loosing fire #5 cyl, coil is good

[walkaboute]

2000 0x66 250 hp, #5 cylinder looses fire after warm up. if engine already warm fires for 10 secs after start up and then quits, swapped coil with a known good coil. What would cause this too to happen???

faulty CDI? possible lean condition on #5?
I'm at a total loss for what would be causing this after swapping the coils around.....

[Ken]

walkabout,
There are some Yamaha V-6 (8?) outboards that don't fire two of the cylinders at idle - could that be what you are experiencing?
Ken K

[jb123]

yes, check to see if the # 2 is also not firing, while runnin pull the # 2 and #5 with rubber handled pliers and listen for the rpm change and spark jumping or not. under load,underway how does it run ? you may want to run it at night and look for spark bleeding out. i remember seeing something in another post about resistors? in the big block spark plug ends, might want to check to see if you have those.

[walkaboute]

dont think so, found this one not firing as a result of trying to figure out why I was seeing fuel or oil coming out exhaust appearing as "droplets" on the water and also unstable rpms, see post in early july titled "fuel out exhaust, unstable rpms".......we tested by unplugging plugs one at a time till we found #5 made no difference in motor attitude when unplugged...then restarted motor with screw driver stuck in plugwire and crossed to plug and watch arch to plug, by observing this we were able to see exactly how long coil was sending fire...long story short other five cylinders are fine, as well as other six on the port engine, I have already ruled out problems with O2 sensors, spark plugs and coil by means of swapping with other engine, the compression is also ruled out...
It appears that the computer (called CDI unit I think) is cutting that cylinder off but WHY?

[walkaboute]

jb, you and I were writing at same time, so I didn't see your post until I posted last post. To answer question about under load, the last time it was out it had already displayed the fuel or oil on the water and I was testing it after a local yamaha mechanic had replaced the diaphragms on the three small pumps that as he said spit fuel through crankcase wall.. they are located just to the right of the vapor seperator..anyway ran for about an hour before started experiencing rpm fluctuations just as it does reving engine at dock ie run up to 2500 it will go up to 3300 or down to 1700.... before that both engines were fine with max rpms around 5600

[jb123]

did he test the fuel pumps or just assume because it was spittin fuel that they were bad, and after replacing its still doing the same thing ?

http://www.yamahaoutboardparts.com/c...c;f=1;t=001134

[walkaboute]

local yam mechanic assumed without testing and replaced the diaphragms, it did not fix, fuel or oil still appears on water. In addition after the replacement was the first time I had seen any unstable rpms which occurs whether idle or under load. The local yamaha mechanic says he doesn't want to work on it any more. So I have done some elimation and had a knowledgable friend help yesterday and located the problem with #5. So far I havent mentioned we also checked fuel pressure which appears good, key turn yields 36 lbs-- key off slow return to 33 lbs and holds. Do you think a flash code tester would be beneficial and if so where can I get/buy one??

[prhnkp]

I have twin 1996 225 HP V-76 saltwater series engines. Same issu on port: cuts out past 4100 rpm and starts to hunt for rpm. Varies between 2900 & 4200, whenever I try to go over 4100. Mechanic says the lower cylinders on each bank are cutting out. I ttried to locte the flash harness on the web, and can't find it. My mechanic says he doesn't know what's wrong. Anyone else with any ideas. Thanks

[jb123]

i have 2k 200`s and understand them much less than carbed motors but possibly intake/reed issue? post your question again until boats.net answers as he is the pro and wont reply after others have replied.great luck please post your fix.

[prhnkp]

As a follow up: mechanic says the reeds are good, and speculates it's an electronics problem. He's not a factory authorized guy though, and doesn't have access to yammi testing equip or tools. The local authorized shop will look at the engines, but not for 3 weeks, and then I find out what the problem is, and estimated costs of repair. Then another 2 - 3 weeks before repairs completed. Here in Ohio, that's close to the end of the season, so any help will be appreciated.