engine shuts off at cruising speed

T

tugger

Member
Nov 11, 2019
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boatless
Engines
boatless
I have a 2007 320 sundancer with 2 mercruiser 350 mag mpi engines with v drive. I can idle out of my marina and can go 1000, 1500, 2000 and 2500 rpms with no problems. When I get it up on plane at about 3800 rpms it runs beautifully for 2-3 minutes and then the starboard engine shuts off like I hit a kill switch. No sputtering, just shuts completely off. It happens at the exact same spot every time meaning I'm going the same time and distance. I have talked with mercury techs who have been great but running out of ideas. Hoping for some help. This is what I have done: water pressure and water temp is fine, oil level and pressure is fine and voltage is spot on. Distributor and components look good. Fuel pressure is right on (at idle, I havent had a guage on it when it cuts out) and when I pull the line off the fuel regulator it rises within range like it's supposed to. Gas is good with fresh couple of tanks with fuel treatment always added. Replaced the fuel relay and checked the 50 amp breaker. Fuel module stays cool after running. I tried to inspect all grounds and connections. I switched ignition coils hoping that would be it with no luck. My suspicion is a bad high pressure fuel pump but would it run for awhile and almost for the exact same period of time EVERY time before shutting down? I talked to a fuel pump guy and he said they usually run or they don't, not run for awhile and then stop. Any experience on that comment? when it cuts out it starts again but it seems to take longer and longer every time I go out to start back up and then I can idle back to the dock and run at lower speeds. Throwing up a hail mary here hoping someone has had the same problem or has an idea. Thanks so much for listening.
 
Get a fuel pressure gauge on it when it stops. Sounds like a fuel problem. Is your tank vent clear?
 
Distributor and components look good. What does this mean? This happens at a specific rpm at a specific time. Check that the distributor cap is fastened tight with loc-tite
 
Thank all, this is very helpful. what and where is the tank vent and how would I clear it? Is that where the fuel overflows if you overfill it out of the side of the boat? As for the distributor, I just took off the distributor cap and rotor and visually inspected everything looking for corrosion or something unusual. The cap is back on nice and tight.
 
Could the high pressure fuel pump work intermitantly, working fine sometimes and then shut off? Or when they are gone they are gone?
 
Yes I do have a cool fuel 3 module with the low and high pressure fuel pumps. Filter has just been changed.
 
My buddy had the same issue on his 4.3's. Turn out to be a bad computer. Swap the computers and see what happens. If it cuts out on the other motor than you know you have a bad one. Takes all of 5 minutes to swap them from one to the other.
 
It comes up in the parts schematic as a PCM, propulsion control module, is this the one you mean? I have also heard the term ecm, engine control module, is it the same thing? Thank you
 
PCM or ECM same thing. Be sure to have your battery switches off be fore disconnecting the ECM.
 
tugger said:
Yes I do have a cool fuel 3 module with the low and high pressure fuel pumps. Filter has just been changed.
Click to expand...
When my CF3 went bad, I had the same symptoms, but I changed it quickly so never experienced the repeatability you have.
 
9854.gif

Number 5 is the ECM.
 
Nope, fuel and ignition. Ignition sensor controls both and no way to look at it and tell if it is bad or not. I'd try this first since it is $80 and a very quick fix before you start down the more expensive roads.
SENSOR ASSY-IGN
892150Q02
ign sensor.jpg
 
You have the "crab" style distributor caps correct? If so, replace them no matter how they look. They have several issues but there's a specific one where, as I recall, the cap gets carbon tracks and hairline cracking and when you get above 3500 RPMs, spark advances and cross fires in the cap.
Agree with the guys above about checking coil and if you haven't already then clean/check all electrical connections starting at battery terminals, through to the coil: alternators, starter, slave solenoid etc. A short/open can throw off voltage and make you PCM/sensors act funny.
 
tugger said:
I have a 2007 320 sundancer with 2 mercruiser 350 mag mpi engines with v drive. I can idle out of my marina and can go 1000, 1500, 2000 and 2500 rpms with no problems. When I get it up on plane at about 3800 rpms it runs beautifully for 2-3 minutes and then the starboard engine shuts off like I hit a kill switch. No sputtering, just shuts completely off. It happens at the exact same spot every time meaning I'm going the same time and distance. I have talked with mercury techs who have been great but running out of ideas. Hoping for some help. This is what I have done: water pressure and water temp is fine, oil level and pressure is fine and voltage is spot on. Distributor and components look good. Fuel pressure is right on (at idle, I havent had a guage on it when it cuts out) and when I pull the line off the fuel regulator it rises within range like it's supposed to. Gas is good with fresh couple of tanks with fuel treatment always added. Replaced the fuel relay and checked the 50 amp breaker. Fuel module stays cool after running. I tried to inspect all grounds and connections. I switched ignition coils hoping that would be it with no luck. My suspicion is a bad high pressure fuel pump but would it run for awhile and almost for the exact same period of time EVERY time before shutting down? I talked to a fuel pump guy and he said they usually run or they don't, not run for awhile and then stop. Any experience on that comment? when it cuts out it starts again but it seems to take longer and longer every time I go out to start back up and then I can idle back to the dock and run at lower speeds. Throwing up a hail mary here hoping someone has had the same problem or has an idea. Thanks so much for listening.
Click to expand...

Did you ever figure out what the issue was? The exact same thing is happening to me.
 
paulswagelock said:
When my CF3 went bad, I had the same symptoms, but I changed it quickly so never experienced the repeatability you have.
Click to expand...
Hello! I'm having the same issues. When you say CF3 what do you mean. Specifically what part was changed?
 
mcelmur said:
Hello! I'm having the same issues. When you say CF3 what do you mean. Specifically what part was changed?
Click to expand...
I changed the cool fuel module. On mine, it would make 45psi fuel rail pressure and instantly and randomly got to zero pressure. Shut off for a few minutes and it would work again.
 
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