Twin 150 ox-66 one burning more fuel than the other

[Down Time II]

This is sort of dovetailing on the post about the fuel burn on the 232 Gulfstream with twin 150 ox 66's. I spent a little time running the boat yesterday. At 4000 rpm im crusing about 32 mph and burning 20-21 gph, 1.8 or so gpm. I am slowly beginnig to accept that this is how its going to be. I did notice that my starboard engine idles higher than the port, approx. 900-1100 and it consistently burns approx 2 gph more that the port all through the spectrum. What would cause this? Except for the slightly high idle, both engines run as smooth as silk. Start and run great in cold weather, no sneezing etc.

 

[seasick]

Regarding higher consumption at 'idle' but not across the range. At idle the SXs run on 4 cylinders. At about 1200 revs or so, all 6 cylinders are firing so if your idle is high, you will burn more fuel at idle. Of course, that wouldn't explain higher burn at all speeds. You have checked that the props are the same spec and in the same shape I assume.
Your across the board fuel burn could be affected by a bad/dirty O2 sensor or thimble. If blocked, the O2 will run the motor rich.
Improperly synced throttle bodies can do the same. One body may have a wider throttle opening than it should.
A bad or sticky injector can cause excessive burn also.

My first action would be to remove the spark plugs in order and compare the color of the porcelain to see if one or more cylinders is running rich. Depending on what you find, you will have an idea of what to look for next. You may also want to compare plugs between both motors. Looking at the motor with the better burn rate will give you an idea of what the plugs should look like.

 

[Tucker]

Seasick, I thought only the 3.1 dropped cylinders. Yea, sounds like some maintenance is well in order. Several comprehensive threads on THT about maintenance. It's hard playing catch up but after that it's not bad.

 

[Grog]

I thought only the HPDI series dropped cylinders at idle, I don't think there are enough "brains" in the OX series to handle it.

Once you're sure both motors are running properly don't rule out the possibility of the flow meter(s) being off.

 

[seasick]

I thought only the HPDI series dropped cylinders at idle, I don't think there are enough "brains" in the OX series to handle it.

Once you're sure both motors are running properly don't rule out the possibility of the flow meter(s) being off.

All of the 6 cylinder OX66 ( non HPDI) that I have worked on ran on 4 cylinders at idle Maybe not all SX run that way.