Running SC + Dwell Meter...anyone?
 

I bought a dwell meter this morning to test the ongoing issues with my CIS car. I wanted to see what kind of results I got. I don't understand these results...and/or I hooked it up wrong.

First photo is while the car is warming up from sitting all night. Second photo is after I took it for a short drive to warm it up....barely get a register. The Bosch book says to compute against the 4 cylinder scale, this one doesn't have one. Can I use the 6 cyl scale? I can't interpret this...can you?

Also, does anyone have a well running 81-83 SC who could hook up your dwell meter and get a similar photo? I don't know what the heck I'm looking for out of this....I expected the numbers to be higher.

Even weirder, I found that when I disconnected the lead on the test port with a warm engine, I heard a distinct buzzing sound start. It was not buzzing while lead was connected.

In the second photo, if I started the car, the needle would initially go up as high as the first photo for a couple of seconds and drop back as you see it.

http://img228.imageshack.us/img228/3...old6297618.jpg

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Your car has to be warmed up for you to meaningfully read the test port results. As it says on the face of your meter, double the eight-cylinder scale for four-cylinder values.

Ultimately, you want your mixture set so the frequency valve duty cycle is at ~50 percent, which would be 22.5 degrees on the eight-cylinder scale.

Brian

Sounds like the meter or your hookup is grounding the circuit. Does the meter have a +12v and ground connection ?

OK I was overthinking it since it's a 6 cylinder car.

Has two wires, green and black. Green went to the green/white pin in the port, black to ground. Which based on your comments sounds like I was in error. :confused: Neither the instructions, the Bentley or the Bosch guide say exactly what to hook it up to.

An engine's actual cylinder total doesn't matter in this case. The engineers back in the day decided that the common convention for lambda language would be four cylinders, thus the use of the four-cylinder duty cycle scale. Or something like that.

Brian

make sure your 02 relay under the pass. seat is working.

That is what I was trying to test. If the relay was working, the FV would work and indicate *something* on the meter, correct? Do I have the meter hooked up correctly? The actual O2 sensor is disconnected from the circuit.

I have a digital O scope if you want to see the duty cycle and wave form. The shop is open Sat a.m.

I saw that, thanks!....I'll bring my garage monkey if yours will be there. No swimming this time.

well, just to be clear, where/how do you have the meter hooked up?

Green from the meter to green/white in the test plug. Black to ground.

My shop monkeys will be around. Koi ponds are covered for the winter.;)

You know...I have the same exact meter and I've been having the same exact problem as you. I thought it was the O2 system not functioning correctly...but now I'm wondering if this type of meter will not work for this application. I even get the frequency valve to stop buzzing like you.

Here is my thread...

http://forums.pelicanparts.com/porsche-911-technical-forum/555089-help-troubleshooting-o2-sensor-system.html

I wonder if anyone else who has this brand of meter has gotten it to work correctly.

My Question is how can I adjust the Duty Cycle?? I would like to have a reostat on my dash "Power / Fuel Mileage!"

I have the same dwell meter and it works as it should; works as described in the Bentley.

The duty cycle adjusts according to the mixture. I have taken note from Don_Gilbert and am plumbing an adjustable full pressure regulator into the cabin. The reg. takes the place of the WUR (control pressure reg) and allows me to change the pressure at will. Thus allowing me to twist a knob for mileage or power.
I am also making some plans to modify the WUR and attach a cable and lever. That way I could adjust pressure without plumbing fuel into the cabin.

My Question is how can I adjust the Duty Cycle??


that is the 02 sensors job. You can adjust freq. of dwell by moving your 3mm allen screw to get it with spec. If the 02 relay is working, you can feel the freq. valve vibrating. Your freq. valve (just an inline injector that bleeds press. off in the lower chambers of your fuel dist.) also is what richens your mix when you go past the 35 degeee throttle switch. with it inop, you could be in a lean situation at wot. (not good)

http://forums.pelicanparts.com/uploa...1291124611.jpg
my control press regulator, can adjust afr on the fly intantly.

Anyone have any additional data points on this? We were unable to get a reading with the digital oscilloscope.