Does the switch box impact the rev limiter?

[richw46]

I just installed a new CDI brand stator and switch box on my 1995 Mercury 115. The engine now starts and runs very well. I'm happy with that. However, it now seems to be hitting the rev limiter at 5,000 RPM. With the old switch box I never experienced that. I'm pretty sure it's the rev limiter because it hits 5,000, falters, runs up to 5,000 again, falters and so on. It runs fine up to 4,800 RPM.

So I'm wondering if it's the new switch box that's causing the problem, since there are connections from the rev limiter to the switch box, or is it the rev limiter? The limiter was replaced 3 years ago because it was grounding out for a fraction of a second above 35 mph.

I have, for the time being, disconnected the black /yellow wire for the limiter off the switch box to verify it's the problem.

 

[Chris1956]

What makes you think there is a rev limiter at 5000RPM?

Sounds more like a fuel delivery issue. You might pump the primer bulb and see if she will hold 5000+ RPM.

 

[richw46]

Newer fuel line/bulb 3 years ago, fuel pump rebuilt a few weeks ago with no debris inside it, new fuel filter on port side last fall, new small fuel filter on starboard side 2 weeks ago. No problems at WOT 5200 RPM last fall except the motor would shut down below 1200 rpm and not restart until cool again.

I can run all day at 4800-4900 with no problem, but if I bump up to 5000 it immediately shuts down; immediately. When it was still running, before I replaced the CDI stator, it would go up to 5200 with no issues and that was before the rebuild on the fuel pump.

I had a previous problem with the rev limiter about 3 years ago. At 35 mph it would run just fine but go above that and it would have a fraction of a second stop with a chirp from the alarm. It felt like you hit something, a good solid BAM. I found a post where someone had a similar problem and replacing the rev limiter fixed it. So I replaced mine and never had any more problems til the stator went out.

I have disconnected the black w/yellow rev limiter wire from the switch box. I'm waiting until after the Memorial Day holiday to see if that makes a difference. If it runs up to 5200 then it's either the rev limiter or the new switch box causing the problem. If not, I'll check fuel lines.

I really feel that the new CDI switch box is responsible, since it's the only new part other than the stator. I'm tempted to put the old OEM Mercury switch box back on to see if that fixes it. I know that's dangerous and could take out the new stator, but I don't think it was damaged by the bad stator; just a hunch.

Hence my question about the switch box affecting the rev limiter.

 

[racerone]

What is the part # of the rev limiter you replaced ?

 

[richw46]

821889A51
That's what's listed at the Mercury online parts catalog site

 

[Chris1956]

Pump the primer bulb at high RPM and see if that fixes it. 5000 RPM would be an unusual Rev limiter. They would usually be at 6200 or more.

 

[richw46]

Okay, Chris. I can head to the lake next week. The limiter is supposed to be set to operate at 5250, which is just above the normal 5200 for my motor. I think the CDI switch box is affecting this somehow.

I will head there next week and report back. Everything that floats will be on the water tomorrow through Monday. Tuesday is looking good weather-wise.

 

[flyingscott]

Pretty sure only the jet models of that motor had a rev limiter and it was a separate module.

 

[richw46]

It is a separate component, but my motor has one. I've already replaced it once. It stacks on top of the temp sensor alarm, right/port side of the motor.

 

[flyingscott]

Do you have the factory manual for your motor? Pretty sure that motor can run without the Rev limiter attached.

 

[richw46]

It doesn't require the rev limiter. I have disconnected the black/yellow wire from the switch box for the limiter and will test next week after the crowds go home from the lakes.

Yes I do have a factory service manual, but there are errors in it. For example: If you have the stator removed in order to do the ohms test between the red stator wire and ground, use the black wire.... only there is no black wire. I have found that the ohms readings they provide don't even match a brand new stator, which is working on my motor now.

NOTE: In my previous post I said Right/Port...it should say Right/Starboard.

 

[Dukedog]

it should run jus fine without tha limiter.. not all stators are gonna have a "black" wire.. depends on brand/manufactor.... All are grounded thru tha frame so any part of it thats bare steel serves tha same as tha black...........

 

[richw46]

I agree, but I tried measuring the resistance between the red wire and the base, old and new stators, but there was none. There may have been too much paint on the metal and I didn't want to scratch it in case I need to return it.

Without the limiter I'm thinking it will run like before, up to 5250. But without the limiter, if I strike an underwater obstacle and sheer off some or all of the prop, my RPMs would probably go beyond that. But then, it's a 29 year old motor and the Blue Book is about $1500. In all the years I've been boating I've struck something severely just one time, about 3 years ago. My insurance bought me a new lower unit and prop. So the limiter is disconnected and if it still stalls on my test next week I'll be squeezing the fuel line bulb to see if that helps.

 

[flyingscott]

The rev limiter should be set at about 5500. 5250 is the top rpm of the motor to prop for.

 

[Texasmark]

821889A51
That's what's listed at the Mercury online parts catalog site

On another site where I have been working with you, balls in your court on waiting for your results with the kill wire disconnected from the RL. There is no wiring connection from the RL back to the SB serving as an input.

 

[richw46]

The rev limiter should be set at about 5500. 5250 is the top rpm of the motor to prop for.

I totally agree but it's cutting out exactly at 5000. I never had the problem with the OEM switch box and this rev limiter (new in 5/2020). When I replaced the stator and switch box last week I was able to start and run the motor up to 4800 for several miles with no problem. I just can't go full throttle now. So I've disconnected the rev limiter and I'll head down to the lake, probably next Wednesday. I'll see what that does and if it doesn't help I'll try squeezing the fuel line bulb. If disconnecting the rev limiter does help I will consider putting the OEM switch box back on, since the motor did run sometimes with the old stator. I don't think it shorted, just has an open wire in the low speed winding.

 

[richw46]

On another site where I have been working with you, balls in your court on waiting for your results with the kill wire disconnected from the RL. There is no wiring connection from the RL back to the SB serving as an input.

Hi Mark I was wondering when you'd find me over here. I've been watching that thread as well as this one. I posted in 3 forums I believe, but got responses in just 2.

You and I are in agreement on disconnecting the rev limiter, just waiting for the holiday to be over to prove us right.

According to the wiring diagram in my book there are 4 wires:
Black - Ground
Purple - To ignition switch
Black/Yellow - Capacitor charge from CDM (Coil)
Brown - Signal from trigger for RPM

The purple wire activates the RL when the key is turned on.

The brown wire from the trigger sends a signal for RPM to the limiter. If it exceeds the maximum the limiter will ground out the charge going to the BLK/YEL wire from the CDM on the black wire. (My manual has this section only for units with CDM, not coils like mine has. I assume operation is the same.)

The brown wire from the trigger goes to the SB and then to the RL. The capacitor charge also goes to the SB. In that circuit the only thing that has changed is the SB. I believe the SB is affecting the signal on the brown wire, so by disconnecting the BLK/YEL from the SB the RL will not send the charge to ground and I should be able to go past 5000 (or it's a RL/fuel/other problem).

Mercury recommends replacing the SB and stator at the same time because failure of one can cause the other to fail, but the trigger coil is independent and will not damage/be damaged by failure of either SB or stator.

 

[houndman]

If all else fails, try unplugging the yellow stator wires going to the voltage regulator and see if your problem goes away. I would be interested in the results given the problem with my 115 that you are aware of.

 

[richw46]

When mine was running, before I replaced the stator, voltage on the battery was around 14.4 volts and the motor ran fine until you got below 1200 RPM. Eventually it wouldn't start even when cold. I've replaced the stator and switch box and the battery is still charging at the same 14.4 volts. I replaced the voltage regulator many years ago, probably at least 15 years now.

If I can get the 5000 RPM problem solved I'll be in tall cotton.

 

[richw46]

I have a couple of threads in here and I didn't mean to cross post. The other one is in regards to the entire problem I have been having with the motor. This thread deals with any interaction between the switch box and the rev limiter.

I went to the lake today and had success in running at WOT with the rev limiter disconnected. The motor ran up to 5250 with no stalling or other problems. I ran about 2 miles down the lake at WOT, stopped and fished for a while, then made the return run; no problems.

So it's not a fuel problem and disconnecting the rev limiter shows that the stator isn't the problem. That leaves the switch box and the rev limiter. I suspect the switch box (rev limiter is 3 years old with no problem before the stator went out) and the vendor has offered to send me a different model of it that is compatible with my motor.

I'm waiting on the vendor to reply about the order but the motor is running very well again.