1999 225 Optimax Misfire

[brinson]

My 1999 225 Optimax serial #0G814230 has developed a random misfire in the last two days. The engine began to drop a cylinder or two at idle and would clean up when going to full throttle. When I would slow down the misfire would come back occasionally. I changed the spark plugs NGK 5887 gapped at .033" and it did not help. #2 and #6 plugs had a little more carbon than the rest but I did not think it was too bad as the plugs were fairly old. I plan on changing the fuel filter tomorrow and cutting open the old filter to see if there is any water. Any suggestions on what else to check would be appreciated.

[Savage]

Coil(s).
Coil wires.
Reeds.

[Rip Bass]

Savage is right,check the reed valves. A broken reed will cause a low rpm miss that goes away with a little throttle. If it is broken,you should try to find the broken piece,if it’s still in there,the chip can cause major problems. I had a reed break in half on my Opti,I found the broken piece stuck in an oil,puddle at the bottom of the reed block. Lucky me.

[EuropeanAM]

+2 to Savage's suggestions above.

Once you've checked those, also look for sources of "un-metered fuel or oil" entering the engine. This can include leaking o-rings, tracker valve, fuel pressure regulator diaphragm, pulse fuel pump diaphragms, over-filled remote oil tank, faulty crankcase pressure check valve (among others).

[brinson]

Thanks, I inspected the red valves today and were in good shape. I will start checking the other items tomorrow.

[Savage]

If the reeds are steel, then get rid of them. That motor came stock with steel reeds.

[brinson]

After inspecting the reed valves, I found the tracker valve diaphragm was torn. The motor runs great now. Thanks for the help.

[EuropeanAM]

[brinson]

Update on my Optimax. I have not used the boat much lately and the misfire is back. I had it scanned and had multiple misfires on #1 cylinder only. The plug was black and wet with fuel. Changed the plug and gapped to .032 and motor ran well until I let it idle for a while and the misfire was back. Once it begins to miss, I can change the plug and it will run well until I let it idle around for more than a few minutes. I checked the tracker valve diaphragm and it was good. I scoped the reed valves and they appear to be ok. I changed the coils and wires on #1 and #6 cylinders with no luck , changed the fuel and air injectors on #1 with same outcome. Each time #1 cylinder begins to misfire. Also, the pulse fuel pump diaphragm has been changed. Has anyone ever experienced a faulty computer such as coil or injector drivers? I have not checked the crankcase pressure check valve yet. It will literally kill a plug within minutes of idling.

[EuropeanAM]

Need to pull the air handler and inspect those reeds from the crankcase-side. I suspect you have a chipped or broken reed on that cylinder, which is limiting how much "clean and oxygen-rich" air you're getting to that cylinder.

[brinson]

Thanks, Don will do today.

[brinson]

https://postimg.cc/yD4PxJfm
https://postimg.cc/WdG7k2KQhttps://p...mg.cc/mzJZRGbr
I did not see anything obvious. Is it necessary to disassemble them to inspect further?

[brinson]

https://postimg.cc/mzJZRGbr
https://postimg.cc/4KXQvDRn
https://postimg.cc/qgFQfDyZ

[brinson]

Reeds are good I saw no chipped reeds. I removed the crankcase pressure check valve and will replace it as it's never been changed. It seems to be working ok though. Just about of things to check. Any suggestions would be appreciated. Computer issues possibly?

[JOE54]

dout it, see if its losing spark

[EuropeanAM]

Would be pretty rare to have a single-cylinder computer failure on this particular model.

Good idea to replace those reeds while out. Also- check for any that have excessive standoff, or chips/cracks in the rubber that could be "catching" a reed.

Almost looked like something at the right-bottom of this image: https://postimg.cc/yD4PxJfm

Otherwise- it would almost have to be one of the "swap" tests you did was mistaken in it's results. Keep in mind- if a component is causing a skip in #1 and you move it elsewhere, it likely will not ELIMINATE the skip, it will simply "relocate" the problem to a new cylinder.

[brinson]

Thanks, Don. I would love to replace the reeds but, I would like to see it run first as I have spent considerable money in 3 different Mercury shops with not good results. I'm reluctant to spend too much more and at some point need to "cry uncle" and just buy a new motor. I did find a pinhole in the crankcase pressure valve also. It seemed to be stuck and would not check off. I could see a pinhole in it. I puchased a new one today.

[brinson]

I could have easily made a mistake on one of the swaps as nearly every component on fuel and spark has been changed or inspected. That being said I can still install a new plug on #1 and it will not miss until it fouls. That was before this last round of checks. I will run it tomorrow again.

[JOE54]

if you were looking at the early larger shoulder 15/16 size press check valve pin hole suppose to be there air psi relief for oil tank engine off , assuming you have bore scoped cyl for partial spun sleeve

[EuropeanAM]

And to triple check- #1 as in Starboard, Right, Top spark plug (correct)?