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.