What a difference an 02 Sensor can make!! (250OX66)

[Salinity Now]

Just thought Id share the good news from the boat, been having some gremlins on the port 250OX66, wouldnt reach WOT, infact anything above 4000 started to cause it to lag and hesitate, it was using literally twice the fuel as the stbd (3800 RPMs synched up, I was burning 30GPH+ (port motor using 18-21GPH, stbd 9-11GPH)....now shes running a steady 20GPH+/- (10 & 10) at about 28kts.

WOT is running great, opened up at all RPMs, still cant get but 5300 out of both, but thats in choppy seas, full of fuel, saw 42kts today.

Cant believe its been almost a year since I got it (2001 265 Express....) looking forward to a good striper season this year in the Ches Bay.

If anyone is having OX66 issues, I HIGHLY recommend troubleshooting the O2 sensor (i had already cleaned it/decarbed), I changed VSTs, plugs, spin on filters, inline filters, cotton motor filters, LP pumps, adjusted idle, and probably more I just forgot the list got pretty long, but this fixed it right up (Im sure the other stuff will help too)

Still awfully thirsty though, takes alot of gas to move that boat, the Suzuki dealer here in the Hampton Roads area is trying to sell me on repowering with twin Suzuki 175's.....I bet the economy would be great, but something about losing 150HP seems weird on a repower.

Come on cold water!!!!

 

[ocnslr]

Glad to hear you have found, and corrected, the cause of your problem(s).

We had a single 250HP OX66 before we repowered (>1100 hours ago). Great engines. Strong and reliable. But so thirsty.

PM me if you might be interested in our Tidewater Grady-White Club.

Brian

 

[Salinity Now]

Thanks Brian,

I actaully am a temp member of the club, signed up earlier this year thinking I was gonna be around more, but my ship got extended overseas this summer compliments of Gadafi.

We just got back Friday, I was over at Cove Marina today messing with the boat, where do you run out of?

(Im looking for a fiberglass guy in the area, got any recommendations?, thinking about removing some old transducers and replacing with a new one)

 

[family affair]

Sal,

Would you say the engine was surging over 4k rpm? We are still chasing an issue on our '99 225 OX66. Idle, rough mid-range, and starting stalling have been fixed, but over 4200 the engine surges. At 4200, the engine runs up to 4800, then 5k, and back. Fuel consumption seems high too.

Thanks

 

[DaleH]

FYI, here's a link to a GREAT article by a noted on-line OB motor guru, Mr. Bill Grannis, that tells YOU how to DIY service your Yam motor O2 sensor: www.boatsetup.com/O2sensor.pdf

 

[Salinity Now]

I cant say that the motor was surging, actually lagging is more like it, anything above 4200 or so RPMs it would start to hesitate and the RPMs would fall back off, then flucuate up and down.

The problem got progressively worse, didnt really notice it at first as I dont normally run it at high RPMs, but once I started seeing the fuel economy almost double it got me started on the troubleshooting, ironically enough, the first thing I checked was the 02 sensor, found the pick up tube totally clogged, but I never did the true multimeter test of the O2, should have tried that from the start.

 

[seasick]

I cant say that the motor was surging, actually lagging is more like it, anything above 4200 or so RPMs it would start to hesitate and the RPMs would fall back off, then flucuate up and down.

The problem got progressively worse, didnt really notice it at first as I dont normally run it at high RPMs, but once I started seeing the fuel economy almost double it got me started on the troubleshooting, ironically enough, the first thing I checked was the 02 sensor, found the pick up tube totally clogged, but I never did the true multimeter test of the O2, should have tried that from the start.

If the tube get clogged, the ECU will make the fuel mixture richer. That will of course uses more fuel and can potentially foul the plugs. I am not sure why the motor bogged down at high speed though. Perhaps, since the ECU though the mixture was too rich, it stated to shorten the injector pulses. Did the motor smoke more than usual?

 

[Tucker]

Salinity did you buy the Yamaha 02 testor harness?? What was the voltage reading of the bad 02 sensor? Was the reading any different after you cleaned the clogged port next to the sensor? Thanks for sharing the good news. We don't see this often enough.

 

[Salinity Now]

Ya know the biggest part of irony in this whole thing (fuel consumption and high RPM loss/lagging) started AFTER I pulled the O2 sensor to clean/check it. Since the motors were new to me in Jan, I had been slowly going through the systems to learn the condition of things and get a feel for the condition of the motors, the port was using a considerable amount more oil and smokey; so I started with the 02 sensor as the source, found the clogged pick up tube and thought that was the problem, fixed it, reinstalled with new gaskets and went on using the boat (sparingly due to work).

The more I used it, the worse the fuel consumption got, the oil consumption got better because I also adjusted both oil rods, but the lagging and high fuel consumption started, I initially just thought I was chasing a new gremlin, assuming I had fixed the O2 by cleaning the clogged pick up tube, so I started trouble shooting all the other systems. It was the article DaleH posted a link to that I read a few months back that really hit the nail on the head for me and fit my symptoms to a T.

I never did the full monty diagnostics on the O2 sensor, in hindsight I wish I would have, but at the same time in hindsight I had a mixed bag of people saying "if aint it broke, dont fix it" (meaning pulling the 02 sensor intially) and the folks saying "clean/check 02sensor every couple years"......either way, its running great now (granted this is only after about 1hour run time and about 10miles worth of cruising) but Im glad i was able to really freshen up the motors, learned alot, and feel much better about them knowing Ive got a much cleaner running fuel system and baseline for maintenance.

 

[Lew]

I have an 250 ox66 on a voyager 24. and the service dealer (Grady) has cleaned the oxygen sensor. I am not so technical but I gather that it is important to change the sensor rather that just clean it at certain times ? So how do you know when to clean vs. replace and what is cost--i remember it was pricey (mostly labor anyway) to clean sensor. Would it be prudent to just tell him to replace the sensor ? Thanks Lew :uhm

 

[Salinity Now]

If I were more thorough, I would have done the actual multimeter tests as described in the link at the top of the post, that seems to give a good idea of proper operation by the numbers for diagnostics.

In my particular case, given the symptoms still existing; I just opted to change it out, paid $268 + $18 for the gasket kit from SIM.

As far as install, its REDICULOUSLY easy; 2 10mm bolts for the cover (use caution when removing the boot at the top of the sensor, it sticks and age + heat can cause it be worse) there is a notch in the back of the plastic cover to help ease it over the wires, you cant see it from the front, but its there, kinda have to feel around the back side for it); once the cover is off, the 02sensor screws into a special adapter bracket, the first time I took it off, I removed the 02 sensor first, that actaully requires a special 22mm tool (boxed in wrench with an opening for the wires) but you can just un-screw the 3 10mm bolts to remove the bracket, then use a regular wrench to get the sensor off. Once you get the bracket off, you can inspect the pick up tube, it pulls right out from the block, you can check to see if its blocked or dirty build up, you can do the same in the bracket housing (all of this can be done without phyiscally removing the O2 sensor if you just want to inspect it, the sensor itself has 2 quick disconnect fittings so you can remove it from the motor to clean it up, they only fit one way so its pretty easy to put back together.

Things to note.....(I learned the hard way) be sure to be careful pulling the bracket housing away from the block, I got in a hurry and actually pulled it off the stbd motor and the sniffer tube (pick up) came out with the adapter and fell out and on to the ground, unfortunantly I keep my boat on a lot, where I back it up over grass, and could not for the life of me find the darn thing, that was a $62 mistake.......

May sound tricky, but at $100 an hour, you can learn very fast how to do it, with the OEM tech manual and some trail and error, internet searches etc Ive gotten very fimiliar with these motors this year.

 

[seasick]

I have an 250 ox66 on a voyager 24. and the service dealer (Grady) has cleaned the oxygen sensor. I am not so technical but I gather that it is important to change the sensor rather that just clean it at certain times ? So how do you know when to clean vs. replace and what is cost--i remember it was pricey (mostly labor anyway) to clean sensor. Would it be prudent to just tell him to replace the sensor ? Thanks Lew :uhm

Without the test harness, it is difficult to test the sensor while still mounted on the motor.
Note that there are several failure modes for the sensor: The pilot tube gets plugged and the sensor makes the mixture rich. (The pilot tube was designed from the original SX version to help reduce clogging).
The sensor get plugged, same thing happens. The sensor completely dies: This is the worst of the failures since the motor may run lean. It is easy to crack the sensor also when removing so be careful .
The less common failure and the one that is rarely tested is the O2 heater. The sensor needs to be at 600 degrees or better to function. If the heater dies, the readings will be incorrect.
A common user mistake is contamination when cleaning. Yamaha has a special cleaner for the sensor but Ring Free can be use as a soak. Do not immerse the whole sensor, just the bottom part where the holes are in the metal sleeve. Personally, I think more harm can and is done by improper cleaning than there are actual failures so unless I have reason to suspect an issue, I leave it alone. And yes, the part is not cheap.
A lot can be learned from reading the spark plugs. You can see lean vs rich operation as well as excessive oil. Since the sensor often degrades slowly, the plug readings can be enough to make you suspect possible sensor issues.
One more thing that I am weary of but do not have scientific evidence is what effect additives can have on the sensor. I don't use anything in season other than Ring Free. I do not decarb and do not fog through the throttles. I do not want that stuff getting into the sensor.

 

[Tucker]

I'm in agreement with seasick about the test harness. Yea, you can rig something with paper clips but risk damaging the connector. Just bought a TPS test harness for $40 and will be ordering the test harness for the O2 sensor. Part number was in that write-up link. Interesting theory about decarboning. If you run ring free continuously why decarbon? If it's doing it's job shouldn't have to. This is a good thread to print.