you asked >Ca
you asked >Can you actually watch/see the duty cycle change as you change the mixture settings manualy? <
- Engine warm, closed loop
- Hook up a test connector between the connector/harness that plugs into the freq valve and the freq valve connector that gives you some bare wires to attach some lead to (in other words, you want it to operate as normal but you want to be able to tap into both wires )
- using a dwell meter set to 4 cyl scale, connect the two leads of the dwell meter to the two wires of the Freq valve
- the dwell meter should swing back and forth between 45 - 55 % if everything is set correctly and operating within range
(above 60% duty cycle i.e. the system is trying to correct for too lean a mixture)
(below 40% duty cycle i.e. the system is trying to correct for too rich a mixture)
I never had much success with a dwell meter so I used a hand held oscilliscope (about 6 years ago).
** it matters which wires from your meter connect where. In other words, if your reading a 43 % duty cycle and you switch the wires it would then read 57%...so you need to be on the correct wires to your dwell meter or you're reading the inverse duty cycle ("off time" i.e. not "on time" which would then be incorrect)
So you need to figure out which wire goes where. i.e. force a lean condition and make sure you get a reading below 45% then you know that's the correct way.
(you're right, it's a pain in the ass to get right)
Then, once everything is hooked up and the engine is running, as you turn the 3mm adjustment screw clock wise and CCW you'll actually see the dwell meter (aka duty cycle) change. The key is to than get it to oscillate between 45% to 55 %
The problem with this whole method is (just one of many in my opinion), if you have for example a failing O2 sensor sending a bad signal to the ECU (low output i.e.), you're then gonna think you need to make up for it by cranking up the CO and what you're really doing is over-enrichening (off baseline).
A 5 gas analyzer wouldn't let you do this.
That's why after you had taken the time to help that guy on FC to tweak his CO using an EGA, and then he goes and does it using the duty cycle method and still gets poo poo results...blew my mind why he went and did that...but oh well.
The O2 sensor senses Oxygen. Why would you wanna use that to tweak CO if you had a EGA? (2 diff. gasses)
But, as you adjust CO, the pulse frequency on the freq valve changes anywhere from 5.1 KHz to 9.5 Khz (or something like that, I can't remember exactly...that's what's happening ...but with a 5 Gas EGA who would care cause your reading the final results which is what truly matters)
All this is written up in several Bosch manuals.
I tried using this techinique on a 1984 308qv I had but it never truly got the car dialed in, some guys still do this but I think they're missin' the boat.
My 3.2 still has virgin plugs on the Fuel Dist....but that will all change once I get my 5 gas EGA