Re: [doc] Erratic

[Nick Tomlinson <nickandkathryntomlinson@xxxx>]

Hi Martin,
 
Few comments added:
 
You can use the diagnostics socket on the side of the engine to perform these tests too.
 
See you at the NEC, but I'm not bringing my oscilloscope as it's too big !
 
Best regards,
 
Nick.

Martin Gutkowski <webmaster@xxxx> wrote:

Hi Nick - I have a few comments below

Nick Tomlinson wrote:

>Here goes - Unplug the oxygen and sensor but still leave the frequency valve connected. This should give the freq valve a fixed duty cycle.
>
When you unplug the oxygen sensor, the lambda computer thinks it has 
failed and puts the mixture into "limp home" mode which is over-rich.
Nick: There is no such limp home mode as compared to newer cars with backupfixed ecu memory maps. If the O2 sensor is dosconnected the duty cycle of the freq valve is fixed at 50%. The result of this is a slightly richer mixture, assuming that the base CO is correctly set. The base CO can be set within 0.5 and the lambda system compensated. If the system is set up so thatthe freq valve oscillates between 45-55% cycle then the increase in richness if the o2 sensor fails will not be too different (I have done this on mycar and my Bosch manual recommends it is done like this).


>If the engine now idles OK, use an oscilloscope on the oxygen sensor and see if it switches OK (should be a square wave between 200mV and 800mV with frequency of approx 1Hz). 
>
Even when you've unplugged it? The oxygen sensor works like a tiny 
little battery and provides a voltage according to how much oxygen is in 
the exhaust - the more oxygen there is, the leaner the mixture. If 
you've unplugged the sensor, it'll stay constant at "too rich" - or am I 
missing something here?
Nick - O2 sensor doesn't work quite like that as it switches square wave pulse at approx 1 Hertz between 200 and 800 millivolts. The duty cycle of this signal results in the RMS value of a fixed 200-800mV signal hence an oscilloscope should be used to measure waveform not a voltmeter as this samplesthe voltage.

To test the lambda ecu, you need to earth this point and the duty cycle should be greater than 80%, apply a 1.5v battery (positive to the wire, negative to the engine block) and the value should be less than 20%


>If you have a cat bypass you could leave the oxygen sensor unplugged and set the CO to 1.3-1.5% to run in open loop mode and reconnect the oxygen sensor. The CO should drop to less then 0.3%.
>
This is waaaaay to lean. The lambda system is designed to function at 
around 1.0%, however without a cat you can partially eradicate the 
effect of the lambda system by tuning the engine to 1.5%, which is how 
the B28E is set up. If you adjust the mixture so that when the lambda 
sensor is plugged in it reads 0.3%, it'll be a tough car to start on a 
cold morning, and you'll lose a lot of power.
Nick - Not true, you set the base system to 1.0-1.3% (as per my Bosch manual), the Lambda system will reduce this value and the cat will do the rest. I'm sure I have uploaded the Bosch K-Lambda system on this newsgroup.

Best WIshes

Martin

Nick - Thank-you.



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