TheSamba.com :: View topic - Automotive Multimeter

Mon Jul 15, 2024 4:23 pm

Hey guys,

I purchased a PT Automotive Multimeter to measure my bus rpm's.

The instructions indicate that the rpm's should equal what is shown on the screen x 10.

When im running the engine its showing numbers not at all consistent with that. I.E. the multimeter shows 2.0k (which would mean the bus is running at 20k? rpms)

Has anyone had any experience with these sorts of tools? Hard to tell by sound exactly, but it sure sounds close to 2k. Does this multimeter perhaps show exact measurement in certain situations?

I've got the multimeter set to the right settings (4cyl) with a verified good ground and connected to negative side of coil.

Mon Jul 15, 2024 10:45 pm

Buy one of these

Innova 5568 Pro Digital Timing... https://www.amazon.com/dp/B000EVU8J8?ref=ppx_pop_mob_ap_share

Mon Jul 15, 2024 11:17 pm

Connect it to another 4 cylinder car which has a tach and compare. Technically, it's not that hard to measure rpm from either the points signal or a plug lead signal...

Tue Jul 16, 2024 5:36 am

I'm betting the meter you have is made in China.
I'm also betting that like so many other tools made in China that a lot of info contained in the instructions was rendered useless in translation.

That said I'm thinking that the 2.0k reading might translate to 2000rpm. but that is just a guess. Also if the meter does not have an inductive pick up and uses the wire leads make sure you are properly connected to the ignition coil. Black to ground red to #1 lead of the coil. :)

Tue Jul 16, 2024 6:11 am

This one?

https://www.amazon.com/Performance-Tool-W2972-Mult...9.AzkAotsb

Fri Jul 19, 2024 9:24 am

Yup that’s the one Jir,

I ended up borrowing a neighbors dwell meter from the 70’s and it’s much better then this PT. Loads more accurate. The PT was off by about 500rpm’s.

In other words, maybe the PT isn’t the best tool for swell and rpm, save that to equipment specific for it.

Fri Jul 19, 2024 10:00 am

Mpec2 wrote:
In other words, maybe the PT isn’t the best tool for swell and rpm, save that to equipment specific for it.

My gut feeling: the more features something has, the less useful it is.

Robbie

Fri Jul 19, 2024 10:30 am

Mpec2 wrote: Yup that’s the one Jir,

I ended up borrowing a neighbors dwell meter from the 70’s and it’s much better then this PT. Loads more accurate. The PT was off by about 500rpm’s.

In other words, maybe the PT isn’t the best tool for swell and rpm, save that to equipment specific for it. That's been my experience with one or two Multimeters for RPM checks. One older meter with an Induction Clamp for the spark plug wire, actually was pretty steady and decent for checking, but the smaller, newer ones that I bought as store-on-board type meters have been a bit flaky in that department.... :roll: :roll: :roll:

Fri Jul 19, 2024 12:17 pm

One older multimeter I purchased had a variable sensitivity adjustment.. It would read more or less what it felt like with different placement of the pickup and the sensitivity control... looked suspiciously like that Amazon unit but sold by a now defunct UK chain store.

It took a lot of iterations of software on my home made rev counter to overcome miscounting caused by e.g.

Triggering on "spikes" when the points close as well as opening.
Triggering each time the plug "fires" - with a condenser, the voltage may "ring" several times per points opening.

My first effort recorded 60000RPM at idle, some of the "ignition pulses " it recorded were under 10 microseconds wide.

All the same things that sometimes demand resistors, diodes and other voodoo for a dash mounted rev counter on a bus at the other end of a 15 foot wire..

Mon Jul 22, 2024 6:01 am

My Blue Point Multimeter has an "Avarage" feature for the dwell function. It smooths out the inputs to the meter from the ignition system and displays the info in a usable form. So setting and reading the dwell of the points has not been a problem.

Mon Jul 22, 2024 7:23 am

I very seldom use a dwell meter or tach for anything, but I did pick up a nice Sun tuneup set for $10 or so at a yard sale.

Mon Jul 22, 2024 10:46 am

I agree with aeromech: that Innova 5568 has the works. It’s a sweet tool for a hundred bucks. I like mine.

Mon Jul 22, 2024 3:14 pm

mikedjames wrote: One older multimeter I purchased had a variable sensitivity adjustment.. It would read more or less what it felt like with different placement of the pickup and the sensitivity control... looked suspiciously like that Amazon unit but sold by a now defunct UK chain store.

It took a lot of iterations of software on my home made rev counter to overcome miscounting caused by e.g.

Triggering on "spikes" when the points close as well as opening.
Triggering each time the plug "fires" - with a condenser, the voltage may "ring" several times per points opening.

My first effort recorded 60000RPM at idle, some of the "ignition pulses " it recorded were under 10 microseconds wide.

All the same things that sometimes demand resistors, diodes and other voodoo for a dash mounted rev counter on a bus at the other end of a 15 foot wire..

is there a Samba thread for your home made rev counter?
sounds like a cool project