2005 Nissan 18HP 4-stroke won't shut off

[msaunoras]

Hi guys, new member here with a problem. I've got a 2005 Mirrocraft MV175 rigged with a Nissan NSF18B2 EP that has been nearly trouble free for the last 7 years. Only one problem I have... last year it started not shutting off when the key is turned off. Even pulling the safety chain for the stop switch won't shut the engine off. It's been totally intermittent until today, most of the times I could eventually get it off. Now the engine absolutely will not shut off unless I pull a plug wire.

The stop switch on the outboard itself was not connected so I reattached it with no change in the concern. I ran the engine today with a hose hooked up at home where I had a chance to wiggle around some wires and inspect for any chafes. I did not find anything.

I am suspecting a CD unit but honestly I have no way of verifying this. I am going to take it to the dealer if i can't figure anything out soon, I hate being out a boat this time of year but it's my own fault for letting it get this bad.

Thanks

-Matt

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

http://forums.iboats.com/showthread.php?t=543584

I found this thread and it sounds like the same situation. I need to look closer for this brown wire. If I ground this wire it should kill the engine? I found a wiring diagram in the back of the owners manual, the Br wire goes right into the CD unit, if the wire load tests good and grounding it doesn't kill the engine should I condemn the CD?

unfortunately it's dark right now and I doubt my neighbors would like me running my outboard at night I'll check back tomorrow.

 

[pvanv]

Re: 2005 Nissan 18HP 4-stroke won't shut off

The brown is the cd kill. Grounding it stops ignition. That's what the stop switch (either on the motor or RC box) or ignition switch does. If grounding that wire does not stop the motor, either that wire is broken (more common), or the cd is faulty (rare).

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

The brown is the cd kill. Grounding it stops ignition. That's what the stop switch (either on the motor or RC box) or ignition switch does. If grounding that wire does not stop the motor, either that wire is broken (more common), or the cd is faulty (rare).

Thanks for your input paul, I'm going to go check it now and report back later.

I am a ford tech so the outboard engine diag is a little new to me.

Edit - Okay I found the brown wire underneath the engine cover where the takeout is for the cowl mounted stop switch(not connected). Jumping it with the ground did not shut the engine off. So I removed the top covers to access the CD unit connector. I backprobed the connector and verified it has .4 ohms resistance with the brown wire further down the engine harness. Jumping the backprobed brown wire to ground did not stop the engine.

I'm sure I need a CD unit now. The question I have is....there are 2 CD units listed for an 18B2, how can I tell which CD I need?

Edit AGAIN - I pulled the CD unit out of the engine. The number stamped on it is 7241, looks like I need 3V9-06060-2

I also found a pretty good kink in the brown wire under the CD that looks like it would be a good chafe/break point for the wire. No resistance change was found wiggling it though, the wire load tests good too.

 

[pvanv]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Double, triple check that the brown wire in the harness is not bad. I would expect that brown wire to have considerably less than 0.1 ohm resistance. If you need a new harness, the correct part is 3V9061670M, CORD ASSY, C.D. UNIT, $72.36... Or you may be able to repair the wire if it is marginal.

The correct CD depends on the serial number of the motor:
18B2#01549~ (and up) 3V9060602M C.D. IGNITION UNIT MFS9.9/15/18B (CU7241) $191.31 (probably the unit you need); OR:
18B#00001~18B2#01548 3V9060600M C.D. IGNITION UNIT MFS9.9/15/18B (CU7220) $193.41

Parts are available from any dealer, including me.

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Thanks Paul for your help, I appreciate it. I ordered a CD today (none of my local dealers had one) and had them send it out 2-day. I will let you guys know if this fixes my concern or not. I'm not one to throw parts at anything, I really wish it was a wire.

I would have ordered the harness too but a $200 module wasn't in my budget this week.

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Paul I've got some other questions too. I've been reading up a little on the forums now and being the kind of guy that tinkers a lot I was wondering about changing the prop pitch on the 18 for a little more speed.

I don't have a tach right now. Do you think my remote control box might have output wires for a tachometer? I have a spare gauge spot in my console I could use. Does Nissan offer a plug and play tachometer?

I need to double check my speed off my GPS but the speedo on the boat gets up to 20mph with just me and a 1/4 tank of fuel. Does it sound like I could get a couple extra MPH out of the Nissan? I believe the pitch is around 9. I was thinking of trying a 10

 

[pvanv]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Prop selection is always a bit of trial and error. You must use a tach to determine your WOT RPM. More pitch=more speed (within power limits of the rig), but slower acceleration. Less pitch=better hole shot, but less top speed. Too little pitch, and you will hit the ESG wall, where you are attempting to over-rev, and the CD is preventing it by staggering the ignition.

Depending on the RC box, there may be leads for the tach. Use either 3AC726400M (BLACK) OR 3AD726400M (WHITE) tachometer, $77.96. You can also get 3R0725371M LEAD WIRE, METER $58.94 to connect the tach. Full wiring diagrams are in the Factory service manual. All this stuff is available from any dealer, including me.

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Well Paul. I'll hand it to you. I totally botched that diagnosis. CD unit? nope not the problem.

Was it a loose ground wire at the right hand top of the electrical bracket? yep

Only after I back probed all the grounds out of the cd unit connector did I find it. I got about a 1/4 turn out of that bolt and it was tight. visually you would have never seen it was loose.

So now I have a spare CD, I doubt I'll get rid of it. I'm a sucker for spare parts

 

[Sea Rider]

Re: 2005 Nissan 18HP 4-stroke won't shut off

If your boat, you and gas weights more more than 280 KG, achieving 20 MPH is perfect, place a tach as recommended by Paul, this is not a rpm guessing issue if wanting to be top rpm for than engine before ESG kicks in.

Happy Boating

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

I'm definitely over that weight. For starters I weigh 180lb and the dry weight of the boat is 600lbs. Add an engine and fuel and we're well above that.

I will get a tach and go from there

 

[pvanv]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Well Paul. I'll hand it to you. I totally botched that diagnosis. CD unit? nope not the problem.

Was it a loose ground wire at the right hand top of the electrical bracket? yep

Only after I back probed all the grounds out of the cd unit connector did I find it. I got about a 1/4 turn out of that bolt and it was tight. visually you would have never seen it was loose.

So now I have a spare CD, I doubt I'll get rid of it. I'm a sucker for spare parts

Easy to miss. That's why I recommend double, triple, quadruple checking the wires.

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Yeah I wouldn't normally overlook something like that but we all make mistakes from time to time. Thanks for your help

 

[msaunoras]

Re: 2005 Nissan 18HP 4-stroke won't shut off

GPS confirmed 21mph tonight in calm water. Held it steady for 10 minutes of running. I'm showing a half tank of fuel too which is about 6 gallons.

Now I'm wondering if I could benefit at all from a stainless prop of the same pitch.

 

[pvanv]

Re: 2005 Nissan 18HP 4-stroke won't shut off

Your current top speed is fine.

Verify wot rpm with a tach. The ss prop will flex a little less, so will act as a slightly steeper pitch, which will lower rpm some. The 4-strokes prefer to be in the factory-specified wot rpm band. If you are near 6,000 now, changing to an ss prop may be ok; If currently at 5,000 wot rpm, any ss prop will want to be a little less pitch.

If your wot rpm drops too low, you will be lugging... intake vacuum will be lower at almost all rpm ranges and loads, and you won't get as decent overall performance.

Check out the prop forum on this board for more details.