OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

[ultimatehometeam]

Ok purchased a boat with twin 225's 1999 ox66's...

Before buying the boat I put in new plugs for the sea trial and both engines turned really well into the 5300-5400 area.

Current situation not even 2 weeks later - port motor will not fire on the bottom left cylinder and will only turn 4,600 trimmed down and max at best 4,900 trimmed up.

I did all the regular stuff someone should do with one of these engines per rodbolt etc..
- Low Pressure Fuel Pumps
- Clean VST's
- Clean o2 and then voltage test the voltages on the water - all in spec
- Check compression 105-115 on all cylinders
- New Plugs
- Oil Pump adjustment
- TPS adjusted to .50
- Sync and Link
- All new plug boots / caps
- Check vst output at 35 psi steady at all rpm's

Ok... bottom left spark plug no fire at all not at idle or speed... put in a new plug and run it at all rpms and the plug looks brand new. It has a gas odor to it... here what I have tested on that cylinder:

- Spark... used a light tester it works... then used a gap tester at 7/16 as per rodbolt... it performs just like the good engine with no issues. Idle or with rpm up to 2,500 no difference it still sparks.
- Swapped the affected cylinder's coil / wire with the known good engines coil and no change.
- Fuel ... After running the engine with a new plug and removing after about 5 - 10 minutes running the plug smells like gas and is clean like it never fired.
- Compression... even on this cylinder with the others on the engine.

I am perplexed I live by the spark, compression, fuel modo and cannot figure out why this cylinder is not firing.

My starboard engine after all the service runs like a top turning 5,300 even with the other engine holding it back. I have went over everything twice and still cant figure it out.

I even swapped injectors from the cylinder next to it with no change in spark condition.

Is it possible to gas foul so much that a new plug won't fire either?

ANY help would be super appreciated thanks so much!

 

[Inducted]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

It seems like from your testing your ignition system is generating proper spark, and you have fuel but no combustion? Double check compression, compression tests are not foolproof Maybe only one of the piston rings is any good and it fails at high rpms. How about a leak down test? Remove spark plugs and see if you can see anything different. Reed valves might be deflected. Maybe too much carbon buildup is goofing up compression buildup?
Just throwing out some ideas if its not ignition and fuel must be something?

 

[99yam40]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

Like you said if you have good compression and good spark at the proper time, then you are missing the proper fuel/air mix.
Too much is just like to little, the cylinder will not burn the fuel properly.
may need to check to see if the injector is firing properly and for the proper time.
Make sure the fuel pump is not leaking extra fuel into that crankcase if one is using that one for a pulse.
vacuum leak on the bottom seal if that is the very bottom cylinder

water getting into cylinder is something else that will kill a cylinder

 

[mobilemike]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

Can't do a leak down on a two stroke. I'm with 99yam40 on this one.I can't remember if one of the primary fuel pumps picks up the pulse from the #6 cylinder or not,but i would look there next. Clean plug sounds like too much fuel.Just for testing, you might try to unplug the injector for #6 and see if it trys to pick that cylinder up from the excess fuel.

 

[jeffersondodson561]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

Can't do a leak down on a two stroke.

Why not? Bring the piston up to TDC and put at least 100 psi and document leakeage percentage. I guarantee anyone who cranks the motor long enough will get the appropriate amount of compression percentage. The only reason dealerships don't do leak down test is because of the time it take to do it. Leak down "dogs" compression tests, 2 or 4 stroke.

 

[yamatech43]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

You need to do a leak down....and yes you most certainly can......i would suspect reed valve is open....remove air box and run at speed....stop...tilt motor up right away and see if fuel comes trickling out....you have a MECHANICAL problem obviously since sounds as if plug is being washed with gas(looks brand new...smells like gas....)

 

[mobilemike]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

Sorry,I should have said that yamaha considers a compression test on a two stroke engine to be enough to diagnose a compression issue (according to my factory tech guy). Four strokes, on the other hand, can give good compression readings and still have running issues (usually carbon on the intake valve seat due to long idle/trolling speeds).Still sounds like too much fuel on #6 to me or no spark at speed. Try running the engine with a spark tester on #6 to check for weak or no spark at speed.Also, you can swap the injector leads to see if it may be a problem with the ecu not providing a signal or holding the injector open.

 

[ultimatehometeam]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

SOLVED

Ok... well pathetic enough since all signs of everything including compression looked good.

Went to basics and took off the trottle body air hood (plastic) and low and behold after looking at the throttle body connectors the bottom connector to the valves the little plastic circle piece popped off the pin that opens and closes the bottom throttle body.

So I was pretty excited when I saw this.

Before I put it on I even put the throttle in full open and could see that the bottom cylinder throttle body was no opening.

So that cylinder was essentially at idle when all the other would go wide open. Thats why the engine ran great but it just would not hit WOT rpm.

So put the connector back on... inspected the plastic to make sure it was 100% and off to the water to test it.

Boat ran perfect again.

Gosh taking 1 night off from looking at it and giving it a fresh basic start was the key. To just eye over the simple stuff again.

Thanks for the help!

 

[99yam40]

Re: OX66 1999 225 - No Fire in one cylinder totally confused... Any Help Appreciated!

Strange out come, but good to here it was simple fix.
Need to find out why it popped off, as they do not just pop off normally if something is not broken