Fuel Pump

[Imthemole]

Short story: Boss has given me older la barisa (97). fuel not getting to carbarator. fuel pump appears to be initiating yet no fuel pressure in carb. Boat has not been run in 18 months. any suggestions?

[rludtke]

Well, carberators do not require fuel pressure, just flow. The float chamber is vented, and the fuel level within the chamber is controlled by a float controlled valve machanism simular to the float valve in your toilet tank. When adequate fuel level is reached, the float closes a valve and the fuel flow into the float chamber from the pump slows and stops. As the fuel is metered to the engine, and the float chamber level reduces, the float opens the valve (needels valve as it is called) and fuel enters the chamber to refill it.

Fuel will not flow into the float chamber if the float valve (needle valve) will not open, or if the needle seat is clogged, regardless of how much pressure the pump can create. Of course, the fuel pump is regulated to prevent excess pressure.

Do you know for sure that the pump is supplying fuel? You could disconect the fuel supply line at the carb and monitor it while cranking. If you get a good solid stream tof fuel then your pump may be ok. The next step would be to overhaul the carburator. Overhaul kits are availible from skidim for about $50, and I have found them on ebay stores for about $25. The kit supplies all of the critical internal parts that could be causing your carb problems. The orignal OEM carb for the PCM 351 is the Holley model 4160.

Cheers,

[Imthemole]

i followed ur instructions and there is no fuel getting to the carb at all. i disconnected and checked the valve and there is no pressure at all. fuel pump?

[rludtke]

i followed ur instructions and there is no fuel getting to the carb at all. i disconnected and checked the valve and there is no pressure at all. fuel pump?

Well, if no fuel is leaving the pump, then I think the pump is your culprit. The diaghram inside the pump may have dried out from sitting. Their is always the possibility that a fuel line is clogged up stream from your pump, preventing the pump from recieving fuel. Before you replace your pump, you might try disconnecting the fuel pump supply line and blow back to the tank with pressurized air, and listen at the filler cap for bubbling and/or air venting out.

If you have a fuel/water separator, you may need to disconnect the fuel lines at the separator, and blow back from the separator supply hose, as the air may not blow backwards through the separator. Getting air to flow through both supply hose segments (pump to separator, and separator to tank) will demonstrate that the hoses are clear.

Once clear, re-assemble and try cranking with the carb supply line disconnected again to see if fuel will pump out the carb supply line.

How old are your fuel lines? If old, you might just consider replacing them with new, as they will break down with age.

This check will demonstrate if your fuel delivery system is functioning, as it may not be. Clearing / replacing hoses is a lot cheaper than a buying a new pump if you don't need too. If the problem continues after checking the hoses, then I think you need a new pump.

What do you mean when you said you disconnected and checked the valve? Which valve? The needle valve is internal to the carb, is this the valve you disconnected? There are no other valves in the fuel system.

[Imthemole]

I checked the valve on the carb (outside). No fuel squirted out. That was initially. The pump appears to running which would lead me to believe it is not the problem. however, there is no fuel leaving the pump. I am going to check tonite and see if it is entering the pump. When I opened the bolt at the bottom of it, some fuel came out of it.

BTW - thanks for the suggestions. Kinda new to this...if you haven't guessed that already.

Is there anything online that would indicate the flow of the gas for this particular motor?

[Imthemole]

ok...i disconnected the lines at the carb from the small pressure pump...nothing. i tried to turn over and engage pump and got no gas flow at all. I disconnected the lines from the filter and was able to blow air up throught the lines so i dont think they are clogged. i checked the power source to the low pressure pump AND the high pressure pump and voltage was slightly over recommended amount. this leads me to believe that the low pressure pump is out. am i on the right track?

[rludtke]

I must admit that I am a little confused, I was giving you advice on carburators, when I now think you have fuel injection. You mentioned two pumps, a low pressure and a high pressure. Are both of these pumps electric? Typically electric pumps are used in fuel injection systems, because a mechanical pump will not generate adequate pressure early enough in the starting sequence. Electric pumps will pressure up immediatly after they are turned on, and they can be turned on before the engine begins cranking, which is required for starting a fuel injected engine.

Fuel injection requires a minimum pressure, much higher than carburators do, in order to start. In fact, the fuel pressure must be high enough to overcome a pressure sensing flow shut-off valve, so that the fuel flow won't trickle up during start up, or trickle down during shut down. This valve could be problematic. Either pump could be problematic as well. You will want to be sure that the electric pump(s) do indeed function when the key is turned to the run position. Because they are electric, you may have wiring problems preventing a pump from running, so be sure to check that out. Both pumps should trun on when the key switch is turned to the run position. If the pumps run they will most likely move fuel, but to be sure remove hoses from each pump (one at a time) and monitor the pump output for fuel flow.

If the pumps work, then your troubles may be with the Fuel Injection system. Is this a throttle body injection system, or port injection?

[Imthemole]

i have changed out the low pressure pump and still cant get fuel stream. it is now functioning because it now clicks on. Still cant get a stream. Im sure there is no clog. I cant seem to figure this out and its pissing me off. Why would the fuel not pump through the lines if the pump is working? Filter is good. starts when there is gas in carb but i cant seem to get gas to it. i hate to take it to the shop because i know its something i can fix. very frustrated

[fastab]

What engine is in this, and is it a fuel injected or carbed engine, they will run different delivery systems as mentioned in previous replies. Have you checked things like the fuel filter and pickup, is the gas tank venting? Is there any kinks in the fuel lines. Is the anti-siphon valve functioning properly?

[rludtke]

Yep, what Fastab said. Fuel pumps, both mechanical and electric have by-pass features which limit the output pressure, and allow fuel to bypass from the outlet of the pump back to the inlet of the pump. This protects the pump when the outlet is clogged and fuel can't flow. This could be the reason that fuel does not flow when the electric pump is turned on, and you can hear it running. The line downstream of the pump may be obstructed.

The line upstream of the pump may also be obstructed, preventing fuel from reaching the pump. This could do damage to the pump, as it may overheat without fuel for cooling.

Make sure all lines and equipment allow fuel to pass. Replace hoses if they are old, or blow them out if the are relatively new.

[Imthemole]

okay...fuel is coming from everywhere except the fuel pump i just changed. at one point fuel came through it, then stopped when i did it manually (with a hand pump). I have fuel all the way to it, but not through it. remember, it is a new pump. there is about 2 inches of hose from the t bar to the low pressure pump. i can create suck but it wont suck fuel...only air. im so confused...please dont give up on me yet. feel like im close!!!

[fastab]

What engine/fuel system do you Have? Each system will have different requiremnets for fuel delivery. Multi port will run a lot higher fuel pressure than tbi and it runs higher pressure than a carbed engine.

If you take the fuel pump out and stick a line on the pump and put it in a jerry can of fuel does it pump? How high can you go before it doesn't pump.