Multimeter tach reads RPMs too high

[banderberg]

I purchased an Actron CP7677 automotive multimeter. Hooked up red lead to negative side of coil, black to ground. Set the dial to 4 cylinder. With the engine idling it says my RPMs are ~2500. I know my engine is idling faster then it should but I also know it's no where near that fast.

The engine is 3.0L with points ignition.

Anyone have any suggestions? Thanks in advance.

 

[nola mike]

Is it supposed to be connected to the coil neg or the #1 wire? Looks like it's counting every pulse and should only be counting 1/4

 

[banderberg]

The instructions say to connect to negative on the coil.

 

[nola mike]

The instructions say to connect to negative on the coil.

What does your boat tach read?

 

[banderberg]

What does your boat tach read?

It reads waaay too high. It's on my list to fix.

 

[banderberg]

I've been doing some reading and found that some engines have a "wasted spark" - that is they spark on both compression and exhaust. Does this points ignition do that?

 

[itsathepete]

I've been doing some reading and found that some engines have a "wasted spark" - that is they spark on both compression and exhaust. Does this points ignition do that?

Distributor is driven by camshaft so it spins at half of engine rpm. No wasted spark. I have had success calibrating a tach with a digital strobe. You can download a free app on your phone for a strobe tachometer. Make a white mark on your crank pulley and set the strobe frequency to make the mark stand still like a timing light.

 

[nola mike]

It reads waaay too high. It's on my list to fix.

Like, in the neighborhood of what the dvm is reading? FWIW, I can't get a good rpm measurement using my dvm set to hz. Too sensitive I think; the hz on mine is very erratic, so it isn't getting a clean signal. Don't know if your reading is stable or not.

 

[banderberg]

Distributor is driven by camshaft so it spins at half of engine rpm. No wasted spark. I have had success calibrating a tach with a digital strobe. You can download a free app on your phone for a strobe tachometer. Make a white mark on your crank pulley and set the strobe frequency to make the mark stand still like a timing light.

Thanks I'll try the app.

 

[banderberg]

Like, in the neighborhood of what the dvm is reading? FWIW, I can't get a good rpm measurement using my dvm set to hz. Too sensitive I think; the hz on mine is very erratic, so it isn't getting a clean signal. Don't know if your reading is stable or not.

the dashboard tach reads even higher like 3000. It's relatively stable.

 

[itsathepete]

Disconnect the throttle cable from the carburetor and make sure that the throttle is closed or very near closed.

 

[banderberg]

Disconnect the throttle cable from the carburetor and make sure that the throttle is closed or very near closed.

Thanks. At this point I'm less concerned about the high idle than I am about getting an accurate read on the RPMs. I will make sure to check that though.