Lambda Sensor

I just had a by-pass pipe installed on my 83SC.Before I took her in my idle speed was
varing between 800 and 1000rpm,it wasn't bad
so I kinda ignored it.The lambda sensor was
out for the swap and I was told the sensor
was the reason for the unstable idle speed.
It was recommended to unplug the sensor.
I was told no harm would be caused and the
only negitive effect would be a possible
reduction in gas milage.My question is
do I need the sensor ??

That is correct. When the sensor is unplugged the fuel mixture goes to default which is rich. The lambda sensor is an add on to help pass smog.

The lambda sensor (oxygen sensor) is quite important. The readings from the sensor dictate the fuel mixture adjustments. Without the adjustments, you could be running rich or lean. If you run too lean for too long you can kiss your valves good-bye. Too rich is a waste of fuel and will make your exhaust go nuclear.

A fluctuating idle on your K-jetronic system could indicate an uncontrolably rich mixture. I believe the procedure for the mixture adjustment is decribed on the Pelican site.

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Graham Archer
83 911SC Cab

I believe this. The CIS system does an excellent job of metering the fuel, which is a VERY important thing. When it's done right, you have instant starts at every temperature, smooth acceleration, good mileage, cool running engine, etc., etc. When it's done wrong you have erratic idle, burnt pistons and valves, white hot catalytic converters, lousy performance, etc, etc.

When these symptoms occur, if it's not something simple (which it usually is) then there is often a part that is not working properly and you just have to replace it. That's the bad news. the good news is your car returns to instant starts at every temperature......etc.

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'83 SC

Hi Chuck

The lambada sensor if not installed will cause the engine rpm to surge. You may be able to reinstall it by drilling a hole in your bypass, threading it and reinstalling the lambada.

Regards

Steve

Thanks for everybodys response, I've
ordered a new lambda sensor and plan to replace it.I have to say that my car has
never ran better since unplugging the sensor. The idle is rock solid
and is as smooth as snot on a glass door knob.The reason I'm replacing it is that
I've always enjoyed fantastic gas milage
I have always averaged around 400 miles
on a tank of gas.I want to ensure a trouble
free engine and get the best milage I can,
from what I have been able to tell,the sensor
plays an important part in that,so ...
a new sensor is on the way!

[This message has been edited by chuckr (edited 06-03-2000).]

Your car should run better. Rich fuel = HP. Ever see ANY race car that didn't run rich? Back when these Lambda add-ons were new it was a common fix to remove them, the early SCs did just fine without them. An adjustment was made to the default fuel mixture setting and off they went!

I agree with RarlyL8. I've had some experience in this area. My SC had the fluctuating idle that went away when the lambda sensor was unplugged. After investigating, I found that the CIS basic mixture was set too lean. The fluctuation comes from the frequency valve making frequent adjustments that causes the idle speed to fluctuate as well. If you reset the basic mixture to be slightly rich, (45% duty cycle or so), the fluctuating idle will go away and you can plug the lambda sensor back in. The car now idles rock-solid at 900 rpm.

Greg

Just an additional note about the Lambada Sensor (oxygen sensor)The purpose of the Lambada sensor is to detect imbalances in the air fuel ratio so that the ECU can make minor adjustments.

The sensor consists of a Zirconium oxide ceramic which becomes conductive for oxygen ions at 600 deg F. The Lambada sensor output voltage varies from about 100 to 900 mV during normal engine operation.

When the engine is running rich, ther is a low oxygen content in the exhaust, thus a high voltage is produced. When the engine is running lean, there is a high percentage of oxygen in the exhaust, thus a low voltage is generated. At the point of perfect combustion the sensor produces 450 mV.

Most circuits having a Lambada sensor have a high impedance circuit that replace the missing Lambada sensor signal with a default voltage of 450 mV. That is why many engines will run without it.

However, as rpm's vary so does the fuel and air mixture. Without the Lambada sensor, it is possible for the engine to run rich, with too much fuel and not enough air, or too lean, with too much air or not enough fuel. As you can see, the Lambads sensor corrects this problem for emmission control more so than anything else. Hope this info is helpful.

Regards


Steve

(Information taken from How To Tune & Modify Bosch Fuel Injection by Ben Watson)