Yamaha 225 ox66 rough idle

Decoy

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Jun 13, 2004
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Recently had fuels pumps replaced to correct a problem with the starboard engine cutting out at higher speeds. Now the engine runs very rough at idle. It seems to smooth out at higher speeds but still seems not to run as smooth as the port engine. Also the top rpms on this starboard engine is about 300 less than the port engine. Dealer suggested additives in the fuel and to run it hard for a while which should correct the problem. Been running it hard now for several weeks. No improvement. Very annoying.
 

rodbolt

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Sep 1, 2003
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20,066
Re: Yamaha 225 ox66 rough idle

wow<br /> next the dealer will sell you a new power head.<br /> that motor is dying. keep running it hard and it will self destruct. its trying to tell you its sick. make it well or bury it. I would start by finding a real dealer. one that will tell you to duimp some snake oil in the gas and run it is one that is looking to do a power head job. test the o2 sensor. did you replace the plugs. do a leak down to see how well the cylinders are sealing. a quick way to blow up an ox66 or anyother oil injected yammi is to run it with leaking fuel pumps. that is why I say every 3 years replace the fuel pumps. did you already replace the pumps on the other engine or is that going to happen at powerhead replacement time?<br />I have no mercy on customers that have neglect failures but sometimes its due to a **** poor dealer not telling the consumer what must be done and why. also test the spark plug caps. the ox66 is a reliable basic system. but if the o2 sensor is not cleaned regularly every 100 hours or at least once per year then it fails. a new one is about 360 dollars. a new one with a new power head is still about 360 dollars.<br /> see where I am going ?<br /> but if a dealer actually told you to just run it please find a different dealer. good luck and keep posting
 

Ray Neudecker

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May 25, 2004
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1,656
Re: Yamaha 225 ox66 rough idle

Harsh as it sounds, rodbolt couldn't be more right. Lack of proper maintence can easily be the death of your powerhead. A servicer who gives that kind of advice should be replaced immediately.
 

rodbolt

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Re: Yamaha 225 ox66 rough idle

hello<br /> yall gotta forgive me for sounding harsh sometimes but it gets the point acrossed. I hear it all the time. the last ox66 powerhead I did was a week ago, cause of failure was water in the remote tank. cause of water in the tank you ask? the guy cross threaded the remote tank fill cap and walked away from it. then ran it till it puked rods out the block. cost almost 5 grand to reassemble a 2 year old motor.<br /> all due to neglect.<br /> good luck,keep posting and yall have a nyce day now ya heah :)
 

sschoener

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Jul 18, 2004
Messages
34
Re: Yamaha 225 ox66 rough idle

Originally posted by rodbolt:<br /> hello<br /> yall gotta forgive me for sounding harsh sometimes but it gets the point acrossed. I hear it all the time. the last ox66 powerhead I did was a week ago, cause of failure was water in the remote tank. cause of water in the tank you ask? the guy cross threaded the remote tank fill cap and walked away from it. then ran it till it puked rods out the block. cost almost 5 grand to reassemble a 2 year old motor.<br /> all due to neglect.<br /> good luck,keep posting and yall have a nyce day now ya heah :)
 

sschoener

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Jul 18, 2004
Messages
34
Re: Yamaha 225 ox66 rough idle

RODBOLT, I HAVE A YAMAHA S250TXRV (97 EFI 250) WHICH UNTIL LAST WEEK RAN PERFECTLY. NOW IT RUNS ROUGH UNTIL ABOUT 2000 RPM AT WHICH POINT IT INSTANTLY KICKS UP TO ABOUT 2300 (ALMOST AS IF A CYLINDER KICKED BACK IN). THEN OCCASIONALY IT WILL DROP ABOUT 600 RPM FROM 4800 TO 4200 EG) MY MECHANIC SAYS THAT NUMBER 5 CYLINDER IS NOT FIRING SAT LOWER RPM AND AFTER DIAGNOSING IS ABOUT TO REPLACE THE CDI CONTROL MODULE. WHAT CAUGHT MY EYE IN THIS POSTING IS THE FACT THAT SYMPTOMS ARE VERY SIMILAR WITH A O2 SENSOR PROBLEM. AND I FISH THE BOAT A LOT IN AREA WHERE IT IDLES FOR EXTENDED PERIODS. THE 02 SENSOR HAS NEVER BEEN SERVICED OR REPLACED TO MY KNOWLEDGE (I GOT THE BOAT TWO YEARS AGO WITH 280 HOURS AND NOW HAVE 369 HOURS)
 

rodbolt

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Sep 1, 2003
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20,066
Re: Yamaha 225 ox66 rough idle

the test harness is relativly inexpensive and there is a tech bullitin on how to test it. usually once they go to long youcant clean them<br /> I would verify the CDI failure or at least get it in writing that if a CDI replacement does not cure it you dont have to buy it. sounds like some poke and hope testing is afoot. be careful.have the low pressure pumps been replaced? they are due<br /> and has the vapor seperator filter been serviced? its due as well<br /> good luck and keep posting
 

sschoener

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Jul 18, 2004
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Re: Yamaha 225 ox66 rough idle

I DO NOT HAVE A RECORD THAT THE LOW PRESSURE PUMPS HAVE BEEN REPLACED - SO I WILL DO THAT. THE VAPOR SEPARATOR FILTER IS SERVICED EACH FALL.<br />THANK YOU AND I WILL KEEP YOU POSTED.
 

sschoener

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Re: Yamaha 225 ox66 rough idle

RODBOLT - I MET WITH MY FRIEND THE MECHANIC TONIGHT AND WE TESTED AND REPLACED THE O2 SENSOR.<br />THOUGHT WE HAD THE PROBLEM LICKED - ENGINE STARTED AND RAN PERFECTLY THROUGH WARMUP AND IDLE DOWN - THEN NUMBER FIVE CYLINDER DROPPED OUT AGAIN. NO SPARK OR VOLTAGE TO THE COIL UNTIL ABOUT 2100 RPM WHEN IT KICKS BACK IN. ACCORDING TO THE MANUAL, THE CDI CONTROLS SPARK TO NUMBER FIVE AND NUMBER TWO. HOW WOULD I VERIFY A FAULTY CDI SHORT OF TRYING A NEW ONE.
 

sschoener

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Jul 18, 2004
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Re: Yamaha 225 ox66 rough idle

BEFORE WE CONTINUE WE ARE REPLACING THE TSTATS, WATER PUMP - THEY ARE DUE - AND RE-TESTING THE THERMO SENSOR
 

rodbolt

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20,066
Re: Yamaha 225 ox66 rough idle

hello<br /> remember if this motor has the smart system it will run on 4 or 5 cylindrs<br /> you may be chasing a non issue<br /> someplace about here I have a list of engines but I think yours is one. its incredibly rare to see a bad CDI on the ignition side.<br /> I will try to look for more info on the CCS system. or have your mechanic read up on the yamaha controled combustion system that the V76 225's used. your engine also incorperates SMART as well.<br />good luck and keep posting
 

sschoener

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Jul 18, 2004
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Re: Yamaha 225 ox66 rough idle

RODBOLT - MY MECHANIC IS ON HIS WAY OVER NOW. IF BY SMART SYSTEM YOU MEAN THAT THE ECU CONTROLS CYLINDERS 2 AND 5 - I BELIEVE THATS WHAT HE FOUND OUT. WHAT LED HIM TO THE TEMP SENSOR OR MORE ACCURATELY A HIGH TEMP CONDITION IS THE FACT THAT THE TSTATS ARE OLD AND THE WATER PUMP IS DUE. HE READ IN THE SHOP MANUAL THAT IF IT'S HOT, THE ECU WILL ACTUALLY DROP A CYLINDER OR TWO TO PROTECT ITSELF.
 

sschoener

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Re: Yamaha 225 ox66 rough idle

WHAT IS DIFFERENT ABOUT THE WAY THE MOTOR RUNS NOW AS OPPOSED TO LAST WEEK IS THAT IF IT CUT OUT A CYLINDER AT LOW RPM BEFORE, IT KICKED BACK IN MUCH MORE SMOOTHLY AND AT LOWER RPM. ALSO ON TWO VERY BRIEF OCCASIONS, IT CUT BACK AT HIGH RPM (5000)
 

rodbolt

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Re: Yamaha 225 ox66 rough idle

have your tech hook up the diagnostic lamp also known as the winky blinky. if no codes are set when its running badthen we are back to a fuel issue most likely. just remember that with the lamp inplace no oil trnsfer occurs but all of the alarms are still operative. this motor is usually a straight fwd testing procedure. did you use a test harness and a multi-meter to verify the o2 sensor is functioning? I have replaced 4 so far this week that look great they just did not work.<br /> good luck and keep posting
 

sschoener

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Re: Yamaha 225 ox66 rough idle

RODBOLT - WE REPLACED THE O2 SENSOR LAST NIGHT WITH A NEW ONE - JUST IN CASE. TONIGHT I THINK WE ARE ZEROING IN ON THE PROBLEM - THE TEMP SENSOR. WHEN WE DISCONNECT IT, CYLINDER NUMBER FIVE IMMEDIATELY FIRES - THE IDLE IS ALMOST THIRTEEN HUNDRED RPM - SO THIS RESISTANCE NEEDS TO BE PRESENT I THINK - BUT I THINK IT IS TELLING THE ECU THAT THE ENGINE IS RED HOT. RESISTANCE IS HALF A MEG AND DOES NOT CHANGE WITH THE ENGINE GOING FROM COOL TO HOT. WE WILL GET A NEW ONE TOMMORROW AFTER WE CHECK THE PROPER RESISTANCE FOR THE SENSOR AND VERIFY THAT IT IS OUT OF RANGE. ALTHOUGH THE FACT THAT THE RESISTANCE DOES NOT CHANGE IN THE THYRISTER WITH TEMP CHANGES LEADS US TO BELIEVE IT IS FAULTY.
 

sschoener

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Re: Yamaha 225 ox66 rough idle

UH OH - AFTER LOOKING AT THE PARTS FICHE IT TURNS OUT WE WERE LOOKING AT THE KNOCK SENSOR
 

sschoener

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Jul 18, 2004
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Re: Yamaha 225 ox66 rough idle

IS THE SHARP INCREASE IN RPM AND THE RETURN OF NUMBER FIVE SPARK SUPPOSED TO OCCUR WHEN THE KNOCK SENSOR IS DISCONNECTED??
 

rodbolt

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20,066
Re: Yamaha 225 ox66 rough idle

if it overheats it will drop to about 3000 rpm and miss like crazy. it will give an audible as well as a visual indicate. I really dont think your overheating.<br /> did you check the plug wire caps?
 

sschoener

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Re: Yamaha 225 ox66 rough idle

RODBOLT, AFTER TWENTY FIVE YEARS AS A PORSCHE AUDI DEALER I SHOULD KNOW THE VALUE OF QUALIFIED TECHNICIANS WITH PROPER EQUIPMENT. TODAY I DROPPED MY BOAT OFF AT THE LOCAL YAMAHA DEALER AND THOUGH HE IS NOT CERTAIN YET - HE THINKS THE PROBLEM IS - AS YOU SUGGESTED - FUEL RELATED. IN FACT HE HAS HAD MULTIPLE PREMATURE FUEL FILTER PROBLEMS DUE TO THE ALCOHOL CONTENT IN THE LOCAL FUEL. EVIDENTLY THE ALCOHOL CLEANS THE DEPOSITS IN THE TANK AND LINES AND SENDS IT ON TO THE FILTERS. I WILL KEEP YOU POSTED. THANK YOU VERY MUCH FOR ALL YOUR VALUABLE HELP AND GOOD ADVICE.
 
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