MPI low pressure pump

[metsfan3197843]

I have read that the low pressure pump is not needed and that the engine will run fine on just the high pressure pump. Tracking down a fuel pressure drop to nothing on my engine I discovered a bad connection on the booster pump and it was not coming on. Fixed that and took the boat out and now it runs great. Cruised at 3600 for about 30 minutes with no issues. I have to believe that the booster pump solved my issue but I’m confused on if this pump is just for vapor lock or if it’s needed to feed the suction of the HP pump????

 

[Bt Doctur]

the boost pump sends the fuel to the high pressure pump

 

[muc]

0M656133
This serial number is affected by Service Bulletin MC-2006-002. This service bulletin needs to be addressed. Please complete the required service work regarding this issue.

Some engines with cool fuel 2 came stock with a boost pump (yours did) some it was an add on to cure vapor lock.

 

[metsfan3197843]

0M656133
This serial number is affected by Service Bulletin MC-2006-002. This service bulletin needs to be addressed. Please complete the required service work regarding this issue.

Some engines with cool fuel 2 came stock with a boost pump (yours did) some it was an add on to cure vapor lock.

If I’m looking at the right bulletin it’s for digital throttle and shift which I don’t have. So am I correct in saying that the boost pump is needed in my configuration or is it a sign my HP pump is going out that it needs to have the booster running?

 

[muc]

You have the Outboard bulletin. The MerCruiser recall is for a wiring problem at the alternator.

If the boost pump it there (trying to draw gas thru it) it needs to be working. If you remove the boost pump and it's filter, your engine will probably run. But I recommend boost pumps on all cool fuel 2 systems. It helps that much.

 

[metsfan3197843]

You have the Outboard bulletin. The MerCruiser recall is for a wiring problem at the alternator.

I can’t seem to find it online, I’m guessing it’s not for the general public. I’m on an island with no dealer or even a shop that works on I/O’s so of you know a place I can find it or are willing to share more details that would be great, if you can’t I understand. Thanks for letting me know

 

[alldodge]

Didn't find the bulletin but did find a guy which listed what it is. Need to trace the orange wire thru and find where it is rubbing

NOTE: You also need to have the orange wire on the alternator looked at by your dealer; if routed wrong may have the orange insulation about rubbed through to expose bare wire by now. MerCruiser Service Bulletin # 2006-002. Their service people will know exactly what you're talking about. I still do about 5 boats a summer for this recall that the owners for whatever reason haven't had any idea they had a recall on their engine.

Each and every one of the improperly routed orange alt. wires were close to 'sparking up' too.

 

[wingless]

The Mercury Mercruiser Vapor Lock Service Bulletin 99_07 describes following lots of steps, that were ineffective on my engines, to prevent vapor lock, then adding the 862264A 3 fuel pump, plus other parts.

My solution was instead to add thermostatically-controlled high-volume ignition-protected heat exhaust blowers to my engine room. These automatically cycle to maintain the engine room at the setpoint temperature and have been 100% effective in tropical temperatures.

 

[muc]

I can’t seem to find it online, I’m guessing it’s not for the general public. I’m on an island with no dealer or even a shop that works on I/O’s so of you know a place I can find it or are willing to share more details that would be great, if you can’t I understand. Thanks for letting me know

Yes, the outboard S.B. Was all I found during a quick search. If you look at the bottom of each of the pages of that bulletin, you will see why I can’t post it.

I do feel that it is important for you to read the service bulletin. It has a very good description of the issue and detailed pictures of the right way and wrong way. It also lists what parts and procedures are needed to determine what (if anything) should be done.

MerCruiser has the wrong address for the owner of this engine.
My suggestion is to call Mercury Marine and get your address updated or registered in your name if you bought it used. While you’re talking to them explain your situation and ask if they can do anything to help out. It’s in their best interest that you don’t die, so I’m guessing they will find a way to help.

 

[metsfan3197843]

Thanks. Yeah I’m not big on dying so I’ll look into it and get the boat in my name in the system

 

[alldodge]

Yeah I’m not big on dying

Everybody wants to go to heaven but nobody wants to go now

Those that have gone have not come back complaining

 

[muc]

Everybody wants to go to heaven but nobody wants to go now

Those that have gone have not come back complaining

Ha ha, I like that.
Hope you didn’t copyright this, because I’m sure going to use it.

 

[metsfan3197843]

I have reached out to mercury thanks again everyone for your input

 

[alldodge]

Ha ha, I like that.
Hope you didn’t copyright this, because I’m sure going to use it.

The first one is from a country song by Kenny Chesney

 

[QBhoy]

Does vapour lock only effect some of these mpi ? I’m not sure I’ve seen it happen to any of the 2003-2005 mpi 5.0 and 350 at all. The ones I know of anyway. Is it a cool fuel thing ??

 

[wingless]

My boat had ZERO heat soak vapor lock problem when operated in New England and always had the problem when operated in the tropics, until my custom-designed thermostatically-controlled heat extractors were added. Now I again have ZERO heat soak vapor lock problems.

My engines do not have the "cool fuel" system, and instead have a different OEM system that transfers heat from the pressurized fuel line and from the fuel pump to the raw water circuit.

Mine never had any vapor lock problem, except after the boat sat for over an hour in the tropics, then it would fail to start until the pressurized fuel line / rail would cool.

The heat extractors I added automatically kick on and off to maintain the engine room temperature, during operation and especially while stopped.

 

[muc]

Does vapour lock only effect some of these mpi ? I’m not sure I’ve seen it happen to any of the 2003-2005 mpi 5.0 and 350 at all. The ones I know of anyway. Is it a cool fuel thing ??

Vapor lock Can affect any engine. We had a lot of trouble with it back in the 80’s when they started changing the reed vapor pressure of the fuel here in the USA. Some engines are more prone to it and the boat the engine is in can play a bigger part.

The fix that wingless came up with is one way that works if you have enough battery capacity.

​​​​​​​EFI is more more at risk to vapor lock because extra fuel is always moving. This is why Marine engines that can’t return excess fuel to the tank will have some sort of fuel cooler installed. And will sometimes need a boost pump.

 

[wingless]

The Mercury Mercruiser Vapor Lock Service Bulletin 99_07 describes following lots of steps, that were ineffective on my engines, to prevent vapor lock, then adding the 862264A 3 fuel pump, plus other parts.

My solution was instead to add thermostatically-controlled high-volume ignition-protected heat exhaust blowers to my engine room. These automatically cycle to maintain the engine room at the setpoint temperature and have been 100% effective in tropical temperatures.

The fix that wingless came up with is one way that works if you have enough battery capacity.

EFI is more more at risk to vapor lock because extra fuel is always moving. This is why Marine engines that can’t return excess fuel to the tank will have some sort of fuel cooler installed. And will sometimes need a boost pump.

My boat has six 125Ah Group 31 batteries, so yes plenty of reserve.

The Mercruiser solution was to add a small low pressure pump, but I didn't select that solution.

My boat has a seating area above the engines. If I raised the engine compartment lid when stopping, then all that residual heat escaped and zero vapor lock. That wasn't a possibility w/ guests aboard, sitting in that area.

When I return to dock at the end of day, to put the boat away, as soon as I raise the engine compartment lid the thermostatically controlled heat exhaust blower stops cycling, because all that heat rises and escapes.

 

[Stinnett21]

My 2002 5.0 MPI (OM345638) vapor locked. The fix was to replace the Check Valve Assembly, part #21-864206A1. I believe this is what stops hot water from the engine from backing up into the fuel cooler.

 

[wingless]

My 2002 5.0 MPI (OM345638) vapor locked. The fix was to replace the Check Valve Assembly, part #21-864206A1. I believe this is what stops hot water from the engine from backing up into the fuel cooler.

Good you have a solution. My boat does not have that part, item 2 on the image.