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Fuel Pressure PCM

RickR90s

Contributing Member
I have a 2002 PCM (350 HO) in my MB Sports Tournament Ski Boat. Hours are 792.

I'm reading 30psi off the Shrader valve on the Fuel Control Cell. That seems a bit low to me.

What should the continuous pressure be?

Also, with key turned on, engine not started, the pressure will rise to 30psi and then fall to zero. But starting the motor, raises the pressure to 30psi again, where it stays.

Shouldn't the pressure stay at 30psi even if the engine isn't running as long as the key is on? Or is the engine computer intervening somehow to determine if the engine isn't running?

thanks,

RickR90s
 
going off memory, I'd say you are correct....think more like 50 psi.....you should check the service manual to be sure!!

It may be designed to fall to zero, but very slowly....if its a rapid drop, then something in the fuel system is leaking - again, the service manual can fill in those voids.

The computer usually 'primes' the fuel circuit for startup....and then turns the pump on once it determines the engine is running....the fuel pump needs to maintain the spec PSI all the way up to WOT...if not, performance will suffer.
 
thanks makomark,

the pressure is maintained up to WOT, just seemed a little low to me. I have the service manual so I'll check that out. thanks,
 
This past weekend I was winterizing the boat. So I wanted to start it up to get the oil warmed prior to changing. The same fuse kept blowing again.

I'll address it further in the spring by further testing each pump. (low pressure and FCC)

thanks,

Rick
 
may be a bad connection in the circuit(s) protected by the fuse....especially on the ground side....a voltmeter can be used to check for voltage drops across the connectors...an IR gun can be used too but doesn't always show the issue...
 
hi Makomark,

That's something I considered and will look at next spring. I have the PCM schematic so I sort of, kind of, have a place to look for that condition.

I am concerned about the low FCC pressure though. It was only 30 psi, so I'll be looking at both high pressure and low pressure pumps in the spring.

thanks,

RickR90s
 
2002-2003 Engine MODEL MP 5.7L (330 HP)
Displacement 5.7L (350)
Fuel Pressure 55-62 psi
See page 52 +/- for more engine specifications, http://www.planetnautique.com/CorrectCraftManuals/PCM Owners Manual.pdf

This engine is said to have a high and low fuel pump. Typically the first thought with fuel pressure dropping quickly to 0 would be the fuel pressure regulator but if you seem to be blowing a fuel pump fuse then that would tend to indicate more of an possible internal issue within the fuel pump such as a bad motor and/or stuck internal check valve...If not then possibly a power and ground issue within the wiring circuit someplace.

Have a read on page 34+ while your in the owners manual linked above too.
 
Good afternoon everyone. So good to see Spring around the corner. So I picked up my boat today out of storage and replaced the low pressure and high pressure pumps (fuel control cell) as well as the FCC filter. If you recall last fall, I winterized the boat but the fuel pump fuse kept blowing.

I also installed an inline fuel filter between the low pressure pump and the fuel tank.

The boat started fine, and no blown fuses, but checking the fuel pressure at the FCC Shrader connector shows about 33 psi, when specs say it should be 55-62.

Am I missing something here? To the best of my knowledge, there isn't fuel pressure regulator.

Appreciate the help,

Rick
 
Since this engine uses a dual venturi throttle body, does it even have a fuel pressure regulator? If not, I assume fuel pressure is maintained by the FCC pump.

Thank,

Rick
 
Could be a couple things a check valve in the fuel pump allowing fuel to bleed back into the fuel tank or leaking injector/s. Is it hard starting like it is flooded?
 
It starts and appears to run perfectly fine. (in the driveway anyway). I'm just wondering if the fuel pressure is a little low.
 
If you have new pumps and the pressure is low, I'd think the regulator would be the next item to check....if the pressure is the same with the previous pumps, then they are likely still serviceable.

BTW, its likely to run fine in the driveway....the pressure really needs to be checked under load. if the pump won't maintain pressure at WOT the issue still isn't resolved.
 
If you have new pumps and the pressure is low, I'd think the regulator would be the next item to check....if the pressure is the same with the previous pumps, then they are likely still serviceable.

BTW, its likely to run fine in the driveway....the pressure really needs to be checked under load. if the pump won't maintain pressure at WOT the issue still isn't resolved.

I guess my question is whether the system has an additional fuel pressure regulator. I don' believe so because it's a throttle body system, not multi-port where there are 8 individual fuel injectors AND a fuel regulator on the fuel rail.

Rick
 
Ok....the link provided earlier in the thread is for the MPI version....if you have a TBI unit, that's not the correct manual....I'd suggest first off, getting the serial number from your engine and then getting the correct spec - the factory help line is the best if you dont have a local dealer....you mentioned earlier you have the factory data - make sure it is correct for what you have...

The MPI systems run higher than the TBI version.....and the TBI stuff had a very short time....so parts are not common or cheap. The late 90's merc spec for TBI is 30 psi so you may be ok there (if you have the TBI), provided it is help across the load range.

Finally the GM TBI system has a regulator inside of it.....the only ones I've seen that don't were custom mods where an external unit was used.
 
Mako, Thanks so much for your expertise. I'll contact a PCM rep, but I believe also that 30+ psi is going to be fine for a throttle body system. I drop my boat in this week, so I'll be checking the fuel pressure at full throttle.

Kindest Regards,
RickR0s
 
I think that Mark is giving you spot-on info.

I also installed an inline fuel filter between the low pressure pump and the fuel tank.

Rick, the in-line fuel filter media is far too small, and if this is the plastic body style, they are not legal in a marine application.
You will want to install a canister style fuel filter system. RACOR (w/ the metal bowl for inboards) is one of the best out there.



.
 
I think that Mark is giving you spot-on info.



Rick, the in-line fuel filter media is far too small, and if this is the plastic body style, they are not legal in a marine application.
You will want to install a canister style fuel filter system. RACOR (w/ the metal bowl for inboards) is one of the best out there.



.

Hi Ricardo, I believe I did just that. I got the metal style unit from Miami Nautique, as they sell parts for PCM applications.

I was thinking I would get a glass, style unit so I could view when to change it or clean it, but Miami Nautique advised the same as you.

Thanks for the info.

Rick
 
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