Digital Tachometer (Rpm Meter) - How To Fix

Nishan.dj · May 22, 2014

Hi Friends,

I need to fix a Digital Tachometer (RPM Meter) to my jeep (4dr5) and I checked on eBay. There are many and found this can be easily fitted to the dashboard ( Which I made with fiberglass for additional meters such as volt meter, vacuum ). The tachometer comes with a proximity sensor. Frankly I do not have an idea whether this is the most suitable tachometer i can use. So I need your expert advice on how I can do this. If I buy this, Will I have to fix the proximity sensor closer to the fan or somewhere around the alternator? Please advice and highly appreciate your reply to this post. Thanks.

Edited May 22, 2014 by Nishan.dj

Rumesh88 · May 22, 2014

It is not the best but perhaps the cheapest ! This particular product you've mentioned need a magnet attached to the shaft or the wheel to measure the RPM. (But the magnet is not included in the package. Why?). The only accessible place where you can attach the magnet is the crank pulley. But considering the location I wonder if it is practical at all to fix a detector there. Other alternative and the best method is a tacho based on a piezo-electric type sensor (the type used at ECO test to measure RPM) but they are really expensive AFAIK . Other methods such as tapping into the alternator, inductive pick ups etc., need you to calibrate the tacho.

Nishan.dj · May 22, 2014

On 5/22/2014 at 7:14 AM, Rumesh88 said:
It is not the best but perhaps the cheapest ! This particular product you've mentioned need a magnet attached to the shaft or the wheel to measure the RPM. (But the magnet is not included in the package. Why?). The only accessible place where you can attach the magnet is the crank pulley. But considering the location I wonder if it is practical at all to fix a detector there. Other alternative and the best method is a tacho based on a piezo-electric type sensor (the type used at ECO test to measure RPM) but they are really expensive AFAIK . Other methods such as tapping into the alternator, inductive pick ups etc., need you to calibrate the tacho.

Thanks for the reply. Little differences on actual RPM is not an issue for me. I just need to know the rough figures. and considering the cost, the one you have mentioned is not practical. Using alternator is also impossible. Anything you think, please suggest me a way. Thanks.

tiv · May 22, 2014

On 5/22/2014 at 8:09 AM, Nishan.dj said:
Thanks for the reply. Little differences on actual RPM is not an issue for me. I just need to know the rough figures. and considering the cost, the one you have mentioned is not practical. Using alternator is also impossible. Anything you think, please suggest me a way. Thanks.

Whats the issue with the alternator? Sometime back I had an Autogauge Tach wired to the alternator, was a matter of wiring it into one of the 3 coils and calibrating it during the emissions test

Nishan.dj · May 22, 2014

On 5/22/2014 at 9:01 AM, tiv said:
Whats the issue with the alternator? Sometime back I had an Autogauge Tach wired to the alternator, was a matter of wiring it into one of the 3 coils and calibrating it during the emissions test

The pulley system has increased the alternator's RPM to get more current out of it. I think it doesn't give the correct RPM reading because of that reason. Am I correct?

Edited May 22, 2014 by Nishan.dj

Davy · May 22, 2014

On 5/22/2014 at 9:13 AM, Nishan.dj said:
The pulley system has increased the alternator's RPM to get more current out of it. I think it doesn't give the correct RPM reading because of that reason. Am I correct?

That is not actually an issue. As tiv has mentioned, the tach can be calibrated to match the vehicle's actual RPM. This is a one time job and the unit will keep showing the correct RPM from there onwards. This is the best option IMO.

Rumesh88 · May 22, 2014

On 5/22/2014 at 9:01 AM, tiv said:
Whats the issue with the alternator? Sometime back I had an Autogauge Tach wired to the alternator, was a matter of wiring it into one of the 3 coils and calibrating it during the emissions test

On 5/22/2014 at 9:57 AM, Davy said:
That is not actually an issue. As tiv has mentioned, the tach can be calibrated to match the vehicle's actual RPM. This is a one time job and the unit will keep showing the correct RPM from there onwards. This is the best option IMO.

Both are correct for a gauge which is analog with a calibration pot. Here OP is trying to get a digital tacho fixed. This particular gauge is made to capture one pulse per revolution. If you pick up the signal from the alternator for each revolution of the crank there will be an unknown number of pulses depending on the pulley ratio and number of alternator poles. True, the ratio crank to alternator RPM is fixed, but in a digital system you need to divide the pulses by an exact factor.

bycap · December 17, 2014

Digging up an old thread.

I've seen in some cars they have fitted separate RPM meters (and some other meters too battery level meter etc. ) on the dash board. I need to fix a separate rpm meter. How can I do that ? Is there any specialist who does such things ?

Edited December 17, 2014 by bycap

tiv · December 17, 2014

On 12/17/2014 at 7:08 AM, bycap said:
Digging up an old thread.
I've seen in some cars they have fitted separate RPM meters (and some other meters too battery level meter etc. ) on the dash board. I need to fix a separate rpm meter. How can I do that ? Is there any specialist who does such things ?

This thread contains almost all the answers to your question(s); do a search any you'll find more, even the names of the respective dealers

Buy a Rev Counter / Rpm meter / gauge, take it to an electrician (also indicated in many posts)

The Don · December 17, 2014

The pods you fix meters to are available in a lot of places including companies which sell these meters.

As for what is needed it depends on your car. In petrol cars you can sometimes get a pulse from the ignition system to power the rpm meter, but you need to figure out what wire to tap (in older distributor based systems this was pretty easy).

Usually the meters come as a set of a sender unit and actual gauge to display other items like oil and water temperature. You can sometimes tap into existing sensors etc for these readings and the battery or alternator for voltage.

bycap · December 18, 2014

Thanks tiv and Don. I actually did a thorough search, but I couldn't find a proper dealer or a specialist. may be I have not used proper words in the search. My car is a starlet EP 91 (patrol).Simply I want to know a good dealer and a specialist. I'm looking for an analog tachometer.

Edited December 18, 2014 by bycap

The Don · December 18, 2014

On 12/18/2014 at 3:23 AM, bycap said:
Thanks tiv and Don. I actually did a thorough search, but I couldn't find a proper dealer or a specialist. may be I have not used proper words in the search. My car is a starlet EP 91 (patrol).Simply I want to know a good dealer and a specialist. I'm looking for an analog tachometer.

I think any company who sells these or auto electrician will be able to fit it on. Don't some of the famous car audio joints sell the meters? Its a very simple job for your car I think.

Hoonigan · December 22, 2014

Thanks tiv and Don. I actually did a thorough search, but I couldn't find a proper dealer or a specialist. may be I have not used proper words in the search. My car is a starlet EP 91 (patrol).Simply I want to know a good dealer and a specialist. I'm looking for an analog tachometer. <br />

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My bike didn't have a tacho from the factory so I bought a digital unit from eBay (not a generic Chinese one though). THis unit came with the sensor and magnets for the speed reading and a wiring 'harness' with a diagram which we used to tap into the existing electrical system. The tacho pulse could be taken from the coil or a plug. We wired it to the coil.

You can find these online for fairly cheap, even analogue ones, which your mechanic should be able to wire relatively easily.