I recently bought a good digital multimeter for non-automotive applications. It, obviously, does not have an RPM setting on it. I was wondering if there was a way that I could use it to check my idle or am I forced to pick up another multimeter with the proper calibration on it?

Thanks in advance....

 

Nobody knows or nobody likes me because I am new?

 

what are you trying to do exactly? the reason the automotive ones can do rpm is because the dmm reads the number of pulses in the tach signal

 

Both.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by integra-modder &raquo;</TD></TR><TR><TD CLASS="quote">the dmm reads the number of pulses in the tach signal</TD></TR></TABLE>

That answers the question that I *should* have asked. Thanks for the help.

 

Some DMM's (like my Fluke 179) can measure frequency in Hz. I haven't tried it yet, but I suppose there's 2 pulses per revolution, so you multiply Hz x 30 to get RPM. (3 pulses per revolution for a V6)

 

Im sure there is a way to do it. On the older hondas the tach wire from the distributor sent out a pulse when the cam and crank signals are synced, which can only happen at 1 time during a rev. The newer one take their tach reading directly from the ecu, which essential just mirrors half of the coil output.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">I haven't tried it yet, but I suppose there's 2 pulses per revolution, so you multiply Hz x 30 to get RPM. (3 pulses per revolution for a V6)
</TD></TR></TABLE>

I think CKP sensor emits four pulses for each rotation of the camshaft from my D16Y7. The crankshaft rotates at twice the speed of the camshaft.

So if I take a frequency measurement by backprobing the CKP connector at the distributor and divide by four that is the camshaft rotational speed in Hz. Multiply that by two to get the crankshaft rotational speed. Also a comversions from Hz to RPM since my meter reads in Hz. Therefore,

(Frequency from CKP in Hz) * 30 = (Crankshaft rotational speed in RPM)

Did I do that right?

Thanks again for the input.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mct121 &raquo;</TD></TR><TR><TD CLASS="quote">I think CKP sensor emits four pulses for each rotation of the camshaft from my D16Y7.</TD></TR></TABLE>As long as that's true, you're right. Check it against your tach at a few different speeds. You use the DMM at idle because your dashboard tach isn't very accurate down there. But it won't be off by a factor of 2...

Even though the tach signal is generated by the ECM, I figured it had one pulse per spark, so 2 pulses per crank revolution. Pretty much the same as what you said.

But if it's like integra-modder says (1 pulse per crank rev), then take Hz x 60 = RPM.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">Check it against your tach at a few different speeds.</TD></TR></TABLE>

That is what I intended to do. Thanks for the help.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">But if it's like integra-modder says (1 pulse per crank rev), then take Hz x 60 = RPM.
</TD></TR></TABLE>

Sorry, didnt mean to confuse you. The one pulse occurs only when the Cam/Crank sensors are synced. You are completely, theoreticaclly, correct about the fact that the coil output gets 2 pulses for a complete revolution. Then again, this is all theoretical until someone tests it.

 

I still have not had a chance to hook it up. (sorry, been busy) But I did find this in a search:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mct121 &raquo;</TD></TR><TR><TD CLASS="quote">I think CKP sensor emits four pulses for each rotation of the camshaft...</TD></TR></TABLE>

According to this thread the CKP emits 24 pulses on my ODB2 engine. That is going to change my math a little bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by integra-modder &raquo;</TD></TR><TR><TD CLASS="quote">Then again, this is all theoretical until someone tests it.</TD></TR></TABLE>

Just to close this out, I did give it a try. I found the external tach connector (I didn't even realize that it existed when I started this thread, pardon my ignorance) and connected my DMM to it with the other lead to the body. The freq that my DMM showed was off of the dash tach by a factor of thirty. That means that there are two pulses per crank revolution on that line.

Again, thanks for the help. I am still learning here.