2001 SX250TXRZ OX66 (one of a pair)

[DJW]

Need help determining what went wrong. The motor has 581 hrs., the vst filter became clogged while I was out. The motor would cut out briefly until fuel pressure returned. I replaced the filter, which was very dirty, and went fishing. I only ran 9 miles and it was running great and then it started losing rpm. I pulled back the throttles and the motor stalled. It would not turn over. I removed plugs and it then would turn over but zero compression on the #5 cylinder. The powerhead has been removed and the #5 piston has the side burned off. Mechanic found no trouble codes active. Only abnormal thing found so far is that the wrong spark plugs where installed. (hotter plug) Can anyone suggest any other things to check that could have caused this? I do not want the same thing to happen to my rebuilt powerhead.

Thanks

 

[cousinabe]

Re: 2001 SX250TXRZ OX66 (one of a pair)

sorry about your powerhead. That sucks.

possibly a clogged fuel injector. if your vst had a lot of crud in it, possibly the fuel injector screens are clogged up too. causing a lean condition on the cylinder caused it to blow.

 

[robert graham]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Wonder if a pair of Racor 2 micron water/fuel seperators might have prevented this? Sorry about your problem and hope they get you back up and running soon. Good Luck!

 

[PBJohn]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Have the injectors sent out to be tested and cleaned. I would replace all the routine items LP pumps, O2 sensor, t stats. Check the oil system clean and replace filters in the oil tank. If your fuel source is from one fuel tank check the other engine VST filter.

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Thanks for the input, I will have the injectors cleaned and checked. I pull fuel from 3 different tanks and have Racors in line to both engines. Already bought the LP pumps, T stats, and O2 sensors.

Thanks again

 

[rodbolt]

Re: 2001 SX250TXRZ OX66 (one of a pair)

2 micron filters most likly will be way to restrictive for a 3.1L motor and most likly will lead to either lift pump failures or another lean out.
Yamaha reccomends 10 micron and a minimum of 90 GPH when the filter is new.
remember the smaller the filtration the more restrictive it is and the faster it starts clogging creating excessive fuel system vacum.

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Well the powerhead has been rebuilt. The mechanic says it sounds great when idling but when giving gas it is stumbling. At this point he does not know what is wrong. Unfortunately he is on vacation for 3 weeks, I knew this before he started the job, and says he will fix it upon his return. He thinks that it is in the EFI system, possibly a sensor malfuctioning. Question, any ideas what could be wrong? Fuel system is 100% correct and tested. Could this have caused the #5 piston to burn up? Any help is appreciated even if it basic repair 101 suggestion, it doesn't hurt to check again.

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

bump to the top

 

[rodbolt]

Re: 2001 SX250TXRZ OX66 (one of a pair)

why would you suspect a sensor malfunction?
and if you do what sensor would you suspect and why?

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

It is not my diagnosis, this is what the rebuilder is leaning toward. He claims the fuel system is working properly, all components have been checked. He believes the problem lies in the EFI loop. The motor ran fine until it blew up. He changed the O2 sensor so far but says there is something not right with how it is running. This is not a Yamaha trained tech, nor does he pretend to be, his business is outboard rebuilds. But he needs to find what went wrong to prevent it from happening again. The #5 piston had the side melted off of it. He says due to a lean condition but cannot find what did or is causing it. I have not heard the motor run since the rebuild but I do not have enough outboard experience to hear anything. Any and all suggestions will be appreciated. I want the rebuilder to complete the job so that there is no issue with warranty if this should happen again. Other wise I would just take it to a dealer for the repairs.

Thanks

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Rodbolt, I didn't answer your question very well because I am unable to. However if there is something that could be causing this problem parts wise, I will buy them and replace just to rule it out. I also have its twin mounted next to it that I can exchange parts with to diagnose. What the outcome, I will be replacing the the same parts on the other motor just to make sure.

 

[rodbolt]

Re: 2001 SX250TXRZ OX66 (one of a pair)

we dont like switching parts, can lead to two bad engines.
did the injectors actually get sent out to a reputable injector service center such as flagship marine for cleaning and flow testing?
a bad O2 sensor can lean out a motor and pop a piston as can a clogged injector or low fuel rail pressure.
your description of the current problem doesnt lead to any sensor failure but its a quick check with a diagnostic test lamp.

 

[DJW]

Re: 2001 SX250TXRZ OX66 (one of a pair)

Rodbolt, thank you for your input and sorry about being away so long. I now have my boat back. The rebuilder said he found a broken, yellow, wire that controlled timing advance. Whether this is true or not, the engine is running. I had it out to begin breaking it in. I am into my fourth hour and have had the motor to 4000 rpms. It runs well but it requires much more throttle lever travel than the other to achieve same rpm. I believe this is caused by all the extra oil being burnt. I added an extra 1.5 gallons off oil to 85 gallons of gas for the new motor, plus what is injected of course. Does this sound right? Also, I found my racor fuel filters to be 2 micron. You stated earlier that this could cause problems so I changed them to 10 micron. I am starting a maintenance schedule per Yamaha reccomendations. Anything I should add?

Thanks, Dan