thanks to everyone who has posted potential sources of my perkins engine fuel problem. i discovered that the low pressure electric fuel pump has not dispensing very much fuel when i disconnected the 'out' hose and turned the pump on. i by passed that pump and just let the lift pump on the engine do its thing. the engine started right up,,,and ran very well. however, when i increased the throttle,,,the rpms only went so far,,,and the boat speed did not increase. after motoring about for awhile,,,with no sputters,,,the engine started to over heat. ive read somewhere before that this is due to running the engine 'lean',,,ie not enough fuel to burn. backing down on the throttle,,,the temp guage went down. i never messed with the high presure injector pump,,,so i didnt disrupt anything there. i thought the low pressure pump was an add on to help in priming/bleeding the engine. am i mistaken here,,,and is this pump necessary to supply the injector pump with the right amount of fuel. i read another post ,,,different forum,,, that the diaphram in the lift pump could be weak. might be worth checking out. comments please. rick MERLIN
perkins 4-108
- Thread starter rick19286
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Sounds like a restriction ......
... somewhere between the lift pump and the dip-tube on the tank. Could also be a blocked vent line on the tank. 1. If you have gauges on the filter set and they are reading high vacuum, then the restriction is between the screen on the diptube in the tank and the downstream side of the filters. If the vacuum slowly increases to high vacuum then the tank vent may be blocked (spider nest or mud dauber, etc.). Just because a filter looks clean is no guarantee that it isnt blocked .... as soft particles can get deeply into the filter media and block it with little visual surface deposition of particles. Blockages easily form (grow) in the tubing as copper is incompatible with diesel oil (its a catalyst for degneration/oxidation, etc.), especially if the tank oil is beyond one year old. The copper can be the 'instigator' to form a 'zone' of sludge 'dropout' in the tube and the restriction gets progressively worse as particulate (even downstream of the filter) agglomerates and makes larger and large particles (particles can 'grow' in size). Many boats have a simple screen over the dip tube inlet thats inside the tank. Particles can agglomerate and 'bridge' such a screen - disconnect the delivery piping downstream and BLOW into the dip-tube piping to make sure its clear. Then, proceed towards the engine by removing the tubing sections and BLOWING through them to ensusre no blockage until you reach the filters. Depending on the manufacturer and the filter housing design .... it is possible to block a filter with AIR. If after you install a new filter and air gets trapped inside the 'bowl' of the filter, that bubble can make the filter media surface unavailable for the oil to flowthrough it. This is especially possible in smaller retention rating filters such as 1µM - 2µM. How to analyse for an 'air-bound' filter. Drain and remove the filter and keep it oriented verticallly; look at the bottom of the filter element and compare the color and the surface deposition on the surface of the 'pleats'. If there is a distinct color or deposition difference (especially a distinct 'zone' difference between the top and bottom of the pleats, then the filter may be simply air blocked. A filter that is operating with a 'bubble' may even have relatively clean areas on the pleats toward the 'top' of the filter element. On a spin-on type of filter, you willhave to cut the outter shell away to observe the pleats. This is quite a rare phenomenon on the crude filters used in oil filtration ... but it 'can' happen. The 'usual' compression fittings on copper boat delivery system are notorious for vibrating loose .... and sucking air when under high vacuum. The remedy is to change to a self venting type of filter system such as one of the later design Racors. Suspect air blockage anytime the in/out connections are on the BOTTOM of the filter or you find a 'loose' compression fitting upstream of the filter. Most common locations of blockage: Mud dauber built a nest in the vent cowl. dip-tube screen is fouled or collapsed, a 'plug' of Gels/wax/or bacteria are growing in a 'low spot' in the tubing - especially near any connection fitting or shut-off valve. Once you do find the restriction/blockage, consider to replace all the pump diaphragms as high load/low flow rapdily reduces the service life of the polymer diaphragms. IF you do find a blockage in the delivery piping consider to replace the whole run of tube with stainless tube with FLARED (not compression) fittings .... and be sure that the filter set is the LOWEST part of the system - so that any water that drops out of the oil will run to the filter by gravity and collect in the filter bowl. Choose a filter housing that you can periodically manually drain the water from it. Just be methodical in looking for the blockage ... start at the tank vent and work your way towards the engine .... you'll find it - and you'll soom learn what diesel oil tastes like. <g> When was the last time you SCRUBBED the inside of the tank ... should be done every ~5 years. Hope this helps.
... somewhere between the lift pump and the dip-tube on the tank. Could also be a blocked vent line on the tank. 1. If you have gauges on the filter set and they are reading high vacuum, then the restriction is between the screen on the diptube in the tank and the downstream side of the filters. If the vacuum slowly increases to high vacuum then the tank vent may be blocked (spider nest or mud dauber, etc.). Just because a filter looks clean is no guarantee that it isnt blocked .... as soft particles can get deeply into the filter media and block it with little visual surface deposition of particles. Blockages easily form (grow) in the tubing as copper is incompatible with diesel oil (its a catalyst for degneration/oxidation, etc.), especially if the tank oil is beyond one year old. The copper can be the 'instigator' to form a 'zone' of sludge 'dropout' in the tube and the restriction gets progressively worse as particulate (even downstream of the filter) agglomerates and makes larger and large particles (particles can 'grow' in size). Many boats have a simple screen over the dip tube inlet thats inside the tank. Particles can agglomerate and 'bridge' such a screen - disconnect the delivery piping downstream and BLOW into the dip-tube piping to make sure its clear. Then, proceed towards the engine by removing the tubing sections and BLOWING through them to ensusre no blockage until you reach the filters. Depending on the manufacturer and the filter housing design .... it is possible to block a filter with AIR. If after you install a new filter and air gets trapped inside the 'bowl' of the filter, that bubble can make the filter media surface unavailable for the oil to flowthrough it. This is especially possible in smaller retention rating filters such as 1µM - 2µM. How to analyse for an 'air-bound' filter. Drain and remove the filter and keep it oriented verticallly; look at the bottom of the filter element and compare the color and the surface deposition on the surface of the 'pleats'. If there is a distinct color or deposition difference (especially a distinct 'zone' difference between the top and bottom of the pleats, then the filter may be simply air blocked. A filter that is operating with a 'bubble' may even have relatively clean areas on the pleats toward the 'top' of the filter element. On a spin-on type of filter, you willhave to cut the outter shell away to observe the pleats. This is quite a rare phenomenon on the crude filters used in oil filtration ... but it 'can' happen. The 'usual' compression fittings on copper boat delivery system are notorious for vibrating loose .... and sucking air when under high vacuum. The remedy is to change to a self venting type of filter system such as one of the later design Racors. Suspect air blockage anytime the in/out connections are on the BOTTOM of the filter or you find a 'loose' compression fitting upstream of the filter. Most common locations of blockage: Mud dauber built a nest in the vent cowl. dip-tube screen is fouled or collapsed, a 'plug' of Gels/wax/or bacteria are growing in a 'low spot' in the tubing - especially near any connection fitting or shut-off valve. Once you do find the restriction/blockage, consider to replace all the pump diaphragms as high load/low flow rapdily reduces the service life of the polymer diaphragms. IF you do find a blockage in the delivery piping consider to replace the whole run of tube with stainless tube with FLARED (not compression) fittings .... and be sure that the filter set is the LOWEST part of the system - so that any water that drops out of the oil will run to the filter by gravity and collect in the filter bowl. Choose a filter housing that you can periodically manually drain the water from it. Just be methodical in looking for the blockage ... start at the tank vent and work your way towards the engine .... you'll find it - and you'll soom learn what diesel oil tastes like. <g> When was the last time you SCRUBBED the inside of the tank ... should be done every ~5 years. Hope this helps.
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