No tach signal from engine???

[ablank]

I have a 1991 35hp that has a terminal bar on the side of the engine block. The treminal bar indicates that the tach signal wire is purple. I've heard that this is a standard configuration. I have power to my tach (it lights up and pegs zero when I start the engine), but stays at zero RPM no matter how much the engine revs, and no natter what pole setting I select on the back of the gauge. I should mention that the gauge is brand new.

Should the purple wire on the terminal bar connect to something else on the motor in order to get a signal for the gauge?

If it isn't obvious by now, this is the first motor and boat that I have owned.

Any help that you experienced mariners may have would be greatly appreciated.

ABlank

 

[maxum247]

Re: No tach signal from engine???

Is your tach a 20 pole tach?
Is your battery charging?
Not sure if the charing system on your engine is regulated or non regulated but if the battery isn't charging it may be that the rectifier/regulator or rectifier is the problem with the tach zeroing out.
One of the functions of the altenator charging system is to provide the signal for the tachometer.
The tachometer simply counts AC voltage pulses coming out of the stator before the AC voltage is rectified to DC. Tachometer failure is therefore related to the charging system, not the ignition system.
Malfuntions in the charging system generally cause the battery to be undercharged and the tachometer to read erratically or totally fail. The following conditions will result in rectifier or rectifier/regulator failure.
Reversing the battery leads.
Disconnecting the battery leads while the engine is running.
Loose connections in the charging system circuits, including battery connections.

max!

 

[john from md]

Re: No tach signal from engine???

Do you know how many poles your tach is set up for? Some are fixed and some can adapt to different engines. If you can't answer this question, take it back to the store you bought it from and ask them.


If it is not the correct configuration for your engine, it will not work properly.

Regards,

John

 

[dr.livingston]

Re: No tach signal from engine???

I recently bought a used boat with a Force 120 on it. The tach does the same thing as described by this post. It jumps to zero when the ignition is turned on and stays there.

Yesteday I noticed something curious. The battery was so low on water that I had to add half a gallon to bring it up to the split rings. That is indicative of two possible things - lack of battery maintenance by the previous owner, or overcharging by the engine. Your mention of tachometer signals coming from the charging system makes me wonder if my regulator is in fact bad.

 

[john from md]

Re: No tach signal from engine???

It could be. Look at the 'stickys' under Force engines and you will find how I changed the rectifier to a voltage regulator from a snow mobile. The water boiling away is a symtom of overcharging for sure.

ps. If you had to add that much water, the plates are probably damaged to the point where you may get stuck out on the lake with a dead battery. I would get a new one.

Regards,

John

 

[dr.livingston]

Re: No tach signal from engine???

Yes, I wondred about the health of the battery due to the low water condition. The battery has a January '08 sticker on the top so it is fairly new. I checked the voltage as soon as I noticed the low water condition and it read 12.73. Tht's not bad for a battery that has been sitting for a week with no charging. Normal resting voltage should be 12.6 under those circumstances, so I'm hoping the battery is ok after all. Now I have to go and check out the rectifier.

 

[john from md]

Re: No tach signal from engine???

I agree, if it is that new, it shouldn't be damaged too badly as the plates are relatively unused. If you have a cigarette lighter outlet, buy a plug in voltmeter from Walmart and monitor your voltage. Mine was going as high as 17vdc before I changed to the regulator. Now, I get 14.2 from 1000 through 5000 and no more water in the battery box.



Regards,
John from MD

 

[dr.livingston]

Re: No tach signal from engine???

1994 Force 120 tach problems:

I investigated the tach problem today with the idea that it was likely to be the rectifier and that a replacement could be purchased at Radio Shack. I got that notion from another post regarding the tach. Here is what I found.

Under the dashboard the purple wire goes from the ignition switch to the tach - a matter of just a few inches. Since the engine starts normally I have to assume that the purple wire goes to the correct location in the engine.

That said, looking "under the hood" so to speak, there is a purple wire that comes out from under the flywheel but it goes nowhere. It is just a few inches long and hangs free with an insulated bullet connector on the end. There does not seem to be any place to plug it in. It seems to be an extra wire that is not needed in this application.

Three other wires are grouped with the purple wire - red, gray, and white with a blue stripe. The white/blue wire loops over the top of the cylinder head, passes between the spark plugs, and connects to some kind of small metallic device pressed into the casting. There seems to be no way to remove that device other than by pulling directly on the wire that connects to it. I was reluctant to do that not knowing what it is and how it is supposed to be removed.

I didn't see anything that looks like it could be purchased at Radio Shack.

 

[john from md]

Re: No tach signal from engine???

A rectifier usually has a red wire, a black wire and two wires, usually yellow with a stripe. The yellow wires go to the stator and are AC. The red wire is outgoing DC and the black goes to ground. A purple wire is usually attached to one of the yellow wires as this is where the tach receives its signal.

The purple wire should go from the terminal block under the dash to the terminal block on the engine. From there, a short purple wire will go to the rectifier.

Whether you have a rectifier or regulator, there has to be some component with about four or five wires going to it. They are usually small, smaller than a CDI unit and the regulators usually have fins for cooling.

Hope this helps,

John

 

[dr.livingston]

Re: No tach signal from engine???

There is a module bolted to the engine close to where the 4 wires emerge from under the flywheel. This module is 2-3 inches square and a half inch thick. It is potted with some kind of clear epoxy. You can see through the epoxy that there is an electronics printed circuit board inside. One corner of the potting material is quite discolored and dark. The rest is fairly clear. Yes there are 4 or 5 wires emerging through the potting material in the vicinity of the darkened corner. I didn't take exact note of the colors but yellow seems familiar.

As for the unattached purple wire, I can't see any obvious way to connect it to one of the yellow wires. The short purple wire from under the flywheel is terminated with an insulated bullet connector. There seems to be no unattached mate for it anywhere inside the engine compartment.

There is another purple wire included in a large bundle that emerges from the bottom of the engine compartment and disappears below deck. I assume that's the one that shows up under the dashboard connected to the ignition switch and the tach.

Am I correct in thinking that I should be able to detect AC voltage on the purple wire under the dash? If there is none then of course the tach won't work. OTOH, if there is AC voltage on the purple wire then the tach itself isn't working and I can stop looking inside the engine.

 

[john from md]

Re: No tach signal from engine???

It sounds as if the purple wire was disconnected from its female partner. The male end should insert into a female end usually inside a plastic protector. The device you are talking about sounds like a retifier. The purple wire may attach at another point than right at the rectifier so look for a female connector. If you can't find one, maybe someone replaced the rectifier and never hooked up the purple wire.

I would do this. Start and see if the purple wire has any voltage to ground. If not, jumper it to one of the yellow recifier wires and see if the tach works. Either yellow wire will work as they are AC.

Let us know,

John

 

[dr.livingston]

Re: No tach signal from engine???

Thanks for the suggestion. I'll head down to the boat this morning and try that.

 

[john from md]

Re: No tach signal from engine???

Must be nice to go out on a boat in November. Up here it was 28 degrees yesterday!

Good luck,

John

 

[dr.livingston]

Re: No tach signal from engine???

Yes, year round boating is the norm here in south Florida. Typically high 70's in the afternoon and low 60's at night. This year it has been unseasonably cold getting down to the 40's at night. Feelin' sorry for me?

Regarding the tach signal, I read the Seloc manual and it turns out that the gray wire from the voltage regulator is the tach signal. Since my voltage regulator is completely fried it stands to reason that the tach won't work. I've ordered a new VR. Hopefully that will solve both the battery problem and the tach problem.

 

[dr.livingston]

Re: No tach signal from engine???

The replacement voltage regulator finally arrived and, as expected, the tach started working and the battery is now being charged. It does seem that the tach needle is physically sticking on something when it is near the straight up position. Looks like I'll have to replace the tach instrument after all.

 

[john from md]

Re: No tach signal from engine???

I would run it a while and see if you can live with it. Mine is not accurate in the middle range but is at low speed and at WOT. I use my GPS for speed and don't really look at the tach or speedometer too much anymore. If you want to check the engine rpm for maintenance checks, buy a cheap hand held tach from sears or ebay.

The problem with replacing tachs is that you have to get one with the right number of poles and that can sometimes be a challange. Additionally, they can also get expensive.

Glad your regulator works.

Regards,

John

 

[dr.livingston]

Re: No tach signal from engine???

Good point about using the GPS as a speedometer. I think I'll browse this forum to see which models to favor and which to avoid - and where to find the best prices in relation to marine applications. Automotive type GPS units are relatively cheap but don't really tell you what you need to know on the water.

 

[john from md]

Re: No tach signal from engine???

I have found that Iboats is very competative in price. Additionally, many of the items I have bought here have free shipping.

When you search, use different terms such as GPS, depthfinder, fishfinder, etc. There is a wealth of knowledge on this forum but, computers being computers, it is sometimes hard to dig up.

Good luck and happy holidays,

John

 

[dr.livingston]

Re: No tach signal from engine???

Good suggestion. I never thought about iboats for electronics like that.

Happy Holidays to you to John.

Tom

 

[Wcsweb]

Re: No tach signal from engine???

I'm kinda having the same issue.

I know the tach works cause I had it hooked up to my other motor.

Someone posted that you can get a tach signal from eithier one of the yellow wires is this correct?