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  #1   IP: 156.34.176.57
Old 09-20-2019, 10:33 AM
amizerin amizerin is offline
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Tachometer install

My Grampian 28 does not have factory installed tachometer - only oil pressure, temperature and ammeter gauges. Some owner before me installed an electronic gauge like on the picture but I don't think it's accurate. The minimum RPM it shows is 2800 when idle. Sometime it shows 5000 - 6000 when pull throttle to push the boat a little bit forward or reverse. All in all, it seems to be not working properly.

A couple questions I have.
Which RPM gauge is recommended?
How to wire it into the engine?
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  #2   IP: 24.152.132.140
Old 09-20-2019, 11:01 AM
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Have you gone through the select button functions to be sure it is on 4 cylinders?
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amizerin (09-20-2019)
  #3   IP: 156.34.176.57
Old 09-20-2019, 11:19 AM
amizerin amizerin is offline
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Quote:
Originally Posted by ndutton View Post
Have you gone through the select button functions to be sure it is on 4 cylinders?
I did not play with the button but probably you're right. There might be a switch between 2 and 4 cylinders.
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Old 09-20-2019, 11:22 AM
jcwright jcwright is online now
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A review of an hour/tach that resembles yours notes the following:

"They always work on one cylinder engines. With multi-cylinder engines they often pick up signals from more than one cylinder."

This might explain why your lowest RPM is 2800 (actually 700?).
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amizerin (09-20-2019)
  #5   IP: 156.34.176.57
Old 09-20-2019, 11:32 AM
amizerin amizerin is offline
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Quote:
Originally Posted by jcwright View Post
A review of an hour/tach that resembles yours notes the following:

"They always work on one cylinder engines. With multi-cylinder engines they often pick up signals from more than one cylinder."

This might explain why your lowest RPM is 2800 (actually 700?).
That sounds like exactly what's happening Well... I'm not sure I like to do the math dividing by 4 every time I check RPM. Is there a solution for that? A gauge that works with 4 cylinders?
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Old 09-20-2019, 11:38 AM
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Quote:
Originally Posted by amizerin View Post
Is there a solution for that? A gauge that works with 4 cylinders?
MMI catalog?
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1977 Catalina 30
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Old 09-20-2019, 11:42 AM
amizerin amizerin is offline
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How to I connect the RPM gauge to the engine?
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Old 09-20-2019, 11:49 AM
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It depends on the gauge. The typical gas engine tachometer such as you'll find with Moyer gets 12VDC + and - plus a wire to the '-' terminal on the coil.

Another style of gauge (diesel style, I have one) gets 12VDC + and - plus a signal from the alternator. Unless your alternator already has an AC tap for this purpose I would avoid this type of tach. It also requires calibration because of different pulley ratios on different engines. In other words, much more hassle.
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Last edited by ndutton; 09-20-2019 at 11:52 AM.
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  #9   IP: 156.34.176.57
Old 09-20-2019, 12:08 PM
amizerin amizerin is offline
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Quote:
Originally Posted by ndutton View Post
It depends on the gauge. The typical gas engine tachometer such as you'll find with Moyer gets 12VDC + and - plus a wire to the '-' terminal on the coil.

Another style of gauge (diesel style, I have one) gets 12VDC + and - plus a signal from the alternator. Unless your alternator already has an AC tap for this purpose I would avoid this type of tach. It also requires calibration because of different pulley ratios on different engines. In other words, much more hassle.
Thank you! I believe any tachometer suitable for 4 cylinder engine will work?
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Old 10-10-2019, 12:20 PM
JackConnick JackConnick is offline
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I'd like to add a 2" tach to my A4. But I have no sensor or previous install to wire to.

If I read the above correctly, it just simply wires to the coil and counts pulses? No other sensor is required?

I've tried some of those electronic ones and agree they are junk...

TIA,
Jack
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Old 10-10-2019, 07:49 PM
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I don't think you need tach installed full time - just when you're doing diagnostics.
My meter is an antique Heathkit dwell/tachometer - probably 50 or 60 years old. Analog meter. It clips to the coil, so you have to set it for the number of cylinders. If it died, I'd look on Amazon - dwell tachometer - and see what's offered. My eyesight being what it is, I'd probably look for a big analog meter. Don't need digital.
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Old 10-11-2019, 04:26 PM
JackConnick JackConnick is offline
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No, I sometimes hear a miss or something while underway, maybe water in my fuel or something. I like to be able to check and also calibrate my boat speed to tach.

Jack
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Old 10-13-2019, 11:12 AM
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Quote:
Originally Posted by JackConnick View Post
...If I read the above correctly, it just simply wires to the coil and counts pulses? No other sensor is required?...
That is correct. The tach hooks to the "-" terminal of the coil and counts pulses as the points (or the EI) brings that terminal to ground.

Most Gas engine tachs have some sort of switch or jumpers to set the number of cylinders (1, 2, 4, 6, 8). Occasionally, this switch will be labeled in "pulses per revolution" instead of "cylinders". For the A4 (or any 4 cylinder 4-cycle engine), this should be set to "2" (1 pulse per cyl every 2 revs x 4 cyls = 2 pulses per rev)
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