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Mar 29, 2002 | 07:47 PM

jds1971

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1971 F100 360 w/C6
I don't have tachometer. Is it possible to take a reading from the coil (neg. post) using a digital multimeter that measures frequency? Or do ya'll think it will fry the multimeter?

Mar 29, 2002 | 11:16 PM

Mil1ion

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[updated:LAST EDITED ON 30-Mar-02 AT 00:17 AM (EST)]No!

You need a tach.

Maybe if you have a 20,000 Volts setting it might work.

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Mar 30, 2002 | 09:34 AM

jds1971

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This will not hurt your meter There is a max voltage range for reading frequency.Check the instructions.You will have to divide by the number of cylinders to convert to R.P.M.

Larry

The above was posted in the other conference by Larry. It makes sense because we will be looking at frequency, not voltage.

>Maybe if you have a 20,000 Volts setting it might work.

Do you mean that there is 20,000 volts on the neg. post of the coil? I thought that was going to the cap via the coil wire.

Mar 30, 2002 | 11:07 AM

Mil1ion

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You're correct,I miss read it.

I'm bad.

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Mar 30, 2002 | 07:18 PM

jowilker

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Mar 30, 2002 | 07:21 PM

lshort

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I went out and got my digital multimeter and tried this on my truck
and it does work.Except to get to R.P.M. first you have to get to
hertz (times per second)meters usually read khz.Then multiply times 60
(to get to times per minute)then divide by the number of cylinders.Also not sure of the accuracy of this as digital frequency counters are very sensitive and will count
electronic "noise" as a pulse.May have to do some input conditioning
to make it accurate.Let me know if you are interested in this.It can be done with a few componets.It would be intersting to compare it to
a tacometer as meter may work ok.Also you can use a annalog meter for a tacometer.

Larry

Mar 31, 2002 | 04:44 PM

jds1971

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[updated:LAST EDITED ON 31-Mar-02 AT 05:46 PM (EST)]Excellent point, Larry-

I tested my theory also and came up with fairly accurate results. After all calculations, I concluded that my engine was turning ~825 RPM. That sounds about right as I always thought it was running a little fast.

Now, according to my manual for the multimeter (Greenlee DM-500), it has a built in line filter that can be set to 50 HZ or 60HZ to reject unwanted noise. Set to 60HZ, I believe the measurement to be very accurate. What do you think?

Joe