Function of Fuel Lift Pump

[TBOT422]

What's the function of the electric fuel lift pump? I suspect that mine is not functioning, but not real sure how to test it.

To get the air out of the system when changing the fuel filters, it was suggested to open the vent on the top of the secondary fuel filter and just turn the switch to the 'glow' position. It would pump fuel into the secondary filter and purge the air. I tried it and never got a drop of fuel into the secondary filter. Eventually I disconnected the line from the lift pump and poured fuel directly into the secondary filter with the vent open. Closed everything up and started the engine. It ran fine for over 1/2 hour at the dock.

From this experience, I suspect my lift pump is not functioning. I can hear a click when I turn the switch to the 'glow' position. I think that is the solenoid kicking in, but I don't hear a click-click-click like a pump is running. It's hard to tell from near the helm, and I have bad hearing to boot. Next time, I will have some "crew" with me when testing so I can be in 2 places at once.

Apparently the engine will run fine without the fuel lift pump, so what is it's function? If it's not working, when will the failure be evident (other than when changing filters like I just did)?

Thanks

[wolfe10]

As you suggest, I always use the electric fuel pump to purge the air after filter changes-- in fact did it again last weekend.

To test it, forget about going out to the cockpit. Remove the top engine access panel in the aft cabin.

You will find (at least on 350 #180) a female connector on the positive lead from the pump. Just to it's port is the large solenoid. One of the large lugs on the solenoid is always hot (battery side). Touch the positive lead of the pump to the hot lug and the pump will start clicking away and pumping. With a socket on the bleed bolt on the secondary filter, you can easily sit there and see when air and bubbles turn to fuel (yes, have paper towel or something to catch the diesel coming out of the bleed hole so diesel doesn't get in the engine bilge). Remove the pump wire from the solenoid (or, of course, any other 12 VDC positive source) and tighten the bleed bolt.

Start engine and motor happily off.

Brett

[TBOT422]

Brett,

Thanks for the test procedure. I'll give it a try. But my question is what is the function of the lift pump? I don't think ours works. But it doesn't seem to matter. Apparently the lift pump is only on when the switch is held in the 'glow' position. For the first 3 months we owned the boat, I didn't even know there WAS a glow position. The boat starts fine in a second or two after pressing the crank button. So what is the lift pump supposed to do? What other type of failure (other than changing the filters) will a failed lift pump leave me stranded?

Thanks

[lyle]

The fuel lift pump normally runs anytime the ignition switch is on - not just when you twist the switch to the glow position. The purpose of the fuel lift pump is to provide positive fuel pressure to the engine driven pump. I'm not a mechanic but my guess is the engine may run with only the engine driven pump operating but I would think it may be more prone to sucking air especially under heel or in big seas.

[R.B.]

Having just replaced my lift pump, I can tell you for certain that your engine will NOT run without the lift pump working. In fact if you look at the wiring diagram, if your oil pressure drops, the oil pressure switch will cut power to your lift pump to prevent engine damage.

Also note that this is a self bleeding system, just get your lift pump working for a bit and you can then start your engine after changing the fuel filters.

[TBOT422]

Thanks for the feedback.

From what I've read on C34 and C36 boards, the fuel lift pump on the newer M35B only operates when the switch is in the glow position OR the engine is running AND the oil pressure is up (switch would be in the ON position).

However, I also read that the fuel lift pump may not be necessary if the fuel can gravity flow to the engine (i.e. the fuel level in the tank is above the engine). Apparently this scenario exists in the C34 if the tank is more than 1/2 full.

The reason I began to question whether my fuel lift pump was working is that after changing filters, I opened the bleed vent on the secondary filter and put the switch in the glow position over a minute and did not have a single drop of fuel in the secondary filter. I was only successful in being able to start the engine after I manually poured fuel into the secondary filter to get the air out. Then everything worked fine.

I haven't had a chance to "hot wire" the pump per Brett's suggestion yet, but I did have some "crew" with me yesterday and observed the lift pump while the crew put the switch in the glow position. It did not click, whir, buzz, or humm. I placed my hand on it and it didn't vibrate or have any indication of anything moving at all. The solenoid did click when the switch was placed in the glow position, and the blower comes on when the switch is in the ON position. If the lift pump is supposed to make some sort of noise or vibration when working then I don't think ours works. It could be the pump or the solenoid that activates it. I'll need to do some more research to determine why it doesn't appear to be working. By the way, our lift pump is the small rectangular box "electronic" style and not the cylindrical style if it makes a difference as to whether or not it makes a noise or vibration.

Maybe I just didn't run it long enough to get it to "self prime", fill the Racor, and start to fill the secondary filter after changing the filters.

Thanks
Gary

[R.B.]

Yes it should click continuously when in the glow position. Test it as Brett suggested by touching the positive lead of the pump to the hot side of the solenoid. It should click and run.

[TBOT422]

Studying the Westerbeke Wiring Diagram #200360, confirms what I read: the lift pump should be energized by EITHER the key switch in the glow position OR positive oil pressure when the engine is running. I need to hot wire it as Brett suggested or monitor it when the engine is running. If it is "clicking" when the engine is running or hot wired, either the preheat solenoid is not working or the 10A circuit breaker between the solenoid and the lift pump is open. I suppose I could confirm the functioning of the preheat solenoid by verifying that the glow plugs get hot. I do know that the solenoid clicks and jumps violently (it doesn't seem to be solidly attached to it's mounting) when the key is switched to the glow position. That would isolate the problem to the 10A circuit breaker.

Gary

[lyle]

You definitely can hear the pump clicking when it is working. I tried it and you are right it only operates when the glow position is engaged (when the engine isn't running). I'm amazed the engine would start easily without it - does it take lots of cranking to start?

[TBOT422]

Lyle,

Nope. The engine starts within 1 to 2 seconds after pressing the start button. Like I said for the first 3 months we owned the boat I didn't even know there was a glow position on the key switch. I will have to say we live in Florida and since we bought the boat in April, the temperature has not been below 60 degrees, probably never below 70 degrees when I tried to start the boat. So the glow plugs are probably not necessary.

Gary

[jbd3]

I spent much of this summer dealing with lift pump issues and I'm not done yet. My engine would act like it was starving for fuel intermittently. The first thing I found was the wire to the lift pump was poorly attached to the female connector making for an intermittent connection. After fixing this and soldering it I thought I had it solved until approaching a very tight marina in a severe squall, the engine would only exceed idle for a few seconds at a time. Lift pump seemed fine (at least it clicked) but the on-engine secondary fuel filter canister was loose. The local mechanic I hired to help me troubleshoot this said this allowed the system to suck in air. After tightening this, the engine seemed to run fine but our home marina mechanic said that since the fuel is pressurized at that point it should have leaked fuel rather than sucking air which it didn't do. Now I suspect it could still be an intermittent lift pump that clicks but may not be developing consistent pressure. The home mechanic said some engines run fine without the lift pump and others require it. My next step is to do some pressure testing and get a spare lift pump. Hull 394...

[TBOT422]

jbd3,

Interesting. Do you recall the fuel tank level when you seemed to be having lift pump issues?

It may be possible that the lift pump becomes "weak" in that it works well (or maybe isn't needed) with a full tank, and doesn't provide enough fuel flow as the fuel tank level gets lower.

Gary

[jbd3]

Tank was about half full but it has run fine at lower levels since then with the filter canister properly tight.The tank is definitely lower than the lift pump so I think the 350 requires it at least to exceed idle. In all the poor running I experienced, it never dies completely, just required backing off the throttle to idle..

[Ray Edwards]

I had a problem with my lift pump / engine would not start sooo went out and found a new one, installed it, engine strat immediately. When removing orginal pump placed it in a cut off plastic jug and a little fuel came out --- with dirt particles so shook, blew out pump, replaced the new one with old and has been working perfect now for the better part of two years since problem.
Of course now, I have a new pump as a back up being i couldn't return after running fuel thru it.
I also think there is a "small" fuel filter attached to the pump, although I didn't really pay much attention to replacement type but if i remember correctly there was a tag on the pump identifying it with a recomendation of replacing.
Haven't given it much thought, but now with this subject coming up plan on checking the filter issue out?

Ray Edwards
C350 "Maria"
2005 / #293

[wolfe10]

Ray,

Is the "filter" in the lift pump a wire screen or a real filter? Any idea what the debris was that clogged it?

Brett

[TBOT422]

click-click-click. . . I finally heard the fuel lift pump by hot wiring it as Brett suggested. I then did some more testing to find out why it does not work when the switch is in the glow position. My suspicion is that the preheat solenoid has failed. I checked the voltages at 3 test points with the key switch in various positions.

On the 'hot' side of the solenoid there is always 12V-13V. Even with all battery switches OFF, so apparently there are more things that are 'hot' all the time than the bilge pump.

On the solenoid side of the 10amp breaker there was no voltage with the batteries OFF or ON as long as the key switch was in the OFF position. When the key was switched to ON, I read about 9V on both sides of the 10 amp breaker. That was my first clue, I don't think I should ever see a 9V reading.

When the key switch was turned to the glow position, I read 9V on the solenoid side of the 10amp breaker and 0V on the lift pump side (hence why the lift pump doesn't work in this position).

After starting the engine, I read 12V-13V at all 3 locations which I believe would be correct. Apparently the lift pump is getting voltage from the oil sensor switch as it is supposed to, but with the engine running I can't hear the click-click-click.

Now I need to determine whether the solenoid is bad or the 10 amp breaker.

Gary

[wolfe10]

Gary,

To locate the voltage drop, work from the battery end with one lead on each side of the device in question. That will show you the voltage drop across that device.

Be sure to check voltage at the battery as well. A weak battery may, under the load of glow plugs, drop voltage below that required to close the solenoid.

Brett

[TBOT422]

Brett,

Thanks for the input, but its way over my head. I'm a mechanical engineer by education and I've always had trouble with electricity.

I'm pretty sure the solenoid is bad. It's probably been bad since we bought the boat. It's only function is to pre-heat the glow plugs and activate the fuel lift pump when the engine is not running. Neither function is probably needed in summer in Florida unless the boat has been sitting for a long period of time.

The phenolic housing of the solenoid is riveted to a metal mounting bracket. On ours, this connection is loose and wobbly. If the solenoid is getting its ground through this connection, then it can not possibly be working correctly. At $35 probably something I need to get before the winter sets in. I took the 10-amp "circuit breaker" off and tested it's continuity. It's fine. Since there is no way to "reset" it, I would call it a fuse rather than a "circuit breaker".

At least this excercise has taught me how the devices work, and I could probably find a work around for them if needed on a cruise some time (i.e. a faulty oil sensor/broken wire that shut down the fuel lift pump). That's the real goal of doing most of my own maintenance.

Gary

[wolfe10]

Gary,

If you have a voltmeter, let me see if I can better explain what I was suggesting.

If you put the voltmeter leads on either side of any device and set the meter to volts, what you will read is only the voltage DROP ACROSS THAT DEVICE. You could achieve the same result (but a lot more wire involved along with some very basic math) if you put ground lead from the voltmeter on the battery ground and then moved the positive lead from battery to first connection to next connection to one side of the solenoid to the other side of the solenoid, etc.

The objective is to see if there is a significant voltage drop. If so, correct it. no real rocket science.

And to do an emergency "work around" for any solenoid, merely label and remove all the wires from one of the large lugs and temporarily connect them to the other large lug. Everything will function exactly the same as if the solenoid were working properly (solenoid on/with continuity).

Obviously, with a solenoid controlling something like the glow plugs, you would only hold the wires to the other lug for the 10 or so seconds for the glow plugs to warm then return them to their original location.

[TBOT422]

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)?

So if I had the batteries ON and the key switch in the glow position, and connected one lead of the voltmeter to the hot lug on the solenoid and the other lead to the glow plug terminal, the voltmeter should read 0V? with the key switch either OFF or ON, it should read 12V?

I'm not sure how that is any different than what I was doing of putting one lead of the voltmeter on an engine ground, then measuring voltage at each of the solenoid lugs with the key in various positions. I'm sure your method provides me some information, I just don't know what to do with the information.

By the way, I was incorrect in my previous statement that the hot lug on the solenoid showed 12V when the battery switches were OFF. I forgot that this boat has a 12VDC power supply that provides all the DC power when connected to shore power and I hadn't turned it OFF.

Thanks
Gary