Can digital multi meter function as a tachometer?

[JR Ohio]

Well, the dwell/tach that I bought in 1969 finally died! They just don't build them like they used to, or wait a minute - they did build them pretty good back then.

I used the dwell very seldom since adding the Pertronix to my '72 240Z. But I did use the tach function often when tuning carbs or setting timing. Very handy when you don't have a helper!

My question is - I have a digital multi meter (DMM) that has a lot of functions but does not have a tachometer function. I always hooked up the '69 meter up to the distributor side of the coil and the other lead to a ground. Is there a function on these meters that would give me the rpm reading (I understand that there may be a decimal point that might be off)?

Has anyone tried this, is there a simple setting + math, or am I out of luck and will have to buy a new meter just to check RPMs occasionally?

Thank you for any help and advice.

John

[Zed Head]

If you have a DC hertz (DC Hz) setting you can get some numbers and do math. Your coil will fire 3 times per crankshaft revolution, and the meter should pick it up from the coil negative to ground. I've used my Fluke 115 that way to determine that my tach was off by 200 RPM.

The tachometer function on a higher grade meter probably uses the same measurement but does the math for you.

[JR Ohio]

Hi Zed and thank you for the info.

I have an older Fluke 77 but it doesn't have very many settings. I also have a Cen-Tech P37772 that I picked up last spring. Hz is one of the settings, but it does not say DC or AC. I am going to make an assumption that it is DC. Hope so anyway.

I thought I had it hooked up once at some DC volt setting and got a reading similar to the tach, but I could be mistaken.

[Carl Beck]

If you used the old one for 45 years - time to treat yourself to a new one. AMAZON or SEARS..

Sears.com

FWIW,

Carl B.

[240260280z]

I had one of the actron multimeters that read rpm from coil but it failed like most modern junk:

Amazon.com: Actron CP7677 Automotive TroubleShooter - Digital Multimeter and Engine Analyzer: Automotive

I now use a timing light with tach feature that reads off a plug:

Timing Light with Digital Tachometer

You could this type of device with a mark on the damper:

Digital Laser Tachometer | Princess Auto

[TomoHawk]

My tablet PC has an application that can convert the sound to RPM. It's pretty close.

OTOH, we used to build those little converter boards in school to convert stuff (like RPM, capacitance, etc.) to resistance, so you could use the volt meter.

What would be REALLY nice would be to hook up an exhaust sniffer or something to tune the fuel mixture.

Edited October 22, 2014 by TomoHawk