50hp Spark Issue

[buzzer1]

Hi Guys,<br />I am new here and need help.<br />I have a 1989 Mercury 50hp outboard that is giving me a headache. One of the cylinders on the thing keeps cutting out and fouling out. There is also oil in the exhaust leaking from the hub. The carbs have been cleaned and tuned, the spark has been checked and seems strong. I can start the motor and run it at full throttle on the other cylinders very slow and bogging and then it will just kick in clear out and go like hell. Then after a period of just trolling or going slow it cuts out again. Anyone got any suggestions? Do you think it could be a coil? Also the alarm keeps going off during this solid beep indicating overheating. Any help would be appreciated. <br />Here is what I did this weekend. I started the motor and disconnected the bottom cylinder plug wire, no change. I put it back on and disconnected the middle cylinder plug wire, engine stumbled. I put it back on. I then disconnected the top cylinder plug wire and engine stumbled. Next I took the middle cylinder coil and swapped it with bottom cylinder coil. I started the engine and removed bottom cylinder plug wire still no change. I removed middle cylinder plug wire motor stumbled. This eliminates the coil as the problem. Here is where it starts to get tricky. I pulled the plug wire on bottom cylinder and could see and hear the spark to the plug, but no change in engine cylinder definately not working (I'm thinking spark is too weak). Then I rev the engine up and try to change the situation. Next thing is I pull top cylinder plug and no stumble. Now the top cylinder has no spark. I pull bottom cylinder plug wire no change. Engine is now running on only one cylinder the center cylinder. I am thinking that the only thing that could cause this condition is the switch box. The part is $185 new from the parts store. I do not have a dva to test but was wondering if it sounds like the switch box to you experienced folks. Carbs are clean as a whistle and fuel is flowing nicely. Any help would be much appreciated and I will continue to post resolution in order to help others. Thank you.

 

[KCLOST]

Re: 50hp Spark Issue

First make sure that your engine is not set up to only run on two cylinders at idle... I'm not really sure on that, but there are some out there like that.... But now, since you have only good spark on one cylinder, we do have a problem somewhere.<br /><br />Anyway, It could very well be the switchbox, but normally they do not cause a weak spark they either work or they don't! (spark or no-spark)<br />You need three things to have combustion. Fuel/mixture, compression, spark! You say you have a weak spark on the bottom cylinder, but have you checked the strength of it with a spark gap tester. It should jump a 7/16" gap at least. You can buy one at any auto parts store.<br /><br />You say that the top cylinder now has no spark... Whenever you pull plug wires when the engine is running, you want to make sure that the wire is grounded to the block. If the spark pulse cannot reach ground, that can damage the switchbox. If you pulled the wires while running and did not let the spark reach the block you "MAY" have damaged it.<br /><br />Without a DVA meter, or another switchbox it's kind of tough to diagnose the problem. But the top cylinder problem does sound like a possible faulty switchbox. The bottom cylinder problem is a little tricky, it could be fuel, compression related if the spark is ok. Just because the carbs look clean doesn't mean they are. You have jets and floats to contend with that you can't see by looking down the throats.<br />It may just be running rich!<br /><br />Have you checked compression by the way?

 

[KCLOST]

Re: 50hp Spark Issue

buzzer,<br /><br />I don't mean to send you down the wrong road... But the switchbox is expensive and I'd like you to check the compression and spark intensity first...<br /><br />And I forgot to mention this, which is VERY important... If the alarm (contant beeeeeeeeeep) is going off during your bogging times, you are either overheating the engine, or you have a faulty sensor. By the way, is your engine oil injected? It is known that a faulty switchbox can cause an "intermittent" beep to go off because the pulse used for oil pump rotation monitoring can be interupted. But a solid beep I haven't heard of. <br />Your engine may actually have a automatic rpm limiter that kicks in when the engine overheats.

 

[buzzer1]

Re: 50hp Spark Issue

I have purchased a spark gap tester and a compression tester. I also ordered the repair manual so I can do all the tests on the related parts such as the trigger and the stator. I will respond back with what I have discovered. To answer your question it is an auto blend oil system and the beeping you described is exactly what it was doing I don't think it was overheating the engine is cool to the touch.. Try to run at full throttle engine bogs and alarm beeps making me lean towards that swith box again. Thanks for all the brain storming and I will be sure to report back.

 

[KCLOST]

Re: 50hp Spark Issue

If you have an intemittent beep you could very well have a faulty switchbox... You should also pull off the oil pump and check for any gear shavings....<br /><br />Let us know...

 

[buzzer1]

Re: 50hp Spark Issue

Hi Guys,<br />Here is what transpired today. I checked the compression first 140lbs in all 3 cylinders sweet. Then I used the spark gap tester and saw spark on all 3 cylinders however I was not convinced that it was strong. All conditions were exactly as before. Number 3 cylinder not firing, plug wet. Number 2 cylinder fine. Number 1 cylinder spark and fired until engine ran for less than 5 minutes, then no fire or spark on cylinder 1 or 3. Running on one cylinder. So I say time to test the trigger and stator. I got a manual from Seloc, can’t say I am very happy with it however it did have test procedures. I disconnected only the red and blue wires from the switch box. 2 yellow to the rectifier stayed connected as well as a ground from the stator to power head ground (battery was disconnected). I placed the Ohm meter on setting 2m and tested for continuity on the red wire with red probe on red wire and black probe on ground…ut Ohhh it read 0.00 and book states it should read no continuity. Next I place the red probe on the blue wire and black probe on ground it also showed resistance and should have showed no continuity. I am thinking at this point that that is a failed stator test. Also I tested the trigger by measuring resistance between the brown wire and black, the white (actually yellow wire) and black wire and between violet wire and black wire. The reading I got was consistent on all three but it was like 1.2 and the book says it should be between 12-14. Now I have a volt-Ohmm meter that may not have the setting required to make this test. I have included links to pictures of the procedures I did including the meter. One other thing I noticed was I could wiggle the trigger wire back and forth and the trigger actually seemed loose under the fly wheel. I am not sure if that is normal. I did not have a fly wheel puller and tomorrow I will be purchasing one. I want to pull off the fly wheel and check those stator wires because red and blue to ground with resistance seems like a dead short to me. Maybe a broken or cut wire. I need your guys help again and will continue to post until solution. The book says Ohm meter should be at r x 100 for trigger reading. Does my meter have that setting? It also states r x 1000 for stator reading. Not sure if I have that setting either. Please look at pictures and advise. If stator is gone do you think switch box is dead also? What about the trigger? Replacing all 3 is about $490 and I will do it if it means a trouble free fishing season, however I wouldn’t want to replace good parts. All help is greatly appreciated. Picture links below. <br /><br /> http://www.lisaandrussell.com/stator.jpg <br /><br /><br /> http://www.lisaandrussell.com/voltmeter.jpg