Engine stall

[Sabre34]

My westerbeke 27 starts stalling when the fuel tank becomes just under half full. I have replaced both the primary and secondary fuel filters and replaced the electric fuel pump with one from Car Quest that has a flow rate of 30 gallons per hour and a psi of 5-9. Any suggestions?

[Paul L]

Have you checked that the tank vent is clear? A quick check is to open the tank fill and see if the problem persists.

[DeepFrz]

Sounds more like you have a leak part way up the pickup tube. Will work fine until the fuel level drops below the leak.

[svHyLyte]

Originally Posted by DeepFrz

Sounds more like you have a leak part way up the pickup tube. Will work fine until the fuel level drops below the leak.

...Or, the screen on the pick-up tube is partially obstructed. Down to about half a tank, there is sufficient head pressure to force fuel past/through the obstruction. At the half way mark, the head/pressure is sufficiently relieved that the lift pump simply can't suction the fuel through. In the same circumstances, I would try disconnecting the fuel line from your fuel filter and back flowing air through it to the tank which "might" dislodge any obstruction. If that works, the obstruction will surely recur unless the fuel is "polished" to remove debris, which has commonly accumulated in older fuel tanks.

FWIW...

[GordMay]

Greetings and welcome aboard the CF, Sabre.

[Sabre34]

This is great advice guys. Hopefully either the vent or pickup tube/screen will be the problem. Don't fell like purchasing another fuel pump without being certain that is is not the reason for the stall.

[MerryBee]

May I suggest that if you can access the fuel pickup, remove it from the tank and find out if it is broken/bent/clogged, etc.? If you can find out how deep the tank is at the pickup mounting hole, the pickup tube should be about an inch less than that.
I don't believe your fuel pump would be able to tell if the tank is full or not. And if the pickup were clogged, you'd probably have more random stalling issues than what you're reporting.
We'd love to hear what you find...
Oh... and BTW, hang onto the original pump! I'll bet it's OK!

[Sabre34]

My rationale for the fuel pump relates to the questionable psi rating in that a lower psi would be further challenged buy a decrease in the Hydrostatic pressure as a result of a lower volume in the tank. That was my thinking at the time but I think that the fuel pickup tube is the culprit. Thanks

[Sabre34]

Well I think that I might have found the culprit that has grieved me with stalling problems when the fuel tank goes below half full. when I removed the tank I also removed a check valve on the uptake fuel line. The spring that pushes the fuel back flow ball into the recess appears to be soft which would result in some fuel making its way back into the tank creating a low pressure in the fuel line. We will see when the fuel level hits half. I did not get a replacement in time for launch so I installed the original. crossing my fingers

[MerryBee]

I'm puzzled as to why you have a check valve in your fuel line. Has this always been there? What is the purpose of this check valve? And how far from the tank is your pump? From what little I know, these pumps can 'push' better than they can 'draw' . In other words, I believe it'd be better to have the pump close to and more-or-less level with the tank.

[DeepFrz]

Usually the check valves are in the filter housing. At least they are in the Racor filters. I have never heard of them being in the pickup tube.

In order for a check valve to work they have to work against spring pressure. That is when the fuel pump reduces the pressure on the downstream side of the valve the ball will press against the spring, compressing it and permit the fuel flow. When the pump stops the spring will push the ball back into the seat preventing reverse fuel flow. I have a hunch that cleaning the tank and valve (I assume you did) may be the action that has fixed your problem.

If I remember correctly, and I may not, most diesel engine high pressure pumps like about 4 psi at input. But I surely could be wrong on that.

[DougR]

The reason that your tank has a spring loaded check valve at the top of the pickup tube is that ABYC rules require an anti siphon device installed there for GASOLINE systems, and so fuel tank manufacturers install them as a routine matter. Unfortunately these valves often cause problems with diesel installations when they become restricted with debris, or the lift pump can't overcome the spring pressure, etc. The best thing to do is to remove the valve, take a punch or a Phillips screwdriver and knock the ball and spring out and reinstall the fitting. This is routinely done by installers at boatbuilders. You don't need the check valve on a diesel installation.

That said, there is merit in what has also been mentioned regarding cracks in pickup tubes, plugged vent hoses, etc.

Another similar thing I have seen happen on sailboats is when a relatively flat shallow tank is installed beneath a settee. The engine will run fine from a full tank down to an empty tank as long as the boat isn't heeled. But if the fuel level is down to an indicated half tank or less and the boat is heeled away from the location of the pickup tube, fuel runs away from the bottom of the tube and allows air into the system and causes erratic running or stalling. This should also be checked.

DougR

[Sabre34]

Thanks for the input guys. Merrybee, my understanding is that the valve has always been there, and that it functions to prevent fuel from making its way back into the tank resulting in a lower pressure fuel feed to the fuel pump. Apparently diesel engines do not have much tolerance for abnormal fuel pressure and stall when experienced. The valve is located in the fuel line not far from where it exits the top of the fuel tank. For three seasons the engine worked perfectly. The pump is level with the tank. DeepFrz, I did take the aluminum tank out and actually had a new bottom welded in place due to some pin holes in the bottom (33 year old tank). This allowed me to inspect the pickup tube and no cracks/loose connections were found. I was hoping to see a crack half way up the tube and easily fix the problem. The Westerbek dealer indicated that the pressure should be between 6-10 psi. Interesting comments you make DougR about the redundancy of the check valve. I will consider taking the ball out of the valve. My hesitancy lies with the fact that the engine worked perfectly with the valve. Fair winds.