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[VXL V6]

OK, Seem to get this code most of the time now (puts emissions lamp on over a time), it relates to Bank2 Sensor 2 Lambda so I thought i'd do a bit of investigation.

The black trace on the graph relates to this sensor, the blue trace is sensor 1 (or pre-cat). Would anyone agree that it looks a bit hyper?



My concern is that the top two traces (the bank 1 sensors) look a lot lazier, is this purely down to the timing not being 100% or am I barking up the wrong tree totally?

Thoughts please!

[Kevin Wood]

Could just be that one of the pre-cat sensors is a bit slower to respond than the other.

Also, the post-cat sensors are following the pre-cat so the cats presumably aren't hot in this case (would expect the post cat sensors to just read rich).

Can you look at the actual level of fuel trim being applied and compare that for the two banks?

What tool are you using to read live data? Looks good.

Kevin

[VXL V6]

Could just be that one of the pre-cat sensors is a bit slower to respond than the other.

Also, the post-cat sensors are following the pre-cat so the cats presumably aren't hot in this case (would expect the post cat sensors to just read rich).

Can you look at the actual level of fuel trim being applied and compare that for the two banks?

What tool are you using to read live data? Looks good.

Kevin

Hi Kevin

Bank 1 sensor 2 (red) seems to be mimicking  Bank 1 sensor 1 (green) fine but Bank 2 sensor 2 (blue) seems a bit hyper compared to Bank 2 sensor 1 (black) when idling or light revs... seems better at higher revs on the left of the graph but of course it's only a sample, nowhere near as acurate as a scope.

Car was warm (CTS 72 degrees) but not hot

Yes can look at the fuel trims for each bank I think

The software is Opel Autoscan (iggy21uk has the same device), it's expensive but is comprehensive, will do actuator tests, live data, read and delete codes etc etc.

Cheers

EDIT Doh just altered this as I wasn't reading the screen properly, the sensor twos are red and blue!

[VXL V6]

Presumably the fuel trim is controlled by ECU with information from CTS, MAF, Lambda's? Could a slightly mis-timed bank 2 have an effect?

[Kevin Wood]

I see what you are saying, but the bank 2 pre-cat sensor is also cycling a lot quicker than the bank 1 pre-cat, and thus the fuel trim is changing quicker so it could be that, given the delay in response between the two sensors, it's less easy to correlate the two.

If the fault is the post-cat sensors I guess the fuel trim isn't that important but it would be good to see that the quick fluctuations on bank 2 are down to fuel trim adjustments, not just random.

I would have thought, however, that the post-cat sensors would stop cycling once the cats are warmed up -unless I've misunderstood how they work.

Might be worth taking it for a drive with the laptop on the passenger seat and see if they settle once it's all got nice and hot. That may be when you see a problem in one of the post-cat sensors.

Kevin

[Kevin Wood]

A mistimed bank will have an effect due to the slightly different air volume entering the two banks. this is why each bank has it's own lambda sensor and fuel trim. Generally the fuel trim will be decreased by the ECU if the Lambda is reading rich (less than 0.5v typically) and it will be increased if it is reading lean. (>0.5v). This is why the Lambda sensor output cycles around the 0.5v level.

If you look at the fuel trim, or the injector duration for each bank you'll see the result of any imbalance between the two. (not necessarily just timing, could be exhaust blockage, lambda sensor, etc).

Kevin

[VXL V6]

Thanks Kevin

I'll have to charge this up! Might be best to do when someone is in the passenger seat who can watch the screen (Live data filesave is supposed to be implemented in the next version - free update).

At least from the scanning it's the same fault code each time and having had an emissions test done a few months ago I know the Cat's are both fine.

[Kevin Wood]

I'd look at exactly what happens as the cats start working. You might find one post-cat sensor quietens down long before the other, for example.

Kevin

[VXL V6]

I'd look at exactly what happens as the cats start working. You might find one post-cat sensor quietens down long before the other, for example.

Kevin

Got ya, I think! So the codes are only being generated during the switchover period, or inbalanced switchover period (as in one bank goes closed loop and the other doesn't with an acceptable time frame set by the ECU)?

I know that the ECU doesn't put the lamp on until this code has occured a number of times (threshold), presumably to average out the fact that one Cat may be less efficient than the other on warm up.

[magnul]

<snip>if the Lambda is reading rich (less than 0.5v typically) and it will be increased if it is reading lean. (>0.5v). This is why the Lambda sensor output cycles around the 0.5v level.

A bit OT, but it's the other way around. <0.5V=lean, >0.5V=rich