Tach issue..not grounded

[DUKE1]

Hello,

I just did a repower from twin 86 140 Johnsons to a single 99 Johnson 225 V6. My mid 80's vintage OMC tacks worked fine on the 140 and now I can't get it to work on the new engine. I figured out that my rectifier was gone, so I replaced it, and my tach still does not work. I used my MM on VDC and with the key switch on( POS TO PURPLE & GND to BLACK) got 12.5V on the MM. When I switched the BLK AND PURPLE I still got 12.5V.

Electricity not being my strong suit, what does this mean? I'm getting power but I'm not grounded? The T&T gauge right next to it is grounded...can I just unhook my GND wire off of my TACH and jumper one from the T&T gauge? My tach is set to 6 on the back and up until I installed this engine, it worked fine. Does a 1999 V6 require a newer tach? Your help is appreciated.

Duke1

PS- I've triple checked my ignition switch setup and it is by the book. Motor starts and runs great..just no tach.

 

[Joe Reeves]

Re: Tach issue..not grounded

The purple wire is the 12 volt source with the key in the ON position. If you have one meter lead connected to that purple lead and the other meter lead connected to the black wire leading from the tachometer, and your meter registers 12 volts....... then the tachometer is grounded.

Is your tachometer the type that has the wires leading directly internally from the tachometer, OR does it have screw terminals that the wires attach to?

 

[DUKE1]

Re: Tach issue..not grounded

Joe,

Thanks for the response. My Tach is the type with the screw terminals. So just to get this right in my head....even though I get 12v both ways as indicated earlier..this is grounded?

What should I do next? I hooked my CDI rectifier up per instructions with battery unhooked. I've been very careful not to cause any sparks.

Your help is appreciated. I've only got to figure this out so I can safely break-in this re-power in and go fishing.

 

[Joe Reeves]

Re: Tach issue..not grounded

What are those terminals marked on the tachometer? What color wires are running to them? Do you know what the other end of those wires are attached to?

Is there a dial on the back of that tachometer whereas it may be set to 1,2,3,4,5,6, something of that nature, OR is there some other kind of setup on the tachometer to change engine settings?

I don't know what kind of meter you're using to obtain a 12 volt redaing in both directions. Any volt meter I've used would give a positive reading in one direction but a reverse reading if the meter wire were reversed.

 

[DUKE1]

Re: Tach issue..not grounded

Joe,

Here's my info-
Terminals are set correctly purple for IGN/ black for GND /blue for Light and Gray for pulse (GND wire appears to be daisy chained to some other gauges)

I have checked the other ends and they appear to be correct.

There is a dial on the back with 123456 settings...it's set to 6

I'm using a SEARS brand multimeter. It's my ignorance on using a MM but it showed 12.1V on IGN/GND and now that you mention it..it was -12.1V on GND/IGN..does that sound right. I do remember seeing the minus sign.

Thanks
D1

What are those terminals marked on the tachometer? What color wires are running to them? Do you know what the other end of those wires are attached to?

Is there a dial on the back of that tachometer whereas it may be set to 1,2,3,4,5,6, something of that nature, OR is there some other kind of setup on the tachometer to change engine settings?

I don't know what kind of meter you're using to obtain a 12 volt redaing in both directions. Any volt meter I've used would give a positive reading in one direction but a reverse reading if the meter wire were reversed.

 

[Randyg123]

Re: Tach issue..not grounded

When you say the tach does not work, what do you mean?

When you turn the key on, does the tach set to zero?
Is it reading any rpms at all when the motor is running?
Any movement on the needle when the motor starts, runs, shut off?

 

[DUKE1]

Re: Tach issue..not grounded

Randyg123,

When I turn the key to the "on" position, the needle makes the smallest bump..not like when it worked and it would immediately go to zero upon power application.
No reading when the engine is running.
No movement when the engine is off or on. I don't get it..it worked fine with the other engine.

Thanks
D1

When you say the tach does not work, what do you mean?

When you turn the key on, does the tach set to zero?
Is it reading any rpms at all when the motor is running?
Any movement on the needle when the motor starts, runs, shut off?

 

[Chris1956]

Re: Tach issue..not grounded

Duke, That motor likely has the single water cooled voltage regulator mounted behind the flywheel. You might see if you have continuity from the grey wire on the VR to your Tachs grey wire. The engine or boat harness may have an open or melted wire like mine '98 Johnny 150V6 did.

 

[dajohnson53]

Re: Tach issue..not grounded

Just to expand a little on this and what others have said:

First, your multimeter reading is correct: "battery voltage" (~12+ volts) is positive when ignition key is on/ engine not running and when leads are clipped to purple and black, and the opposite or negagive when clipped opposite. You would see the same thing at the battery itself if engine is not running.

Second, even though you have just replaced maybe the new regulator/rectifier (r/r) is bad. What caused you to figure the old one was bad? Have you ensured that all connections to and from the battery are very clean and very tight (tightened with a wrench)? Could whatever the reason the old one went bad have caused the new one to go bad quickly?

Have you at least checked out whether the engine is charging the battery well? When the engine is running high idle, and you have your multimeter on the battery terminals themselves with all connections very clean and very tight, it should be reading 14+ VDC. Should drop down to "battery voltage" (~12-13 vdc) when engine is off.

I had a recent experience where the tach didn't work but the battery was charging fully (14.5+ VDC at high idle). Conventional wisdom would say it was a bad tach rather than bad r/r. I tried a new tach, it didn't work. I tested the r/r using Joe Reeve's excellent and simple procedure:

http://forums.iboats.com/showthread.php?t=190636

Turned out the r/r/ was bad even though it was charging OK. Replaced the r/r and tach worked. In layman's terms, I was told that this sort of r/r has multiple diodes and if only some (one?) of them is blown, it can charge but not give a proper pulse to the tach.

So, my advice is

1. check all battery connections, very clean and very tight.

2. check out status of battery charging. Could tell you if new r/r is bad.

3. if you can, try a different, known good tach jump wired to the tach connections at the dashboard - could tell you if it's a tach problem or a r/r problem.

4. Go through Joe's procedure linked above. To me (a very poor mechanic), it was a little tricky actually getting at the r/r and terminal strip and making sure I properly identified which wires were coming from and going to where. Not a big deal, but just make sure. If you've actually replaced an r/r none of this will be difficult.

I'm curious what you find. Good luck.

 

[DUKE1]

Re: Tach issue..not grounded

CHRIS1956,

I will check for continuity on the wires...that procedure is the red probe on the gray wire and the black to ground? Your right..the motor does have a single water cooled 35amp R/R. I will look for the melted wire as well...some did seem kind "hot" looking.

Thanks
D1

Duke, That motor likely has the single water cooled voltage regulator mounted behind the flywheel. You might see if you have continuity from the grey wire on the VR to your Tachs grey wire. The engine or boat harness may have an open or melted wire like mine '98 Johnny 150V6 did.

 

[DUKE1]

Re: Tach issue..not grounded

dajohnson53,

Thanks for the good post. This is a new to me repowered motor. It starts and runs great...just doesn't have tach. I had some wiring issues early on..but they were harness related so I got a brand new OMC harness and this seemed to do the trick.

As to why it popped the R/R, I think that was my fault, I didn't have my battery unhooked when I did some work and I caused some sparks. Battery is good and strong and connections are clean and tight.

I do have another tach (I had twins) and I will jumper it over and see what happens. I'm just trying to not re-invent the wheel and do this in a logical order. So all ideas are appreciated.

Thanks and I'll let you know what I find.

Duke1

Just to expand a little on this and what others have said:

First, your multimeter reading is correct: "battery voltage" (~12+ volts) is positive when ignition key is on/ engine not running and when leads are clipped to purple and black, and the opposite or negagive when clipped opposite. You would see the same thing at the battery itself if engine is not running.

Second, even though you have just replaced maybe the new regulator/rectifier (r/r) is bad. What caused you to figure the old one was bad? Have you ensured that all connections to and from the battery are very clean and very tight (tightened with a wrench)? Could whatever the reason the old one went bad have caused the new one to go bad quickly?

Have you at least checked out whether the engine is charging the battery well? When the engine is running high idle, and you have your multimeter on the battery terminals themselves with all connections very clean and very tight, it should be reading 14+ VDC. Should drop down to "battery voltage" (~12-13 vdc) when engine is off.

I had a recent experience where the tach didn't work but the battery was charging fully (14.5+ VDC at high idle). Conventional wisdom would say it was a bad tach rather than bad r/r. I tried a new tach, it didn't work. I tested the r/r using Joe Reeve's excellent and simple procedure:

http://forums.iboats.com/showthread.php?t=190636

Turned out the r/r/ was bad even though it was charging OK. Replaced the r/r and tach worked. In layman's terms, I was told that this sort of r/r has multiple diodes and if only some (one?) of them is blown, it can charge but not give a proper pulse to the tach.

So, my advice is

1. check all battery connections, very clean and very tight.

2. check out status of battery charging. Could tell you if new r/r is bad.

3. if you can, try a different, known good tach jump wired to the tach connections at the dashboard - could tell you if it's a tach problem or a r/r problem.

4. Go through Joe's procedure linked above. To me (a very poor mechanic), it was a little tricky actually getting at the r/r and terminal strip and making sure I properly identified which wires were coming from and going to where. Not a big deal, but just make sure. If you've actually replaced an r/r none of this will be difficult.

I'm curious what you find. Good luck.

 

[DUKE1]

Re: Tach issue..not grounded

Here's the latest. I did the JReeves Tach test via rectifier and I got results but don't know how to interpret them.

I did as per instructions and when I plugged my tach gray wire into the yellow-gray wire off of the stator there was no tach operation. I then swapped it to gray tach wire and yellow stator wire...still no change.

I used my other know good tach and got the same results. I did check the rectifier and discovered that it has two good diodes (yellow to red) and two bad diodes (yellow to ground). My other R/R was the same.

I then OHM'd the stator yellow wires and got .5 which means my stator is ok...I think. (same both ways)

I'm begining to think that my gray wire from the tach is screwing things up. I don't know if I did this right but I touched the gray wire from the tack (at harness end) with the OHM meter and the other probe to ground and got a flash to 1000 then to 1. Same thing when I reversed them. Does this mean that my gray harness wire to the tach is faulty?

I'm not the greatest at electronics and would love some help interpreting the results. Also why am I blowing rectifiers at the yellow to ground wires? I've been extremely careful to not make any sparks and have my battery unhooked when I do anything with the wiring. Your help is appreciated.

I could take it to a mechanic...but I really want to figure this out..so I need your help.

Thanks very much.
D1

 

[HighTrim]

Re: Tach issue..not grounded

Tachs read off the alternating pulses from the stator. Any of the leads from the stator charging portion can be used for the signal. The designated tach signal wire is merely attached to one of those.

In reference to what DaJohnson53 was saying, Johnny/Rudes have three wires coming from the stator to the R/R. One is common, and the others lead to separate banks of charging coils. That way, if one of the coils fails, the other bank should still charge. If one of the diodes in a bridge rectifier fails, it will still act as a simple rectifier.

Alternators will only alternate if there is a complete circuit. So when a rectifier fails, the circuit is broken. That's why Johnny/Rudes use two separate banks of charging coils and bridge rectifiers. They allow a back-up should a connection be broken.

Usually the symptoms you describe (half the bridge taken out) are due to loose or dirty connections. Swapping the battery cables will usually take out both sides of the rectifier instantly.

 

[DUKE1]

Re: Tach issue..not grounded

Hightrim,

Thanks for the explanation...but if half the bridge is taken out, then it wouldn't make the tach operate or charge the battery? Can you use a rectifier with only half the diodes?

I did a proper continuity check on the purple wire gray wire from the tach to the end of the harness and I have continuity.

So why is this thing blowing my rectifier...I do have wingnuts on the terminals..and I'll fix that. All my connections are bright and shiney (used a dremel with a wire wheel).

So the two big questions...why isn't my tach working and what keeps blowing my rectifier.

Thanks everyone for the help...keep it coming.

D1

 

[HighTrim]

Re: Tach issue..not grounded

If half the bridge rectifer is shot, your battery could still charge, yet the tach would not function. That is what I feel your problem is. Why you are blowing your rectifier, I am unsure of. The wing nuts are a no no, but if they had been tightened with pliers on clean, shiny connections, you should not have blown a new rectifer like that.

I wonder if you have a short somewhere, perhaps the stator? Have you checked the voltage at the battery to determine if in fact it is charging? What is the ohm reading between the yellow leads from the stator at the terminal strip? Between those wires and ground, there should be no reading. A reading would indicate a short in the stator.

When using your multimeter on the rectifier, be sure to use the "diode test" setting, short of that, use the highest ohms scale.

 

[Joe Reeves]

Re: Tach issue..not grounded

Forget everything except the tachometer for a moment. Even with the "gray" sensor wire detached from the tachometer, the tachometer should zero out when the key is turned to the ON position. Your tach isn't doing this.

The ON position of the key should have 12 volts being applied to the battery terminal of the tachometer. The ground terminal should have a definite ground to the negative battery terminal...... not a ground that may be reading ground by being circuited thru some other component.

I'd suggest that you temporarily run a wire from the tach ground terminal to the negative battery post just as a trouble shooting procedure to eliminate any question pertaining to having a true ground to that component.

With those two wires connected to the tach and nothing else, it should zero out.

 

[DUKE1]

Re: Tach issue..not grounded

Joe,

Thanks...when I work on it again (next week) I'll run a dedicated line from the neg battery terminal to the GND on the tach. When I checked it with the MM I get 12.1V on Purple Wire/Red probe and Black probe/GND and -12.1v when I reverse them.

Hightrim,

I checked the stator but I checked each yellow wire against the other and I got .5 Ohms. I didn't check them to ground. As for my battery cables, there new OMC cables and I did use a pliers to get them on tight, I'll still fix that though.

Thanks,
D1

 

[DUKE1]

Re: Tach issue..not grounded

Gents,

I thought that I should finish off this thread. I believe what Joe had told me, ie-that my tach wasn't grounded as it should be. I put a jumper ground from my volt meter (it's always worked through this process) to my tach and it works.

I also noticed that my volt meter was reading 14 volts when I was running the motor on the hose. Can my R/R still be good even though I tested it and it looked like the two of the diodes were open?

I've got another R/R coming, but now I'm wondering if I should install it.

Thanks again for all the help.

D1

 

[dajohnson53]

Re: Tach issue..not grounded

...
I also noticed that my volt meter was reading 14 volts when I was running the motor on the hose. Can my R/R still be good even though I tested it and it looked like the two of the diodes were open?

I've got another R/R coming, but now I'm wondering if I should install it.

Thanks again for all the help.

D1

Duke - go back and read the exchange you had with HighTrim on August 7. In my recent experience with a very similar rectifier (1990 200 HP V6), my tach didn't work, the Joe Reeve's tach/rectifier test showed the rectifier was bad but I was getting a 14+ charging current at the battery at high idle. So, based on what HighTrim wrote, and my limited experience, yes your rectifier can be bad with a non-working tach, but the battery is charging.

If you followed the Joe Reeve's Tach/Rectifier test and it indicates - based on his criteria - that your rectifier is bad, I think you're down to replacing the rectifier. That's what I did. I also double checked with a "known good tach". It was a tough pill to swallow, because the local price was $250+ (but I was happy because they had it in stock!!), and it was kind of a hassle for an amateur like me to replace... but now my tach works, so it was the correct move.

Good luck.

 

[dajohnson53]

Re: Tach issue..not grounded

As an associated question to this topic - regarding the cause of Duke's probably blown rectifier - and why mine might have blown....

Can you damage a rectifier by not properly grounding spark plug wires during a compression test? I've been trying to figure out why mine was blown. I just can't remember crossing the wires at the battery or a big spark or anything like that On the other hand, I did check the compression last fall and I'm quite sure I didn't ground the spark plug wires.

Or could it have been corroded wires at the battery? I have three wires connected to + and - on my battery: the main (thick) wire going to and from the engine, largish wires providing current and ground to the dashboard area and smaller wires providing non-switched current and ground to the bilge pump. All are now clean and tight, with hex nut attachment. However first thing this spring in getting the boat ready, I did notice significant corrosion at the wire-connector junction on some or all of the wires at the battery. I can't remember + or - or even if all or just some of the wires were involved. I ended up re-doing all the connections at the battery to make everything skookum. Could this have blown the rectifier? I have to admit, this sort of stuff was neglected last year as I didn't use the boat hardly at all.