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Old 07-20-2011, 07:31 AM   #1
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Default 01 225 optimax fouling # 6 cyl sparkplug

I'm hoping the optimax gurus on here can help me out on this one. A while back, my stbd engine began to loose 500 rpms at WOT. I spoke to a friend and he hooked up the ddt and told me that the # 6 cyl was not firing. I changed the coil and the driver and still nothing. turns out to be that the spark plug was completely fouled. put a new one in and engine was back to normal. used the boat for approx 5 hours and the rpms drop again. take out the brand new spark plug from # 6 cyl and it is again completely fouled. WTF???
The plug has a wet look to it and has alot of oil, all the other plugs in the engine are fine.
compression for that cyl is above 90, I changed the direct injector about a year ago and it's working fine.

any body have any ideas here?????
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Old 07-20-2011, 07:57 AM   #2
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How do you know the direct injector is firing? Did you do a cylinder drop test with the new spark plug in? Injectors can go bad and not throw a code. Also check your spark plug wires, i have seen more then a fair share arc thru and cause problems like you have.
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Old 07-20-2011, 08:02 AM   #3
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Yeah my buddy did the drop test after we put the new plug in using the DDT. he also checked it while the engine was off and i could hear it firing. I also replaced the wire since it came with the coil that i bought and did not need.
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Old 07-21-2011, 11:33 AM   #4
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anyone else have any thoughts on this??????
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Old 07-21-2011, 05:59 PM   #5
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check the mechanical fuel pump for leakage causing that cyl to run rich
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Old 11-18-2011, 07:24 PM   #6
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Look at your intake reeds. Have seen quite a few broken reeds on Mercs over the years.
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Old 11-18-2011, 07:48 PM   #7
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If he was having an issue with the reed valve, wouldn't he have a loss in compression? There would also be a lot of sneezing coming out of that cylinder.

What's an acceptable compression range for these engines?
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Old 11-18-2011, 07:59 PM   #8
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check the air and fuel pressure on the rail make sure there within spec and have your air injectors cleaned...a plugged air injector not firing the right amough of air into the cyl behind the fuel will cause a fouled plug in an opti due to poorly atomized fuel....i see it all the time where other techs seem to forget the air injectors when they service the injection system on an opti....
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Old 11-20-2011, 03:14 PM   #9
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Quote:
Originally Posted by Mikerodrig27 View Post
If he was having an issue with the reed valve, wouldn't he have a loss in compression? There would also be a lot of sneezing coming out of that cylinder.

What's an acceptable compression range for these engines?
125 comes to mind for normal, Someone else chime in if I'm not close on comp reading.

Intake reeds being broken usually won't show up in a comp check. Your only checking the sealing components of the cylinder itself.

I usually find broken reeds during a cylinder drop test with my CDS system. Low or no cylinder drop on cylinders with bad reeds. I always check them, especially on the 2.5 liter engines. They seem to break reeds very regularly. We swap to Boyesens and they usually have no issues from that point on. Fuel consumption does go up approx 2 gph with the Boyesens though.

I usually don't see reed issus on the larger disp Mercs, just throwing it out there because it's an easy check with some basic hand tools.
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