Trim Affecting Tach and Performance

[Hydrodreams]

I have been dealing with a bouncing Tach all summer above 3800 rpm. The engine also intermittently misses and bogs down when this happens. After cleaning up some old unused wires, connections, and all my grounds, I did a little testing the last two days. What I discovered is when above 3800 rpm if I trim the engine up or down the Tach works perfect. The miss/bogging disappears and the engine runs flawless all the way to WOT. Here is the kicker...the Tach works perfect and the engine doesn't miss a beat below 3800 rpm whether using the trim or not. It seems as though the problem is somehow related to to the high side of the stator. Any ideas what could cause this?

[SS Minnow]

Almost every time I had an electrical problem that made no sense as to what was causing it, it turned out to be a bad ground.

For whatever that is worth.

[lance]

I had a somewhat similar problem with an old OMC years ago. It had a miss once up to operating temperature and the tach wigged out and the miss was worst every time a hit the trim switch. Everything checked out fine using the shop manual troubleshooting tests. It ran fine on the hose in the driveway. I finally gave up and took it to a dealer. They had it for a week and replaced the stator. I told them the stator had tested fine. Of course, back on the lake, the problem was still there. I decided to get a new coil and ignition wire and started swapping each one at the lake. I found one of the coil mounting bolts, which also grounds the coil, was not screwed in all the way and over the years had developed white corrosion all around it. The bolt was defective and had a slight bend to it. I guess when the engine was originally built, the bolt was never was seated during assembly. The problem was not evident until the coil was removed. Also, the coil passed the shop manual coil ground test when the engine was cold.

Often, when there is a weird electrical problem that makes no sense, start checking for a ground problem. Even then, some grounding issues don't show up until the engine is warm. Circuits have a higher resistance when hot compared to cold.

Good luck, hope you find the problem.

[lance]

Yep, just what SS Minnow said.

[Hydrodreams]

Almost every time I had an electrical problem that made no sense as to what was causing it, it turned out to be a bad ground.

For whatever that is worth.

Thank you SS minnow, I will check them again. I guess the only in high RPM range is the part that makes no sense. By the way, I love your avatar picture of the...you know the thing! Hahaha!!!

[Hydrodreams]

I had a somewhat similar problem with an old OMC years ago. It had a miss once up to operating temperature and the tach wigged out and the miss was worst every time a hit the trim switch. Everything checked out fine using the shop manual troubleshooting tests. It ran fine on the hose in the driveway. I finally gave up and took it to a dealer. They had it for a week and replaced the stator. I told them the stator had tested fine. Of course, back on the lake, the problem was still there. I decided to get a new coil and ignition wire and started swapping each one at the lake. I found one of the coil mounting bolts, which also grounds the coil, was not screwed in all the way and over the years had developed white corrosion all around it. The bolt was defective and had a slight bend to it. I guess when the engine was originally built, the bolt was never was seated during assembly. The problem was not evident until the coil was removed. Also, the coil passed the shop manual coil ground test when the engine was cold.

Often, when there is a weird electrical problem that makes no sense, start checking for a ground problem. Even then, some grounding issues don't show up until the engine is warm. Circuits have a higher resistance when hot compared to cold.

Good luck, hope you find the problem.

Thanks Lance, I put all new coils in, cleaning all the grounds half way through the season with no change. Thanks again!

[David - WI]

I would be looking at the voltage regulator/rectifier. Possibly the diodes are failing when the stator voltage gets to a certain point rather than at a certain rpm. When you run the trim it takes a lot of power (current) so the voltage drops below the "critical" point. Any time the tach acts up I look at the regulator/rectifier first; for what it's worth.

[Hydrodreams]

I would be looking at the voltage regulator/rectifier. Possibly the diodes are failing when the stator voltage gets to a certain point rather than at a certain rpm. When you run the trim it takes a lot of power (current) so the voltage drops below the "critical" point. Any time the tach acts up I look at the regulator/rectifier first; for what it's worth.

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.

[David - WI]

I guess check that the regulator/rectifier has a good ground.
Somebody else here will know, but I thought the high-speed windings on the stator took over at around 2k rpm.
What motor?

[25two.stroke]

I assume you have ditched the idle stabilizer module...but if you have not then that would be my first course of action!

[Hydrodreams]

I guess check that the regulator/rectifier has a good ground.
Somebody else here will know, but I thought the high-speed windings on the stator took over at around 2k rpm.
What motor?

Motor is a 1997 225 ProMax. I am not sure what rpm the high side takes over.

[Hydrodreams]

I assume you have ditched the idle stabilizer module...but if you have not then that would be my first course of action!

Yes sir, that's long gone. Thanks for the possibility though.

[25two.stroke]

Ya, 1800-2000 rpms is where the high side of the stator takes over, thats not to say that it cannot have issues at other rpm ranges. Have you done an ohms test on the stator both hot and cold?

I agree with the others here it sounds like a grounding issue, which is why the charge system and the idle stabilizer modules are both suspects, cause they both stand between the stator and ground (and therefore can fail and send power to ground).

Have you tried disconnecting the tach? Never had a problem with one causing problems, but I would disconnect the tach and possibly try another key switch. These are far fetched tries, but it wounds like you've already done the standard stuff.

Just for reference maybe post some voltage readings at the battery, trim motor (if you are running a remote pump), and at the starter solenoid, both at idle and up at speed if you can. That would be good info.

[Hydrodreams]

Ya, 1800-2000 rpms is where the high side of the stator takes over, thats not to say that it cannot have issues at other rpm ranges. Have you done an ohms test on the stator both hot and cold?

I agree with the others here it sounds like a grounding issue, which is why the charge system and the idle stabilizer modules are both suspects, cause they both stand between the stator and ground (and therefore can fail and send power to ground).

Have you tried disconnecting the tach? Never had a problem with one causing problems, but I would disconnect the tach and possibly try another key switch. These are far fetched tries, but it wounds like you've already done the standard stuff.

Just for reference maybe post some voltage readings at the battery, trim motor (if you are running a remote pump), and at the starter solenoid, both at idle and up at speed if you can. That would be good info.

Tested stator cold not hot and only ohm'd it. I have heard somewhere to test under a load and or with a DVA. I do not know how to do that.
Someone else had mentioned a key switch as well. Trim motor is on the mid. I will try to get the voltage readings you mentioned here soon.
Thanks again!

[25two.stroke]

DVA test is good, you would set the meter to 400 volt setting and test between the blue lead and ground at cranking. But that DVA tests output, and for that to work the leads have to be disconnected. Therefore, you could never test the high side of the stator cause you cant spin it past 2000 with the motor not running and the leads disconnected. (that I know of, maybe someone else has a magic trick)

It is my understanding thats why the book has you do an ohms test first cause that can test all the circuits in the stator, not necessarily the output.

If you have the 3 ram trim in the mid then forget the voltage readings at the pump, but it might be worth taking them at the trim relays and also watch your voltage when you are running and trimming at the same time.

I had a 1988 mariner 2.0 175 on my boat for 3 years commercial fishing. This had the stator/rectifier system, not a voltage regulator like yours. I for 3 years I ran at 17 volts @ 4000+ rpms and 14.5 volts @ idle-2000 rpms. I changed the rectifier, stator, and cleaned all the grounds, replaced battery cables, batteries, battery switches and never could get the voltage down. I would shut my electronics down when I ran around cause I was afraid of frying my GPS/AIS/VHF/Sonar that was worth 3 times as much as the motor...long story short, I never had any problems but it was so weird to me as my friends had the same motor and would run 13 to 15 volts. Ended up repowering with a 150 fourstroke SeaPro and never had to think about it again...