1998 Sportster 1800-abnormal Tachometer readings

[WhiteZombie]

To begin, this is a project boat that I am trying to get in the water soon. I have the jets off, seals out and the shafts out of this boat, so I feel pretty sure I can run the engines safely on a hose for adjustments, etc. About 5 minutes has been my max like one time. So I was adjusting the idle on my newly rebuilt carbs that ofcourse I used OEM kits on. The carbs seemed to work great! I adjusted the starboard side and fogged the engine, and had just started adjusting the port side when the coil gave out on me. No suprise as I had just changed out the seleonoid after having found 4 inches of water in the electical box. Funny thing was the selonoid worked until I dried up the box and after that I probably had it running a handful of times until it gave out. I assume the coil was ok until I reved the rpms up. I verified voltage to and none out at the plug. I ordered a used one off fleabay from a regular parts dealer cause I don't trust aftermarket clone coils due to timing issues I've had on small engines. I'd rather go Japanese 1998 over anything China ever anyways.
So that was that. Another thing i noticed was the tachs were not acting properly. I was planing to use the rpms to make some adjustments I need to do like the steer assist cable adjustments because mine was disconnected. So neither tach read at idle. Right side would finally jump up to 4000 from no reading when i had the engine reved up about half as high as I felt comfortable running it at. It would then gradually go up to around 6000 rpms. Left side was similiar but started showing a reading at 2000 rpms. When reved in Neutral both would make a bogging out sound at around 5000 rpm reading, and I think this should have happened at 3500 rpm if I understand the neutral safety switch operation/function.
So I'm getting very mixed info on this situation. From what I gather the tachs are most likely ok. So I'm more looking at electronics. So what I have done so far is verify connections on tach, checked the ohm reading of the stator connector on the engine, verified battery ok (not with it running, I will check the voltage tommorow on both rectifiers individually on the engine I have running(I already have them out and should be able to change them out to verify left engine as well for correct voltage at battery while running). I say I will do that because if I'm understanding it is the only way to check these rectifiers. I have ohmed and diode tested these based off experience and youtube videos. The problem is it seems there is no true way to verify these electronically with a meter, but some seem to do so on youtube. I looked in my Service Manual several times and to be honest I can't really find anything on the rectifiers except for a pic of one, so no factory ohm readings as there doesn't seem to be a section on it. If I missed it someone please tell me the page number, but I looked under several sections like charging and MPEM system and all (I do have the addendum book as well). I just can't locate the info if it is there. But visually the rectifiers look good, ohm and diode tests seem to be what others seem to get on good rectifiers, and I am using a similiar Fluke 77 meter that some use. I thought about hooking a 24v AC transformer to it to test it but sure as I do something will fry for sure. I may pull the schematic out to verify it is the black and red that gets the voltage. Seems that is right but then I hear power comes from stator on yellow wires so I'll check schematic
Any help or suggestions are appreciated. I want this boat as good as I can get it out of water before I drop her in. Girlfriend is getting antzy and its getting hot to be working on this in the shop. Thanks!

 

[Barnhart501]

So I’m just jumping back on the forums and saw this. I had a similar issue with one of my tachs last year. That’s on another thread here. Read crazy high. I finally tested the tach by using a manual tach back at the driveshaft. You can get them on Amazon pretty cheap. But first I would listen to the engines and use your judgement to see if the tach readings seem accurate, if you haven’t already. I think you can even find a way to test them using ohm readings on this site, not quite sure. Might not be the tachs acting up, but I wouldn’t rule them out without testing them.

 

[WhiteZombie]

I've searched all over and there isn't much info on the tachs. I'm about ready to put it in the water and will check the ohms if I can find the chart you speak of. I hope they are more accurate on water than a hose. Thanks

 

[WhiteZombie]

Can anyone point me to a reliable post on testing the tachometer/wiring. My left side engine is fine. The right side is reading sporatically. More often than not the right side tach reads 0 and then jumps to 5000 and seems to be reading normal after that juding off of the left side tach reading.
I tested the rectifiers a while back as posted above. I was hoping the tachs would work when the motor was loaded up in the water. I will test the wiring and get the ohm or volt readings on the left side circuitry to try to narrow down the problem. If anyone has any ideas please let me know. Thanks

 

[WhiteZombie]

Well, I tested the tachometer wiring as per the manual and it appears I have a not so good ground. The manual called for a constant 12v and I was getting anywhere from 6 volts to 10 on the RH tach and a constant 12.5 on the LH tach. And I have a feeling I know where the problem is. I'm not sure if I posted pictures on another post a while back or not, but the ground lugs located in the steering wheel console had some melted wiring insulation on the wires. I tried to locate a cause and wound up wrapping the wires with electrical tape to same or greater thickness of the original wiring insulation per the National Electrical Code, but that code is mostly on AC type wiring. Never the less the wire itself was in pretty bad shape, so guessing the problem is there. And guessing the wiring just needs to be changed, and my my what a mess it is going to be. At least 10 wires were repaired if I recall, and I think I was wiring off of 2 or 3 of the lugs, which makes sense as they are wired in series (daisy chained so to speak).

I mean there actually is another ground wire on the same quick connect plug as per the schematic, and I could jumper it of find another ground somewhere, but with these electronics I hate to skip steps as no telling what else may be off or happen later.

I'm assuming mostly electrical types will be reading this post, so if you know of any reason a ground wire would melt the insulation, please let me know. I'm used to seeing wiring issues, but never melting on the ground side, but that is mostly on AC voltage, where melting happens on the so called "hot" wire. I've never seen a neutral or ground wire burned unless it was cut somewhat., making a bad connection, etc.

The only idea I have as to what may have happened is an issue when the previous owner changed out the radio. Other than that I would not have a clue what could have caused this, but looking at the corrosion on the wires I would say this has been in this state a while.
I'll post some pics of the ground lug wires when I get started the next day or two. Not going to be fun cause the lugs aren't marked, so hopefully I can figure out what is what with help of the schematic. I mean yeah can always run a new ground, but what might be next as these lugs are written in the manual as being for the accessories.

 

[POPPS]

Should there be any melted wires anywhere on a seadoo ski or jetboat?

 

[WhiteZombie]

Should there be any melted wires anywhere on a seadoo ski or jetboat?

No. Absolutely not. I traced out the ground lug and cleaned it up with some 1000 grit. Lithium grease and got a solid ground and then tested for the 12.5 volts per the manual test instructions. While I have the wires apart I'll look around for the original issue, but wasn't my boat when this mess happened. I mean not as far as I know. I know when I found it I could not smell it, so tells me it is old damage. I should have taken some pics before I taped it up but couldn't find any on my phone. But yeah, has me worried enough I am install battery disconnects on both terminals.
I'll take some pics of this mess tommorow.

 

[RISSilva]

No. Absolutely not. I traced out the ground lug and cleaned it up with some 1000 grit. Lithium grease and got a solid ground and then tested for the 12.5 volts per the manual test instructions. While I have the wires apart I'll look around for the original issue, but wasn't my boat when this mess happened. I mean not as far as I know. I know when I found it I could not smell it, so tells me it is old damage. I should have taken some pics before I taped it up but couldn't find any on my phone. But yeah, has me worried enough I am install battery disconnects on both terminals.
I'll take some pics of this mess tommorow.

Any updates on this one?
I have a 98 Challenger 1800, the MPEM went bad on me, I purchased a used one, when the shop installed it, they found some "electrical issues" and they cut off the tachometer in order to "solve" the issue, well.. I used the boat for one season and now I am having further electrical issues, reading your post, most likely I have an ongoing and similar situation as yours, I just wish I had more experience and be able to trace down the issues like you done.