1999 OX66 250 Spark Plug issue

[PBJohn]

I have a couple questions hopefully you guys can provide some advise. I am finding cylinder #4 spark plug is failing after an hour of use. The plug shows deposits forming and melting the ground electrode. I went through three plugs in the past month. Checked compression on the entire bank and found 100 psi even on all cylinders. Replaced the injector thinking it was maybe going lean. I can hear the injector pulsing. I have spark also. I don't have much experience with 2 stroke but could I have a water leak in the head or gasket and still show good compression? Can the reed valves have an affect on this?. I do not have acess to a bore scope so would removing the head make sense?

 

[yamamarinetech40]

Re: 1999 OX66 250 Spark Plug issue

If the electrode is melting you have a bad problem indeed....what color are the deposits? If I was melting plugs I would pull the head, yes. Check the water passages, I suspect you have blockage....are you in saltwater? Have you swapped injectors to see if problem travels?

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

I replaced the injector with a new one without any changes. The deposits are tan/grey/white and the plug is dry. 100% saltwater use. I suspect a water leak but with good compression it's throwing me off. I inspected the thermostats and didn't see any unusual buildup in the block passages. If the head had a blockage would it also show on the top or bottom cylinder with the water flow? What about reed vales? if one was bad what type of symptoms would that have? Sorry for all the questions my experience is on the automotive side so two stoke is slightly different.

 

[rodbolt]

Re: 1999 OX66 250 Spark Plug issue

2 stroke 4 stroke,its all the same.
melted electrodes are due to the same thing.
heat.
either a local hot spot due to a cooling system malfunction or air/fuel mix.
a bad reed will show a lot of spit back through the throttle shutter,airbox removed,when running.
the 3.1L blocks had pencil zincs about half way up each bank.
they can break off and block the cooling system unless they are regularly maintained.
there are also pencil zincs in each cylinder head that can break off.
myself I would want the head off to check for piston crown damage anyway at this point.
look at the crown for any signs of erosion at the edges.
any sign means its piston time as well.
have you checked the O2 sensor output voltage?
faulty O2 sensor feedback can cause a lean running above 4000 RPM.

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

Yes 02 voltage is within spec. Draw tube is clear. No poping through the intake so I'll take that as the reeds being good. The zincs were never replaced so that's a good possibility. The head has one on each side on the bottom.. How many are on the block? are they replaceable? I'll get the heads off this weekend and inspect.

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

Well got the cylinder heads off. No sign of any water blockage. All the anodes were in place and hardly worn. The trouble cylinder does have excessive carbon as compared to the other five. Piston crowns look fine. My next thought is sending the injectors out to get flow tested. Is it possible to build up that much carbon just in one cylinder and not the rest? Would inspecting teh reed vales make sense? I have pictures but I'm having trouble uploading them on here.

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

Ok I was able to upload a picture. There is carbon on all the pistons but not as much as #4. I sent the injectors out to be flow tested hopefully that will tell me something.

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

Injectors came back all within tolerance. I have an idea what may have caused this but need some opinions. Looking at the picture is it possible to build this much carbon in a cylinder in @ 50 hrs use?

 

[rodbolt]

Re: 1999 OX66 250 Spark Plug issue

possibly a fuel pump diaphram leak or maybe one of the recirc lines are clogged.
I cant remember which shutter the VST is vented to but I think it was #5 could be 4 but I dont think so.
you have 6 engines tied to a common crank, something is different on one.

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

I'm leaning toward a spark plug boot cap. I replaced all six this spring as a PM. My guess is that #4 was bad and over time built up the carbon. Once replaced the new one started to burn the carbon. The fuel pumps hold pressure. I tested with them unbolted from the block. I can blow through all the recirc lines. I plan on replacing that coil just to be safe. Does the pulser coil refrence each individual cylinder? Can one of the poles on that coil be getting an erratic signal?

 

[PBJohn]

Re: 1999 OX66 250 Spark Plug issue

RODBOLT! Help. I'm still fighting with this problem and every test I have preformed comes back with in spec. I am now losing both cylinder #3 and #4 both plugs foul out in a matter of one hour of use. At idle runs like a top. I can only imagine my issue is at high speed with excess fuel or loss of spark on those two cylinders. I was reading some other posts. Does the 250 OX66 use the CPS to control spark on two cylinders and the pulser coil on the rest? Can the injectors be bad even though they were sent out and tested ? I swaped out just about every part and went through the harnesses and can't find what could be causing this. Any suggestions.