Mercruiser 4.3LX Will not start (fuel issue)

1995 Rinker 190 with Mercruiser 4.3LX

This past holiday weekend, I took my boat out on Saturday, it was really difficult to cold start upon launch (hadn't really had too much trouble in the past), but the boat ran great all day, started fine after anchoring and floating, etc. Took the boat out to the lake on Sunday, launched it, it fired right up off of the trailer then idled for 10 seconds and stalled. After this, it absolutely would not start. Got some starting spray, sprayed it right down the carb barrels and it would run for a few seconds while burning the spray then stall. I bought a fuel separating filter from the marina, swapped it out, but that wasn't it. With the air "filter" removed, I can see the carb is totally dry (no fuel). Even when pumping the throttle arm, I am not seeing any fuel whatsoever down the carb. Not only did it suck that I was dead in the water, but even moreso that I had friends come meet me at the lake and I lost a prime Holiday boating day

Can I please get some help?

Re: Mercruiser 4.3LX Will not start (fuel issue)

Could use a serial number but your boat probably has a mechanical fuel pump, correct?
If so, when you pulled the fuel filter was if full of gas?
When you installed the new one did you prime the filter or just put it on and let the engine try filling by cranking the engine?
Pull the fuel filter back off and if not full of fuel fill it and reinstall. Pull the fuel line off the carb and see if you can get fuel to come out while cranking. If no fuel comes out, pull the line between the pump and filter and see if fuel comes while cranking. If no fuel pull fuel pump and check it.

Re: Mercruiser 4.3LX Will not start (fuel issue)

AllDodge said:

Could use a serial number but your boat probably has a mechanical fuel pump, correct?
If so, when you pulled the fuel filter was if full of gas?
When you installed the new one did you prime the filter or just put it on and let the engine try filling by cranking the engine?
Pull the fuel filter back off and if not full of fuel fill it and reinstall. Pull the fuel line off the carb and see if you can get fuel to come out while cranking. If no fuel comes out, pull the line between the pump and filter and see if fuel comes while cranking. If no fuel pull fuel pump and check it.

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I would think it is electronic, no? I did not prime the filter when I installed it. The old one was full of gas, but the engine didn't do anything different when I changed the filter....that shouuld be my first thing to try (fill filter and put it back on)?

Re: Mercruiser 4.3LX Will not start (fuel issue)

My 4.3lx is electric. I have found the electrical connector to the pump not making good contact. I have bent the tabs inside the connector on the wires so they make contact. The pump would run sometimes then quit. I can hear my pump run before starting because the power to it has been bypassed around the oil pressure switch.

Re: Mercruiser 4.3LX Will not start (fuel issue)

dg512055 said:

My 4.3lx is electric. I have found the electrical connector to the pump not making good contact. I have bent the tabs inside the connector on the wires so they make contact. The pump would run sometimes then quit. I can hear my pump run before starting because the power to it has been bypassed around the oil pressure switch.

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Electric fuel pump helps and makes a difference. It could be corrision at the connector, the Pur/Yel wire going to the pressure switch or even your oil pressure switch breaking contact.

Re: Mercruiser 4.3LX Will not start (fuel issue)

I pulled the fuel filter off, it had only a tiny puddle of gas on the bottom. I filled it full of gas, reinstalled, cranked for 10 seconds(ish) and it fired up and runs like a champ now. I ran it for 10+ minutes, ran it up to 2k then 4k rpm and it runs w/o a hiccup.

Is it common that the fuel pump would barely pump fuel while cranking? I had replaced the filter while I was docked and had cranked it for a total of probably a few minutes before I left the lake and it only produced a tiny puddle in the bottom of the filter? I would think it would be half full maybe more?

Also while it was running yesterday, I took the spark arrestor off and watched the carb and I could hear the pssssss coming from the fuel system in the carb but I couldn't really see anything coming out misting...I could barely see fuel on the butterfly, it was so faint it looked like condensation. Is that how it works with that small amount of fuel? Just strikes me as odd that's all.

Re: Mercruiser 4.3LX Will not start (fuel issue)

gbalaz said:

I pulled the fuel filter off, it had only a tiny puddle of gas on the bottom. I filled it full of gas, reinstalled, cranked for 10 seconds(ish) and it fired up and runs like a champ now. I ran it for 10+ minutes, ran it up to 2k then 4k rpm and it runs w/o a hiccup.

Is it common that the fuel pump would barely pump fuel while cranking? I had replaced the filter while I was docked and had cranked it for a total of probably a few minutes before I left the lake and it only produced a tiny puddle in the bottom of the filter? I would think it would be half full maybe more?

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It may not have time to fill it up, but more then just a puddle does sound a bit low. When cranking voltage is bypassing the oil pressure switch by means of the Pur/Yel wire. If there is a bad connection or damaged wire the pump will not pump, or at least not all the time. Reccomend checking your connections and place a volt meter on the wire and see what you get.

Also while it was running yesterday, I took the spark arrestor off and watched the carb and I could hear the pssssss coming from the fuel system in the carb but I couldn't really see anything coming out misting...I could barely see fuel on the butterfly, it was so faint it looked like condensation. Is that how it works with that small amount of fuel? Just strikes me as odd that's all.

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The engine uses very little fuel while idling, and doesn't use much more when reving out of gear. Once in gear and speeding up that's when fuel is need full on.

Re: Mercruiser 4.3LX Will not start (fuel issue)

It could also be your starter solenoid playing up, the purle/yellow is triggered of the starter solenoid to give the pump 12 volts at cranking. If you don't see 12 volts when cranking check the connections is good, remove the purple/yellow from solenoid and check at the solenoid at cranking for 12 volts.
Sometimes the starter will work but there is 12 volts missing from solenoid to the pump.

Re: Mercruiser 4.3LX Will not start (fuel issue)

Well, I know that my pump is working because when I was cranking with no fire while on the lake, when I would stop cranking, I could hear the pump humm for a few seconds. It did this the other day before I filled the filter with fuel too and it was pumping.

From what I can tell visually, the pump was replaced prior to my purchase and it appears there is tape right next to the carb on the wires coming from the pump, probably splicing the wires over to the starter and over to the oil pressure switch. I have not tinkered with the wiring under the electrical tape whatsoever. There is also an extra set of leads from this pump that are disconnected all together, one black, one that appears purple with a yellow stripe. I always wondered what those were for but the boat has always run fine w/o them hooked up?

Re: Mercruiser 4.3LX Will not start (fuel issue)

gbalaz said:

Well, I know that my pump is working because when I was cranking with no fire while on the lake, when I would stop cranking, I could hear the pump humm for a few seconds. It did this the other day before I filled the filter with fuel too and it was pumping.

From what I can tell visually, the pump was replaced prior to my purchase and it appears there is tape right next to the carb on the wires coming from the pump, probably splicing the wires over to the starter and over to the oil pressure switch. I have not tinkered with the wiring under the electrical tape whatsoever. There is also an extra set of leads from this pump that are disconnected all together, one black, one that appears purple with a yellow stripe. I always wondered what those were for but the boat has always run fine w/o them hooked up?

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If you go back to my post #5 and bring up the attachment and print it out. The Pur/Yel wire comes from the starter and is to engage the pump during cranking. The soild Purple wire continues to power the pump after the engine is running and the oil pressure switch closes. Use the diagram and trace out the wires to determine what is not connected correctly. For the short term (do not leave it this way) pull the oil pressure switch off and jumper a piece of wire between the two contacts. Once this is done the fuel pump will run the entire time the switch is on,

Do not leave it this way because it is a hazard.