Dwell Meter vs Multimeter for FV Duty Cycle

[2jmotorsports]

1983 SC running CIS with Lambda

I am preparing to tune my frequency valve duty cycle (for CA emissions testing) and wanted to check with you guys which of these is the better tool for that job.

I have this handy dandy Fluke clone from Amazon:

https://www.amazon.com/AideTek-VC97-Multimeter-Capacitor-Frequency/dp/B008GTEZPI/ref=cm_cr_arp_d_product_top?ie=UTF8



At the moment my mixture is set by ear, pushing/pulling on the air sensor arm by hand to find the sweet spot where it runs well. It is probably set on the rich side at the moment but runs great. Anyway I connected the multimeter to the green wire on the test port and while it warms up it reads a looping duty cycle of 50-80% every few seconds until it reaches operating temp, then it reads a fluctuating 75-82%

Based on this I think the multimeter is doing its job. I mean, the number on the display is a tad jumpy but its readable.

I also have this OG dwell meter leftover from my VW bus days.

https://www.amazon.com/Actron-CP7605-Tachometer-Voltmeter-Analyzer/dp/B00062YUUS/ref=cm_cr_arp_d_product_top?ie=UTF8



It still works. When I connect it, the dial rises to some value and slowly sweeps back and forth within some operating range but I have no idea how to read it. Do I use the 6 cylinder scale or use the 4 cylinder scale as indicated in some prior threads?

Thanks in advance!

[AndrewCologne]

If you have a MM with dutycycle option its the better way IMHO, some people do like analog dwell meters and the way watching the needle fluctuating around the dutyclycle.
But be aware that when measuring DC you must connect the red wire of the MM to the vehicles ground and the black one to the connection of the test port. As the ECU does its pulse width modulation on the ground wire of the frequency valve.

You can check your proper connection when engine is running cold below 15°C where the open Loop mode forces the DC to run at 65%, .... also at 30% open throttle which does result in a DC of 65% as well.

When connection is correct and engine is warm, by adjusting the CO screw try to achieve an average DC of 45% at 950 RpM idle which matches to a CO of más on menos 0.5% and that's the ticket.

[2jmotorsports]

Gracias Andrew! Ill try that method to verify the MM output.

Also, after reading this thread, I think I will put the dwell meter away for use on old cars with point ignitions rather than FV DC evaluation.

https://forums.pelicanparts.com/porsche-911-technical-forum/821090-cis-lambda-frequency-valve-signal.html

I may pick up an oscilloscope too just for fun. It may be helpful in validating the MM DC reading.