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:
    I have an issue with the Stbd motor in my 2000 SeaRay 380DA that I hope someone can help me with.
    Both engines long block rebuilds with about 300 hrs since. No issues prior to trip.

    Prior to our 800 mile trip from Palm Coast to Gun Cay, Bahamas and back...in both engines: changed the fuel and oil/filters, seawater pump housings and impellers, new alternators and new batteries, new serpentine belts, new IAC's and cleaned the spark arrestors and hauled out for fresh bottom paint. Both heat exchangers serviced with no issues or leaks. Manifolds and risers are less than 1 year old. Total replacement of old "log style" wet exhaust to water lift style with all new hoses and mufflers etc. Props tuned and cutlass bearings are in spec.

    The trip was great, zero issues except for one day while in Bimini the Stbd engine stumbled while leaving the harbor at around 1500rpm (sputtered and suddenly revved up to over 2000 rpm without me touching the throttle). It died and I was able to immediately restart it with no further issues all the way back to Palm Coast.

    Never use ethanol gas and ran with Lucas fuel treatment the whole trip.

    We have been back home for some time and about 2 weeks after the trip, the Stbd engine:
    Starts normally, idles normally, runs at 167F max
    Wont rev past 3200rpm (no matter how far I push the throttle), seems like it has no power.

    I have:
    Checked with my Rindal scan tool and the only thing was "MAP sensor voltage low", so I replaced the MAP sensor (even though when testing with vacuum it was within spec)
    Checked vacuum in plenum and it has 15" at idle (factory spec)
    Changed fuel filter (no water or debris in filter)
    Changed spark plugs (they were wet/foul)
    Used in-line spark plug tester and plugs were getting spark
    Distributor cap has corrosion on each rotor/plug lead point (inside cap) so I am replacing caps and rotors to better OEM brass style (currently has aluminum style).

    It seems to me that engine is getting fuel (too much) and it may be weak ignition from the distributor cap corrosion?

    Also checked MAP and ECT sensors as per the Mercury Manual and it points to a bad ECM but when compared to the Port engine sensors(which is running great) it also says the ECM is bad so I wonder about these diagnostic instructions in the manual?

    Fuel pressure?....injectors? I guess the only way to tell is to remove the intake plenum to get to the fuel rail and check pressure and remove injectors?

    Huge thanks to anyone who can help me!!
    Thx
     
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Map pressure sensor low would be the direction I would go first, It relays info to the TPS and controls the fuel.
    Make sure it's getting the 5 volt input from the ecm.

    Are your injectors original? If so , there due for a service at the very least.
     
  3. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Hey:
    Yes, I ran the non-scan diagnostic steps in the Mercruiser Factory manual and it is getting the 5v reference signal.

    I have only owned the boat for less than a year but the previous owner had the injectors service/rebuilt back in 10/2017 (have receipt). Do you think injectors need to be cleaned?
    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
    Can't hurt. If those are 20 year old fuel lines I'd replace them all. Check your fuel pressure, them parts don't last forever.

    Is it still throwing the MAP code ?
     
  5. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    The "MAP voltage low" code was one time and has not thrown it again. I ran the boat a few days ago with the scan tool in "live" and MAP, TPS, ECT all were giving normal readings as they related to increasing and decreasing RPM's. While idling back to the home dock, the engine almost sounds like it is running on certain cylinders and not firing all?
     
  6. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Yup, does sound like a fuel problem and the old mefi won't throw a code for that. If it was my boat, and I have an old 1 too, I would start with a complete tune up and while the plugs are out, check compression.

    I just replaced everything on my fuel system from A to Z, new lines, injectors , pump , regulator and it now runs like the beast it was.
     
  7. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx...
    Compression was 150psi on all, right before I replaced the plugs (hoping plugs were the issue). The plugs that were in the engine was the NGK non-platinum tip and I replaced with the same ones (are the platinum tip necessary?)

    If the new distributor cap and rotor doesnt clear it up, I guess I will pull the intake off and check fuel pressure and pull the injectors
    Thx again
     
  8. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Start with the fuel pressure. Compare it to the other engine. There are lots of threads with similar symptoms always ending up with the fuel pumps/lines being the cause if they haven't been replaced.

    You are fortunate it didn't quit completely in Bimini.
     
  9. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx....the more I read/research, the more it sounds like a fuel pressure regulator issue. Once I have new intake gaskets in hand, I will pull the intake and check the pressure at the fuel rail and then move on to injectors if necessary.
     
  10. 370Dancer

    370Dancer Well-Known Member

    Oct 2, 2006
    Florida - Alabama
    1998 370 Sundancer
    380hp MAG MPI Gen VI with V drives
    Plan on the fuel pump and regulator, and as Scoflaw says, while you're digging around that part of the engine, do the fuel lines between the separator going in and coming out. Mine had kinks in them from how they are plumbed. Still, you gotta pay attention to the fact you only had 1 hiccup and then nothing crossing the gulf stream? Then 2 weeks later of non use, a big difference? Pulling the plenum is not necessary to hook up a fuel pressure gauge, just don't try it hot, and as I learned, measuring fuel pressure while at the dock no matter how much you rev it is no test. You need to be underway at load, at speed to see what's really happening. Since you are going into the top, I would not hesitate to pull the rail, and injectors, and clean or replace them. Find my other thread that went on for months chasing pretty much what you are experiencing now. Pay Attention to Scoflaw, PlayDate, and Douglee if he shows up.
    Good Luck! BTW, I'm sure you don't have a 7.1 liter MAG MPI. Engine serial numbers will help these guys know which plumbing you have. 2000 was a very transition year or two for Mercruiser.
     
    PlayDate and Chris-380 like this.
  11. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx....
    The vessel build date is 2000 but the engines were factory built in the latter part of 1999 apparently. They both are the 454 CID (7.4L) MAG MPI Horizon (Gen VI) with serial # 0L398572 with the MEFI 3 ECM.
    In looking at the factory manual, it looks to me like the schraeder valve is on the fuel rail and buried under the intake? If I dont need to take the intake off at this point, I would rather not.
     
  12. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Not intake but probably plenum. Extend the gas fitting while you are there so to make a simple hook up for the next time you need to check it/
     
  13. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Yeah...reading 370Dancer thread and how he did it
    Good Idea!
     
  14. 370Dancer

    370Dancer Well-Known Member

    Oct 2, 2006
    Florida - Alabama
    1998 370 Sundancer
    380hp MAG MPI Gen VI with V drives
    And, congrats to you for taking gassers to the islands. I am interested in your exploits. Used to do it a LOT, but in a 46 Post. Different time, and different parameters back then. Fresh water at less than 50 cents a gallon was hard to come by unless you made your own. We did. Not so much of an issue now, etc.
     
  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
    15" of vacuum is low if that reading was taken at idle with a known to be accurate gauge.
    How old are the ignition wires and are they routed properly? (not just connected to the correct cylinders)
     
  16. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx Mitch
    According to my Mercruiser Manual for this year and model engine, 15" at idle is the spec.
     
  17. 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

    I like 17" myself. As stated in the below link, altitude does play a part and you haven't complete your profile info. (on the left) so I don't know where your located. Different camshafts will affect vacuum also.

    https://www.freeasestudyguides.com/engine-vacuum-test.html
     
  18. Gallf1

    Gallf1 Member

    34
    Sep 26, 2018
    Palm Coast, FL
    2000 Searay 380
    Mercruiser 454 MAG MPI 7.4L
    Thx Mitch:
    I am in Palm Coast, Fl....just above Daytona. Since I am leaning towards a bad fuel pressure regulator or perhaps the vacuum line to the regulator being bad, it may affect the vacuum in the plenum?
     
  19. 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

    Kinda the other way around, low engine/manifold vacuum will affect the performance of the regulator. The regulator should hold vacuum with a good vacuum pump/tester. The fuel pressure should increase approximately 10 psi with the vacuum hose disconnected from the regulator.
     
    PlayDate likes this.
  20. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers

    Are you sure that is your engine serial number? I get "no results" when I load it into the Mercruiser search database.
     

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