Mercruiser 5.0 dies while idling - no fuel from line

Kman530

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Hello,
I have a 2003 Mercrusier 5.0 with a 2 bbl carb with an electric fuel pump. The last few times out it’s been difficult to start after running. Cold start it fires up after a few cranks. I’ll run it around the lake for about 45 minutes without an issue and then anchor in a cove and swim for a few hours. After a few hours sitting it will start and run for about 30 seconds before it dies. I assume it’s burning the remaining fuel in the bowl. Typically after cranking it a few more times after it dies it will start and have no issues. Today we ran the boat for about an hour and swam for two. Started the engine and it started but after about 30 seconds it died. I tried cranking the starter for about 20 seconds, waiting a minute and repeat with nothing. Took the flame arrester off and pumped the throttle but it was bone dry - nothing coming out of the accelerator pumps. Cranked the engine over again while pumping the throttle and nothing. Then I took the fuel line off the carburetor from the electric fuel pump and cranked - no fuel coming from the line. I thought maybe the fuel pump failed so I spliced the wire and ran a hot lead to the battery. The pump kicked on but still no fuel from the line. At this point I thought maybe the filter was clogged (just replaced a month ago) or the fuel vent was clogged. I opened the fuel cap and ran the pump off the hot wire. About after a minute of running fuel started to flow out of the line. Hooked the line up and took my hot wire off, started the boat and it ran for about 30 seconds and died. Tried cranking and nothing. Hooked the hot wire back up, fired the boat up and limped back to the dock with the hot wire attached. Now safe at the dock I unhooked the hot lead to the fuel pump and let it run for 10 minutes on its normal circuit without a problem. I will add the fuel cap was off for all of this. My thoughts are maybe a clogged fuel vent or some other electrical issue. What are your thoughts and where should I start troubleshooting? Not sure why it runs fine for over an hour under power but has this issue after sitting in a cove while hot. I would think if the vent was clogged it would has some effect during cruise. Maybe the oil pressure switch? Something else?
Thanks for the help!
 

CaptnKingfisher

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How long did you crank for with the hotwire before deciding to vent through the filler cap?
 

alldodge

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Check the antisiphon valve at the tank. Its the barbed fitting the rubber fuel line connects to

Place a fuel pressure gauge after the pump to see what kind of pressure your getting. Should be around 6/7 psi
 

Kman530

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Check the antisiphon valve at the tank. Its the barbed fitting the rubber fuel line connects to

Place a fuel pressure gauge after the pump to see what kind of pressure your getting. Should be around 6/7 psi
Forgot to mention this is 2150 Bayliner with a fiberglass tank. The fuel filler hose connecting to it is about 1 inch in diameter. I have siphoned gas from the tank before so I don’t think it has anti-siphon but I’ll check. I’ll check both items you mentioned. Just need to find a fuel pressure gauge.
I’m still not sure why it would only happen after it’s hot and not while it’s running from a cold start. One would think it would happen under power and not only after it has been ran and sitting.
 
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Better than a fuel pressure gauge, is a fuel pressure/vacuum gauge. Something like a Craftsman 282179, which is an old part. You can put the gauge before the pump also and it will show a restriction with increased vacuum.
 

Lou C

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It could also be a clogged screen in the fuel pick up tube; if you replace the anti siphon and still have the same problem,
 

Kman530

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Better than a fuel pressure gauge, is a fuel pressure/vacuum gauge. Something like a Craftsman 282179, which is an old part. You can put the gauge before the pump also and it will show a restriction with increased vacuum.
I’ll see if I can find one on eBay and give it a test!
 

Kman530

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Does anyone think it’s electrical related? Or should I cross that off the list?
 

Kman530

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Check the antisiphon valve at the tank. Its the barbed fitting the rubber fuel line connects to

Place a fuel pressure gauge after the pump to see what kind of pressure your getting. Should be around 6/7 psi
Ok my bad I now know what you’re talking about. The anti-siphon valve on the fuel tank pickup side.. that’s a good point, and would explain why the fuel line was empty when I disconnected. The gas flowed back into the tank. How do you check that and where can I buy a replacement? I’m pretty sure it’s a 3/8 barbed fitting. Thanks!
 

Kman530

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CaptnKingfisher

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Valve just look for 3/8 anti siphon valve.
This is one at summitt
https://www.summitracing.com/parts/moe-033801-10

Connect the gauge direct to the fuel line going to the carb and crank the motor to see what pressure is there

To check vacuum, need to make a Tee fitting up and place between tank anti siphon valve and fuel filter
Hope this doesn't count as hijacking, but maybe this is the same for OP, if the fuel pump has steel fuel lines how do you proceed? I haven't been able to figure out a fitting I can use to connect my gauge
 

alldodge

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Hope this doesn't count as hijacking, but maybe this is the same for OP, if the fuel pump has steel fuel lines how do you proceed? I haven't been able to figure out a fitting I can use to connect my gauge
With an electric fuel pump, take a piece of fuel line and streatch it over the end of the line and attach gauge to it
 

Kman530

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Ok so I rented a fuel pressure gauge from autozone and had to do some custom work to get a reading. Like the other poster stated I have metal lines so I used a AN adapter and made it work.
Fuel pressure was at 6 PSI.
Took the anti siphon valve out and it seen better days so I replaced it. Problem was still there. Run for 30 seconds and stall - fuel line was dry.

I checked voltage at the coil, good. At the starter, good. Turn the key to ‘start’ and voltage to the pump was good. Checked voltage to the pump with a wire splice while running and it was receiving battery voltage but it would still stall after about 30 seconds. At this point I was really confused and frustrated.. I wasn’t sure why the pump was showing voltage but the engine was stalling.
Next step I jumped the oil pressure switch as a Hail Mary and to my surprise the engine didn’t stall after 30 seconds. It kept running for over 5 minutes! Took my jumper off and reinstall the factory pressure switch harness and it stalled out and died within 30 seconds of running.
New oil pressure switch is on order and should be here this week. Hopefully that fixes my issue.
 

crazy charlie

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I had similar or same .Idle for 30 seconds and cut out.The problem was the filter on the carb.Caked up with what looked like a gel.It was half filled with the gel.Took out filter and cleaned it with whatever I had on hand ,brakecleaner,Put it back on and problem solved.It was the last thing that everyone recommended so I figured to start at the carb and work backwards.Charlie
 

Kman530

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I had similar or same .Idle for 30 seconds and cut out.The problem was the filter on the carb.Caked up with what looked like a gel.It was half filled with the gel.Took out filter and cleaned it with whatever I had on hand ,brakecleaner,Put it back on and problem solved.It was the last thing that everyone recommended so I figured to start at the carb and work backwards.Charlie
Charlie, Thanks for the recommendation but I don't believe my carb has a filter. I replaced the carb last season and I just took the fuel line off and looked into the bowl and didn't see a screen or anything. I do have a spin-on fuel filter that I replaced.
 
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