After months of persistant problems of either air in my fuel line and/or gunk getting into my diesel I have purchased an in line fuel pump to pressurize the fuel intake. I know I have a lifter pump on my engine, nut I have read several posts where people say this helps. Does anybody see a downside to this? I have done the following to the engine: new racor (9 micron) new lifter pump, rebuild of injectors, new hoses. Fuel looks fine and engine runs after being bled. However, thirty minutes of run time and suddenly the rpms "walk up then down" with gradual loss of power and eventually she dies. Since purchase of the additional pump,I have not been down to my boat to check where I might run the fuel return back into the tank. Any suggestions? I am assuming I can put a "t" in the hose between my secondary filter and my injectors and run that back to the tank. Should I put the pump before the primary filter or after the primary filter? Please help, I don't want to be stuck in my slip over Memorial weekend.
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Fuel Pump
If I understand what you are saying here, I think your barking up the wrong tree. Since you stated that the system needs to be bled regularly, I would be looking for an air leak in the system. But if you mount a pump near the tank, I think you will soon find your air leak. As it is apparently sucking air, the leak has to be between the pump and the tank.
If I understand what you are saying here, I think your barking up the wrong tree. Since you stated that the system needs to be bled regularly, I would be looking for an air leak in the system. But if you mount a pump near the tank, I think you will soon find your air leak. As it is apparently sucking air, the leak has to be between the pump and the tank.
One more thought
You stated that you have replaced the fuel hoses, and again making an assumption, I presume all hoses. This being the case, I would check the pickup in the tank. Does it do this with a completely full tank, half tank etc.
You stated that you have replaced the fuel hoses, and again making an assumption, I presume all hoses. This being the case, I would check the pickup in the tank. Does it do this with a completely full tank, half tank etc.
Thanks
Thanks for the toughts. I have not checked the pick up line. The problem started after I filled the tank up the first time since buying the boat (1979). Maybe the pick up line is blocked. My first mechanic ruled out gunk in the tank, but maybe he didn't check either. I thought by pressureizing the system it would be less affected by any air leaks. Overall I thought the auxilliary pump would give my old boat "more margin for error". Is this incorrect?
Thanks for the toughts. I have not checked the pick up line. The problem started after I filled the tank up the first time since buying the boat (1979). Maybe the pick up line is blocked. My first mechanic ruled out gunk in the tank, but maybe he didn't check either. I thought by pressureizing the system it would be less affected by any air leaks. Overall I thought the auxilliary pump would give my old boat "more margin for error". Is this incorrect?
Contant bleeding means LEAK
Constant requirement for bleeding clearly indicates a leak. If you recently changed the filters, start there and reinstall new filter gaskets. If you changed the retention size of the filter media ..... going from larger retention to a smaller retention (usually a BAD idea).... ie: going from 10 to 2µM will greatly aggravate any air leak as it requires MORE differential pressure (vacuum force) to make the smaller filter 'work'. The flat gasket seals on filter housings are notoriously easy to damage when installing, especially if you didnt lubricate them with oil before assembly. LIft pumps can develop pin-holes in the diaphragm. All the delivery tube fittings are very subject to leakage.... compression fittings relax and are easy to crack when tightening, flared (better than compression fittings) can also leak if they werent 'smoothed' after the flairing process- also easy to crack when tightening. To keep things simple - assume that the fuel system was intact before you started your maintenance. Go back and carefully check and reinstall ALL those connections and filters that you installed ... looking for micro-rips in gaskets (install NEW gaskets and lubricate them with oil), stripped threads in fittings or cracked fittings that were 'overtightened'. Examine all the fittings with a powerful magnifying glass .... looking for teeny 'lines' across the nuts - that shouldnt be there. I give it a 99% chance that the air leak is between the lift pump and the filter closest to the tank. Probably a fitting that you recently tightened. DO NOT use a teflon pipe dope, teflon tape is OK if you have to but NOT dope. Best is to assemable the fittings 'dry'.
Constant requirement for bleeding clearly indicates a leak. If you recently changed the filters, start there and reinstall new filter gaskets. If you changed the retention size of the filter media ..... going from larger retention to a smaller retention (usually a BAD idea).... ie: going from 10 to 2µM will greatly aggravate any air leak as it requires MORE differential pressure (vacuum force) to make the smaller filter 'work'. The flat gasket seals on filter housings are notoriously easy to damage when installing, especially if you didnt lubricate them with oil before assembly. LIft pumps can develop pin-holes in the diaphragm. All the delivery tube fittings are very subject to leakage.... compression fittings relax and are easy to crack when tightening, flared (better than compression fittings) can also leak if they werent 'smoothed' after the flairing process- also easy to crack when tightening. To keep things simple - assume that the fuel system was intact before you started your maintenance. Go back and carefully check and reinstall ALL those connections and filters that you installed ... looking for micro-rips in gaskets (install NEW gaskets and lubricate them with oil), stripped threads in fittings or cracked fittings that were 'overtightened'. Examine all the fittings with a powerful magnifying glass .... looking for teeny 'lines' across the nuts - that shouldnt be there. I give it a 99% chance that the air leak is between the lift pump and the filter closest to the tank. Probably a fitting that you recently tightened. DO NOT use a teflon pipe dope, teflon tape is OK if you have to but NOT dope. Best is to assemable the fittings 'dry'.
Location of electric pump......
Put the electric pump between the tank and the FIRST filter. Easier to bleed the filters when changing. Leave the electric pump OFF when the engine is running ... the orientation of pump valves will allow the fuel to flow through the pump without it working. Lift pumps and auxiliary electrical pumps are usuallly located between the filters and the engine - creates a vacuum motive force in the lines and if (when) you develop a leak, the system will suck air and shut down. The danger with putting a pump between the tank and the first filter is that if its operating and a fitting 'lets go' you will fill the bilge with oil. Filters will do a better job in particle retention and will last LONGER in service if they are pressure fed (pump delivering TO the filters) ... the risk is oil in the bilge and big bill to be paid to the EPA and USCG for oil cleanup. Your choice - my electro pump is on the tank it just sits there hardly ever energized and is a standby back up if the lift pump ever fails; plus, I can very quickly bleed the whole system in a matter of seconds. Dont leave such a pump ON .... intermittent bleeding or emergencies only. If the electric pump is at the tank, you can with the engine off energize the electric, pressurize the system and look for oil coming from a leak !!!!! BTW - make sure that such a pump is constructed with EPDM (EthylenePropyleneDiamineMonomer) gaskets, seals and diaphragm .... longer lasting and more chemically compatible with fuel oil than Buna, Neoprene, etc. Most auto shops willhave NO idea what the 'rubber' components of an electric pump are.
Put the electric pump between the tank and the FIRST filter. Easier to bleed the filters when changing. Leave the electric pump OFF when the engine is running ... the orientation of pump valves will allow the fuel to flow through the pump without it working. Lift pumps and auxiliary electrical pumps are usuallly located between the filters and the engine - creates a vacuum motive force in the lines and if (when) you develop a leak, the system will suck air and shut down. The danger with putting a pump between the tank and the first filter is that if its operating and a fitting 'lets go' you will fill the bilge with oil. Filters will do a better job in particle retention and will last LONGER in service if they are pressure fed (pump delivering TO the filters) ... the risk is oil in the bilge and big bill to be paid to the EPA and USCG for oil cleanup. Your choice - my electro pump is on the tank it just sits there hardly ever energized and is a standby back up if the lift pump ever fails; plus, I can very quickly bleed the whole system in a matter of seconds. Dont leave such a pump ON .... intermittent bleeding or emergencies only. If the electric pump is at the tank, you can with the engine off energize the electric, pressurize the system and look for oil coming from a leak !!!!! BTW - make sure that such a pump is constructed with EPDM (EthylenePropyleneDiamineMonomer) gaskets, seals and diaphragm .... longer lasting and more chemically compatible with fuel oil than Buna, Neoprene, etc. Most auto shops willhave NO idea what the 'rubber' components of an electric pump are.
Pressure in the system
Harvey, If you put pressure in the system, behind an air leak, then you will have a fuel leak. If you put a pump in front of an air leak, you will still have an air leak. Look at it this way, a leak with vacum on it will suck air, that same lead with pressure on it will leak fuel.
Harvey, If you put pressure in the system, behind an air leak, then you will have a fuel leak. If you put a pump in front of an air leak, you will still have an air leak. Look at it this way, a leak with vacum on it will suck air, that same lead with pressure on it will leak fuel.
Fuel Pumps
Electric fuel pumps usually have these little filters inside and on the bottom. Most boat builders incorrectly place them before the first filter. This is wrong, since the little filters in the fuel pump get gunk-ed up. The first filter should be before the electric fuel pump. As far as pumping and filling the filter with the pump, it makes no difference whether the pump is before or after the first filter - it's a pumping system: fuel tank to filter to pump to engine; the pump, if installed in that order, will pull fuel through the filter. I have re-plumbed our boat this way and don't even fill the filter with fuel before I install a new one. I put the new filter on, then turn on the fuel pump and easily bleed the engine. Stu
Electric fuel pumps usually have these little filters inside and on the bottom. Most boat builders incorrectly place them before the first filter. This is wrong, since the little filters in the fuel pump get gunk-ed up. The first filter should be before the electric fuel pump. As far as pumping and filling the filter with the pump, it makes no difference whether the pump is before or after the first filter - it's a pumping system: fuel tank to filter to pump to engine; the pump, if installed in that order, will pull fuel through the filter. I have re-plumbed our boat this way and don't even fill the filter with fuel before I install a new one. I put the new filter on, then turn on the fuel pump and easily bleed the engine. Stu
Not necessarily true ......
Stu - The reason for the pump in front (upstream) of the first filter is that when you pull a vacuum is that you 'may' start to 'boil' the fluid (vapor pressure) and cause any dissolved gasses in the fluid to come out of solution ... hence more bubbles. Pressure will cause any bubbles to collapse or 'coalesce' and stay in solution so that the disolved gas portion goes all the way through to the combustion chamber and never forms a 'gas bubble'. When this happens with gasoline on an automobile, we call it 'vaporlock'. Those 'filters' on such pumps are not filters per se but are 'screens' so sized to prevent 'chunks' from passing through and getting stuck in the pump (check) valves ... thus making the pump inoperative.
Stu - The reason for the pump in front (upstream) of the first filter is that when you pull a vacuum is that you 'may' start to 'boil' the fluid (vapor pressure) and cause any dissolved gasses in the fluid to come out of solution ... hence more bubbles. Pressure will cause any bubbles to collapse or 'coalesce' and stay in solution so that the disolved gas portion goes all the way through to the combustion chamber and never forms a 'gas bubble'. When this happens with gasoline on an automobile, we call it 'vaporlock'. Those 'filters' on such pumps are not filters per se but are 'screens' so sized to prevent 'chunks' from passing through and getting stuck in the pump (check) valves ... thus making the pump inoperative.
Screens
Rich, I agree about the nomenclature of the "filters" in the pumps as "screens." They do, however, tend to get plugged up. As an engineer, I agree wholeheartedly, philosophically and rationally with your analysis about pumps, which includes negative suction head and velocity pressures (for those who care about these mundane but important pump selection engineering issues). It, however, doesn't enter into this conversation because of the fact that the atmospheric pressure on the tank and therefore the pressure to the pump more than compensates for the friction loss through the piping from the tank to the pump, including the filter first. It is also the setup on just about every diesel truck ever made - if the pump was ahead of the filter, the driver's'd be pulling fuel pumps off to clean their screens all the time. Again, it works, and we have suggested to all of our association members to make the "correction" to their factory installed piping to avoid a shutdown of their engines because of clogged pump screens. I don't know if Catalina is still doing it backwards out of the factory, but I'll check a new boat in the near future and report back. I believe the C36s do so as well. Stu
Rich, I agree about the nomenclature of the "filters" in the pumps as "screens." They do, however, tend to get plugged up. As an engineer, I agree wholeheartedly, philosophically and rationally with your analysis about pumps, which includes negative suction head and velocity pressures (for those who care about these mundane but important pump selection engineering issues). It, however, doesn't enter into this conversation because of the fact that the atmospheric pressure on the tank and therefore the pressure to the pump more than compensates for the friction loss through the piping from the tank to the pump, including the filter first. It is also the setup on just about every diesel truck ever made - if the pump was ahead of the filter, the driver's'd be pulling fuel pumps off to clean their screens all the time. Again, it works, and we have suggested to all of our association members to make the "correction" to their factory installed piping to avoid a shutdown of their engines because of clogged pump screens. I don't know if Catalina is still doing it backwards out of the factory, but I'll check a new boat in the near future and report back. I believe the C36s do so as well. Stu
Fuel pumps, filters, etc.
I'm glad I followed this discussion all the way to Stu's post, because that is the way my boats have been arranged for several decades. What i'm going to do now is stop reading any more discussion on the matter. Incidentally, I do not understand why any filter reacts differently to upstream and downstream pumps. It passes fuel because the pressure at the inlet is higher than at the outlet. What difference does it make how that is effected? The original post asked about the fuel return, and suggested a tee between the second filter and the injector pump. Usually engines come with a hose connection in that area, don't they? Anyway, I installed a tee at the vent fitting on the tank and ran the return to it.
I'm glad I followed this discussion all the way to Stu's post, because that is the way my boats have been arranged for several decades. What i'm going to do now is stop reading any more discussion on the matter. Incidentally, I do not understand why any filter reacts differently to upstream and downstream pumps. It passes fuel because the pressure at the inlet is higher than at the outlet. What difference does it make how that is effected? The original post asked about the fuel return, and suggested a tee between the second filter and the injector pump. Usually engines come with a hose connection in that area, don't they? Anyway, I installed a tee at the vent fitting on the tank and ran the return to it.
THE SAGA CONTINUES
Thanks for the advice guys. Since my last post I found the vent to be clogged with either carbon or dirt dobber nest. Thinking I had solved the problem (the engine ran like a top for 40 minutes in gear/tied in the slip) we departed Memorial day. made a Portside turn and she started "walking down and up" again. Air again in the system. My mechanic now says he traced the fuel system back to the pick-up tube and everything seems to be in order to that point. However, the position of the tank and the build of the boat necessatates the pick up tube enter at a narrow angle. He calculates that at 30 degrees the pick up tube is not in the fuel. However, my diesel problems occur when motoring and I'm not at 30 degrees. He thinks the sloshing may cause the pick up tube to suck air. the Yanmar 3QM30 will not vent air off because there is no return. His suggestion is to put a "day tank" in the boat and run an electric pump from the "big tank" to the day tank. But where do we put the excess fuel return? I thought I'd put this out to the "brain trust". I think this mechanic knows his stuff, but I wonder why this problem wasn't addressed in the previous 26 years of the boat's life.
Thanks for the advice guys. Since my last post I found the vent to be clogged with either carbon or dirt dobber nest. Thinking I had solved the problem (the engine ran like a top for 40 minutes in gear/tied in the slip) we departed Memorial day. made a Portside turn and she started "walking down and up" again. Air again in the system. My mechanic now says he traced the fuel system back to the pick-up tube and everything seems to be in order to that point. However, the position of the tank and the build of the boat necessatates the pick up tube enter at a narrow angle. He calculates that at 30 degrees the pick up tube is not in the fuel. However, my diesel problems occur when motoring and I'm not at 30 degrees. He thinks the sloshing may cause the pick up tube to suck air. the Yanmar 3QM30 will not vent air off because there is no return. His suggestion is to put a "day tank" in the boat and run an electric pump from the "big tank" to the day tank. But where do we put the excess fuel return? I thought I'd put this out to the "brain trust". I think this mechanic knows his stuff, but I wonder why this problem wasn't addressed in the previous 26 years of the boat's life.
give this a try
run the engine off a two gallon can right to the lift pump. leave the return hooked to the main tank. if the problem goes away and with all the new parts you have it might be a clogged pick-up tube in the tank. you can use compressed air to blow back into the tank to clear it. my only other thought is a hole in the side of the pick-up tube. note tank level when the problem occures. rich b
run the engine off a two gallon can right to the lift pump. leave the return hooked to the main tank. if the problem goes away and with all the new parts you have it might be a clogged pick-up tube in the tank. you can use compressed air to blow back into the tank to clear it. my only other thought is a hole in the side of the pick-up tube. note tank level when the problem occures. rich b
Thanks guys! New question?
It was/ is the pick up tube. I think I might just go ahead and put a new fuel tank in. The current tank doesn't not allow for good placement due to the cockpit coaming and required height of the tank. Has there ever been debate on this thread about copper versus flexible pick up lines?
It was/ is the pick up tube. I think I might just go ahead and put a new fuel tank in. The current tank doesn't not allow for good placement due to the cockpit coaming and required height of the tank. Has there ever been debate on this thread about copper versus flexible pick up lines?
bad pickup
Have you checked the fuel in your tank. We had same type of problem and it was large pieces of junk blocking pickup.Cleaned out tank helped solve problem.If your boat is ok at the dock but not when you moving it could be this.It creates such a vaccum even if your system is ok you will find air. Good luck
Have you checked the fuel in your tank. We had same type of problem and it was large pieces of junk blocking pickup.Cleaned out tank helped solve problem.If your boat is ok at the dock but not when you moving it could be this.It creates such a vaccum even if your system is ok you will find air. Good luck
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