Stock Lambda settings?

Ben Louis

Ben Louis

True Classic
While sorting my X I noticed that the Lambda adjustment screw on my car's AFM has been drilled out. I suspect that it has been messed with, why else would it be drilled? I've looked everywhere for the stock settings and can only find 'no specified adjustment during service life'.

Can someone please tell me how many turns out it should be?
 
This is the FI equivalent to a mixture screw; to use, disconnect the exhaust gas sensor and monitor it with a voltmeter-adjust to the point where the voltage oscillates from approximately 0.4 to 0.8 (vdc versus the chassis ground); higher voltage is richer, lower voltage is leaner.
My cap wasn't drilled when I got my car; I drilled it and pulled it out, the cap wasn't required for emissions compliance here.

Jeff
 
Thanks for the info. Let me clarify a little to make sure I've got it.
Is this at idle? Or is the Delta 0.4 - 0.8 through the rev range? Do you know the Stoichiometric for these values, should be around 14.7 or something?
Unfortunately I'm in Ca and am getting the car ready for smog so I need to be spot on, then just a little lean for insurance during the test.

I would still like the stock turns as a base point because I don't know how much it's been messed with. I'll test the voltage as is because it runs alright and report.
 
I was on the road, speaking from memory when I posted here last Monday; now I'm home, I looked it up in Probst's "Bosch Fuel Injection and Engine Management" to refresh my memory-
The oxygen sensor makes more voltage with a rich mixture; if you monitor the connection the voltage (hence, the mixture)


will oscillate trying to cross the stoich point, when correct it will go from about 0.8vdc (slightly rich) to about 0.2 vdc (slightly lean).
When disconnected, it will not oscillate, as the computer has lost the input from the control loop, and you have control with the screw on the airflow meter.
These settings are usually checked at idle; the changeover is quite sharp.
This has worked to pass emissions here in Oregon on my '86 X and my '89 Volvo 745turbo with LH Jet.
HTH

Jeff
 
If your O2 sensor is good, it will sweep when the mixture is correctly set. If you go too much (in adjustment) one way or the other, the voltage will sit either high or low. Hook up a volt meter (max 2v scale) peeling back the O2 connector boot so you can check it while connected to the system. If you want to test the O2, introduce some propane into the intake. Unheated O2 sensors don't last long - 30K is the typical service (replacement) interval. Less if the car hasn't been running well...
 
I checked the old O2 sensor and it was bad (reading only -voltage). That answers my question. You should test while connected, got it. I just got my timing and idle perfect yesterday so Ill do the mixture today. It cant b too far off the car runs but Id like it to be ideal.
 
After reading this thread I checked my O2 and it was also dead... The car runs much better with a new sensor... I actually think my sensor was working properly for a while and then gave up sometime over the last month or so.

Thanks @carl for giving me a hand...
 
Hmmm so I tested the brand new sensor while connected and it sits right at .48v no oscilation. Car runs well so its a bit odd. I do notice this wire happens to be right above the exhaust and is quite hardened. Is it worth tracing the lead back and re-splicing before it enters the comp? Does this reading go through the FI multiple relay?
 
Is this on the front or backend (of FI comp) of fuel mixture signal? If at all
IMG_6392.JPG
 
Ben Louis said:
Hmmm so I tested the brand new sensor while connected and it sits right at .48v no oscilation. Car runs well so its a bit odd. I do notice this wire happens to be right above the exhaust and is quite hardened. Is it worth tracing the lead back and re-splicing before it enters the comp? Does this reading go through the FI multiple relay?
Click to expand...
Did you test this on a fully warmed up engine? The oxygen sensor does not start producing a valid output signal until it reaches ~300°C (~600°F)

If you want to check the wiring, keep in mind that this is a shielded cable; There is an inner conductor for the signal, then plastic insulation, then a wire shield, and finally another layer of insulation.
 
Is your meter fast enough to catch the oscillation? If not, it may be averaging to 0.48v; try the mixture adjustment screw and see if it changes- make note of where you start with the screw, then return it there, that's about the right place.
You may also want to check the computer connector if your double relay has issues.
 
I think a couple things are going on (seems to b a theme). Fix one thing find two others....

The wire has a spot that has rubbed to the shielding. I dont think replacing a shielded wire is reasonable. So Ill do my best to re-insulate it. Also try driving the car 10-15 and then re test the O2. In the mean time decided a 4th day off would be a good time to re do my carpets
 
Only to, not thru the shield? tape or heat shrink, no biggie.
Nice looking floors- hope the carpet comes out well!
 
IMG_6403.JPG
Yeah car is Bertone so its pretty good rust-wise. Carpets are not a direct fit for sure but with some work turned out pretty good. Waiting a bit for it to settle before I tack it all down. Proof Im not a total dweeb!
 
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