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5.7 litre merc runs for 20 to 30 seconds then quits

S

supernill

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another newbie here Iam having a problem and am hoping some one can help please. I have a 99 merc that runs for about 20 seconds and then just shuts off, I changed the fuel water separator/filter. I took the carb apart and cleaned everything out, ran an external fuel source with fresh fuel does same thing.
 
the remote tank eliminates fuel issue, engine fuel pump?. when is does quit and you pump the throttle does fuel squirt from the carb? Yes ,then its not a carb issue. No, a carb issue or fuel pump issue.
other causes could be a coil getting too hot and failing, the dist sensor failing, the main module failing.
 
Welcome aboard !

If you have a electric fuel pump i would think the oil pressure switch nor sender might be fugazied.

This is what happens you turn the key the fuel pump works you crank the engine the fuel is in the carb the oil sender or switch thinks you have no oil pressure and shuts off the pump. Bingo you run only 15-20 seconds cause the bowl is empty.

What to do, does the oil pressure come up when it's running for that 15 seconds ?

Wires coming off the pressure sender ok, the wires going to the switch ok ? Maybe you need to clean connections.

You might need to stick in a manual gauge in the pressure sender hole and check the oil pressure when it is running for a few seconds or bypass the oil pressure switch or put steady power to the fuel pump as a test and see if it keeps running.

My way is the last way.

Again does the oil pressure gauge on the dash show oil pressure for those few seconds ????

Pick your poison do the test and post back we will go from there.
 
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That happened to me once. I found the barrell plug had loosened. Tightened the plug and it never happened again.
 
Follow the purple wire at the fuel pump along the harness to where there is a mechanical junction. It can get corroded.
 
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