1999 Yamaha ox66 225 - Fuel injectors?

[JahDW]

Let me begin with what I've replaced so far.

Spark Plugs
fuel filters
3 LP fuel pumps
opened VST, replaced filter even though it was clean when i opened it up

My issue is some cutting off at idle/low rom, then a jumpy RPM, so if I am cruising at say 1200rpm it will jump around to about 1700rpm and back to 1200. Then when i increase throttle it will get to about 4100/4200rpm it won't go any farther. The other motor goes over 50 (i don't WOT).

Fuel injectors? what else can i do?

 

[SkunkBoat]

see these threads
OX66 -fuel injector man

OX66 225 "stumbling" when running over 3500 rpm

 

[seasick]

It could be injectors but it could be a ton of other things too.
First question. Did that motor run OK in the past?
A simple easy test to try is to pull spark plug wires one at a time with the motor running at about 1500 rpm and note if the engine runs rougher and/or revs slow. If so that plug is probably good and the cylinder is firing correctly). If nothing changes, that cylinder is not working correctly.

When you changed the plugs, did you take a good look at the old ones and if so, how did they look?
Have you done a compression test?
Have yo done a fuel rail pressure test?
Have you checked spark?
Have you examined and tested the O2 sensor as well as cleaned the spool that allows gases to get to the O2 sensor? ( kind of a last resort, I don't like folks taking the O2 sensor out unless you have a pretty good idea it may be acting up) If the O2 sensor fails, more often then not, the motor will run rich and foul the plugs)

The rough idle is a symptom of a lot of things. The 'hunting' or rev swings can be spark, fuel, fuel air mix, TPS issue or injector.
The loss of high end revs can be spark or fuel flow issues. ( less likely something really serious

My steps would be, take a look at the plugs (of course you changed yours so you may not get a lot of info)
Run a fuel rail pressure test.
If nothing found, check spark and compression.

A simple easy test to try is to pull spark plug wires one at a time with the motor running at about 1500 rpm and note if the engine runs rougher and/or revs slow. If so that plug is probably good and the cylinder is firing correctly). If nothing changes, that cylinder is not working correctly..
Yu can't do the plug test at low revs since that motor shuts off 2 cylinders at low revs

 

[Capt. Bruno]

Check for air leaks in fuel system. Saw similar behavior on boat with twin 225s and the problem ended up being the valves to switch between tanks - air was getting in top of worn valves. Sucked enough air on idle for engine rpm to run rough and/or die. Ran ok at mid range. valve replacement solved the problem. No fuel leaked out of valves, only air went in - also saw owner testing with a vacuum pump Saw a mechanic troubleshooting the valves by putting wheel bearing grease around valve stems and and see if it get sucked in or temporarily solves problem.

 

[Stefan]

Check fuel pressure under a load
If fuel pressure is down, change filters and consider strainer on VST
If its been a long time since the injectors have been rebuilt, consider having them serviced

 

[Grady_Crazy]

I had a 2000 OX66 225. Here's what mini did.

If I throttle up slowly checking the RPMs when it gets to 2000 it sorta "kicks in" and speeds up to 2600 and stays constant. After researching this on the net I read that many others have this same issue. I guess that is the way it is.

It runs on 5 cylinders up to 850 rpm, 4 850 to 2000, and all 6 2000 and up. When they all kick in it really scoots.

 

[seasick]

I had a 2000 OX66 225. Here's what mini did.

If I throttle up slowly checking the RPMs when it gets to 2000 it sorta "kicks in" and speeds up to 2600 and stays constant. After researching this on the net I read that many others have this same issue. I guess that is the way it is.

It runs on 5 cylinders up to 850 rpm, 4 850 to 2000, and all 6 2000 and up. When they all kick in it really scoots.

Did you state that correctly. My 2001 SX150 at idle ( about 700-750 rpm) fires 4 cylinders. I am not aware of a 5 cylinder range, as far as I am aware, it jumps from 4 cyl to all 6. Honestly though, I never looked at spark at speed. It does not 'kick in' at 2000 revs and there is no noticeable jump in revs, Throttle response is smooth all the way.. I suppose the 225 could operate differently than the 150.

 

[JahDW]

COIL PACKS. fixed it.

 

[Parthery]

Jah - glad it's fixed.

Seasick - the 225 OX is on the 3.1 / 76 degree block. It doesn't fire all 6 cylinders until 1700 rpm. They are notorious for a lumpy idle. I've owned 3 of them and have yet to have one that didn't shake at idle/low speed.

 

[seasick]

Jah - glad it's fixed.

Seasick - the 225 OX is on the 3.1 / 76 degree block. It doesn't fire all 6 cylinders until 1700 rpm. They are notorious for a lumpy idle. I've owned 3 of them and have yet to have one that didn't shake at idle/low speed.

Good to know. thanks

 

[family affair]

Jah - glad it's fixed.

Seasick - the 225 OX is on the 3.1 / 76 degree block. It doesn't fire all 6 cylinders until 1700 rpm. They are notorious for a lumpy idle. I've owned 3 of them and have yet to have one that didn't shake at idle/low speed.

Maybe I got lucky, but try cleaning all of your electrical grounds to your power head. I was amazed how well an ox66 225 can run when dialed in. After trying everything else I would get intermittently good low speed performance. After cleaning all grounds, my low speed performance was consistently smooth.