Weak spark - Nissan mfs6a

[svscott]

I've had a 99 Nissan NSF5A since 2005 and it suddenly shut off today and wouldn't restart. Hopefully someone has experience with these engines and can point me in the right direction?!

Launched for the season yesterday was running well yesterday. Today, it ran great for 20 minutes and then the engine suddenly died. It was getting fuel but the spark seems weak. It was full sun so I couldn't see well but I didn't see any spark. I got brave and grabbed the electrodes on the spark plug and pulled the cord. My fingers tell me there is definitely spark but it didn't feel very strong. I pulled the spark plug wires apart to clean connections and trimmed a quarter inch off the female portion to hopefully get clean wire contact.
I didn't have the main sail up or the jib even on deck when we lost power. We'd just exited Presque Isle bay's channel into Lake Erie under power and after several pulls showing no sign of life, we hoisted the mainsail to gain some control. I then rigged the 87 jib and got to enjoy the exciting 15-22 knots of wind and 3.5' waves.
After enjoying some good sailing for awhile, we turned downwind and sailed back through the channel and into the protected bay, where we heaved to and attempted to get the engine running again but without luck. I then pulled out the anchor and hastily dropped the sails so we could focus on outboard repair.
After checking for fuel flow and reworking the spark plug wire, it started and stalled once but then it restarted and seemed to run normally.

[Dougiestyle]

glad it worked out

[Jimmyt]

Sounds like it either cleared up (bad fuel issue), or you fixed it by noodling with the plug wire.

If you haven't changed the plug lately, I'd do that. Bad plug can behave like many other problems.

If it's running normally now, it will be virtually impossible to determine what was wrong with it. Keep your sails (and anchor) at the ready.

[Interim]

You might want to check the spark a little closer. Seems like a more objective measure might be in order. I change mine every year as part of winterizing, largely because I am an outboard hypochondriac.

You might also have a fuel flow issue, either a plugged filter or a leak in the line. Mine used to start fine after I primed the bulb, but would die after a few minutes. Priming it would give it enough to run for a while, but a leak would start sucking in air and thin the mixture too much. I clipped the end of the lines and put the connectors back on, and problem solved. Filters will settle when there isn't flow, but once you start pulling fuel through it will plug up again.

--john

[svscott]

Thanks for the replies!

I believe the gas is ok. Plus it wouldn't run on starting fluid.
It's fairly new ethanol free that ran great at week prior. As part of my fiddling about. I startrd by pulling the fuel line from the carb and pumped the primer and it was pushing fuel. I then checked the spark plug and it was soaked in gas so I installed a brand new spare. After that failed, I took the fuel line apart and deleted the primer ball in case it was leaking air there. When that didn't work, I changed the carburetor, and lastly, I messed with the plug cap and wires.
I've already got all new fuel lines and internal filter to install. I'm ordering a new ignition coil for good measure. Hopefully it's not the CDI box. I don't know exactly how to test that and it's pretty expensive.
I'm only ten minutes away from the lake but I haven't gone back to check it over. The boat's a muddy mess from the anchor and chain. The sails didn't get rolled or folded. I simply plugged in the battery tender and walked away. I was a combination of relieved, excited, and more than a little bummed out because I maintain that engine religiously and it unexpectedly put me, my friend, and our young boys at risk. I go to great lengths to have everything maintained, fixed, and operational... to the point that I keep an extra spark plug, carb cleaner, starting fluid, motor oil, and a complete extra carb (I upgraded my 5 hp to 6 hp) plus the necessary tools on board at all times.
Rookie me would've been in deep poo poo if this happened fifteen years ago!

[Jimmyt]

Well, that's a lot of critical info. If it wouldn't run on starter fluid, you had a spark issue. Wet plug almost positively confirms that. New plug eliminated the plug as the problem. Seems like the only thing you fiddled with in the spark system that changed anything was the plug wires.

You didn't mention how long the engine ran before it died the first time vs how long it ran after you "fixed" it. Did it run as long or longer after the repair? I'm wondering about electronics overheating and breaking down as the issue. It sounds like it had a while to cool off while you worked on it.

Sounds like you've got an excellent approach to maintenance and repair for your motor. Better than most, I would say (how many have an extra plug and carb handy?). I'd be very comfortable sailing with you from that aspect. You are doing a very reasonable job of making sure you can be your own rescue.

Stuff happens. I see new cars on the side of the road, too. Machinery breaks down. Unless you are going to totally rebuild it every season, putting in all new ignition parts, there will always be a chance of a breakdown. Even then, a tank of bad gas could get you.

Be glad it was a motor breakdown and not a 70 knot squall... Sounds like you handled it well and everyone got home.

[svscott]

Before the engine shut off, I'd been motoring at full throttle for about 40 minutes. After we got it running again, it was maybe only 10 minutes to get into the marina.

I spent a couple hours on the boat late last night and got the anchor and sails properly stored. When iv turned attention to the outboard, I could not get the engine to run at all last night. In the dark, I visually checked spark and it's there but very weak. I pulled the spark plug wire apart again and reinstalled but to no avail.
I'm ordering a new ignition coil and CDI box. Hopefully it's not the CDI box and I can return that $150 part. Due to The Covid, and weather holding up my bottom paint job and new windows installation, I got a late start this season and I really don't want to be down for two or more weeks, waiting on parts.

What is the best way to post photos to the forum?

[Jimmyt]

Type your text. Then, look just below the text entry box on left. There is a white P in a blue box and Add image to post beside it. Hit that. It flips you to Postimage App, and hit "choose images". If the image is on the device you're working with, pick photo library, select the image, then hit done.


If this doesn't work, describe the device you're using to post and we'll try again.

[svscott]

A quick update on my continuing engine troubles...

I brought the outboard home to work on it and have been throwing parts at this thing. So far, I have replaced the spark plug 3 times, the ignition coil, and swapped in a new CDI unit. I also tested the kill switch wires and performed a valve adjustment. After gapping the spark plug, it began running OK in the bucket. I let it run for a half hour and it restarted with no issues. I took it to the boat and it took 10 pulls to start and then I shut the engine off to sail and it wouldn't restart after 40 minutes of run time on the water. Fortunately, I just picked up an old 40 lb thrust Evinrude trolling motor as a backup and it works acceptably well to get back home. At full throttle, the trolling motor pushes my 26d at 2 knots. A strong head wind over 10 to 15 mph may overpower the electric motor though. Even when I get the gas engine going again, I'll be keeping the trolling motor on board got fishing and as a backup.

The work i have done to the Nissan engine so far is as follows...

I began with the kill switch and a multimeter and have mostly ruled that out. The multimeter changes every time I hit the kill switch, plus there has been weak spark all along (I'm assuming its weak spark since there is spark but it didn't hurt to hold the spark plug while pulling the starter).

I then replaced the igniton coil and still it wouldn't run.

After the ignitiion coil didn't make a difference. I temporarily swapped in a new cdi unit (thankfully the supplier sent this 150 dollar part in an unsealed bag so I may be able to return it). Still didn't wouldn't work.

I pulled the valve cover and found that both valves were tight. I adjusted both valves into the mid-range of their spec. Still didn't work.

I checked the pulser coil gap and found it was over spec so I ovalled out the mounting holes and reinstalled with the gap in spec. Still didn't work.

Next, I installed another brand new, properly gapped spark plug, and she came to life on the 2nd pull, and seemed to run right after running in the bucket of water for a half hour. I felt a bit foolish for not having tried another new spark plug right away.

We took the engine back to the boat and it was sluggish to start but then ran ok. We sailed for an hour or two and while sailing wing on wing, tried the engine but it wouldn't fire up. Changed the spark plug again. Still didn't work.

The only ignition part I've not replaced is the pulser coil. The new part will be here next week and I'm REALLY hopeful that works. Otherwise, I'm thinking it'd have to be worn piston rings non giving compression.

I'm glad the trolling motor will at least get me on the water when weather is fair. The silence while motoring with the evinrude is amazing. Too bad it isn't faster!

[Jimmyt]

Sometimes, throwing parts at it seems like the right thing to do. Sounds like you are getting close to the end of likely suspects. Hope you get it soon!

Thanks for posting the great sailing pics!

[adudinsk]

Please keep us informed..
Similar probs here

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[svscott]

I replaced the pulser coil and the engine came to life on 4 pulls and ran well while on the dock for about twenty minutes. I shut it off and it fired right back up with one pull.
I waited 20 minutes fur the engine to cool off and again, it started with one pull . Weather rolled in while I was test running the engine so I couldn't actually get out and out it under load fur an extended run. Crossing fingers it was a failing pulser coil all along and that between that and the other maintenance, it'll run like new again.
I'll report back with the good news later this week, after I run her hard for awhile.