OBD readers..........

[gnhuk]

Not sure where to ask this so I'll start here. I've bought an ODB interface so I can read the codes, this has partial compatability with the EODB compliant ECU in my car and I can read codes (there are none at present) and monitor assorted sensors. Being able to read the sensors is great but for one small problem: I'm seeing numbers but how the hell do I know if these are correct? For instance the O2 Sensor 1 and Short Term Fuel trim are jumping about - are these expected to do this?

Raw data is useless without having something to measure it against so the question has to be is there somewhere I can find a list of what the ranges for acceptable values? Or does someone have a list?

The engine is a B4184S2 by the way...

Thanks

[vjck_uk]

there are lists on the voc site and if you google for obd11 you will find everything you could wish for

[gnhuk]

I must have been doing a search for ODB2 instead of ODBII............. Will do a search again.

[classicswede]

The short term trim should move about quite a bit. This is showing you the lambda correction. The long term trim should be around zero, dont worry about low numbers under 10. The long term is what it says the perminant amout of lambda correction needed.

[gnhuk]

Thanks - I assume that the O2 sensor 1 jumping around is to be expected as well? The long term fuel trim is rock solid as you suggested - though I'll check what the numbers actually are during the week. I'm gradually gaining an understanding of what is happening as I attempt to cure the occasionally awful fuel consumption.

I'm still tempted to replace the ECU temp switch - unless someone can tell me how to test it - as I'm sure it's not working correctly. The temp gauge is working properly after changing the thermostat however.

[classicswede]

At idle and under cruise the lambda should scan between 0 and 1 volt. When you are acellerating the lambda should sit somwhere between 0.8 and 0.9.

[gnhuk]

I think at idle the reading is between 0 and 1.25v (ish) - Just dug out the figures which I'd posted in another thread - 0.1v@-0.78% to 1.275v@3.91% - does this range look okay? Is a reading over 1v an indication of a fault?

[classicswede]

Provided it is a 0-1 lambda them it is runnig very rich! or the lamdba is not working correctly.
If it is a 0-5volt lambda then thing are lean. What about when driving what readings are you getting.

[gnhuk]

Hi Dai,

If the tail pipe is anything to go by (very black) it is running rich which is what the fuel consumption suggests - though it is better on a decent run. I'm suspicious of the Lambda and the ECU temp switch. I think the Lambda is expensive. Is there any way of testing it?

I have yet to try getting readings while driving it but I've now bought a 12v adapter for the laptop (battery isn't the best) so I'll try to have a look tomorrow, it'll have to be glances because the software doesn't allow me to "capture" data..........

[gnhuk]

I changed the ECU coolant temp switch today. The old one had a fair amount of scale on it. Plugged in the laptop and looked at the sensor data - it was immediately obvious that some things had changed. I'm now getting variation on the O2 sensor 2 readings (solid on 1.275v before) and the coolant temp was not making sudden jumps of 4 or 5 degrees. Left the laptop plugged in, as I don't have the ability to record the data, and went for a 10 mile drive and the car felt considerably smoother. The displayed values, within the limitations of how often I was able to check them, looked vaguely reasonable.

Will report back on how the fuel consumption is going.....