2001 7.4 MPI Horizon Issues

Mauler34Rod

Mauler34Rod

Well-Known Member
SILVER Sponsor
Aug 26, 2020
827
Chicago Lake Michigan
Boat Info
2001 380 Sundancer, Raymarine Electronics
2022 Highfield CL310 Dinghy with 20 HP Suzuki
Engines
454 MPII Mercruiser w/ V Drives
Filled both tanks with fresh fuel for a 55 mile run last weekend. So yesterday was out for a short cruise and stopped and threw out the hook for a swim to cool off. Stayed about an hour and when I went to start engines, both would crank and crank and crank and then fire and bogg down and quit running. First initial thought was I had taken on bad gas, but I ran through a half tank with no issues and the boat was running great prior to stopping to anchor. Pulled the starboard water/fuel separator to inspect the fuel. The fuel looked clean no water or cloudyness. The smell of gas was present so I assumed maybe flooded, so I waited a while and tried again. This time port motor fired and continued to run, starboard motor would not fire. So limped back to the harbor. Both water/fuel separators were changed in the spring and both motors had tune-up this off-season.
Going back to the boat tomorrow to troubleshoot. I will try to start it first and then I was going to pull the plugs to inspect them for fouling.
Does anybody have experience with these engines and this particular problem? Any advise on what else I can look for? I don't know much about vapor lock, but seems strange both engines acted the same upon restart and then eventually the port engine fired and ran fine back to the harbor. Could these engines experience vapor lock and if so what is the cause?
Any suggestions are welcome.
 
Mauler34Rod said:
Filled both tanks with fresh fuel for a 55 mile run last weekend. So yesterday was out for a short cruise and stopped and threw out the hook for a swim to cool off. Stayed about an hour and when I went to start engines, both would crank and crank and crank and then fire and bogg down and quit running. First initial thought was I had taken on bad gas, but I ran through a half tank with no issues and the boat was running great prior to stopping to anchor. Pulled the starboard water/fuel separator to inspect the fuel. The fuel looked clean no water or cloudyness. The smell of gas was present so I assumed maybe flooded, so I waited a while and tried again. This time port motor fired and continued to run, starboard motor would not fire. So limped back to the harbor. Both water/fuel separators were changed in the spring and both motors had tune-up this off-season.
Going back to the boat tomorrow to troubleshoot. I will try to start it first and then I was going to pull the plugs to inspect them for fouling.
Does anybody have experience with these engines and this particular problem? Any advise on what else I can look for? I don't know much about vapor lock, but seems strange both engines acted the same upon restart and then eventually the port engine fired and ran fine back to the harbor. Could these engines experience vapor lock and if so what is the cause?
Any suggestions are welcome.
Click to expand...

Mercury has a tech bulletin on Vapor lock which outlines causes and possible solutions. FWIW, the check valve solved it for me. My engines came equipped with the booster pump from the factory.
 
scoflaw said:
Sounds like vapor lock. Did you try advancing the throttle while cranking?
Click to expand...
I did but I think it flooded it worse.
So if I go there tomorrow and it starts then I can assume vapor lock? Thoughts?
 
Thank you I will try to find the bulletin and check it out.
 
Full advance cuts off fuel. When it happens you can push on the shrader valve to see if there is air in the rail.
 
scoflaw said:
Full advance cuts off fuel. When it happens you can push on the shrader valve to see if there is air in the rail.
Click to expand...
“Full advance” meaning throttle full forward?
Pushing on shrader valve will also release fuel correct?
 
If your Horizon's are the same as my 1999 Horizons, they have a fuel cooler built into the system to help prevent vapor lock. They are located on the port side of the block, behind the motor mount. This isn't any suggestion, just an FYI.
Were they smoking when you initially tried to start them, ie when it was "bogging down"? This would indicate excess fuel (ie flooded). Do you run your blower while cruising to help keep the engine room cool? My manual mentions this, but I don't recall the details for the point.
Have they been burning any excess fuel recently? This could foul plugs and cause issues.
Have you checked for any engine alarms? Yours probably have the MEFI 3 or 4 and with a loop of wire and a voltmeter (or little light bulb) you can read any codes they have thrown.
My engine Service Manual has around 400 pages of details on the fuel system and MEFI. I attached a smaller service doc that talks about the alarms.
 

Attachments

  • MEFI 3 Audio.PDF
    48.4 KB · Views: 59
I found this line in the Bulletin to be rather interesting...
"Move the fuel line to be as close to the bottom of the boat as possible to keep it in the coolest area...."
My lines run from the hull bottom up to where Mercury mounted the fuel filters on the Horizon MPI, 2 inches from the exhaust port on the #2 cylinder, and the alternator. I think there was supposed to be a heat shield on that port, as I found a heat shield that fits, in a box of leftovers on board, but the holes are smaller than the manifold bolts. I opened them up slightly to fit. The other is missing entirely.
 
Fuel injection or carburation leave the throttles all the way forward that's usually a clear flooded mode and just if it kicks pull it back very very quickly
 
John E3 said:
If your Horizon's are the same as my 1999 Horizons, they have a fuel cooler built into the system to help prevent vapor lock. They are located on the port side of the block, behind the motor mount. This isn't any suggestion, just an FYI.
Were they smoking when you initially tried to start them, ie when it was "bogging down"? This would indicate excess fuel (ie flooded). Do you run your blower while cruising to help keep the engine room cool? My manual mentions this, but I don't recall the details for the point.
Have they been burning any excess fuel recently? This could foul plugs and cause issues.
Have you checked for any engine alarms? Yours probably have the MEFI 3 or 4 and with a loop of wire and a voltmeter (or little light bulb) you can read any codes they have thrown.
My engine Service Manual has around 400 pages of details on the fuel system and MEFI. I attached a smaller service doc that talks about the alarms.
Click to expand...
I’m not sure about the built in fuel cooler but I’ll check it out.
1. Did not experience excess smoking, but did smell fuel (blowers were on and I turn them on when off plane) to ventilate the ER.
2. Not burning excess fuel
(didn’t think it could burn more than it already does, lol)
3. No alarms thrown
I’m leaning towards vapor lock after reading through the bulletin. I will be at the boat tomorrow and so we shall see.
Thanks for your reply.
 
Mauler34Rod said:
I’m not sure about the built in fuel cooler but I’ll check it out.
1. Did not experience excess smoking, but did smell fuel (blowers were on and I turn them on when off plane) to ventilate the ER.
2. Not burning excess fuel
(didn’t think it could burn more than it already does, lol)
3. No alarms thrown
I’m leaning towards vapor lock after reading through the bulletin. I will be at the boat tomorrow and so we shall see.
Thanks for your reply.
Click to expand...
Sorry if my memory is wrong, but haven't you had this boat for a while?
 
Scott215 said:
Fuel injection or carburation leave the throttles all the way forward that's usually a clear flooded mode and just if it kicks pull it back very very quickly
Click to expand...
Thanks I found that out the hard way. I must of only pulled it back very quickly rather than very very quickly……hahahaha.
 
You must log in or register to reply here.

Forum statistics

Threads
113,217
Messages
1,428,798
Members
61,114
Latest member
Hercy911
Back
Top