Ford Lehman 120 Tach Died

Hi,
I have a new to me trawler with Single Ford Lehman 120. Tachs worked ok at first. They looked like they were "sticking" for a little bit then died on a cruise. A couple times it looked like they were coming back to live, but they are dead.

Need help to start debugging the problem. Not even sure where signal comes from off engine. I have pics of alternator and awoke senders attached.




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Raymond Goff
1978 Marine Trader 34

Www.libertytrawler.com

This is a link to the Lehman manual if you don't already have one. This page detail where you may want to begin looking.

Page 23

And here is a link to the complete service manual:

http://www.jachtenonderlinge.nl/upl..._2700_range_diesel_engine_workshop_manual.pdf

It isn't a searchable pdf, but at least you can begin to find your way around your diesel. Takes a while to download.

mike

Also look here:

http://www.trawlerforum.com/forums/s32/ford-lehman-120-guage-set-up-22940.html

This might help

Looks like an alternator regulator in the last 2 pics.... cant be sure but some regulators have the tach takeoff from there.


If not there is an ice cream cone looking tach sender on the starboard dside of the engine, low, about 2/3 of the way back on the engine.

Greetings,
Mr. RG. Possibly NOT a solution but at some point I can see your electrical connections benefiting from a good clean up. One at a time, carefully remove each connection, and remove corrosion. Replace each with a coat of your favorite corrosion stopper. Do this with the battery disconnected.

I've found a Dremel with a small wire wheel attachment to be useful.

I installed one of these and am very happy with it. Cost about $100 and is much more accurate.

https://tinytach.com/diesel.php

RT Firefly said:

Greetings,
Mr. RG. Possibly NOT a solution but at some point I can see your electrical connections benefiting from a good clean up. One at a time, carefully remove each connection, and remove corrosion. Replace each with a coat of your favorite corrosion stopper. Do this with the battery disconnected.

I've found a Dremel with a small wire wheel attachment to be useful.

Click to expand...

What he said.

READY2GO said:

I installed one of these and am very happy with it. Cost about $100 and is much more accurate.

https://tinytach.com/diesel.php

Click to expand...

Did you install one at both upper and lower helms?

The tinytach website didn't provide much info. It installs in the fuel line?? I have been looking to upgrade mine. Can't seem to get exact info for tach tach off parts on stbd rear. I only have a plug there. Do you have a pdf of install directions?

The white lead coming from the R terminal goes to the tach on mine. It is a pulsed signal that varies with speed. You should get about 6 volts out, which you can check at the lead into the tach at your helm. Judging from your engine wiring, you may be dealing with a bad ground in your helm station.

All:
Sorry for delay in replying. I am trying to figure out how my tach was wired. Many mentioned a starboard side sender, but I don't see anything. Is there where is WOULD be if I had one? Based on other pics on the web, I think it is....

If that is where is would be if I had starboard sender, I guess I don't have one. In that case, would it be coming off the alternator some how?

Ray

If you don't have the sender than the tach is most likely driven off the alternator.

In your photo of the back of the tachometer the white/blue pair of wires are outputs. On my boat the white R goes to the tachometer. Try measuring for voltage between the wire going into your tach and a ground wire in your instrument cluster with the engine running. You should see some voltage (? 6 volts ac). If you don't it looks like a wiring problem. You can also measure the voltage out of the R terminal on the alternator with the engine running. Some voltage regulators have a delay in alternator output when the engine is first started, so wait a few minutes to get a reading if it's 0v ac. That blue wire from the P probably goes to the external voltage regulator.

It looks like I am getting about 1v at idle and around 2+ with some throttle. The alternator had a bad shimmy due to a bad spacer. Could the alternator be having issues?

Is that at the tach or the alternator? That terminal on the alternator is a tap to the common point between the stator coils before it is rectified into dc voltage. It should read approximately 1/2 the output voltage. How much voltage is the alternator putting out? Check between the B terminal with the heavy red wire and ground. Also, run just that engine while testing; all other charging sources should be off.
Yes, the alternator could be bad, or the wiring.

I talked to American Diesel. They suggested i jump the oil pressure switch and see if the switch is bad. I will be doing this later today to see if the switch is causing charging and tach issues.

RG

raymond.goff said:

I talked to American Diesel. They suggested i jump the oil pressure switch and see if the switch is bad. I will be doing this later today to see if the switch is causing charging and tach issues.

RG

Click to expand...

Update:
I did the test suggested by American Diesel, no luck. Pulled the alternator and brought to a local shop. Bench test showed it was pretty much dead. They actually had a re manufactured in stock and ten min later they swapped pulley and I was out the door.

I will put it in tonight and see if all is good.

RG

Well, the alternator seemed to fix the issue. Currently out on a test run. Everything looks to be normal.

Awesome! Good idea to double check the pully alignment so you don't get vibration or belt wear. Now you know all about your alternator. 999 systems to go!

Ran 10 hrs over weekend and worked perfectly. Mark this one done. Next on list, got forward holding tank to pump out.


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Raymond Goff
1978 Marine Trader 34

Www.libertytrawler.com

Tach runs off alternator. There must be a load for it to work. Turn on some lights and see if it functions.