Mercruiser 5.0l MPI Fuel Pressure

[r2d2a]

Mercruiser 5.0L Bravo III MPI, I think it needs a new fuel pump but thought I would see what you guys think as never had to do one on an mpi yet.

Runs for a few seconds then stalls. Checked the fuel pump fuse and it is fine. Can hear the pump turn on for about three seconds. Have almost 5psi tops at the fuel rail schrader valve when the pump turns on and when I can get the engine to run for a minute it stays around 5 tops. Bypassed the anti siphon valve but no change (there was very little fuel in the lines there like the pump wasn't even pulling any fuel).

Anyway, those were my checks. What happened was I was cruising along for a while and had a fine day. Came back into the creak and it stalled when I was going slow. From these checks I think I need a new fuel pump but I just wanted to see what anyone else thought. I didn't see any vacuum hoses off of the pressure regulator connected to the fuel rail.

 

[bolo78910]

Re: Mercruiser 5.0l MPI Fuel Pressure

change the the oil pressure safety switch and go and have fun with the boat.

it is a switch that attach to the oil pressure switch, good luck

 

[Bondo]

Re: Mercruiser 5.0l MPI Fuel Pressure

Have almost 5psi tops at the fuel rail schrader valve when the pump turns on and when I can get the engine to run for a minute it stays around 5 tops.

Ayuh,... Off the top of my head, that sounds Awfully Low....

Check the manuals up in the Adults Only section at the top of this forum...

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

Ok thanks I will check out that manual in the other section. Just out of curiosity about that oil pressure switch, that wouldn't cause low fuel pressure when you turn the key on and the pump runs for about 3 seconds would it? Like I said, I do hear the pump run when I turn the key to run only but there is almost no pressure, I wouldn't think at this point the oil pressure switch would have anything to do with the fuel pressure but am just curious.

 

[Bondo]

Re: Mercruiser 5.0l MPI Fuel Pressure

I wouldn't think at this point the oil pressure switch would have anything to do with the fuel pressure but am just curious.

Nope,... It's a simple on/ off switch....

 

[Don S]

Re: Mercruiser 5.0l MPI Fuel Pressure

The oil pressure switch is ONLY used on carbed engines. NOT EFI.

We need to have a Mercruiser Serial Number to give you any kind of accurate information. Granted 5 psi is too low, but troubleshooting the why it's that low is what you need to do now. And without knowing exactly what you have, the best you will get is "I replaced the #2 widget on my boat and it fixed it."

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

"I replaced the #2 widget on my boat and it fixed it."

LOL
Here is the serial number, sorry I didn't post it earlier as I didn't have it with me. OW356239. Thanks

 

[Don S]

Re: Mercruiser 5.0l MPI Fuel Pressure

Ok, now I know what you have.
Go to the link below and download the manual.
Then go to page 2A-16 and follow the troubleshooting chart for the fuel pump.
Steps 1 and 2 are earlier in the same section (2A) be sure to do them first or you could waste a lot of time looking for someing not mentioned later.

http://www.4shared.com/file/137527284/f35ced2b/Service_Manual_36_Rev_1_SBC.html

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

ok i took a look at the manual. step 6 on 2a-16 asks if there was fuel pressure present, i don't know if 5psi was enough to say yes but I did just incase and went to step 7 which asks if the fuel pressure drops to 0 psi and it doesn't, it then tells me to retest the system.

I then went the other way and assumed that 5 psi wasn't enough to say yes at number 6 and it told me to go to chart a-3 but that eventually led me back to where i was.

Just to double check that it wasn't anything on the boat side I connected the fuel pump to a separate tank and it still wouldn't suck.

So after checking through the list I found
-Fuel pump does turn on for the right amount of time when key is turned to run
-builds up a very small amount of pressure and stays

But, I got bored of testing and started to take apart the fuel cooler to see what I could see. So far the only thing I see out of the ordinary, and I can't find it in any diagrams, was a layer of what looks like dried paint covering the regulator nipple and screen. At first I thought it might be a diaphragm or something but can't find a picture of it in any book. I'll post a picture of it later but here is the part number #892681. If you take a look at it you will see the part that goes into the cooler was covered with this stuff. I'll post a picture later.

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

Ok here is the pic, the regulator is there with the stuff on top of it. Kinda hard to see but the stuff there is block and was blocking the screen. I don't know what it is or how it got there.

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

one final thing, i hooked up 12v. to the low pressure pump while I had it out and it turned on. I hooked up 12v to the high pressure pump but that one didn't turn on. So I'll probably just replace that and put the regulator back in without that stuff there.

 

[r2d2a]

Re: Mercruiser 5.0l MPI Fuel Pressure

made some calls and found out the paint is known to come off the inside of the fuel coolers. so i guess that is where the stuff came from.

 

[ksliger]

Re: Mercruiser 5.0l MPI Fuel Pressure

Curious, did this fix your problem?