000, then it goes to 3200-3300 with leg all the way down, then when i trim it up it picks up some more rpm.

    Will replace fuel filter before next run and get timing light to check advance.
     
    Last edited: Aug 18, 2019 at 10:53 PM

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