Recommendations for RPM meter?


#1

I have an RPM meter for my 40 year old truck with a points ignition system. It has both a rpm and dwell function. My Corolla has an electronic ignition system and doesn’t use points and so I don’t think that meter will work on the Corolla. The Corolla has a tach signal point I can access at the diagnostic connector. And I can access the plug wires of course.

You might wonder how I’ve measured the RPM up to now? I mean the car is over 20 years old. Well, either I’ve let them set the RPM for me when I do an emissions test, or I’ve used a lab o-scope and wrapped a few turns of wire around the number one spark plug wire. But that is sort of awkward.

I’d prefer a small hand-held battery operated rpm meter. It seems like an rpm meter wouldn’t even be as complicated as a DVM, and Harbor Freight hands out DVM’s for free sometimes. Being a frugal sort, free sounds good, but something less than $50 would be ok. So what do you folks recommend for an RPM meter suited for electronic ignition systems that is only used once or twice a year, like for a frugal DIY’er?


#2

On the very cheap end you could use something like this:

On the higher end you could get one of these (if your Corolla is OBDII). The benefit of this is that it gives you a ton of other engine parameters and reads codes too:


#3

Thanks. Not entirely sure how a photo-tach works. Would you point it at the crank pulley, like doing a timing measurement? That might work. No, it’s not an OBD II model.


#4

You just stick a piece of reflective tape on the pulley so the laser will reflect.

I’ve never used one, but you might even get away with just a chalk mark instead of the reflective tape.


#5

Here’s a brand new ‘old school’ dwell/tach/volt meter. I remember using a similar device back in my hot rod days with points ignitions and carbs. http://www.amazon.com/gp/aw/d/B00062YUUS/ref=aw_d_pd_automotive. In case the link doesn’t work, it is an analog dwell/tach/volt meter from Actron, available at Amazon.com for $26. It will work with any igntion system with plug wires. I remember using an unbent paperclip to slide in the spark plug boot to clip the high tension lead to. Worked like a charm.


#6

I’m leaning towards the laser rpm meter at this point. Low cost, light-weight, portable, small, plus it seems like it would be the most versatile. Works for all car engines irrespective of the ignition system, would even work for diesels. And could be used for measuring motor shaft speed and fan speeds, both of which I’ve wished sometimes I could have measured in an easy way. hmmm … ok, one more idea, I could use it to measure the prop speed on my toy gasoline/nitro fueled airplane too.


#7

My scanner has an rpm function, though it might be hard to read from under the hood.


#8

The tach connector provided will work with your old tach/dwell meter. There are no points but the principle is the same, one rise and fall per spark on the four cylinder scale. Just shove a paper clip in the tack port and hook up the rpm lead from your old meter.


#9

re: The tach connector provided will work with your old tach/dwell meter. There are no points but the principle is the same, one rise and fall per spark on the four cylinder scale. Just shove a paper clip in the tack port and hook up the rpm lead from your old meter.

@rattlegas … the shop manual goes out of its way to say to not to use anything other than a high impedance meter (one that is battery powered, which my old for the truck one isn’t) on the IG- test point, or risk damaging the ignition module.

I borrowed a high impedance battery powered frequency meter to experiment with. It reads in hertz. Does anyone know how to convert the Toyota OBDI IG- signal frequency measured in hertz to engine rpm?

The IG - test point is located on the diagnostic check connector on the 4AFE engine. I think it is functionally equivalent to the coil negative, and pulses each time a spark plug fires. So how do you convert engine rpm to each ignition firing in pulses per second? This is for the Toyota 4AFE 4-cylinder engine.


#10

1 hertz equals 60 RPM. But, your car is a four-stroke so it will fire 2 times per revolution. The proper conversion will be half that, or 30 RPM. Proper idle at 750-800 RPM should read 25-27 Hz.


#11

George, this is what I would do . . . and have done in the past, with other cars

Find the factory cluster WITH the rpm meter at a pick your parts junkyard, or on ebay

Make absolutely sure the cluster will work for your application before hand . . . automatic or stick

And remember . . . the odometer must reflect your vehicle mileage, NOT the vehicle it was pulled from

I suspect somebody will condemn me for this . . . my 1995 Corolla didn’t come with an rpm meter.
So I bought the higher end cluster WITH the rpm meter on ebay. The ebay cluster had WAY more miles than my car, so I had to roll back the odometer to reflect my own car’s mileage.

My brother’s Tercel is the base line model. It came WITHOUT trip meter. I found a Tercel cluster with trip meter at the junkyard. Once again, I had to roll back the odomter to reflect the car’s actual mileage.

This is NOT illegal. It would have been illegal if I had installed a lower mileage cluster and not corrected it, without informing DMV. The official DMV website says quite clearly that the odometer must reflect vehicle mileage. A lot of people think that anything related to the odometer is always illegal. This is not always the case.

By the way, for those who are still reading and still don’t think I’m a low down dirty liar and tamperer . . . rolling back those 2 odomters was definitely not child’s play. It was delicate work, and it really strained my eyes. Everything had to be lined up perfectly, and that took quite some time.


#12

That’s what I’m coming up with too BK. I didn’t do it with the simplicity you used, I was figuring how many time the distributor turns per crank revolution, etc. But like you, my calculations are that 800 rpm (the engine’s idle speed spec) should read around 27 Hz on the IG- test point.