4.3 LX Fuel Pump
 

Does anyone know if the electric fuel pump on the 4.3LX should come on with the key in the on position?

Re: 4.3 LX Fuel Pump
 

It should come on. Mine does!

Re: 4.3 LX Fuel Pump
 

Thanks for the answer. My boat is extremely hard to start when it hasn't run for a few days. My fuel pump doesn't come on at all it seems. The pump still works, I was able to get it to run by connecting it directly to the battery. I'm guessing I have a bad connection or ground going to the fuel pump. Once I get the motor running it runs like a charm and doesn't have any problem being restarted....

Re: 4.3 LX Fuel Pump
 

Have you checked the breaker by the motor? I just read about someone having a short between that breaker and the pump. They said it was rubbing on the manifold. Good Luck!

Re: 4.3 LX Fuel Pump
 

I don't know a lot about the 4.3LX engine so bear with me. I am assuming that you have an electric fuel pump. Some engines with an electric fuel pump have an oil pressure sensor with a relay that turns on the electric fuel pump when the engine turns over (producing oil pressure and activating the pump) , and some do not. If your engine has this pressure sensor safety feature it would not pump fuel just because the key is on. Hope this helps

Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

The breaker has not been tripped. I'll have to check and see if I have the oil pressure switch as well.

Re: 4.3 LX Fuel Pump
 

My 4.3 electric fuel pump doesnt turn on until it senses oil pressure. My guess would be to check the choke to see if its working properly since youre dealing with a cold start issue.

Re: 4.3 LX Fuel Pump
 

I've checked the choke. It's staying closed when trying to start. When I pump the throttle I don't see any fuel squirting into the carb...

Re: 4.3 LX Fuel Pump
 

I read on another forum that there is another hot wire that goes from the starter solenoid to the fuel pump that turns on the pump momentarily when the starter is engaged to help prime the carb. I can't remember the the forum though. I found it by googling "does the 4.3lx have a fuel pump relay". Sounds like you might need to find an engine wiring diagram that shows this part of your system.

Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

Just had the exact same problem, took hoses off and jumpered out relay pump. Pump seemed to struggle pumping would only run for a few seconds. Kept trying and all of a sudden a splurt of gas came out of hose and everything works fine now, suspect something may have got caught in fuel pump (but not sure). Pump sounds good now, my pump does not come on until the engine turns over must be connected to starting sytem.

Re: 4.3 LX Fuel Pump
 

Did a littlel more trouble shooting today. The power for the Electric fuel pump runs off the Starter Solenoid. I was able to hot wire the pump on direct from the battery and the motor started fine. After the motor was running I put a volt meter on the power wire going to the pump and it was only reading 2 Volts. I put the probes on the starter solenoid where the power for the pump attaches and it was reading 2 Volts as well. I'm assuming I should have 12 volts running through to the pump at all times correct?

Re: 4.3 LX Fuel Pump
 

There may be a secondary power source coming off the oil pressure sensor. The starter activation of the pump is probably only momentary when the engine it turning over. Just something to check on.
Good Luck
Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

Ok, still trouble shooting. Checked the voltage at the fuel pump again when cranking. Shows 12 Volts now. Oil pressure switch is fine, shows 12 volts on each side of switch. Motor still won't fire up cold, unless I hot wire the fuel pump direct to the battery to prime the carb. Looks like I'm going to have to hook up one of the Ancillary switches direct to the fuel pump to prime it when the engine is cold....

Re: 4.3 LX Fuel Pump
 

If you could describe you normal cold start routine. Are both the choke and the accelerator pump on you carb working properly? I ask this because running direct power to the fuel pump can mask certain problems. 12v to the pump when the engaging the starter should be no different than putting a switch in the circuit, either one should properly energize the pump. 12V on each side of the oil pressure switch should be only when the engine is running. Is this what you mean when u say oil pressure switch is fine? Let me know what you find out.
Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

My normal start routine is to move the throttle to the stops then pull it back to it's 1/4 open position and try to start. I've also tried giving it 2, 3, + Pumps of the throttle and none of the above seem to work. I agree that putting a switch in the fuel pump line and just turning the starter should do the same thing, not sure why it doesn't seem to work though. Yes, when the engine is running and I check the voltage on the oil pressure switch I'm getting 12 Volts on both sides of the switch. The choke seems to be working fine, it's closed almost all the way when starting it cold. I'm not sure about the accelerator pump though. How do you test the accelerator pump?

Re: 4.3 LX Fuel Pump
 

You said earlier that when u pump the throttle u dont see in fuel squirting into the carb. That is the way I test the system too. The carb bowls have to contain fuel first. Remove the flame arrestor, look into the carb with a flashlight,have a buddy work the throttle fully open and fully closed a couple of times, look and listen if it squirts it should be good. Another indication is if u get a momentary stall on the water when you rapidly advance the throttle on takeoff. The only problems I see with a toggle switch controlling you fuel pump would be that it could force fuel through the carb into the engine, and if you ever forget to turn off the switch after killing the motor you could fill you motor up with fuel. Let me know how it goes.
Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

I checked the carb again tonight. Each time we pump the throttle we get one drop of gas goes into the carb. I do get the momentary stall on the water as well when I pass about 1/2 throttle or so, then it runs great again..

Re: 4.3 LX Fuel Pump
 

From everything you have said I am thinking accelerator pump. If the carb is full of fuel, you should get a spurt/stream of fuel squirting into the carb , much more than one drop. You may want to do a carb kit since you have to take off the top to change the accelerator pump. The service procedures for your motor are on page 3 of the mercruiser manuals section of the forum. If you do a rebuild, follow the steps exactly. And make sure it is completely clean before reassembly. Where it says measure a linkage, do it. That is an area where many people mess up, and if one component is not in spec it can mess up the function of the carb. If you decide you still want to be able to activate the fuel pump manually, I would do it with a push button and not a toggle switch, that way you wont have to worry about leaving it on accidently. Mid range stall can be caused by a couple of other things too, but I would get the carb straight first. Let me know how things are going
Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

Sorry if I missed it, but have you changed the fuel filter? Since you are getting some fuel to the carb and not a nice flow, could there be a restriction? Filter, something stuck in the line maybe?

Re: 4.3 LX Fuel Pump
 

I've already checked the fuel filter, I think it's fine, when I took the fuel line off coming from the filter and ran the fuel pump, it had a good stream of gas coming out. I'll see if I can find a carb kit somewhere and rebuild it, hopefully it's just an accelerator pump issue.

Re: 4.3 LX Fuel Pump
 

Replace it, how do you have confidence in checking it?:confused:

Re: 4.3 LX Fuel Pump
 

I figure it's fine, because the only issue with the boat is cold starting. And a momentary loss of power when pushing the power up. Other than that it runs fine all day. If there was an issue with the fuel filter I would suspect there would be issues running the boat wide open which there isn't.

Re: 4.3 LX Fuel Pump
 

Napa sells a rebuild kit for around $40 and the only thing you would need is a gasket from the carb to manifold ($5). There are 2 filters where the fuel line meets the carb. 1 on each side that filter before it fills up the bowls. My filter on the opposite side of the fuel line was nasty! water also got in there and formed some rust on the primaries and secondaries. This kit (Napa 2-5763A) came with everything but the right gasket I stated above, even comes with the acc pump. It will save you about $100 or so.
Good Luck!

Re: 4.3 LX Fuel Pump
 

Ok, I should have tried this before ordering the carb kit, oh well. I took off the fuel line from the fuel pump and checked to see if any fuel was flowing from it when cranking the engine. Nothing is coming from the fuel pump while cranking. Took the electrical connector off the pump and cranked engine again. Shows about 9-10 volts at the connector. Tried connecting the fuel pump directly to the battery (with alligator clips) and a steady stream of gas comes out . Tried connecting the electrical plug for the fuel pump again and no fuel coming out. Still shows about 10 Volts at the connector though... So what are the chances there is something wrong with the electrical connector? Maybe it's not making a good contact with the connector on the pump itself.... Anyone?

Re: 4.3 LX Fuel Pump
 

You will have some voltage drop when cranking just from the drag of the starter. If the motor spins fine it could be a bad connection from the starter to the pump wire, a bad pump wire, or something internal to the starter solenoid. I would make sure all of the connections are clean. I don't think a 2 volt drop should be enough to prevent the pump from filling the carb though. These dang boats can be aggravating can't they. Let me know what you find out.
Happy Boating
Dan

Re: 4.3 LX Fuel Pump
 

When I get back home, I'll check to make sure all the connections are clean. I'm thinking it's the plug that goes into the pump that is the issue. Maybe it's not making good contact with the pins receptacles in the pump...