Mercruiser 4.3 MPI stalling and running rough...

pilot4net

Seaman
Joined
May 24, 2005
Messages
57
Good afternoon all, just ran into a problem this morning with our 2013 Tahoe with the Mercruiser 4.3 MPI. We took off from the launch no problem and ran perfect for around 30 minutes or so ranging from WOT to slow running, all without the slightest glitch or hiccup. We pulled up to the beach nearby and stopped and sat for maybe 1.5 to 2 hours while the kids played in the water and sand.

When we were ready to head back and pickup something for lunch, we backed off the bank, and took off like normal. We ran at about 3/4 throttle for about 5 minutes when we got one long beep. We had to slow down to minimum speed for a no wake zone and when we went to take off again, the one long beep went off again and the boat would not accelerate above 1150 RPMS and if I pushed the throttle further to get more power, the engine would backfire, sputter, and try and die. I shut the engine down and opened the engine compartment to check for any problems and didn't see anything out of the ordinary. The oil pressure was running normal, water temperature was just under 160 degrees, drive lube was good, power steering fluid full, so I couldn't think of something other than a fuel delivery issue. If we let it idle for a few minutes, we could get it to accelerate for a few seconds but then it would go back to the same symptoms as if it was slowly starving more and more for fuel.

Since we were in the middle of a large lake with the wind blowing strong, we ran the motor as slow as we could and keep it running so we could get to the safe harbor of a launch.

I get it back on the trailer and start trying to troubleshoot and thought maybe it was a plugged fuel filter or water in the fuel. I went and picked up another filter. When I removed the old filter, I poured the gas in a clear glass mason jar to check for excess trash and water. No water was found and just a very minute bit of trash was in the jar which may have come from the outside of the filter... So, I installed the new filter (after filling the new filter with fuel) and since I jointly suspected a faulty anti-siphon valve, I routed the fuel lines around the anti-siphon valve to help rule that out also. I restarted the engine and within a few seconds, got the same long beep along with the same symptoms. If I try to just throttle up the engine without putting it in gear, it will stall and run rough and backfire the same as if in gear.

At this point I don't know what to think. I am looking for any information anyone can lend me on this and may e give me something else to check on.

Thanks to everyone in advance for any help you can lend and I look forward to your ideas.

Thanks!
 

MikDee

Banned
Joined
Jun 6, 2007
Messages
4,745
Re: Mercruiser 4.3 MPI stalling and running rough...

Make sure your gas tank vent is clear, or else you'll probably be pulling a vacuum on the tank.
 

pilot4net

Seaman
Joined
May 24, 2005
Messages
57
Re: Mercruiser 4.3 MPI stalling and running rough...

Thanks MikDee, I did check to make sure the tank was not in a vacuum state as I removed the sending unit leaving the top of the tank open (1.5" hole) and tested the motor but to no avail.... The problem still persists.

Any other ideas anyone?
 
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