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Old 09-06-2017, 04:50 PM   #1
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Default Air in Fuel System

Hi all, any help would be appreciated. I bought a 2001 1900sc a number of months ago (love the boat). On a regular basis, I have discovered that there is air accumulating in the fuel filter/hose to the tank.
The fuel pump has been replaced, along with the anti-siphon valve at the top of the pickup tube, and also the hose from the tank to the filter.

Any ideas?

Also the fuel pump is constantly running, even when ignition is on but engine hasnt been started, is that normal?.

Boat runs beautifully, once it has fuel.

Thanks for the help.
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Old 09-06-2017, 05:51 PM   #2
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Welcome aboard

You did not say which engine you have but I'm assuming it's either a 4.3 or 5.0 with an electric fuel pump based on your statement that it keeps running even with the engine off.

Sounds like someone has modified the wiring to it and thus is a safety concern. The way it should work is the fuel pump gets power from the starter soleniod when cranking and once started there is an oil pressure switch that closes to provide power. This is a safety switch that removes power if the oil pressure is low or the engine stalls so the carb is not flooded which can cause an explosive atmosphere which is not good when you try to restart. Under Documents you will find the manual for you engine and it has the wiring diagram so you can correct this.

Regarding the air is it causing an issue or just an observation?
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Old 09-06-2017, 06:26 PM   #3
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Hi Mike,
Sorry, I should have mentioned, its the 4.3 carb engine. I couldnt find the fuel pump details in the schematic. So, with the ignition switched on, the fuel pump should not operate?. There does seem to be some connection coming back from the oil pressure switch. Could be bypassed elsewhere.
Oh its causing a problem indeed, too much air and cant get fuel through. I've had to prime the hose back to the filter several times this summer. I've ordered all of the pipework and fittings between the filter and the pump, must be letting air in somewhere.
thanks for the help. Cyril
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Old 09-06-2017, 08:06 PM   #4
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Google mercruiser 4.3 wiring diagram, came right up for me.

Does the engine run ok initially then have issues after ten or more minutes? If so may be a clogged vent for the tank. Removing the fill cap will let the tank breath and if the engine runs doing so it's the vent.
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Old 09-06-2017, 08:15 PM   #5
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Ah ok, that wasn't too difficult to find. Thanks

The vent sounds like a good culprit, I'll check that out on Friday. It could run for 2 hours before I start getting fuel starvation problems.

Will check the wiring and vent over the weekend and let you know. Appreciate the help, thanks.
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Old 09-06-2017, 08:17 PM   #6
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Quote:
Originally Posted by lree12 View Post
Ah ok, that wasn't too difficult to find. Thanks

The vent sounds like a good culprit, I'll check that out on Friday. It could run for 2 hours before I start getting fuel starvation problems.

Will check the wiring and vent over the weekend and let you know. Appreciate the help, thanks.
Cool hope you can resolve it easily enough. Not sure where your at but the season is running out here.
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Old 09-06-2017, 08:20 PM   #7
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I'm in Ireland, on borrowed time here too!. Would like to get it sorted before taking it out. Would be once less project for the winter!
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Old 09-06-2017, 08:23 PM   #8
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Quote:
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I'm in Ireland, on borrowed time here too!. Would like to get it sorted before taking it out. Would be once less project for the winter!
Thought you might have been from Ireland by your user name. I know the feeling, unfinished projects bug me all winter.
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Old 09-06-2017, 08:45 PM   #9
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Hopefully it's just the vent. You have to be an optimist if you're involved with boats 😀
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