I did a search but couldn't find anything on this. Was wondering if anyone can tell me where to hook the leads of my multimeter up to so I can measure the rpm's on my car. It's a 92 z28, and though the tach fix has been put in, I am sure that the reading is not entirely accurate. I need to know the rpm's so I can set minimum idle as I am replacing my IAC.

thanks for any help.
JS

 

No way to do that.

You need a frequency counter, with approporiate conditioning (similar to what the tach has) on its front end, to filter out the "ringing" of the coil.

Best way to check a tach is with a more accurate tach.

 

If you can beg or borrow a scan tool that will report an accurate RPM.

RBob.

 

http://www.harborfreight.com/lcd-aut...kit-95670.html

as usual the answer depends on what multi meter your using

 

Both suggestions would be consistent with

 

A basic multimeter with ohms, volts and amps can't do it. You need an automotive multimeter with a rpm or frequency feature.

Harbor freight or other places like that may have a laser tach. You put a small strip of reflective tape on the balancer and aim the laser tach at it. Every time the tape goes past the laser, it's recorded as a cycle. This was the best way to measure rpm of the old mechanical diesel engines or any other turning shaft such as a PTO.

Factory tachs are highly inaccurate. Using a scan tool is the best way since that's the rpm that the ECM is detecting. Any good aftermarket tach will be a better choice than the factory one.

I've got a 5" Autometer playback tach in my race car. The playback feature is nice because I can play back a run and see exactly the peak rpm I shifted at and how far back the rpms drop after the shift. While racing, I never use the tach. I use it to watch rpms while I'm idling or testing stuff but I use a shift light to tell me when to shift.

Although it looks impressive to have a big 5" tach in a car, it's not really required. Nice to know what rpm you're at while driving down the highway to know just how fast you're burning fuel but for racing, it's very difficult to watch the tach and out the windows at the same time. NASCAR drivers use it because they know that at XXXX rpm and in X transmission gear means they're not going to speed down pit road.

 

Thanks for the info guys!