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Loss of fuel pressure 5.7 Vortec MPI

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    #16
    I'm kinda pulling this out of thin air but I would be looking at the "cool fuel" unit. That's where the high pressure pump is. From what I have read there are a couple of different models. One of them is notorious for paint flaking off ending up in the fule rail and injectors. All of these units are based on the GM high pressure pump that is a real POS. I cant tell you how many I have changed out over the years in cars and Chevy pickups. In the auto world they go bad from heat especially when unning around with less than a 1/4 tank of gas. The pump is in the gas tank and is cooled by the fuel in the tank. Merc came up with the cool fuel unit that does basically the same thing with raw cooling water. The unit is on the raw water side of your cooling system just down stream of the power steering cooler. I hate to suggest throwing parts at a problem but I cant think of a good way to test my theory.
    1992 2452
    5.0 alpha1 gen2

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      #17
      Ok I will admit it I'm sitting here thinking about your problem to keep from crawling back in my boat and sanding more fiberglass! The pump I talked about in my last post is powered from an oil pressure sensor. If that sensor was going bad it might be shutting the pump down intermittently. Again I'm just pulling ideas out of my a$$ but it is where I would be looking.
      1992 2452
      5.0 alpha1 gen2

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        #18
        The Fuel system is a G Force as used by Marine Power USA,
        I don't believe they have the paint problem as a Mercruiser does.

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          #19
          I still feel the issue is electrical, at least you have ruled out the coil.
          1997 Maxum 2400 SCR 5.7LX Bravo II

          Mike

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            #20
            I just looked at Marine Power"s web site. They seem to be using the Delphi/ GM fuel injection system. I wasent suggesting it might be a paint chip problem. On the GM / Mercuiser system high pressure fuel is delivered by the pump in the cool fuel unit. I would look for however they have the high pressure pump plumbed and all the electrical that powers it.
            Do you have Marine Power"s aluminum exhaust manifolds? I'd love to here more about them.
            1992 2452
            5.0 alpha1 gen2

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              #21
              So after around six weeks of researching all sorts of possibilities, today I went down and started back at the basics.
              Started motor and after 10 minutes it started to play up again.
              Started checking all the electrical components that can affect fuel/ignition components. Learn't over the weeks about Hall effect sensors, resistance values, voltage, earths, Mepi 3 etc.
              While head down under the engine I checked the connectors on the low pressure pump and noticed that one wire was loose at one connector. Strange, as I had recently replaced the Crank Angle sensor, and though I had checked and pushed home these connectors. These connectors are mated to a screw type male receptor and the wiring a female type. I pushed the connectors home firmly and then checked how much force was needed to remove them. One was firm, but the other rather loose. I recrimped the connector and pushed it back in place where I felt a firm contact.
              I then thought what the hell lets run it up again and see if this connector was the root cause of the problem.
              I ran the motor up again with no load and no problem running up and holding it at various rev ranges where it had cut out before, no problem, put it in gear and ran it under load alongside the dock running it at 10 minute intervals at 1900 rpm, 2300 rpm up to 3200 rpm for a total of 30 minutes with no sign of THE PROBLEM.
              Is it possible that a loose connector slipping down and perhaps maintaining some form of circuit just, be the source of my dilemma?
              I must admit the motor sounded sweet, and I had my IR gun and multimeter along checking all sorts of connectors for heat but nothing out of the ordinary.
              The motor has done this before and then out of the blue it developes problems. I am unable to take it out due to current weather conditions but will hopefully Wednesday.
              What's the consensus?

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                #22
                Today I had the opportunity to do a full on water test, and the result was, a complete waste of time.
                It will run fine in the idle to 2200 rpm range but when asked to run in the 3500 rpm range it lasted for about 3 minutes before backfiring through the intake, lost all power and causing me to shut the motor down.
                I anchored up for about 30 minutes and checked connectors and other wiring again,
                Motored back to the marina on both motors at 1700 rpm for about 30 minutes no problems.
                After a long period trying to rectify this problem I officially admit defeat.
                Only thing I can think of now is Hall effect sensor in the distributor.
                It is such a shame that the motor is so unreliable, the wife and family don't want to go out on the boat anymore as they have a total loss of confidence in it.

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                  #23
                  You obviously have checked more than I could figure out...as a simple minded member i will ask it. Do these symptoms not sound consistent with a fuel vent line being clogged??

                  just wondering if you have tried running it with loose fuel cap to see if vent issue
                  2008 H210SS Four Winns
                  Volvo Penta 5.7 GISX
                  Prior: 1997 2050SS Bayliner
                  Brad / Texas Gulf Coast

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                  • Nauti_Mike
                    Nauti_Mike commented
                    Editing a comment
                    While the lose of power could be from a clogged vent it would not cause the backfire.

                  • TX H210 SS
                    TX H210 SS commented
                    Editing a comment
                    Clear...anxious to hear the fix as I know he is for sure.

                  #24
                  What efi system are you running? MEFI?
                  can you do the test shown in this video? There are others out there on how to set up an led and a short on a plug to do the same thing
                  hope it helps

                  https://www.google.com/url?sa=t&sour...6bw65bbIcBV0Ms
                  1992 2452
                  5.0 alpha1 gen2

                  Comment


                    #25
                    Thanks, LIneman1, that's valuable info. Sorry no Aluminium Exhausts manifolds.
                    I will get down and do that Wednesday.
                    MEFI 3 system.
                    I am also considering ignition module ( Hall Sensor ) inducing the fault.
                    At this stage anything to identify the fault.

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                      #26
                      I am not familiar with your fuel system but most electronic fuel injection systems have an electronic fuel pump control to operate the fuel pressure regulator and fuel pump relay. This could possibly be in the ECM or separate and signaled from the ECM. Also wire harness issues can cause intermittent problems that won't show up on a scan tool. Can the ECM be scanned for stored trouble codes like the OBD II connection on motor vehicles? If so this problem should show up.
                      2550 Cierra, AQ260 Volvo Penta (350 Chevy)
                      Laporte, CO

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                        #27
                        +1 on the suspicion of a clogged fuel vent line. It sounds like it is starving out from a lack of air coming back into the tank.
                        Currently watching from shore while deciding what my next boat will be !

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                          #28
                          Here is another mefi code reader and what some of the codes mean.
                          I have the Motorola 555 based system. So this won't work for me.
                          If it turns out to in fact be fuel pressure. I think I would find the high pressure fuel pump bypass the power wireing and put a wet oil pressure gauge in(old school with a tube and fitting into the motor) Then run it and see what happens. The wet oil gauge is to make sure it's not an oil pressure problem shutting down the pump!
                          It would be a pain in the a$$ but if you do get a low fuel pressure code. Maybe swap pumps from one motor to the other.
                          post back after you get more info I'd like to know what fixes this.
                          Good Luck
                          https://www.offshoreonly.com/forums/...%241-00-a.html
                          1992 2452
                          5.0 alpha1 gen2

                          Comment


                            #29
                            Venting of the fuel system has already been checked a couple of times, just to make sure, however it is very doubtful this is the cause as both motors feed from the same tank..
                            I have swapped pumps and replaced a fuel pump.Both low pressure fuel pumps are new. 20 hrs.
                            Even swapped ECU etc over from one motor to the other same result.

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                              #30
                              Where is the High pressure pump on this system??
                              1992 2452
                              5.0 alpha1 gen2

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