2000 MAG 454 MPI, loss of power

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Gallf1, Aug 2, 2019.

  1. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Hi:
    Yes, #L398572 is what is on the block....when I plug it in to website (like:www.mercruiserparts.com) and others it comes up as: 454 MAG MPI Horizon 7.4L
     
  2. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's

    Thanks for completing the info. in your profile (I whish everyone did) as it helps us, help you.
     
  3. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Hi Mitch:
    So i went out to the boat today to install a new Distributor cap and rotor on the problematic engine (just as part of normal maintenance. I was thinking about the discussion of having fuel in the fuel pressure regulator vacuum line and decided to check it....I disconnected it at the hose barb down by the fuel pump and it appears to be dry inside.
    I decided to start up the engine and:
    Now vacuum at idle is only about 8" and with a fuel pressure gauge installed on the fuel rail I got 35psi with ignition on but engine off...I then got a rock steady 43psi at idle. The 43psi does not go up or down when the vacuum line to the regulator is removed and when i put it in gear and throttle to 2,000rpm the pressure stay steady at 43psi.

    Does this sound like a vacuum leak somewhere or a bad regulator?

    I think i need to pull the plenum to see better
    Thx
     
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    You need to have the fuel gauge on it when it hits the rpm wall underway. There is another rubber vacuum line under the plenum that could have failed.
     
  5. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx....I think I am going to pull the plenum and at least clean it out and inspect/replace all vacuum lines. Then I am going to do what you suggested and pipe the fuel rail schraeder valve out and above the plenum so that I can install the fuel pressure gauge and watch it while running the boat on a plane at 3200rpm and see what it is doing as I push the throttle.
     
  6. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's

    All bets are off with only 8" of vacuum. There's a leak, you got misfires or it's mechanical...
     
  7. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Yeah....weird as a few days ago it was at 15" while at idle and the only thing that has changed is today i disconnected and reconnected the fuel regulator vacuum line while testing the fuel pressure (no pressure change).
    I am going to remove the plenum and see if something else is leaking underneath
     
  8. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    So finally back at the boat....installed new distributor cap, new PCV valve, checked coil (ok) checked oil pressure sensor (ok). Fuel pressure remains constant at 43psi (manual spec) at idle and under load and when I remove vacuum line nothing changes....I even added all the way up to 25 inHg of vacuum to regulator with vacuum pump with no change in fuel pressure? Is this a sign the regulator is "stuck open and allow too much pressure at the rail for idling conditions?

    I thought that the fuel pressure should change by 3-5psi with vacuum on and off?

    If the fuel regulator wouldnt hold a vacuum doesnt this mean the diaphram is broken and as a result low fuel pressure?

    Thx!
     
  9. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Yah the reg. isn't working. 39#'s at idle and 43 at speed is normal. So your fuel pressure is high at idle but doesn't explain why it doesn't rev out. What was the FP doing at WOT ?
     
  10. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    Dallas, TX
    Cruisers 3575
    Twin 7.4l
    The diaphragm in the FP regulator likely has a hole in it. That's why it doesn't respond to vacuum.
     
  11. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    My dock is 30-40 mins from an area were I can open the throttles and get on a plane (canal system with no wake zone). I did change the plugs when this all started but I think the high fuel pressure has fouled them again before I can open it up?

    Sounds like I need a new regulator and change the plugs again....any value in going to the Iridium/Platinum with this model motor? I am running the stock NGK's that the manual calls for.
    Thx
     
  12. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    Dallas, TX
    Cruisers 3575
    Twin 7.4l
    NGKs are fine for that motor.
     
  13. Cdb

    Cdb New Member

    4
    Oct 10, 2019
    2000 34’ Sea Ray Sundancer
    454 V-Drives
    Hi just seeing if you found the problem? Thanks
     
  14. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Hi:
    Well....the fuel pressure regulator was stuck “wide open” meaning fuel pump was delivering 43psi even at idle, I also took off the air plenum and found it was coated with oil inside as was the vacuum hose leading down to the regulator. Also the small hose from the plenum to the intake horn (closest to the flame arrestor was not sealing so I replaced it as well.
    New fuel pump, regulator, vacuum hoses, cleaned out plenum and to be safe replaced intake sensor, ECT sensor and MAP sensor. I also went ahead and replaced the coil and Ignition module.

    Engine starts right up and idles well, next week will take out for test at speed!
     
    Chris-380 likes this.
  15. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    What is your manifold vacuum reading now?
     
  16. Cdb

    Cdb New Member

    4
    Oct 10, 2019
    2000 34’ Sea Ray Sundancer
    454 V-Drives
    Thanks for the update, I hope all is good now I am in the process of what seems to be the same issue.
     
  17. Cdb

    Cdb New Member

    4
    Oct 10, 2019
    2000 34’ Sea Ray Sundancer
    454 V-Drives
    Cdb Hi just curious with the issue you were having did you get one long beep when you turned on the ignition switch on the dash? Thank you.
     
  18. 370Dancer

    370Dancer Well-Known Member

    Oct 2, 2006
    Florida - Alabama
    1998 370 Sundancer
    380hp MAG MPI Gen VI with V drives
    the starboard side should always give you 1 beep. Port side, 2 beeps.
     
    Chris-380 and Cdb like this.
  19. Cdb

    Cdb New Member

    4
    Oct 10, 2019
    2000 34’ Sea Ray Sundancer
    454 V-Drives
    Oh ok thank you. I’ve got a lot to learn.
     
  20. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Hi:
    Was looking through my posts and realized that i didnt really "close the loop" on this one and thought I might post this in case it helps another boater:
    After all the fuel related part replacements etc in this thread, what I discovered was that:
    (1) I had two Injectors on the Port motor (the one with the loss of power) and one injector on the Stbd motor ( which I thought was running ok) that were broken at the plastic body. It appears that the previous owners' mechanic had pushed in the injector by the body and broken the wires inside the plastic body thus giving me intermittent fuel delivery issues. I replaced the bad injectors and had the others ones professionally cleaned. The injectors were actually in pretty good shape as far as flow and spray pattern.
    (2) When I replaced both of the original Ignition Modules inside the Distributor, I was not aware that you had to reset the base timing for the ECM of each motor. In effect both engines base timing was off and was causing loss of power (along with the bad injectors), rough idle and low vacuum readings. All readings: fuel pressure, vacuum, timing, WOT etc are now within spec now.

    Now the engines purr at 600rpm idle and at my preferred cruise of 3200rpm I am getting 20 knots.....

    :)
     
    Chris-380 likes this.

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