250 OX66 Fuel Problems

[jwbergeron]

I've got twin 1998 250's and am having fuel problems with one. At cruise, port throttle needs to be advanced beyond starboard to synch the motors. At the same rpm, the port burns about 4gph more than starboard. I've run them up and down and notice at WOT, port gets up to 4500rpms at most (and bogs out with more throttle), and starboard runs great and will get up to about 5200.

The motors are new to me this year. They had low hours on them (150), but I believe were not maintained by the old gentleman that I purchased from. I've cleaned the VST filter, which wasn't too bad. I've also removed and soaked the 02 sensor in ring-free. The sensor itself didn't have much build up on it, but there was a lot in and around the tube, and especially on the outside of the tube (the handle of the barbell if you will). I cleaned it up and replaced.

Before I bring this to a yamaha dealer (which for me is pretty inconvenient), is there any other maintenance items I should address? Should I just replace the 02 sensor? Is there some way to quickly check the fuel pumps, or should they be rebuilt or replaced periodically?

Rodbolt, I'm sure you've beat this one to death. I've searched past threads for a few hours and can't find what I need. Any help is always greatly appreciated.

Thanks.

 

[rodbolt]

Re: 250 OX66 Fuel Problems

before continuing to run it ya gotta find the problem, a bad O2 sensor can quickly pop a piston above 4000, yes the lift pumps fail quite often and I reccomend replacing every 3rd year just cause.
you need to check fuel rail pressure as well as O2 sensor output voltage.
have you ever seen the run correctly and do you have a service manual ?

 

[jwbergeron]

Re: 250 OX66 Fuel Problems

Rodbolt, thanks for the reply. I replaced all 3 pumps today (it was nice to see they're only about $35 a piece). I was optimistic when I noticed a little fuel dripping out of the crankcase when I removed the bottom pump and thought I had a bad diaprhagm. Unfortunately, this didn't fix it. Still bogs out. Didn't know about the potential of damaging a piston, I hope I didn't do any damage. I've only owned since March, never ran right. I rarely take it over cruise (about 3700 rpms) and didn't realize I had a problem. I had thought the reason I was advancing port throttle to synch engine speed was due to a needed adjustment in the cable.

This whole thing started when I cleaned the 02 sensor. We took it out and I noticed port was buring 30gal an hour at 3500 rpm (starboard was burning 10!). After stopping to inspect for about 10 minutes, it improved.

I don't have a manual. What do you recommend?

 

[rodbolt]

Re: 250 OX66 Fuel Problems

finding why the fuel curve on the port motor is so high, first test compression and spark.
then we start looking for bad VST needle valves,stuck injectors or fuel rail pressure regulator.you will need a voltmeter,digital type. a TPS test harness an O2 sensor test harness. a fuel pressure guage that fits the schrader valve on the VST and a service manual, a marine tech manual from about 04 will help as well.
a quick check with the diagnostic test lamp will help as well.

 

[jwbergeron]

Re: 250 OX66 Fuel Problems

Rodbolt, I'm back into it. Believe its a bad 02 sensor. The sensor I had cleaned 2 days ago is plugged wih crap. The tube is almost completely packed again.
I am taking the sensor itself to yamaha today, they say they can run a test on it to determine if its bad.

I determined a ticking noise in No. 1 cyl was actually that tube slapping around, although it did not appear to be excessively worn. Do you see this a lot?

How do you recommnend 02 sensors be cleaned? I haven't touched the starboard motor that runs great, but I'm sure its not far behind.

Thanks for all your help. I'll post the results after today's test.

 

[rodbolt]

Re: 250 OX66 Fuel Problems

yes I see the tube slap a lot on neglected motors.
if you look you will see the ends are shiney. it will sound just like a wristpin slap.
there is no bench test.
well there is but it is absolutly useless.
if they say they can bench test it I will say they are crazy.
there are some running tests that can be done.
all tests MUST be done with the lower unit submerged .
requires a digital voltmeter and the test harness.
50 buxs for both.
make sure your tubes are the updated ones. there is a tech bulliten on the 3.1L tubes.

 

[heatz]

Re: 250 OX66 Fuel Problems

I am having a very similar on one of my 250 0x66s. Very high fuel burn and cant get rpm over 3600. Running very rich. O2 sensors are ok. Mechanic found that the stator was bad and is replacing that. I hope this cures it (not sure how...). Fuel pumps are ok.
Eric

 

[jwbergeron]

Re: 250 OX66 Fuel Problems

It was my 02 sensor! Replaced and it runs great. Fuel consumption is way down. Ran about 4 hours this weekend and it ran like a top the whole time. Parts cost me $385 for new sensor, gaskets, and the tube. The slap is gone with replacement of the tube.

Rodbolt, Yamaha dealer confirmed that the only test on 02 sensor that was realiable had to be done in-situ. As always, thanks for all your help.

Heatz, be sure the test was done the way described by rodbolt. Your symptoms sound very similar. I've learned over the past few weeks that the Yami dealers can't keep those 02 sensors on the shelves.

 

[heatz]

Re: 250 OX66 Fuel Problems

Glad you solved your problem. I switched the O2 sensor and tube from 1 engine to the other and the problem did not follow to the other engine. The stator is pretty fried and the mechanic believes a new one will solve the problem, but i dont really understand how.

 

[rodbolt]

Re: 250 OX66 Fuel Problems

if you suspect a stator its easily confermed with a peak reading voltmeter,the test harness a a quick run.
failure of the cdi charge coils are rare on efi, i have seen one in 7 years.