Logo
FULL SITE MENU

2001 Mercruser 5.0 EFI - Runing Rich

G

ggonxhi

New member
Good evening

I have a 2001 mercruser that is running rich / Rough and can't figure out what it is.
I have so far changed
Distributer cap
Spark Plugs
Spark wires
MAP sensor

Will do throttle body rebuild this weekend.

See Diacom video
 
Don't throw parts at it until you KNOW they're bad.

How long had it been running before you collected this data? If it was "warmed up", the coolant temoperature is too low- measure the resistance of the ECT (it has two wires) and if it's not within the range of the chart, test it by letting it reach ambient temperature, measuring its resistance and comparing with the chart. If that's wrong, replace it. If it's OK, put it in warm and hot water, measuring the temperature each time and compart the resistance at each temperature with the chart.

A cold engine isn't an efficient engine and if it's hot but the ECM thinks it's cold when it's actually warmed toi normal operating temperature, it will run rich.

If the thermostat has never been changed, I would recommend testing it, at the minimum. Replacing it wouldn't be wasting money- buy the 'fail open' type.


1774710953544.png
 
you can use an IR Thrmometer gun as well, to verify the accuracy of the ECT...

To put it another way, if the temp gauge showed normal (> 140 deg F) when you grabbed the DIACOM data, its very like the ECT has lost its accuracy. Its still working but not accurate which is why no DTC has set...
 
makomark said:
you can use an IR Thrmometer gun as well, to verify the accuracy of the ECT...

To put it another way, if the temp gauge showed normal (> 140 deg F) when you grabbed the DIACOM data, its very like the ECT has lost its accuracy. Its still working but not accurate which is why no DTC has set...
Click to expand...
Sender, or gauge? A 2001 boat should have two senders- one for the gauge and the two wire sender for the ECM. Mercruiser may be different, but I don't remember the Indmar engines having only one sender when the boat had the Medallion or Borg-Warner instruments/black box.
 
jimn said:
Sender, or gauge? A 2001 boat should have two senders- one for the gauge and the two wire sender for the ECM. Mercruiser may be different, but I don't remember the Indmar engines having only one sender when the boat had the Medallion or Borg-Warner instruments/black box.
Click to expand...
That is correct my boat has 2 one with 1 wire and one on the right side with 2. I actually purchased one with 2 for testing. Also got a kit to check the fuel pressure.
 
ggonxhi said:
That is correct my boat has 2 one with 1 wire and one on the right side with 2. I actually purchased one with 2 for testing. Also got a kit to check the fuel pressure.
Click to expand...
While you're at it, find a clean, dry, clear bottle (I use plastic) and use the gauge's purge valve and clear PVC tube to take a fuel sample. Let it sit on the bottle for awhile and look for particulates, water beads/droplets and a milky layer. The milky layer is p[hase separation and needs to be removed. If you have a fuel water separator, check it for the contents and if you don't remember it being replaced, do that.
 
I’m thinking it’s the gas since about 15 gallons are about a year old and I put in 20 additional gallons and fuel stabilers. I also changed the fuel filter. It ran fine for a bit.

Will run the engine on an external can to confirm it’s the gas and than clean the tank. Just don’t to figure out how to get this all out.
 
ggonxhi said:
I’m thinking it’s the gas since about 15 gallons are about a year old and I put in 20 additional gallons and fuel stabilers. I also changed the fuel filter. It ran fine for a bit.

Will run the engine on an external can to confirm it’s the gas and than clean the tank. Just don’t to figure out how to get this all out.
Click to expand...
I bought a boat that had been treated like a farm animal and needed a lot of repairs. I ran it on the lake a couple of years ago and found that the upper needed seals and a bearing, but didn't have time to address those until last year. It still had stabilized gas in the tank from running it in 2023 and before I ran it again last Summer, I took a whiff and it smelled like fresh gas, also looked fresh when I took a sample. When I took it out last Fall, I added gas to counteract any Octane loss and it ran great but it had no water or debris- I stored in in my garage the whole time. If it had gone bad, it would have been easy enough to siphon or pump it out but I didn't need to- take the fuel sample and be sure.

When I worked for a boat dealer, I had to empty the tank because a previous service shop had replaced the fuel gauge sender, but they didn't position if correctly, which left gaps all around where the gasket should have sealed it and when it rained, water filled the tank because the bopat owner had inadvertently flipped the bilge pump switch to OFF.

The tank was completely filled with water, so I went to the closest NAPA store and bought some fuel line and a basic volume-type fuel pump. I wired a harness with battery clips, a fuse and a switch so it could be turned on & off from where I was working, and used whatever I could find for containers to fill. When it had almost nothing left (only a few ounces), I stuck towels in to soak it up, added about a gallon of Denatured Alcohol and raised/lowered the bow, to let it slosh around and collect any water that was left. Once I had pumped that out, I reinstalled the sender correctly, filled the tank with fresh gas/stabilizer and used the fuel line's Shrader valve and pressure gauge's purge valve as a path to remove any water from the fuel line by connecting the fuel pump to power until it was clean.
 
Back
Top