Low fuel pressure on 350 MAG MPI

[toy4two]

no luck, tried routing the return fuel line different ways assuming it was kinked, no change.

I pulled the FPR vacuum line off the top of the engine 3 way fitting and sucked on it as hard as I could and its not leaking, nearly sucked my tounge out. Didn't feel any "give" as I assumed a FPR diaphram would do when sucking on it, but I have no experience but at least it means its nice and tight on the FPR. Followed it down and no kinks in the vacuum line and no fuel in my mouth

New FPR, new pump, and very high pressure points to a kinked return line but nothing I can see. I'm dreading pulling that &%*(@** Cool Fuel II box out again but seeing no other choice. Triple checked the regulator and the original which has a brown and blue mark on it is the same model I put in.

 

[Fun Times]

The green, brown and blue colors are just for fuel pressure references to help match up in certain types of service manuals that offer fuel pressure specs for each engine model and probably to help keep track during the manufacturing process, etc. etc.. There's nothing to be concerned with the green ring and should be left on.

I checked the color codes for your engine in an older Mercuiser training manual and they are all a match so "technically speaking" you should be alright there....Does the fuel pressure seem to change when you disconnect the vacuum line going to the regulator? The fuel gauge should move roughly 5ish psi while R&Ring the vacuum line.

Also if you haven't yet, use the fuel gauge air bleed button to make sure you're getting a solid flow of fuel to the gauge.

If possible try to measure the new low fuel pump pressure to see where it's at too as it could have an effect to the high pressure side.

You may want to carefully try unconnecting the return line at the fuel filter base then let the fuel dump into a good gas can and see where the fuel psi goes to.

If that little screen gets clogged or the fuel flow system part of it all, it will run the fuel psi high.

Where did you buy the fuel pump/s? Do all the numbers of the pump/s seem to match up? (< Low and High)
https://www.mercruiserparts.com/bulletins/001/04//2004/EN_05.PDF

Also just to let you know the engine serial number you provided seems to suggest the engine is an Mercruiser 5.0L MPI BRAVO with 3" exhaust risers...Not a 350 Mag.

 

[toy4two]

The green, brown and blue colors are just for fuel pressure references to help match up in certain types of service manuals that offer fuel pressure specs for each engine model and probably to help keep track during the manufacturing process, etc. etc.. There's nothing to be concerned with the green ring and should be left on.

I checked the color codes for your engine in an older Mercuiser training manual and they are all a match so "technically speaking" you should be alright there....Does the fuel pressure seem to change when you disconnect the vacuum line going to the regulator? The fuel gauge should move roughly 5ish psi while R&Ring the vacuum line.

Also if you haven't yet, use the fuel gauge air bleed button to make sure you're getting a solid flow of fuel to the gauge.

If possible try to measure the new low fuel pump pressure to see where it's at too as it could have an effect to the high pressure side.

You may want to carefully try unconnecting the return line at the fuel filter base then let the fuel dump into a good gas can and see where the fuel psi goes to.

If that little screen gets clogged or the fuel flow system part of it all, it will run the fuel psi high.

Where did you buy the fuel pump/s? Do all the numbers of the pump/s seem to match up? (< Low and High)
https://www.mercruiserparts.com/bull...2004/EN_05.PDF

Also just to let you know the engine serial number you provided seems to suggest the engine is an Mercruiser 5.0L MPI BRAVO with 3" exhaust risers...Not a 350 Mag.

Since I am going out of town I have turned over the troubleshooting to a local mechanic and shared this link if he wants to participate, otherwise I would do the remaining tests above.

861156A1 Fuel pump came from : https://www.ebay.com/itm/Electric-Fu...72.m2749.l2649

It was an exact match, correct non-threaded fitting. I have kept the original pump just in case I need to put it back. Based on a pin hole leak in the fuel cooler, original regulator corroded and the amount of rust on the cool fuel bracket I'd say the sea water leak has destroyed at minimum the original regulator and likely the high pressure fuel pump.

The engine is a remanufactured Mercruiser direct from them in 2013 with B3, they gave me the serial number they used to rebuild it. The plastic cover on it reads 350 MAG MPI and punching that serial into a marine engine parts site also says its a 350 MAG MPI:

​​​​​​ [h=1]350 MAG MPI ALPHA/BRAVO - 0M600000 THRU 0W059999[/h]

 

[toy4two]

found the problem. The new fuel pressure regulator came with a black rubber plug on the bottom of it, I assume to keep it clean inside during shipping. Took the whole fuel system apart again, and found this. Beneath it is the o-ring set into the metal on the FPR which goes on top of the screen. So yes it was the FPR, just installation error, look for and REMOVE THE BLACK PLUG on the bottom of the FPR before screwing it to the cooling tube.

One other tip for the next guy, wrap the fuel lines that go to the fuel water seperator in a ziploc bag and then zip tie it to seal it as you drag it through the bilge. This will keep all the muck out of the lines. My muck consists of bilge pads that the fuel disintegrated and ate through and turned into a nice floating mess of tiny wet foam pieces that are ripe to clog a line.

I also put a zip tie on the vacuum line to hold it to the FPR. Another tip a cooling hose "hook" tool is a MUST to not only remove the hoses, but to put back on the S-shaped one that goes to the thermostat looking housing in the front port side. Dawn dishsoap and water is a MUST when putting the rubber coolant line hoses back on their fittings. Also mark/score the coolant lines that connect to the fuel cooler BEFORE you remove, so they go back in the same angle, you are NOT going to be able to massage them one the fuel cooler assembly is back in the engine compartment.