Rear O2 normal sine wave function for good CAT efficiency

[Gelf VXR]

Monaro just scrapped thru last MOT on emissions, it should have failed on natural idle. I had been using innovate LC-1 in pseudo NB output but after discussing with innovate tech they advised against it unless using an aftermarket ECU.

For the MOT I bought a pair of upstream O2's from eBay in the US (Bosch 15364 for £40), they do seem to be lazy at idle, not even switching once per second, they maybe OK at higher rpms. Ive now got a pair of Bosch 15284, and i just found the two original O2's i moth balled when i fitted the WB to put back in and test. I'm in middle of taking the headers out to get extra O2 bungs welded in to get the WB back in.


Any way the rear O2's sine wave function doesn't look normal to me, i thought they should be consistently 450mv unless the PCM is running diagnostics, are my CATS done?

Here are some charts for a journey i logged, green line is down stream O2's


Start up



FTC 17 idle



FTC 2



FTC 3



FTC 7

[stevieturbo]

Max explains it well here, and no the rear sensor should not be stuck at 0.5v or thereabouts.

http://www.pistonheads.com/gassing/topic.asp?t=162...

And how fast they read will also depend on how hot they are, even with an inbuilt heater this can be slower at idle etc.

As for cats being done....really you'd need a gas analyser to see that. Done could mean different things to different people.

They might be done in terms of passing an MOT ability...but still flow well so some may not care and the engine will still run great. Or they may be restricting flow heavily yet still functioning as a cat in terms of emissions. I know which one I would not want on my car.
Or they may be bksed all together. But a lambda sensor only has limited ability to diagnose what is really going on.

But definitely do not be comparing anything coming out of a wideband, especially Innovate for the purposes of this type of thing.

[Gelf VXR]

In my logs the rears switching frequency looks similar to the front withless amplitude, no MIL codes present thou.

[FoxdieUK]

Hi Gelf,

The narrowband O2 signal should not be constantly 450 mV unless there is a problem (with either the sensor, or how the LC-1 is programmed). All cars with narrowband O2 sensors will "hunt" for stoich by repeatedly fluctuating between slightly lean and slightly rich (which is reflected in your sine waves).

When did you last calibrate the LC-1?

What I think may be happening is your LC-1 may need re-calibrating or not have its narrowband emulation set optimally, can you post a screenshot of the narrowband emulation graph?

If you're worried about cat failure, Stevies suggestion about a gas analyser sounds perfect. If you're simply trying to get your car through an emissions test, most engines can be safely run at a slightly leaner mixture for idle and cruise which naturally reduces emissions and adds a slight amount of economy. You can do this by changing the offset of the narrowband emulation voltage.

The exact AFR you can safely run I cannot say exactly, I strongly suggest you do your research in advance, but I've been using 15.2:1 as a target in 6A13TT tuning for 6-7 years now and never had an issue. LS1 forum posts seem to suggest 16.2:1 for idle / cruise is acceptable but I personally wouldn't trust that without extended testing.

Remember; if the car feels like it's hesitating, revert your changes.

I shouldn't need to state this as it should be common sense, the above advice covers idle and cruise, nothing more than low load conditions. For all all other conditions (typically 20% or more throttle) you should continue to target the widely accepted high 12s, changing the narrowband output will not change this, only tuning the PCM ECU (or perhaps fudging the wideband output if it's connected to the PCM ECU) will affect this.

Also, this is Internet forum advice, if in doubt consult a professional tuner.

[Gelf VXR]

Thank you for your reply, just to confirm, I have logged brand new stock O2's sensor performance for which it failed emmisions. Previously past emissions with NB simulation with LC-1s which I programmed and passed at lambda 1.03.

I decided to re install stock O2s for closed loop after contacting innovate tech support, I'm taking headers off to get the additional bungs welded in for WB sensors.

Not that I've had any issues with LC-1s controllers, I replaced sensors once since 2012 and that's because they didn't like the location they had been in the stock headers frequently over heating, I am now thinking about AEM X series now that EFILive has managed to connect to them on the OBD2 can bus and they have a response speed higher than the aging LC-1 which is still around 3rd place in comparison tests

[Mud_]

FoxdieUK said:

...

The exact AFR you can safely run I cannot say exactly, I strongly suggest you do your research in advance, but I've been using 15.2:1 as a target in 6A13TT tuning for 6-7 years now and never had an issue. LS1 forum posts seem to suggest 16.2:1 for idle / cruise is acceptable but I personally wouldn't trust that without extended testing.

Remember; if the car feels like it's hesitating, revert your changes.

...

Here's the manufacturer commanded lean cruise values for an LS1 (I've taken the EQ modifier to calculate the absolute values, assuming stoich of 14.63).



IIRC there's no facility for lean cruise on LS2 (at least without a custom OS, a la EFI live b3647?), but I include it here just as info to think about idle. My cammed LS1 idle is around 12.5-13g/sec (currently set a bit high at ~850rpm IMO), so that's ~0.23g/cyl?

Edited by Mud_ on Sunday 13th November 09:53

[stevieturbo]

Without details of why it failed emissions....it's impossible to suggest what may be wrong.

And you need gas analyser results for that.

[FoxdieUK]

Mud_ said:

IIRC there's no facility for lean cruise on LS2

I don't know whether the LS2 PCM ECUs have a wideband and run closed loop to target a specific cruise AFR, but chances are it's narrowband and as such, because of the steep swing on the narrowband output voltage the actual AFR target for these will actually be determined by the narrowband O2 sensor.

This is where a wideband O2 kit with a programmable narrowband output can come into its own, it can offset the AFR without the PCM ECU being involved or even knowing. Great for economy improvements but as with all tuning, there's a risk of going too far, just have to keep common sense close and possibly implement extra monitoring of things like oil and exhaust gas temps

As I've not actually looked into LS tuning, is there any firmware for the PCM ECU to alert the driver to knocking ie. flashing the check engine light? That would be highly beneficial.

[Mud_]

The standard LS2 OS doesn't use widebands. I think we're talking at slightly cross-purposes as I'm thinking how I'd fiddle the AFR just within a certain part of the map based on my LS1 knowledge - the LS2 OS is a little different, but not a million miles removed. I assume tweaking simulated narrowbands is a global operation that will affect all closed-loop usage scenarios, and so not very desirable. I know Gelf has the kit and is experienced in fiddling his own tune though, and I'm probably not telling him anything new (just perhaps reminding him that he could go OL on idle (via b3647 SOL table) with a different AFR to see if it improves things).

Edited by Mud_ on Sunday 13th November 12:18