Universal Diesel tach wacked

[Skipper]

I posted something like this awhile back, but still don't have a remedy. Now am about to buy a new tach, but thought I'd chime in here again just in case.

Maybe there is a Universal mechanic out there who knows this to be a common issue with this setup.

Have a 1984 Universal Diesel M-18 2 cylinder. Panel originally had tach, temp, amp, glow, start, oil light. I've just replaced the ammeter with a volt meter, and bypassed the long charging circuit, plus added an oil alarm. -but the tach issues were there long before.

Since obtaining the boat a few years ago, have always had Tach issues: Tach sits on 0 after starting motor, then when the alt kicks in and the volt meter shows charging, the tach starts jumping around like a gymnast. Then it might settle for a bit, then start again. Wherever it is, it's usually obviously inaccurate. Although, sometimes it reads correctly, but rarely.

The odd thing is that if I knuckle-tap it, it then pegs to max, and regardless of rpm. Sometimes when motoring, I look down and it's pegged even without tapping it.

It's completely wacked. I've checked all the wiring behind the panel and at the alt. Even took some off to inspect, and replaced one connector that was slightly suspicious. Still same issues.

Is it the tach?

I guess I don't really need it, but it's there so it should work.

 

[Stu Jackson]

99 44/100% of intermittent electrical issues are the connections. There are two ends to every wire. Have you checked the back of your alternator? If the wiring at both ends is fine, then there are only two other possibilities: the alternator tach output or the tach itself. You can have the alternator checked at a local alternator repair shop (always good to find a good one). They could also check your tach instrument for you. Good luck.

PS - Tachs are very good to have. They tell you a lot of information: slipping belts, STW compared to knot meter readings, etc. I wouldn't be without mine.

 

[Skipper]

99 44/100% of intermittent electrical issues are the connections. There are two ends to every wire. Have you checked the back of your alternator? If the wiring at both ends is fine, then there are only two other possibilities: the alternator tach output or the tach itself. You can have the alternator checked at a local alternator repair shop (always good to find a good one). They could also check your tach instrument for you. Good luck. PS - Tachs are very good to have. They tell you a lot of information: slipping belts, STW compared to knot meter readings, etc. I wouldn't be without mine.

Thank you.

I never thought about the slipping belt idea. Good advise.

 

[slaume]

It's probably the tach.I went through much the same as you are talking about. Definitely check out the connections. The Universal wiring harness has two trailer type plugs that you need to check as well. Better yet rewire everything and eliminate the plugs for all your engine wires. When my tach acted much like yours it was a simple matter of getting a new one and everything worked beautify.

I always use my tach to set my cruising engine RPMs. I never considered the belt monitoring aspect. If I did see the RPMs drop off but the engine still sounding the same I would have at least wondered what was going on, Steve.

 

[Skipper]

It's probably the tach.I went through much the same as you are talking about. Definitely check out the connections. The Universal wiring harness has two trailer type plugs that you need to check as well. Better yet rewire everything and eliminate the plugs for all your engine wires. When my tach acted much like yours it was a simple matter of getting a new one and everything worked beautify.

I always use my tach to set my cruising engine RPMs. I never considered the belt monitoring aspect. If I did see the RPMs drop off but the engine still sounding the same I would have at least wondered what was going on, Steve.

Thank you. Yes, I'm now highly suspicious of the tach. I'm going to check the wiring again with the multimeter per Stu, and replace one fuse holder\fuse. Then if still jumpy, am going to order a tach I've got my eye on.

 

[Stu Jackson]

Skipper, we might have asked you this before: Have you eliminated the wiring harness trailer plugs from your boat? You know, the "engine wiring harness" issue that Maine Sail and I have been mentioning for many, many years. This one: http://c34.org/bbs/index.php/topic,5078.msg35943.html#msg35943 If the connectors on the wiring are still those trailer connectors, even if you have a voltmeter, then it could be your issue.

 

[Skipper]

Skipper, we might have asked you this before: Have you eliminated the wiring harness trailer plugs from your boat? You know, the "engine wiring harness" issue that Maine Sail and I have been mentioning for many, many years. This one: http://c34.org/bbs/index.php/topic,5078.msg35943.html#msg35943 If the connectors on the wiring are still those trailer connectors, even if you have a voltmeter, then it could be your issue.

Yep still have them. I did do the heavy gauge bypass of the charging circuit at the solenoid/alt, and rr the ammeter with volt. Unrelated: Also did the alt bracket upgrade. So I'm listening ;-)

I opened the trailer connectors up, and they look new inside. Am going to order the tach, I think mostly because it will then match my new volt meter :-D and also eliminate those connectors during install.
Thanks again.