Possible fuel flow problem

[Paulrusso]

I've scanned all the postings but I didn't see one that described my problem. My Mercruiser will idle for approximately 20 seconds and quit (it was running 100% okay prior to this problem). It will restart after a few seconds of cranking and run for another 20 seconds. I pulled the top off the carb and see only a fraction of an inch of fuel in the bowl (not good, I know). The float and needle appear to be functioning properly. The electric fuel pump pumps but I have no way of checking pressure. The fuel filter isn't restricted (I'll replace it since I have it out). The factory manual suggests running the engine from a remote tank which I'm going to try next. It also mentions the anti-siphon valve which I'll also check.<br />I'm thinking that there is an intermittent restriction blocking the fuel flow. Am I on the right track? Is there anything else I should be looking at? Any suggestions will be appreciated.<br />1992 Bayliner Trophy<br />4.3L Mercruiser Alpha One<br />Electric fuel pump

 

[lowshovel1]

Re: Possible fuel flow problem

sounds like the manual is leading you in the right direction. You might try loosening fuel cap and see if it will stay running.

 

[Don S]

Re: Possible fuel flow problem

Since you have an electric fuel pump, you probably have a defective oil pressure switch.<br />The way the system works is this, and it'f for safety reasons.<br />When you crank the engine to start, the start solenoid energises the fuel pump which fills the carb and the engine starts. Once you let off the key from the start position, the engine is running, but the power to the fuel pump is also stopped. The oil pressure switch (Just above the engines original oil filter mount on the block) is engergised because it's a switch not a sender, and once oil pressure builds up, the switch closes and power comes from the ignition side of the wiring. and keeps the pump running.<br />Either the connections on the switch is bad, or the switch itself is bad.<br />Here is a wiring diagram to show the Merc system.<br /><br />

 

[bijou22]

Re: Possible fuel flow problem

I would suggest removing the pipe from the fuel tank to the pump and clean out the gauze which is probably full of s**t. Never run the tank to empty or low on fuel. Worked for me. I went thru hell on the same problem but overlooked the obvious.

 

[Paulrusso]

Re: Possible fuel flow problem

Thanks for the quick replies and good advice. I'll be working on the motor as soon as I finish my morning coffee. I'm going to try running the engine from a separate gas tank to verify if there is an obstruction in the main tank. I will also try a direct DC feed to the fuel pump or to jump the oil sender switch to bypass the issue Don describes. I'll let everyone know what works.<br />Thanks,<br />Paul<br />If you can't see the mountain it's raining,<br />If you can see the mountain it's going to rain.

 

[whywhyzed]

Re: Possible fuel flow problem

Re: Don's response, you could also have a legitimate low oil pressure problem on the engine too....but you could cross check that to the gauge on the dash (I assume there's a sender for a gauge)

 

[Paulrusso]

Re: Possible fuel flow problem

Problem solved. I checked the anti-siphon valve and the pickup in the main tank and both were clean. I then shorted the leads to the oil pressure switch with the ignition switch in the ON position. I could hear the fuel pump activate indicating that the circuit was complete with the switch out of the circuit. I started the engine and it ran fine for several minutes. After cleaning the connections and the leads to the switch and reconnecting the leads the engine ran fine. It appears that the corrosion on the connections at the switch was the problem (same symptoms as a defective switch). Don's trouble shooting was right on and everyone else's suggestions useful. Now that the motor is running I have one less excuse for buying a new boat at the Norwalk In Water Boat Show tomorrow.<br />Thanks to all who replied.<br />Paul