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US Marine Tachometer 4.3l merc signal problem

E

earl pres

New member
Tach quit on my 4.3l merc (96 Bayliner) was told the wiring was ok , tack not working ,so i put a new tack in , hocked it up and still no rpms, ? Turn the key on a it goes to 0 but will not pick up the rpms when running, where does the signal originate? The signal wire coming of the tach is dark grey with white stripe/ cant find anything like that at the engine coil area ? anyone help !
 
If your motor is carbureted it will have one of three ignitions.

Thunderbolt IV

Thunderbolt V without knock sensor

Thunderbolt V with knock sensor.

The Grey wire in all three cases comes from the negative side of the coil and goes to the Ignition timing module mounted at the distributor and to the tachometer.

That grey wire goes to/thru the LARGE black connector mounted on the motor.

My suspicion is the pin to socket connection at the connector is bad/weak,

Pull the connector apart and look at the Male pins. (pin 2 is the grey wire) they have a slot in the and can be spread apart (very careful to only spread apart about .030" 1/32")

Then reinstall connector and see if the tach works.

Highly unlikely the timing module is not working..........possible but unlikely.
 
earl pres said:
Tach quit on my 4.3l merc (96 Bayliner) was told the wiring was ok , tack not working ,so i put a new tack in , hocked it up and still no rpms, ? Turn the key on a it goes to 0 but will not pick up the rpms when running, where does the signal originate? The signal wire coming of the tach is dark grey with white stripe/ cant find anything like that at the engine coil area ? anyone help !
Click to expand...

If your motor is carbureted it will have one of three ignitions.

Thunderbolt IV

Thunderbolt V without knock sensor

Thunderbolt V with knock sensor.

The Grey wire in all three cases comes from the negative side of the coil and goes to the Ignition timing module mounted at the distributor and to the tachometer.

That grey wire goes to/thru the LARGE black connector mounted on the motor.

My suspicion is the pin to socket connection at the connector is bad/weak,

Pull the connector apart and look at the Male pins. (pin 2 is the grey wire) they have a slot in the and can be spread apart (very careful to only spread apart about .030" 1/32")

Then reinstall connector and see if the tach works.

Highly unlikely the timing module is not working..........possible but unlikely.
 
If the big black connector is not the issue you may have a second connector under your dash. Follow the grey wire back from the tachometer to find it.
 
I took the 10 pin connector apart inspected and spread pins slightly , still no rpms at tack.
I didn't wiggle the 10 pin with engine running, is it required to have running?
Also no second connector from tach behind dash , wire goes directly into large enclosed bundle going to rear of boat.
I'm begining to think it is the distributor sensor (in the distributor) is this difficult to change and are any special tools/soldering requuired to change ? thanks
 
I'm begining to think it is the distributor sensor (in the distributor) is this difficult to change and are any special tools/soldering requuired to change ?
Click to expand...

Ayuh,.... The tach gets it's signal from the (-) terminal on the coil,....

Not the distributor,....
 
Does the grey wire from the coil go directly into the 10 point connector, which travels from there to the tach, or does it go to the timing/sensor in the dist then to the 10 point connector and then to the tack?
I have cleaned and checked all the connections and i'm thinking the timing sensor must not be working , you indicated not likely but possible, would the boat still run ok with this sensor not working? others are saying the signal goes directly from the coil ,thru the 10 point connector directly to the tack???
If its direct is there any reason i cant run a new wire from the neg side of the coil to the tack ?
 
Last edited:
Ayuh,.... Hook the tach up with a short wire, right at the motor, 'n try it,....

I'm thinkin' the tach is junk,....
 
earl pres said:
Does the grey wire from the coil go directly into the 10 point connector, which travels from there to the tach, or does it go to the timing/sensor in the dist then to the 10 point connector and then to the tack?
I have cleaned and checked all the connections and i'm thinking the timing sensor must not be working , you indicated not likely but possible, would the boat still run ok with this sensor not working? others are saying the signal goes directly from the coil ,thru the 10 point connector directly to the tack???
If its direct is there any reason i cant run a new wire from the neg side of the coil to the tack ?
Click to expand...



In some if not most cases, there should be two grey wires at the neg side of the coil. Is this true on your motor?


One goes to the timing module and the other goes to the 10 pin connector.

If that is not the case then the three way connection of the grey wires may be in the harness. Not typically.

One grey wire goes to the large connector. from there it goes to the dash. At the dash there may be another connector. Did you look and see if this is so?

My boat has a second connector.

Confirm if you have or have not a second connector.

If you do then check connections if not, now do a ohms test on the wire.

Ignition OFF!!!!!

Remove grey wire form tach, connect to one meter lead.

Make a long jumper and disconnect the grey wire at the coil neg. connect the long ire to the ring terminal of the grey wire.

Connect the long wire to other ohm meter lead.

It should be 0 ohms..........if you meter has a beep selection just use that.

That will tell you if the wire is good from the gage to the coil.

DO the basics first. Conform the wiring is good.

To answer your question about the timing module, if the grey wire feeding the module was not connected or broken the motor would not advance the timing.
The pulse from the negative side of the coil, the same pulse that the tach reads would be missing and the module would not know so to speak that the motor was running therefor would not advance the timing and the motor would run like crap.

Also one other thing, Make sure the ground wire going to the tachometer is a good ground connection. No ground no tach.
 
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