High pressure on Racors

[svspirited]

I am having a bear of a time troubleshooting a fuel delivery problem on a Westerbeke 80-N4. I recently replaced the electric lift pump after it failed and I cannot keep the engine running after priming everything. Once bled the engine fires right up and runs great for a few minutes. The pressure gauge slowly rises from about 5hg to 15hg at which point the engine starts running rough, when it hits 20hg it stalls. This happens more rapidly if I run the engine at full throttle and takes a while if I just let it idle. Oil pressure is right where it should be, water flow looks to be normal, and when it gets up to temperature it holds as it should.

I have a polishing pump and when I run that the pressure holds around 5hg and will happily do so all day long. I can also run my generator, on the same fuel manifold but on a separate filter system, all day with no issues at all.

When the engine stalls I notice the fuel filter is about half full and if I try and start it without first opening the filter and topping up with fuel it will not restart. What I can't figure out is where the problem may be. If it was a clog in the stand pipe of the various fuel tanks or the manifold then I would expect the generator to stall too. I have tried running from every combination of tank I can with exactly the same results. I would also expect to see a pressure issue with the polishing pump but none appears to happen. I have bled the engine to the point where there isn't a single bubble in the stream of fuel but I still continue to have the issue. At this point I am at a loss, could the lift pump be failing in a way as to create a higher than normal vacuum in the filters? All of the o-rings, seals, and filters have been replaced and the fuel must be fine since the generator has no issue consuming it.

[Paul L]

No actual clue to your situation. I'd try the divide and conquer approach. Run the Racor input line into a bucket of diesel. If the pressures persist then the issue is filter to engine. If the pressure goes away, the problem is tank to filter.

[DeepFrz]

I find your post quite confusing and can't picture your fuel system. Perhaps a drawing of your whole fuel system would help be able to help you.

However one thought comes to mind. It could be the check valve in your filter.

[billknny]

Your description in a bit confused, when you say "high pressure" I think you actually mean LOW pressure, or high VACUMM. In other words the lift pump is trying to suck fuel through the filter, but there is an obstruction that is blocking the flow, and as it sucks harder, the pressure goes down, lower and lower as the pump tries to pull fuel, but can't.

If your new lift pump is of significantly higher capacity than your old one, it might not be an obstruction, but just piping too small for the pump (or pump too big for the piping...)

Eventually, one, or two things happen. The pump can't pull any more fuel, and the engine starves, or air leaks in and the fuel system dies with air in the injection pump.

If the generator uses exactly the same piping but does not have the problem, it is likely that is because it uses a lot less fuel. The obstruction is not large enough to starve the generator.

If you have changed the filters, and are SURE they are clean, you have an obstruction somewhere between the end of the diptube and the filters. Most likely right at the intake end of the diptube.

Some diptubes have screens, others don't. If yours does, clean it. If it has significant debris, plan on cleaning the tank, because it will happen again in short order.

I had a similar problem where the 40 year old fuel tank had chunks of "coke" that would bounce around in the tank until they lodged against the diptube and cut flow to the engine. When the pump stopped, the debris would fall away, and after bleeding the engine would start right up again, and run for a random length of time until the floating bit clogged the pipe again! Frustrating to diagnose.

[svspirited]

Ok, to try and clarify I have attached a diagram of what the fuel system layout looks like. When I say high pressure I do mean vacuum and it starts out where it should be, about 3 or 4hg then slowly creeps up to 15 or so where it starts to run quite rough then above 15 it pretty much always stalls out. Given this happens on all three tanks I am thinking a clogged stand pipe is unlikely, and the tanks are so full that to open one up causes fuel to leak, one of the things I will be trying today is to drain some of the fuel from the tanks and checking to ensure the vents are not clogged up. The lift pump is identical to the one that was on there before so I don't think it is a matter of it trying to draw more than the plumbing and the polishing pump is a way more powerful pump and that pulls fuel through just fine. I am also going to pull the lift pump today and try and replace it but I can't see how something on that side of the filter could cause a vacuum situation in the filter itself but maybe I'm wrong there and would love suggestions.

I should also add that the problem occurs regardless of the filter selected or if both are switch on.

Fuel tank diagram.pdf

[captain465]

First of all, check all connections that were disturbed when replacing the lift pump. Look for loose connections and cracked fittings,
Secondly, if you had this problem, you might have changed the Racor filters, if so, did you also replace the top gasket(large diameter with a square section) and also the small red o ring that goes on the t bolt.
These are the most likely places that you are drawing in air, hence the half full bowl, and subsequent ability to run after refilling.

[svspirited]

Yes on all counts, rechecking the two connections that were broken when I put the pump on later today. If that doesn't fix it I will have to pull the filters and pull them apart to see if there is some gunk in there, just hoping at all costs to avoid that as they are not in the easiest place in the world to get to...

Originally Posted by captain465

First of all, check all connections that were disturbed when replacing the lift pump. Look for loose connections and cracked fittings,
Secondly, if you had this problem, you might have changed the Racor filters, if so, did you also replace the top gasket(large diameter with a square section) and also the small red o ring that goes on the t bolt.
These are the most likely places that you are drawing in air, hence the half full bowl, and subsequent ability to run after refilling.

[antoha]

fuel filter = half full: half full of air, or half full of water or deposits (which need to be cleaned out)? if air, do you see air bubbles in the racor bowl when you run your engine? could you be sucking in air from a connection - or from the lid, maybe?

since you're comparing the polishing system with the engine: what's the fuel circulation throughput of either (gph engine vs gph polishing pump)?

can you run the engine off the other filter, just to see where the issue could be?

[antoha]

also, do you think it makes sense to introduce a valve that would switch the polishing pump output to go to the main engine instead of the return manifold? in case your lift pump fails, for example, then you can just use the polishing pump as a lift pump - for running the engine, or for bleeding. (it probably makes sense to have the lift and polishing pumps have similar specs for that to be a compatible setup.)

if you can do that, you can try disconnecting the power to the lift pump and running the polishing pump instead to feed the engine, and if that solves the problem - then you have isolated the issue to the newly installed lift pump?

[Cheechako]

Is your tank vent clogged? Open the fill fitting ... is there a rush of vacuum?

[Dockhead]

You don't show where the gauge is, but we don't normally have pressure gauges in marine diesel fuel systems (unlike race car fuel systems). What we normally have are vacuum gauges, which show whether filters are clogging or there are other obstructions in suck side of the fuel system.


Maybe you can show a photo of the gauge you are talking about?

[S/V Alchemy]

Originally Posted by Cheechako

Is your tank vent clogged? Open the fill fitting ... is there a rush of vacuum?

Thanks to previous experience, I always check this first. Spiders, man...


I also check all connections for evidence of insufficient clamping.

I also confirm there's not little flakes or gunk obscuring the pickup tube in a partial "sticky flap" way.

There's no short answer here. You have to work from the tank forward to the injectors, or, in this case, the filter assembly.

[Boatyarddog]

Originally Posted by svspirited

I am having a bear of a time troubleshooting a fuel delivery problem on a Westerbeke 80-N4. I recently replaced the electric lift pump after it failed and I cannot keep the engine running after priming everything. Once bled the engine fires right up and runs great for a few minutes. The pressure gauge slowly rises from about 5hg to 15hg at which point the engine starts running rough, when it hits 20hg it stalls. This happens more rapidly if I run the engine at full throttle and takes a while if I just let it idle. Oil pressure is right where it should be, water flow looks to be normal, and when it gets up to temperature it holds as it should.

I have a polishing pump and when I run that the pressure holds around 5hg and will happily do so all day long. I can also run my generator, on the same fuel manifold but on a separate filter system, all day with no issues at all.

When the engine stalls I notice the fuel filter is about half full and if I try and start it without first opening the filter and topping up with fuel it will not restart. What I can't figure out is where the problem may be. If it was a clog in the stand pipe of the various fuel tanks or the manifold then I would expect the generator to stall too. I have tried running from every combination of tank I can with exactly the same results. I would also expect to see a pressure issue with the polishing pump but none appears to happen. I have bled the engine to the point where there isn't a single bubble in the stream of fuel but I still continue to have the issue. At this point I am at a loss, could the lift pump be failing in a way as to create a higher than normal vacuum in the filters? All of the o-rings, seals, and filters have been replaced and the fuel must be fine since the generator has no issue consuming it.

Maybe I've misread your post but I believe you're referring to Vaccume in the Racors not pressure.
You've got a restriction behind those filters.
Could you have possibly installed them incorrectly? Or forgot to return a valve to its running positions? Happens a lot.
SV Cloud Duster

[stormalong]

A simple way to check if the fuel vent is clogged is to run the engine with the fuel fill cap open. If the vent is clogged your engine will run fine.

It would not be a leaky fitting because you are pulling a big vacuum. If it was sucking in air without the big vacuum it might be a leaky fitting.

My money is on a clogged fuel pickup. Many of them have screens on them and high fuel flow will cause gunk in the fuel to clog them. Pull the pickup and look at it.

[Redline452]

I would suspect the vent(s)... the polishing pump returns fuel to the tank while the engine drains it. The gender consumes much less so might take a lot longer to get to that point.