1999 Mercruiser 4.3 cool fuel pump pressure

[Bakers Creek]

O.K. here we go. Mercruiser 4.3 throttle body injection cool fuel pump making a very loud noise and low pressure around 10-8 psi under load. Engine looses power and will not come up on plane. So I replaced the fuel pump on the cool fuel unit with an Airtex E11004. This pumps max pressure is 125 psi. Now fuel pressure is at 65-75 psi...not good, way too much. My manual calls for 30psi continuous . Removed fuel pressure regulator and verified it is not stuck, reinstalled and verified flow from the regulator while running, still pressure at 65 psi. The mercruiser part number for the fuel pump lists 861156A1. So I sent the Airtex back and purchased a pump that claimed it was a replacement for the 861156A1, Still same issue. .The fuel pump alone is obsolete and it's possible I may have to purchase the complete unit. There's got to be someone out there that supplies a 40 psi cool fuel pump replacement. Engine serial number is 0l082909. Several of the sites claim it is a 86156A1 replacement but I think there are several different fuel pumps that are listed as a 861156A1 but are pressure specific to the engine serial number. ……...Anyone got a match

 

[alldodge]

Most all fuel injection pumps can produce at a minimum of 60 psi, and most even more. The item which keeps the pressure down is the fuel pressure regulator. If the reg is working correctly, then the return line back to the fuel filter is clogged. If line is clogged then the reg cannot return excess pressure

You either have a bad reg or clogged return line

 

[Bakers Creek]

Removed fuel line and plugged return to filter housing. Placed fuel line from regulator in a container, Plenty of fuel flow there while engine is running. Removed the regulator, using a small screwdriver from the outlet side, made sure the regulator was not seized by depressing the spring inside. seems to move freely. Pressurized the regulator from the inlet side and with a gauge inline it released at 30 psi. this tells me reg is good and no restriction in return line. but it's possible 'm a dummy yet.

 

[Bondo]

then the return line back to the fuel filter is clogged. If line is clogged then the reg cannot return excess pressure

Ayuh,..... Crazy thought,...... What if the fuel Filter is restricted,..??

BC, have ya inspected the Contents of the fuel filter,..??

 

[Bakers Creek]

Removed filter housing and cleaned out, replaced filter, remover anti siphon valve and cleaned, removed anti siphon valve all together, each one of these trails ended with same results.

 

[Bakers Creek]

Funny thing is when I shut it down, the fuel pressure returns to 30psi. It may be restricted to the point where it's not letting enough flow thru, but still bleeds down and holds 30psi.

 

[alldodge]

Removed fuel line and plugged return to filter housing. Placed fuel line from regulator in a container, Plenty of fuel flow there while engine is running. Removed the regulator, using a small screwdriver from the outlet side, made sure the regulator was not seized by depressing the spring inside. seems to move freely. Pressurized the regulator from the inlet side and with a gauge inline it released at 30 psi. this tells me reg is good and no restriction in return line. but it's possible 'm a dummy yet.

Says your regulator is working, but does the pressure going into the TBI go back to 65 and 75 psi?

If it does, then your TBI is clogged up

http://www.mercruiserparts.com/bam/subassembly/31496/2692/170

 

[Bakers Creek]

ok big update here! Finally tracked down issue, First issue was fuel pump, replaced it and fuel pressure went from almost nothing on the old pump to 70-90 psi or so . After a lot of investigation found there are several different pressure regulators for the cool fuel unit. Even though they have the same part number there are different pressures. The TBI unit requires one with a pink mark, yes pink. It regulates the pressure to 32psi. So don't be like me and replace the pump and not the regulator. I did and deadheaded the first new pump and destroyed it. So when I did replace the regulator with the correct one I had already killed the new fuel pump and it would loose pressure after 15 min of run time. So new pump and regulator. I am thinking when the regulator went, it destroyed the original pump. So that's my two cents. Boat is back to customer and I can move on to next one.

 

[alldodge]

Thanks for the update and good to here your up and running

Dead heading a fuel pump should not damage it, Merc even has a test procedure to test the pump by dead heading it to ensure it will reach at least 60 psi. The fuel line is removed from the TBI or MPI fuel rail for the test. Your motor has 2 regulators and if either of regulator's is subjected to these same pressures they can be damaged.

Item b is the regulator on the cool fuel module