Function of Fuel Lift Pump

[wolfe10]

Gary,

Voltage drop across a solenoid, connection or other devise would ideally be zero or close to zero.

Any voltage drop from one side to the other would indicate resistance and if more than a very small amount, would indicate the need to replace, clean, make better contact, etc.

It is basically the "report card" for how much you are losing in the wiring, connections and devices. It is a real issue on a boat to have a battery at 12.2 VDC (about 50% discharged) and have enough resistance in the wiring and devices that things do not operate properly. Hard to condemn a 12 VDC device that won't work properly at 9 VDC!

And, if you are more comfortable checking voltage at the battery and then at each connection and each side of every device, you will end up with the same information. Either way will identify WHERE the voltage drop is occurring.


Brett

[TBOT422]

Brett,

Thank you so much for bearing with a novice. I think I am beginning to see your logic.

Wouldn't the voltage 'drop' across a solenoid depend on whether the solenoid is 'activated' or not. For instance, if the glow plug circuit is not activated (i.e. the solenoid is open) I would expect to see a 12V drop from the hot lug to the glow plug lug on the solenoid. Yet when activated (solenoid is closed) I would expect to see 0V or near zero voltage drop.

Similarly if I connected one lead of the voltmeter to an engine ground and measured 12V at the hot lug of the solenoid, I would measure 12V at the glow plug lug when the solenoid was closed and 0V when it was open. In this case, the same information.

However, when I measure 9V at the fuel lift pump lug prior to the 10amp fuse with the key switch in the ON position, your method would produce a 3V drop between the hot lug and the fuel lift pump lug. That may or may not be a faulty solenoid because the key switch and all of its wiring is also in that loop. If I were to also check the voltage drop from the hot lug to the "S" terminal on the solenoid (the wire connected to the key switch), I could determine whether the voltage drop is in the key switch and wring or the solenoid without dismantling the helm to get to the key switch wiring. Excellent!

I still suspect it is the solenoid just due to its physical condition, but it would be nice to confirm through actual testing.

Thanks
Gary

[wolfe10]

GARY,

MY RESPONSES IN SOLID LETTER CAPS-- NO, NOT YELLING, JUST WANT TO ADDRESS EACH QUESTION IN ORDER.

BRETT

Wouldn't the voltage 'drop' across a solenoid depend on whether the solenoid is 'activated' or not. For instance, if the glow plug circuit is not activated (i.e. the solenoid is open) I would expect to see a 12V drop from the hot lug to the glow plug lug on the solenoid. Yet when activated (solenoid is closed) I would expect to see 0V or near zero voltage drop.

CORRECT. YOU WOULD ONLY GET A VALID "RESISTANCE/VOLTAGE DROP WHEN THE SOLENOID IS "ON". OBVIOUSLY, THAT IS WHEN YOU ARE CONCERNED ABOUT A VOLTAGE DROP.

Similarly if I connected one lead of the voltmeter to an engine ground and measured 12V at the hot lug of the solenoid, I would measure 12V at the glow plug lug when the solenoid was closed and 0V when it was open. In this case, the same information.

LET ME REPHRASE. IF YOU MEASURE 12 VDC TO THE ALWAYS HOT LUG OF THE SOLENOID WHEN THE SOLENOID IS NOT "ON", THAT IS INTERESTING, BUT NOT OF REAL VALUE IN TERMS OF DIAGNOSTICS. YOU ARE MUCH MORE INTERESTED IN VOLTAGE DROP UNDER LOAD (HIGH AMP DRAW). SO, HERE IS HOW I WOULD PROCEED: HAVE SOMEONE TURN THE KEY TO TURN ON THE GLOW PLUG SOLENOID. MEASURE VOLTAGE AT THE BATTERY. IF THE BATTERY DROPS QUICKLY TO BELOW 12.2 VDC (ASSUMING IT IS FULLY CHARGED), THE BATTERY IS SUSPECT. GO NOW TO THE SOLENOID "ALWAYS HOT" SIDE. WITH THE SOLENOID ON, IF THERE IS LOWER VOLTAGE THAN YOU MEASURED AT THE BATTERY, IT IS WIRING OR TERMINAL ISSUE-- YOU HAVE RESISTANCE THAT IS LOWERING THE VOLTAGE BETWEEN THE BATTERY AND SOLENOID. NOTE, IF YOU ARE CHECKING THE SOLENOID FROM HOT TO GROUND ON THE ENGINE, THE ISSUE MAY ALSO BE A POOR OR LOOSE CONNECTION ON THE GROUND SIDE.

HERE IS WHERE MY " PUTTING THE LEADS ON EITHER SIDE OF A DEVICE" COMES IN HANDY" IF YOU MEASURE A VOLTAGE DROP ACROSS THE SOLENOID WHEN IT IS ON OF MORE THAN A FEW TENTH OF A VOLT, REPLACE IT. AND A LOSS OF 3 VOLTS INDICATES A LOT, REPEAT LOT OF RESISTANCE.

DON'T GET CAUGHT UP IN YOUR METHOD OR MINE-- BOTH GIVE THE SAME RESULTS. I USE MINE BECAUSE I CAN INSTANTLY CHECK A DEVICE WITHOUT RUNNING A GROUND WIRE ALL THE WAY BACK TO THE BATTERY.

However, when I measure 9V at the fuel lift pump lug prior to the 10amp fuse with the key switch in the ON position, your method would produce a 3V drop between the hot lug and the fuel lift pump lug.

CORRECT.

That may or may not be a faulty solenoid because the key switch and all of its wiring is also in that loop.

CORRECT. SEE ABOVE. ALSO, YOU CAN DETERMINE HOW MUCH OF A DROP IS ACROSS THE SOLENOID BY EITHER MY METHOD (LEAD ON EITHER SIDE OF THE SOLENOID) OR YOUR METHOD BY CHECK VOLTAGE AT THE "ALWAYS HOT" LUG AND THEN THE "ONLY HOT WHEN ON" LUG. CLEARLY EITHER METHOD WILL TELL YOU THE SOURCE OF THE RESISTANCE/VOLTAGE DROP.

If I were to also check the voltage drop from the hot lug to the "S" terminal on the solenoid (the wire connected to the key switch), I could determine whether the voltage drop is in the key switch and wring or the solenoid without dismantling the helm to get to the key switch wiring. Excellent!

LET ME STATE THAT A LITTLE DIFFERENTLY. YOU ARE CORRECT--FOR A SOLENOID TO FUNCTION PROPERLY, IT'S SIGNAL WIRE MUST HAVE SUFFICIENT VOLTAGE TO PROPERLY CLOSE THE SOLENOID. HERE I WOULD MEASURE FROM THE "S" TERMINAL TO GROUND. MEASURING FROM S TERMINAL TO HOT LUG COULD INDICATE THAT THERE IS LITTLE DIFFERENCE IN VOLTAGE DROP, REPEAT LITTLE DIFFERENCE IN THE VOLTAGE DROP, BUT THERE COULD BE A SIGNIFICANT VOLTAGE DROP ON BOTH OF THEM. EQUAL BUT SIGNIFICANT DROP WOULD STILL BE BAD. BETTER TO CHECK THAT THE SIGNAL TERMINAL IS GETTING 12+ VDC.

I still suspect it is the solenoid just due to its physical condition, but it would be nice to confirm through actual testing.

AS INEXPENSIVE AS INTERMITTENT DUTY SOLENOIDS ARE (ANY PARTS HOUSE AS LONG AS YOU KNOW THE AMP RATING OF THE SOLENOID), AND YOU KNOW THAT IT IS DAMAGED, I WOULD JUST REPLACE IT.

ALSO, WITH ANY ELECTRICAL SYSTEM, PARTICULARLY WITH HUMID CONDITIONS AND VIBRATION (I.E. BOAT), CHECKING ALL CONNECTIONS FOR CLEANLINESS AND TIGHTNESS ONCE A YEAR IS A GIVEN.

Thanks
Gary

[digitalvillager]

I'm disappointed to see this thread end without a conclusion as I am having an identical issue: I live in North Florida, ignition on, solenoid clicks, no signs of life from the fuel pump. The difference is that when the engine starts (easily), the fuel pump begins to function. I can put a positive power lead to the fuel pump and it works fine. I believe it's a wiring issue, but I don't know how to solve it. I'm neither a mechanical or electrical engineer, but I'm pretty certain that the fuel pump should be trying to pressurize the system when the ignition switch is turned on. The only reason I could think of why the pump shouldn't run is when you pull the shut off lever and don' turn off the ignition key. This is my first post, so please bare with me.
Digitalvillager
Quit In Time
Hull #285

[TBOT422]

DigitalVillager,

In my case, I believe the fuel lift solenoid is bad. I haven't replaced it yet, because it doesn't seem to be necessary, the engine starts fine without the glow plugs or fuel lift pump being on. I suspect this is true because we live in a warm climate and use the boat regularly. The glow plugs probably are needed in colder climates, and the fuel lift pump may need to be activated if you haven't ran the engine in months and the fuel in the system has drained down.

It sounds as if you have a similar issue. You can check it the same way I did. Check the voltage at the 3 lugs on the solenoid with the ignition key swith in various positions.

You should have 12V at the hot lug on the solenoid with the key switch OFF. The other lugs should be 0V.

With the key switch moved to the ON position, you should get 12V at the lug with the 10 amp breaker. (Mine measures 9V - hence why I feel the solenoid is bad). The lug to the glow plugs should still be 0V.

With the key switch moved to the GLOW position, you should get 12V at the lug for the glow plugs, and you should hear the click-click-click of the fuel lift pump. (Mine shows 0V and no clicking of the fuel lift pump).

After the engine starts, you should see 12V at all the lugs, as power is supplied to the fuel lift pump through the oil pressure switch.

[digitalvillager]

I'll look at that, but it appears that the engine is doing what it is expected to do, not what it should be doing. I think we need to figure out how to re-wire so that the fuel lift pump receives power when the key is turned to the on position.

[TBOT422]

DigitalVillager,

That is not how the system is designed. If you study the Westerbeke wiring diagrams, you will see that the fuel lift pump should get power from EITHER the key switch being in the GLOW position OR from the oil pressure switch (engine running with good oil pressure) when the key switch is in the ON position. This design will shut down the fuel lift pump if you loose oil pressure even though the key switch is ON. This is a safety feature to keep from destroying the engine in the event of a loss of oil pressure. If you re-wire the system so that the fuel lift pump gets power any time the key switch is in the ON position and you happen to loose oil pressure, the engine will continue running until you shut it off and you may cause further damage to the engine.

[digitalvillager]

Okay, that makes sense. So, in order to charge the system when replacing fuel filters, we will continue to have to jumper a hot lead to the fuel lift pump to purge the air from the system. Seems like there would be a better way rather than using a jumper or just grinding on the starter. We have several Catalinas on the dock (I'm the only 350) and all of the other boats' fuel pumps come on with the ignition key in the on position pressurizing the system prior to the starter being engaged.

[wolfe10]

Brett,

Would I be correct in assuming that the voltage 'drop' should either be 12V or 0V across a switch (which I believe is all a solenoid is)?

Thanks
Gary

Gary,

No, the voltage drop being discussed is when you have much higher voltage at the batteries than "further downstream"-- at the glow plugs in this discussion example. Usually caused by corrosion or loose connections or too small a wire gauge for the load.

You are correct in that a switch/solenoid/relay should have either zero volts at the "out" large lug or full voltage as seen at the "in" large lug.

So if 12.7 VDC at the constant hot large lug of the solenoid, with the signal wire OFF/zero volts (i.e. ignition off) at the other large lug ("out" lug) should read zero. When the solenoid receives the signal (12 VDC) to make contact, the "out" large lug should read the same voltage as the large lug on the "in" side.

Solenoids can fail-- no contact at all, or can fail with high resistance. With high resistance failure, there voltage at the large "in" lug will be higher than at the large "out" lug with the difference converted to HEAT in the solenoid.

Brett

[russp]

Hi All,
I have just read through (carefully) all the previous posts on this topic and am more confused than ever. Appreciate any thoughts on what follows. I will start by noting that I have Universal 35B and a 3 position keyswitch, Off/On/Glow with the glow position momentary. I don't believe I have an Admiral or Captain panel, and the wiring diagram doesn't show a 3 position switch (that I can see)

With the Captain and Admiral panels you appear to have to switch on the keyswitch to energise the preheat switch to energise the start switch and the Manual statement "...electric fuel pump, which is energised by the key switch/preheat button, ...." is correct. But on the 3 position switch this doesn't appear to be the case, fuel lift pump is energised directly from the On keyswitch position and it is possible to start the engine without preheating. With the Admiral and Captain panels you "have" to preheat before you can start.

Based on what I can see of the wiring diagrams (p 26 of Operators Manual for C350), the lift pump is energised by the key switch in the "ON (I)" position, not just the "Glow (S)" position. When I tested mine today I found:
a) when I put a voltmeter across the terminals of the oil pressure switch (ops) and turned ign switch ON (but not glow position) I got 4V, big voltage drop for a supposed closed (no oil pressure) circuit.
b) when I measured the voltages at each terminal I got 12V at the supplied terminal, and 8V at the terminal connected to the lift pump/alarm and again with the ign switch in the ON position only
c) when I put 12V direct on the lift pump I can easily hear it clicking (as per Brett's suggestion)
d) when I jumped the cables connected to the ops, and thus got 12V at the lift pump, I could hear it clicking with the ign switch in the ON position. I.e. at least on my boat, with I think std wiring, the lift pump comes on as soon as the ign switch is turned to the ON position whereas all the posts above suggest it has to be in the glow position (S position) to be energised. This is consistent with how I read the wiring diagram (hence my confusion re previous posts)
e) I reconnected the cables to the ops, tried again, and with ign switch on (NOT glow position) no clicking of lift pump.

My guess on why the ops also connects to the preheat solenoid, is that it somehow "enables" the preheat solenoid when the engine is not running, but once there is oil pressure and the ops goes open circuit, the preheat solenoid is "disabled" so that you cannot turn on the glow plugs once the engine is running. This would also mean that once the oil pressure comes on, the lift pump stops working. I.e. it is only there to pump up fuel until the engine is running and the engine driven high pressure fuel pump takes over. This would also be consistent with some posts which say that the engine runs fine without a lift pump at all (probably most of the time).

So, my current conclusion, faulty ops with high resistance causing significant voltage drop, and 8V is not enough to run the lift pump, so my lift pump hasn't been running for indeterminant period.

This fact seems to link to another post of mine under Engines, about engine failing to start after hard sailing. What (I think - appreciate any views on this) is happening is:
a) when sailed on its ear, on a port tack, the fuel intake tube lifts out of the fuel in the tank
b) because there is no non-return valve, fuel drains out of the line and perhaps out of the top of the Racor down to the fuel tank
c) when it comes time to start the engine, my lift pump wasn't working, so the injection pump sucked a little bit of fuel and ran for a few seconds, and then sucked air and stopped running, leaving the air lock in the intake line.
d) after "enough" brief tries of cranking the engine and the mechanical fuel pump pulling fuel up the line, the engine gets fuel and runs again.

In my head all of the above ties together, but it is so different from what others have posted, and the Manual is no help whatsoever, that I would appreciate thoughts anyone might have.

Regards
Russ Peel
Avalon #150 (launched Oct 2003)

[leigh weiss]

Russ and others,
My interpretation of the electrical diagram:
The key switch is a three position "off,on, glow" switch
It is shown as two switches on the diagram.
With key "on" and engine not running the fuel lift pump should not run, the oil pressure switch is normally open (NO).
When you energize the glow plugs the fuel lift pump is running "on".
When you energize the starter the fuel pump also is energized "on" as you crank the engine.
After the engine starts the oil pressure switch closes which "holds" the fuel lift pump "on".
If you loose oil pressure, the lift pump should be off and the engine should stop (an important safety feature).
As for your hard sailing and the engine not starting, I am still thinking!!!
Some first thoughts:

You might want to use the glow plug position to "prime" as the fuel pump will run with the glow plug circuit. Rather than long cranking of the starter.
You might want to check the fuel filters for a very small leak of air. The system from the tank to the fuel pump will be the suction side. When the tank is lower than the pump this small leak will let air in, but may not show any fuel leak during normal operation.

Best of luck with your investigations!
Let us know how it turns out.


Leigh Weiss
Brisa #155

[TBOT422]

Russ,

Note to ALL: The following information is related to Catalina 350 with an M-35B engine and a 3-position ignition switch (Off, On, and Glow).

Let me update some information. I finally replaced my pre-heat solenoid and now have a working (click-click-click) fuel lift pump when the switch is placed in the momentary 'Glow' position as designed. I went nearly 18 months without having any starting problems with a failed pre-heat solenoid. I will say the engine now seems to start almost instantly after turning the switch to the Glow position whereas before it might crank for 2-3 seconds before starting. The only way I knew it wasn't working, is that I couldn't get fuel to flow when placing the switch in the Glow position to purge air aout of the fuel lines after replacing the fuel filters. Russ, this may be very analogous to your hard-sailng scenario and I believe your explanation makes sense. The voltages I took at various lugs of my old pre-heat solenoid were similar to those you measured. I was also able to get the fuel lift pump to click by applying 12V directly to it, so I knew the fuel lift pump itself was not the problem.

Russ, from everything you say, I suspect your pre-heat solenoid is faulty. Mine was also loose and wobbly in it's mounting indicating that previous engine vibrations may have essentially shaken it apart internally. You can purchase one directly from http://shop.torresen.com/ships_store/in ... ch&q=24639 for $37.29 plus shipping. That's one reason I waited nearly a year to replace mine since it wasn't really causing me any problems - I wanted to wait until I was ordering some other stuff from Torresen to save on shipping.

As to the wiring diagram, check out Wiring Diagram #200360 on page 96 of the Westerbeke M35-B Service Manual. You will see 2 purple wires (16, 17) that can provide power to the fuel lift pump. Wire 17 comes from the Oil Pressure Switch, and Wire 16 comes from the 10A circuit breaker attached to one of the lugs of the pre-heat solenoid. So the fuel lift pump is pumping when it receives 12V from EITHER of these sources. If you don't hear the fuel lift pump clicking when your switch is in the Glow position, before starting the engine, but you have no other problems with starting or running the engine, then your pre-heat solenoid or the 10A breaker mounted on it is likely bad.

I hope this helps.

[russp]

Thanks gentlemen, your input is greatly appreciated and I now "get it". I was misinterpreting the voltage at the lift pump side of the oil pressure switch when the engine wasn't running. The 8V I measured was coming back from the alarm buzzer circuit via the lift pump wiring, not forward through the oil pressure switch. I double checked and confirmed my oil pressure switch is a clean open circuit with engine not running, and clean closed circuit with the engine running. (Apologies, I should have been more thorough and checked this before posting, I jumped to a conclusion and as a result will now have a spare oil pressure switch!!).

Still not clear on role of the 1k resistor at the 10A circuit breaker, except it allows a certain amount of current to go to ground through the buzzer circuit with 12V on one (+) side of the buzzer and the other grounded through the resistor. Once 12V is supplied on both sides of the buzzer (+ and P terminals) it stops buzzing. If this is the case, then the 8V I was seeing at the lift pump/oil pressure switch is just the result of about 8 mA flowing to ground through the resistor, and 8 mA must be what runs the buzzer.

Next step is to check lift pump operation at the momentary position and if not working, to attack the preheat solenoid/10A circuit breaker circuit. It could be that the no start situation after fuel line backdraining while sailing when well heeled was just the consequence of not holding on the preheat switch on long enough to bring fuel all the way up the line, combined with air in the top of the Racor.

Many thanks again,
Russ Peel
Avalon #150

[wolfe10]

Russ,

You should never get air in the Racor (or any other part of the fuel system).

Does this happen at all tank fuel levels? If not, you may not have the fuel pickup tube in the bottom (actually just close to the bottom) of the fuel tank. Removing the fuel sender unit would allow you to inspect that. Only other cause of air is a bad fuel line from tank to Racor, loose fitting or bad gasket in the Racor.

Brett

[russp]

Hi Brett,

Because I don't put a lot of hours on the engine and was trying to run the tank down before refilling with fresh diesel I have only had about 1/3rd full tank for a while and without being able to see the level inside, the centreline of the tank drying out when heeled hard to port doesn't seem that improbable.

Since refilling the Racor I have been out twice and then checked the level and it hadn't moved so I "think" that the air in it came up through the inlet line and not through an air leak in the Racor or inlet line. Certainly when I forgot to close the tank valves before trying to top up the Racor, diesel was running back down the line to the tank faster than I could pour it in, so it is a quite wide open line from tank to Racor.

I normally keep the tank fairly full, and in the first 3 years of ownership didn't experience this problem, but then I wasn't racing and didn't sail her hard to windward so I probably wouldn't have found out anyway.

BTW, in re-reading all the above posts, which all make perfect sense to me now, it strikes me that the 9V or so that can be read at the preheat solenoid when the ignition switch is in the ON position is the result of the current passing through the low pressure alarm buzzer to ground through the 1k resistor. So my guess is that this isn't due to a faulty component at all, just a normal circuit. Do you understand the 1k resistor to do something different?

Regards
Russ