Mercruiser 7.4L MPI slowing down
07-27-2019, 12:27 PM
#11
I want to say I practically did that. It was running low from the marina testing it and I put in 50 gallons, so there was probably 10 already in tank so about 60 gallons. I ran it and it occurred sooner - usually it was about an hour but this time only 1/2 hour but I was going faster than before because at this point I thought issue was resolved and was just testing it out. Perhaps it would be better to test it at comparable speeds but if it happens sooner by filling the tank that must still somehow be related to fuel system or pump?
07-27-2019, 01:37 PM
#12
Registered
Thanks Griff...… was not aware.
07-27-2019, 03:08 PM
#13
Registered
After you have lost power/mph.. have you let the boat cool right off (hatch open) and run it again to see if it has a shorter span before loosing power on the following run???
Fuel was my first thought but after chasing so much, is there any possibility that the coil is giving up when it's thermally soaked (overheats)? over heat = high resistance/ lower voltage output and the ECM will chase the timing curve to stave off knock which obviously lowers power output....minimal power (Including a 6cyl. option) will push that boat, sea Ray bow rider that 18-20mph w/o effort
**There was a stretch when it seemed certain MPI's were tossing coils for no apparent reason
Fuel was my first thought but after chasing so much, is there any possibility that the coil is giving up when it's thermally soaked (overheats)? over heat = high resistance/ lower voltage output and the ECM will chase the timing curve to stave off knock which obviously lowers power output....minimal power (Including a 6cyl. option) will push that boat, sea Ray bow rider that 18-20mph w/o effort
**There was a stretch when it seemed certain MPI's were tossing coils for no apparent reason
Last edited by speicher lane; 07-27-2019 at 03:19 PM.
07-27-2019, 04:39 PM
#14
After you have lost power/mph.. have you let the boat cool right off (hatch open) and run it again to see if it has a shorter span before loosing power on the following run???
Fuel was my first thought but after chasing so much, is there any possibility that the coil is giving up when it's thermally soaked (overheats)? over heat = high resistance/ lower voltage output and the ECM will chase the timing curve to stave off knock which obviously lowers power output....minimal power (Including a 6cyl. option) will push that boat, sea Ray bow rider that 18-20mph w/o effort
**There was a stretch when it seemed certain MPI's were tossing coils for no apparent reason
Fuel was my first thought but after chasing so much, is there any possibility that the coil is giving up when it's thermally soaked (overheats)? over heat = high resistance/ lower voltage output and the ECM will chase the timing curve to stave off knock which obviously lowers power output....minimal power (Including a 6cyl. option) will push that boat, sea Ray bow rider that 18-20mph w/o effort
**There was a stretch when it seemed certain MPI's were tossing coils for no apparent reason
Maybe it has something to do with a coil it sounds like something could be heating up since it doesn’t happen all the time and has occurred with gas tank at various levels.
thanks
07-27-2019, 04:43 PM
#15
Registered
iTrader: (1)
The boat needs to be ran in the water and under load with a fuel pressure guage attached. It needs to be scanned at the same time.
Doing this should help narrow down the issue.
Doing this should help narrow down the issue.
07-27-2019, 04:46 PM
#16
*
Platinum Member
Do you guys have any consumer protection legislation that prevents you from paying through the azz for guesswork before the real problem is identified and fixed ? I know it's a tiny bit off topic but I've been in this game for a long time and I can't even begin to recall how many people around here have been billed over and over again for work that didn't fix the problem. And like all happy boaters they keep paying with their fingers crossed that one day the mechanic will be right.
They seem to accept this with their boats but if you ask them if they'd keep paying their car repair shop for not fixing their car they say 'hell , no!'
07-27-2019, 09:18 PM
#17
Registered
Has the fuel line been replaced. There has been a big channel in fuel lines since 2001. Ethanol can cause the lining to break down. http://www.bbcboards.net/showthread.php?t=22490
I would see if i could hook up an auxillary fuel tank and run it off of that. If it cures the problem it is related to the tanks and lines.
I would see if i could hook up an auxillary fuel tank and run it off of that. If it cures the problem it is related to the tanks and lines.
07-28-2019, 12:06 AM
#18
Has the fuel line been replaced. There has been a big channel in fuel lines since 2001. Ethanol can cause the lining to break down
I would see if i could hook up an auxillary fuel tank and run it off of that. If it cures the problem it is related to the tanks and lines.
I would see if i could hook up an auxillary fuel tank and run it off of that. If it cures the problem it is related to the tanks and lines.
Thanks
Scott
Last edited by Scottd21; 07-28-2019 at 12:11 AM.
07-28-2019, 12:52 AM
#19
Charter Member # 55
Charter Member
I highly doubt it is a coil problem. Generally when coil goes bad it just quits. If it wasn't putting out enough volts, it would run rich and foul the plugs and have engine misfires.
