"Surging" at Constant Speed

[scarceller]

As mentioned:
1 - unplug the O2 sensor
2 - at idle with it unplugged measure the voltage at the O2 sensor with a good Digital Volt Meter.

if it measures less than 0.5vdc you are lean
if over 0.5vdc your rich and if it's at .8vdc it's way rich.

You can use the existing O2 sensor's output voltage as a ballpark for setting the mixture at idle. But the very best way to setup mixture is with a CO or WBO2 meter.

once you get the current voltage reading you can adjust the mixture screw on the AFM, turn it in (clockwise) richens mixture, turn it out leans it.

What you can do is turn it out till you see the O2 sensor voltage drop to .3vdc then count turns while turning it in till it reads .7vdc then back it back out 1/2 the number of turns and you have mixture set in the ballpark of 14.7AFR.

You may want to first crank the screw all the way in and count turns so you know exactly where it sits at the moment.

If you find that you can not richen it to read .7vdc then you most likely have an air leak. If it richens to .7vdc then you should be ok.

Doing this test procedure first will give us a good idea of where the mixture currently is.

And surging usually is to rich of mixture and/or to much ign advance. Since the advance is pre-set in the DME you most likely are running to rich.
Also is the engine bone stock? any after market exhaust components? anything else we should know?

[Roger 911]

Sal,

I just recently measured my voltage from the O2 sensor with it still connected to the DME. When I do this, the voltage constantly fluctuates between around 0.15 and 0.9, with everything in between. I assume this is a result of the DME receiving signals from the O2 sensor and making constant adjustments to keep it in the appropriate range. Does that sound right to you?

I should add, the car idles and runs great now, just curious about how this operates.

Roger

[scarceller]

With it connected it should do exactly what you describe.
You need to also disconnect it with warm engine at idle and see what it reads.
The idea is to set the base mixture by turning the AFM adjustment screw out (lean it) till you read .3vdc then count turns while turning it in till you read .7vdc then just set it at the 1/2 way point. Or just a tad rich.

You do this with the O2 disconnected and just read the output of the O2. This is a cheap simple way to get mixture in the ballpark.

Once you do this setup you can then test the ability of the DME to respond to O2 signal input with a 1.5vdc AA battery. Here's how:

First leave the O2 still disconnected with the meter reading it's output. It should read somewhere between .3 to .7vdc.

Now take the O2 signal line on the harness side (the line that goes back to the DME) and ground the line. This sends 0vdc back to the DME and tricks the DME to think it's seeing extremely lean mixture. The DME will then command more fuel and you see the meter voltage go into the 0.8 to 1.0vdc. Now remove the line from ground and it will go back to 0.3 to 0.7vdc

Next test: Take the 1.5vdc AA battery place the '-' side to a good ground point then take the O2 signal line to the DME and place it on the '+' side of battery. This sends 1.5vdc back to the DME and DME thinks very rich mixture. DME will now lean mixture and the meter will read less than 0.3vdc.

I came up with this very simple procedure to test the entire O2 sensor circuit.

Originally Posted by Roger 911

Sal,

I just recently measured my voltage from the O2 sensor with it still connected to the DME. When I do this, the voltage constantly fluctuates between around 0.15 and 0.9, with everything in between. I assume this is a result of the DME receiving signals from the O2 sensor and making constant adjustments to keep it in the appropriate range. Does that sound right to you?

I should add, the car idles and runs great now, just curious about how this operates.

Roger