Racor vacuumm pressures

[dfloeter]

I have read through as much of the previous posts as I can  and found nothing specific enough to my issue at hand.  This summer we had a fuel filter blockage where I changed both the 10 micron Racor and the 4 micron secondary engine mounted filter.   A few weeks later the Racor plugged again and I changed just that one.   My post Racor filter vaccuum gauge was reading 11psi after the second stoppage and 8psi after the change.  I don't have any reference to what numbers should be good to start with but at least now I know what does not work.  The engine runs fine now but I am expecting more crud in the filters.  I will add Biobor to the tank soon in hopes of an improvement.

The racor filters didn't look too bad but obviously were bad enough at least for a fuel system that is depending on gravity flow to get through.  As I understand the system, and I may be wrong, once the engine starts the electric fuel pump stops and lets the fuel siphon down and probably gets sucked in by the injection pump hence the vacuum pressure.  To facilitate bleeding after a filter change and to eliminate the blaring oil pressure beep from the panel with the ignition switch turned on, I previously wired in a hot wire that quick disconnects to the pump's positive wire  to keep it running as long as necessary. 

So finally the question is: would there be any harm in running the electric pump continuously if and when the fuel filters start to clog again?  An accessible swith could be installed for emergency use.  That extra pull through the Racor seems like what the halting engine needs to make it to a destination without the drama of dodging a regatta and maneuvering a few turns into a marina. 

I wish to avoid the drama.   

[Ron Hill]

Dietrich : Don't know where you got the idea that the electric fuel pump turns OFF when the engine starts ??  Because it should be ON (pumping) all the time there is OIL PRESSURE!!
The mention of syphon is that the C34 fuel tank is higher than the engine and IF the fuel pump fails/cuts OFF the fuel will syphon to the injection pump and the engine will keep on running - but that's not normal!!

A few thoughts

[Stu Jackson]

Dietrich,

You may have missed this:

Fuel Starvation and The Obscure Check Ball Valve
https://c34.org/bbs/index.php/topic,10681.0.html

The electric fuel pump on my boat runs all the time the ignition switch is on.  The only time that pump stops is on later boats and only when the glow plugs are energized.

The engine fuel filter is reported to be 25-30 micons.

Fuel Filtration 101 (with both primary Racor and secondary engine filter identification)
http://c34.org/bbs/index.php/topic,1124.0.html and http://c34.org/bbs/index.php/topic,6475.0.html

I discussed some of this here, page 4, reply #52:

https://c34.org/bbs/index.php/topic,3347.45.html

[dfloeter]

Thanks guys for clarifying my fuel pump misconceptions.  And it totally blows my plans right out of the water! I thought I got the idea that the fuel pump stops after ignition from this site but I must be mistaken and I will erase that thought.  As far as the micron numbers, it would appear that I am over doing both of them.  The next time I change filters I suppose I will change to a 30/10 combination of the two and let a little tiny crud get through. 
Thanks for straightening me out.

[Jim Hardesty]

Dietrich,

I also installed a vacuum gage and monitor it.  Don't find it to be very useful.  FWIW, I use the 10 micon raycor and Universal spin-on. 
My filter check is to run the boat at full throttle in calm water if it builds to full rpm, 2850+ for Shamrock, the filters are good enough for me.  If not, I change both filters at first convenient time.  I have cruised for a day or two till I got to a place to dispose of the old filters and rags with no problem.  Changing one hasn't worked.
IMHO.  Changing fuel filters on a schedule isn't always useful.  With good, clean fuel the filters stay clean a long time.  Many fill ups and seasons.  Dirty fuel may need many filter changes with one bad fill up of dirty fuel.

Jim

[Ron Hill]

Stu & Guys : The convoluted systems are on the M25XPB, M35 and M35BC engines. They have the fuel pump come ON when the glow plugs are engaged. When the glow plugs are turned OFF (engine running) the fuel pump continues to run because the Oil pressure is up!!
The whole idea of that goofy system was to have the engine shut down (Safety feature - because the electric lift pump would stop running) if the engine lost oil pressure. The problem is that the C34 has the fuel tank higher than the engine and fuel will syphon down to the injection pump (flowing thru the OFF lift pump) and the engine will still be running with NO oil pressure.

That's why I stripped all that wiring OFF my new M25XPB engine and wired/plumbed it like the M25XP engine that was removed!! 

A few thoughts

[KWKloeber]

@Dietrich

<<<the 4-micron secondary engine mounted filter>>>

Where are you getting information that there is a 4-micron, on-engine, secondary filter?
What brand are you saying is 4u?

-Ken

Racor (Parker) recommends against using less than a 10u as the primary filter.