Couple questions about Mercrusier 4.3 L engine


Old 06-14-18, 09:43 AM
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Join Date: Jun 2018
Location: USA
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Couple questions about Mercrusier 4.3 L engine

Does anyone know an easy what to test: - Having trouble with hard starting, engine gracefully stalling out after a few mins of idle. A week or so ago, it ran beautiful for a about 2.5 hrs. This past time, i just suddently shut off on me twice and couldnt get it restarted while on lake the second time. But since it's home i can get it start, sometimes even on the first key turn...but it kind of dies out. I have spark to the cylinders even up until it dies out. Not sure if this indicates fuel related issues?
  • Electric fuel pump is working
    • I think i can verify voltage is there by trying to start engine ( voltage sent by oil pressure swtich?)
    • If engine is running, if i look down carb i should see fuel?
  • Test the oil pressure swtich while connected to engine block
    • or do i need to take it out?
    • should this get 12V with key in on position?
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Old 06-14-18, 10:01 PM
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Join Date: Oct 2012
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Welcome to the forums.

Not a pro on this engine but have worked on them. The oil sensor that runs the fuel pump should be a two wire sender. When the key is on I believe you'll get 12v on one side.... nothing on the other side. Once you crank the engine... the dead side should become 12v powering the fuel pump.

If you think the fuel pump is losing power..... try connecting a small 12v lamp to that circuit that you can monitor while running. As soon as the engine stalls it will go out.
Old 06-15-18, 05:54 AM
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Join Date: Jun 2018
Location: USA
Posts: 2
Ok thanks Pete. I did confirm the 12v to switch with key and nothing to pump unless engine running/cranking. I can get the engine to run for a few mins and determined that I am getting power to fuel pump and i even disconnected fuel inlet to carb and its pumping fuel. So no idea why it wont remain running, carb issue? Not sure if a dist cap would be a problem since it runs.

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