Trim Affecting Tach and Performance

[phillnjack]

add an earth wire from powerhead to engine clamp/trim.........

[Hydrodreams]

Thanks guys for the pointers, I will do some more testing and see if I can figure it out.

[Motv18]

Almost sounds like a magnet. That will cause wierd pulses to the tach and misfire. And a loose one will occasionally flip out when trimming or hit rough water.

the grey wire I think should read 3 hz per revolution same on the power wires. More or less then say 1800hz at 600 rpm is a cracked more hz or loose less hz. That’s if I remember this test correctly. Most just pull the flywheel.

[Hydrodreams]

Almost sounds like a magnet. That will cause wierd pulses to the tach and misfire. And a loose one will occasionally flip out when trimming or hit rough water.

the grey wire I think should read 3 hz per revolution same on the power wires. More or less then say 1800hz at 600 rpm is a cracked more hz or loose less hz. That’s if I remember this test correctly. Most just pull the flywheel.

Hey Motv18 great suggestion, I swapped flywheels and had the exact same result. Thanks for the input!

[Motv18]

Cool, that puts it in the electronics. Back to grounds and circuits

[David - WI]

Thanks Dave, both regulators are new and they OHM'd good. The info with the trim taking a lot current away is helpful. Sounds like there is too many volts getting to the system one way or another. Stator was also new at the beginning of the season. The regs and stator are all CDI parts and I have heard some less than positive feedback on them. Yesterday when I was approaching WOT I was working the trim up and down repeatedly and she was running like a sewing machine. As soon as I stopped that it was as is a governor kicked in bogging the engine down. Another tidbit of info I forgot to give was it seemed to do it a little less when I first took off and the engine was a little cooler. Thanks again, I struggle with electronics and wiring.

Ohms don't really tell you anything until a diode fails completely... yours (I think) are only shorting out under high voltage & temperature. My guess is when the diode shorts your voltage drops too low for the ECU, injectors, and/or fuel pump to function properly, so the engine stumbles.

Running the trim dissipates enough power to keep the diode from overheating and shorting out, so you maintain your 12v (or 13.5 or whatever it is) DC and everything stays happy.

When the diode heat up and "leaks" voltage...you lose either the high or low part of the AC wave so the tach signal is "off" and when it's rectified to DC it's less than 12v.

I would look hard at the regulator/rectifier(s). Just my thoughts... or guess, really.

[Hydrodreams]

Ohms don't really tell you anything until a diode fails completely... yours (I think) are only shorting out under high voltage & temperature. My guess is when the diode shorts your voltage drops too low for the ECU, injectors, and/or fuel pump to function properly, so the engine stumbles.

Running the trim dissipates enough power to keep the diode from overheating and shorting out, so you maintain your 12v (or 13.5 or whatever it is) DC and everything stays happy.

When the diode heat up and "leaks" voltage...you lose either the high or low part of the AC wave so the tach signal is "off" and when it's rectified to DC it's less than 12v.

I would look hard at the regulator/rectifier(s). Just my thoughts... or guess, really.

I couldn't run the engine today but I tested the battery, the starter solenoid, and the stator leads today with the switch on. All test @12.65 volts. I did notice this looking at the regulator leads today...

[25two.stroke]

that yellow is disconnected in the pic...have you been running like that?

[Hydrodreams]

that yellow is disconnected in the pic...have you been running like that?

No good spot though This was when I first started separating wires today Thanks though

[Hydrodreams]

Took a test run this afternoon after double checking all the grounds and testing what I could with the engine off and running. Every tested ok as best I can tell. So to update, everything works and runs great on the boat under EXACTLY 3800 rpm all the time. Tach works fine, I can hammer the throttle and she launches but as soon as it hits 3800 she starts to break up. It has to be something that varies yet breaks down at 3800 RPM every time. The tach then goes bonkers and the engine bogs down a bit. I am leaning more and more to the stator, the trigger, and or the regulators. More so the stator or trigger. It's that exact 3800 rpm deal and the fact that everything works great under that speed. What do you guys think?

[25two.stroke]

Do you have a ramp or a test tank that you can easily run the boat at rest but under a load? To where you can do a cylinder drop test at 3800 rpms to see if you are consistently loosing a set of cylinders?

Also, did you note what your voltage did at the motor (if anything) when it started trippin out?

Also, maybe someone here can comment on this idea, but naturally I would want to disconnect the regulators/tach and the whole charging system and go for a run with the engine just making power to keep itself running. That will tell you if your charging system is causing the issue (which would mean its the stator). I do not know with the (presumably 40 amp) system on your motor if it would burn out something if you simply disconnect all those bullet connectors at the regulators or if there's a better way to disable it.

[Hydrodreams]

Do you have a ramp or a test tank that you can easily run the boat at rest but under a load? To where you can do a cylinder drop test at 3800 rpms to see if you are consistently loosing a set of cylinders?

Also, did you note what your voltage did at the motor (if anything) when it started trippin out?

Also, maybe someone here can comment on this idea, but naturally I would want to disconnect the regulators/tach and the whole charging system and go for a run with the engine just making power to keep itself running. That will tell you if your charging system is causing the issue (which would mean its the stator). I do not know with the (presumably 40 amp) system on your motor if it would burn out something if you simply disconnect all those bullet connectors at the regulators or if there's a better way to disable it.

I do have a ramp I can use. I don't think it's a specific set of cylinders because it's so intermittent. There are times above 3800 she just keeps right on pulling. Then there are times it feels like someone is taking one plug wire off, then two, then one, then two...

The voltage on the gauge stays the same. While the problem is happening. Now if I hit the trim it drops a couple of volts. Idle it reads about 12.5 volts. anything above idle to 3800 RPM, even to WOT the gauge reads just under 14 volts. Unless I hit the trim button and it drops down to about 12.5 volts.

As far as disconnecting things and running that is beyond my knowledge for sure.

I have ordered an all new boat harness. I know the key switch can be suspect for problems and few other things along the way. The switch is a bit stiff anyway. I am putting in a new control as well, because the old one has a good bit of slop. Plus as with I believe any boat manufacturer the wiring leaves a bit to be desired anyhow. I have also wanted to clean it up and get rid of a couple splice in jobs that were done by the former owners through the years. If that doesn't help I think I will start replacing parts unfortunately. Starting with a new Mercury trigger and stator and go from there.

Also does anyone know the difference between a 398-9610A27 and a 398-9610A19 stator? They look the same and I have access to a new A19 if I want to try it. I know from my past life in the Ag Parts world. The suffix meant a change in the distributor or manufacturer making the part for the company.

Thanks again!

Thanks again!

[sonicss33]

Not sure on the 2 stator part #’s you have listed but there is a difference in the thickness on some like 1/2” vs 9/16”. Something to that effect, so measure before the swap.

[Hydrodreams]

Not sure on the 2 stator part #’s you have listed but there is a difference in the thickness on some like 1/2” vs 9/16”. Something to that effect, so measure before the swap.

10-4 thanks sonicSS!

[25two.stroke]

A27 was only ever sold on a 150, 200 and 225 promax. the A19 cam on just about everything from 135 to 225...including some 150, 200 and 225 promax motors.

Seems the A19 will work on everything.