2001 F115 EFI Four Stroke Stator problem

[Carlo Castoro]

2001 F115 EFI Four Stroke. Bought a project boat here. Engine is running rough and stumbles when raising the RPM, but can get up on plane and run to WOT. Problem is when trimming the motor the rpm drops about 600-800 RPM. at idle its fine at 2,000-5,000 this happens.

So far I have done this.

Clean VST
Cleaned Injectors
New Batteries
New spark plugs
Tested Ground Wires and all Connections
ECM Peak Voltage 14volts at 750rpm No good
Resistance test on Stator Coil spec 0.2-0.8 reading .3-.6 Good
Stator Coil Peak Voltage Test- low voltage 1-2 and erractic readings No Good

Crank Postiion Sensor-Peak Voltage test - low Voltagle 1-2 volts
TPS Test 0.725
CPS OHMS spec 445-565 reading 0 no good.
Ignition Coil test in spec

Do I need to replace the CPS and Stator? Will the CPS and Stator effect each other? Is there any other test in need to do to confirm this.

Any help would be appreciated.
Thanks Guys

[exeter27]

You need a DMM with a DVA to read the voltage from the stator. Nearly all consumer models of DMM are incapable of reading stator voltage. You can find one here: 640 ESI DVA Adapter .

Use that and report back on your stator. My hunch is that your stator is fine.

[Carlo Castoro]

I like your hunch thats for sure. Learned something new today. Ok I will pick one up and retest. What about the Ohm reading I am getting on the CPS spec is 455-565 reading is 0L.

Origanlly I was checking for a short some where. I think I have checked everything, but I am sure I missed something.

I disconnected the main battery + / - and connected a new battery directly to the engine to rule out the main battery cables and switches. still had the problem. Trim motor is drawing about 25 amps. checked and clean all ground terminal on the block.

[rodbolt17]

I think you need to drop back and punt.

you appearently fail to understand the system your monkeying with.

its a 12V TCI waste spark ign system.

you can toss the stator in the creek and it will have 0 affect on the ign system.
until the battery dies.

there is no CPS.
there is a TPS which tells the ECU throttle angle and rate of acceleration or decelleration of throttle motion.


there are two pulser coils that give information as to crankshaft position.

spark is triggered by this information by the ECU .
the ECU transistors act like points in an old chevy.

they simply break the ign primary 12v circuit.

your describing a faulty ground or 12 feed path.

when you hit the trim the trim motor is going to require current.

so does the fuel pump ,injectors and the ign system.

if not enough current is avalible something has less, that's the RPM drop.

the stator output voltage on the F115 only charges the battery.
has no other function for ign.

my advice is to study the system before blowing much cash buying stuff.

[Carlo Castoro]

Thanks for all the in info Rodbolt. You are right about learning the system, thats why I came to this sight, to help from all. Information is what I seek.

So I am back to the orignal task of finding the faulty ground or 12 feed path.

Any history on this motor with this issue. Any common problems that I should
look into.

thanks

[rodbolt17]

its a rock solid motor.
it uses a speed density type EFI on an open loop.

it uses a 12V TCI ign system.

any sensor failures will result in a fixed base timing of 10*BTDC.

depending on the sensor timing may or may not advance further.
this would result in a high idle speed and top speed may or may not be reached.

based on your description you have an electrical power supply issue.
quit chasing shorts unless you see smoke or blown fuses.

chase poor/open connections.

[boscoe99]

my advice is to study the system before blowing much cash buying stuff.

And again I say, like a lone voice crying out in the wilderness, that it is a fricken shame that Yamaha does not provide theory of operation in their damn, all but useless, service manual.

Another reason that folks can't afford to take their Yams to a Yam dealer. All too many dealer mechanics don't understand the theory of operation of the many frick ing configurations of Yam outboards. Pity the poor customer that pays the dealer while the mechanic is undergoing OJT with a customers motori.

Yam pays the price also by having to have a team available to tell dealer mechs how a motor works and what to do and look for.

Off my soap box now.

[rodbolt17]

its all simple, but you do have to understand speed density open loop EFI, ost GM autos and several others, used closed loop speed density EFI for years.
works about the same on 2 and 4 stroke motors.
biggest difference is the MAP sensor.
on a Yamaha 2 stroke baro pressure is locked in each key on cycle and intake pressure is not monitored.
4 stroke locks in baro pressure each key on cycle but DOES monitor intake pressure.

Yamaha, like most jap and Swedish stuff, sets there manuals up for the trained tech.
not the guy with a handful of Stanley tools and a lot of ambition.

the F115 mercury service manual has a lot of info not contained in the Yamaha f115 manual.

[Carlo Castoro]

Ran the boat yesterday. Engine ran fine all the way up to WOT 5,700. Once in a while though the engine would jump 200rpm then back down. Happened 3 times in about 1 hr at cruisng speed 4,500rpm. Problem with the RPM drop when trimming now comes and goes.

I do not have any smoke and have never blown a fuse.
If I had a failing sensor would that cause this condition.

Still looking for a poor/open connection.