7.4 mpi fuel issues?

[chad99_2002]

Hello, got the boat out today, fired right up, let it idle for about 10 min, got the wife and kids on and headed out, idled out of the cove and brought it up to about 2500 rpm, ran for about 5 min the started to fall on its face then died, boat would not restart, so I crank 4 or 5 times nothing, not even trying to start, so I pull the hatch up and start looking at at distributor and wires don't see anything wrong, so I have the wife turn the key, I hear the fuel pump, so don't think there is a issues there, I let it set for a few min and try starting again, nothing, I then turn the key on 5 or 6 times and the the fuel pump kick it's self on then wait for it to shut off, bam fires right up, I turn around to get back home around 3000 rpms and it runs again for a couple of min then starts to fall on its face then dies. I once again open up the hatch, see no leaks, I leave the hatch up, and start cycling the key on and off after about the 3rd or 4th time I can hear a pitch change from the fuel pump, I cycle it a few more times, then try it, bam starts right up, I finally make if into the cove at an idle and to the boat ramp, and just as I get to the ramp, it acts like it's starving for fuel and dies.

I changed the water/fuel separator a couple of weeks ago, so don't think that's the problem, unless it just now sucked some junk out the bottom of the tank, tank was completely full, just filled up today, was also the frist time out this year, I'm leaning towards a fuel pump or regulator issue, anyone have any ideas or other places to start looking, thanks for any and all help.

The boat is a 2000 Mariah 258 with 300 hrs, I have never touched any of the fuel system besides the fuel separator in the 4 years I've owned the boat.

 

[alldodge]

Being an MPI, I need to know what the fuel pressure is on the fuel rail

Also need the engine serial so as we go forward we know what you configuration is

 

[chad99_2002]

Being an MPI, I need to know what the fuel pressure is on the fuel rail

Also need the engine serial so as we go forward we know what you configuration is

I'm going to get a pressure tester tonight, I'll hopefully have some numbers on that tomorrow, I'll get the serial number tomorrow as well, I have never tried to test the fuel pressure on this engine before, any tips or tricks on doing it?

 

[tpenfield]

What AD said . . . the fuel pump could be fine, but if the pressure pump for the fuel rail is not working or holding enough pressure, then the engine will die out as you described.

Depending on what version of the MPI engine you have (serial number will tell) it could also be a pressure sensor on the fuel rail.

 

[chad99_2002]

What AD said . . . the fuel pump could be fine, but if the pressure pump for the fuel rail is not working or holding enough pressure, then the engine will die out as you described.

Depending on what version of the MPI engine you have (serial number will tell) it could also be a pressure sensor on the fuel rail.

Ok, I'll get that serial # tomorrow, thanks

 

[Fun Times]

chad99_2002 Just wanted you to be able to find your topic easier since we moved it from the Mercury outboard sub-forum down to the Mercruiser I/O sub-forum.

Some other things to inspect would be the fuel tank vent line for debris causing a clog, a sticky fuel tank anti-siphon valve, defective fuel filter, debris in the fuel filter/fuel tank or doubled up fuel filter O-rings causing air to seep in.
Did you prefill the fuel filter to make it easier on the fuel system to start and run? It helps a lot to prefill the filter. Double check the filter is on tight before pulling off for re-inspection.
Is the filter still full of fuel or closer to empty?
Is the filter OEM or aftermarket? Part number?

Since it almost died near idle, sounds like you should be able to duplicate the issue while on the garden hose at home.

If so and things seem to be checking out okay then you could try finding another fuel hose and a small portable fuel tank and connect it up in place of the boats fuel hose to see if the engine runs correctly...All while checking fuel pressure.

Make sure there is no other type of filter or electrical solenoid connected between the tank and engine as "some" boats may have other devices installed that need further inspecting.

If you have the engine model I'm thinking you do (L29), Testing the fuel pressure shouldn't be to difficult as the fuel schrader valve that looks similar to a bigger type air tire filler schrader valve located just behind the thermostat housing area easily connects to a GM type fuel gauge fitting. If it's any other big block engine model then you'll need to get a special fitting from Mercruiser.

 

[chad99_2002]

chad99_2002 Just wanted you to be able to find your topic easier since we moved it from the Mercury outboard sub-forum down to the Mercruiser I/O sub-forum.

Some other things to inspect would be the fuel tank vent line for debris causing a clog, a sticky fuel tank anti-siphon valve, defective fuel filter, debris in the fuel filter/fuel tank or doubled up fuel filter O-rings causing air to seep in.
Did you prefill the fuel filter to make it easier on the fuel system to start and run? It helps a lot to prefill the filter. Double check the filter is on tight before pulling off for re-inspection.
Is the filter still full of fuel or closer to empty?
Is the filter OEM or aftermarket? Part number?

Since it almost died near idle, sounds like you should be able to duplicate the issue while on the garden hose at home.

If so and things seem to be checking out okay then you could try finding another fuel hose and a small portable fuel tank and connect it up in place of the boats fuel hose to see if the engine runs correctly...All while checking fuel pressure.

Make sure there is no other type of filter or electrical solenoid connected between the tank and engine as "some" boats may have other devices installed that need further inspecting.

If you have the engine model I'm thinking you do (L29), Testing the fuel pressure shouldn't be to difficult as the fuel schrader valve that looks similar to a bigger type air tire filler schrader valve located just behind the thermostat housing area easily connects to a GM type fuel gauge fitting. If it's any other big block engine model then you'll need to get a special fitting from Mercruiser.

I'm glad you mentioned that vent line, my wife brought up something I completely forgot. We pulled the boat out of the barn Friday afternoon, I like to start it and let it run 10 min or so on the muffs just, so I it's going to run and not have and issues. While I was doing this, I had the gas cap open adding a couple of cans of seafoam, I never had any issues with it dying. I'm thinking that vent maybe my problem.

 

[chad99_2002]

Being an MPI, I need to know what the fuel pressure is on the fuel rail

Also need the engine serial so as we go forward we know what you configuration is

 

[chad99_2002]

Well, I think I may have found the issue. Hot fuel pump? I always change my own filters and oil, but usually let my mechanic change the impeller and pull the lower unit and check and maintenance it. Today I put on the muffs and had the wife start it, fired right up, I let it run for about 30sec to 1min, no water out exhaust, so I inspect the muffs, make sure covering all intake holes, start once again, run less than 30sec, no water flow still. So I pull the impeller and check it, this is what I find. For a few facts, I never have dry started the engine, impeller is on start of it's second season (mechanic recommends changing every other year), only been run on muffs 2 times start of each year I do, I had some water flow Friday, when I put it on the muffs, took about 15sec to see water, Could I've caused this much damage on muffs, or it is time to find someone else to do the maintance?

One thing I forgot, is when it died in the middle lake yesterday, I did try and start it several times, the lower unit was never out of water or run aground, I would have thought it would have pulled a little water while the engine was turning over, at least enough not to so this kind of damage to the impeller.

 

[bman440440]

you might have "bravoitus" starting

 

[alldodge]

Look closely at the torn impeller to see if the rubber looks brittle, has cracks in the rubber, or it looks fresh and maybe just burned up due to a plastic bag on the drive. If the rubber looks old it won't be the first time someone was changed for something not done. Not saying it was intentional, I don't know your guy. May have been done by another, forgot or thought they did it.

In any cases go find all the pieces in the power steering cooler and oil cooler if you have one.

 

[chad99_2002]

Look closely at the torn impeller to see if the rubber looks brittle, has cracks in the rubber, or it looks fresh and maybe just burned up due to a plastic bag on the drive. If the rubber looks old it won't be the first time someone was changed for something not done. Not saying it was intentional, I don't know your guy. May have been done by another, forgot or thought they did it.

In any cases go find all the pieces in the power steering cooler and oil cooler if you have one.

Yeah, I got the impeller changed, another fuel water separator installed and filled up, got the oil cooler cleaned, plan on cleaning the power steering cooler, and fuel as well, just ran out of time today

 

[chad99_2002]

Being an MPI, I need to know what the fuel pressure is on the fuel rail

Also need the engine serial so as we go forward we know what you configuration is

I've changed the impeller, flushed power steering, fuel, and oil coolers, flushed all the lines associated with the cooling system, I changed the water separator, refilled, and bleed the air out of the fuel system.

Ended up filling up a 45gal tub, instead of running on muffs, started the boat, I let it idle for 30min no issues at all.

My question is what is the correct fuel pressure, when I first turn the key 42psi, engine running a constant 34psi, the engine was only at idle, I thought the pressure was supposed to be closer to 38psi. Thanks for any and all help

 

[alldodge]

Using a 45 gallon tub is not the best way to run the motor, even if it covers the intake holes.

Manual shows 43 psi while running, dropping down to 38 isn't bad but would like to see it a tad higher. With it idling remove the vacuum line going to the regulator and the pressure should increase. The running and then dying could be the pump or the relay (if the pump turns off after stating). I'm guessing your fuel pressure is being lost when your out running. This can be the pump or regulator

Need to scan for codes to see if there are any. If you don't have access to a scanner you could make one with a resistor 12V LED and a paper clip. It is connected to the DLC connecter.

 

[chad99_2002]

Using a 45 gallon tub is not the best way to run the motor, even if it covers the intake holes.

Manual shows 43 psi while running, dropping down to 38 isn't bad but would like to see it a tad higher. With it idling remove the vacuum line going to the regulator and the pressure should increase. The running and then dying could be the pump or the relay (if the pump turns off after stating). I'm guessing your fuel pressure is being lost when your out running. This can be the pump or regulator

Need to scan for codes to see if there are any. If you don't have access to a scanner you could make one with a resistor 12V LED and a paper clip. It is connected to the DLC connecter.

Well crap, thought the tub would be just as good, that way I could make sure it was getting enough water. I never did get 38psi, 42 with key on, and only 34 while at idle, I'm going have to make a code reader. So if I pull the vacuum line a pressure increases, does that mean bad regulator?

 

[alldodge]

Well crap, thought the tub would be just as good, that way I could make sure it was getting enough water. I never did get 38psi, 42 with key on, and only 34 while at idle, I'm going have to make a code reader. So if I pull the vacuum line a pressure increases, does that mean bad regulator?

Under normal operation the pressure should be around 38 and go up to 40 or more when the vacuum line is removed. If you remove the vacuum line the pressure should increase, and if it does then the regulator would be suspect as bad. The reason I say the regulator would be bad is because it should be set at 43, and by removing it should have no effect. If it does not increase then I would lean more toward a weak fuel pump.

To test the fuel pump, it needs to have a gauge connect direct to the output side of the pump and see if it will build close to 60 psi

 

[chad99_2002]

Under normal operation the pressure should be around 38 and go up to 40 or more when the vacuum line is removed. If you remove the vacuum line the pressure should increase, and if it does then the regulator would be suspect as bad. The reason I say the regulator would be bad is because it should be set at 43, and by removing it should have no effect. If it does not increase then I would lean more toward a weak fuel pump.

To test the fuel pump, it needs to have a gauge connect direct to the output side of the pump and see if it will build close to 60 psi

Thank you, and by normal operation, I'm assuming you mean with the engine idling, sorry for all the questions

 

[alldodge]

Thanks you, and by normal operation, I'm assuming you mean with the engine idling, sorry for all the questions

Questions are no problem-o, sometimes I should go in depth a bit more. By normal I mean if everything was working as it should without issues. A pump can normally put out 60 psi of pressure and the regulator keeps in lowered between 38 and 43 psi. Yours is either not getting enough pressure from the pump or the regulator is weak.

If your pump is weak and the regulator is OK, then removing the vac line will have no effect.
If your pump is OK and the regulator is weak, then removing the vac line may show some increase

 

[chad99_2002]

Questions are no problem-o, sometimes I should go in depth a bit more. By normal I mean if everything was working as it should without issues. A pump can normally put out 60 psi of pressure and the regulator keeps in lowered between 38 and 43 psi. Yours is either not getting enough pressure from the pump or the regulator is weak.

If your pump is weak and the regulator is OK, then removing the vac line will have no effect.
If your pump is OK and the regulator is weak, then removing the vac line may show some increase

Thank you, hopefully I can try and get some testing done this evening

 

[chad99_2002]

Questions are no problem-o, sometimes I should go in depth a bit more. By normal I mean if everything was working as it should without issues. A pump can normally put out 60 psi of pressure and the regulator keeps in lowered between 38 and 43 psi. Yours is either not getting enough pressure from the pump or the regulator is weak.

If your pump is weak and the regulator is OK, then removing the vac line will have no effect.
If your pump is OK and the regulator is weak, then removing the vac line may show some increase

Well got a couple of things accomplished, got the tester made up (thanks for telling me about that ALLDODGE), and read the codes, all I had was a 12, from what I can find is normal operation, I did a swap the fuel pump relay, it made no difference on the pressure, started the engine and pulled the vac line, pressure jumped to 42-43 psi, motor seemed to even idle smoother, I haven't gotten a chance to pull the fuel pump and see if I can rigid up something to see if the pump is putting out the 60psi. I'm assuming the regulator is bad, but would like to make sure before I purchase it. Thanks again for the instructions.