LS3 running rich in closed loop

[deano1712]

Help! My car has just failed emissions test as part of its annual check (in UK) so its off the road while I get it fixed. Engine is a LS376/480 fitted to a BMW Z3. Its running in (pure) closed loop fine with small fuel trims. The tester was getting Lambda 0.95 to 0.99 - never over 1, at any speed. It needs to be in range 0.97-1.03 to pass. Its also possibly causing high CO - target is 0.5/0.3% idle/fast idle and these are not met. Values come right down when the engine is revved, when I assume the CATS get hot enough to work, but it soon goes over range as they cool off at idle. The exhaust outlet looks rich and its smelling rich too.

So the question is how can I adjust the settings to change the target stioch mixture? I cant see anything other than voltage limits for the o2 sensors.

I have check the manifolds and there are no signs of leaks anywhere.

I a begginer with tuning - I managed to get the basics sorted (MAF calibration etc) but my knowledge has run out! Existing tune is attached. Help would be most appreciated - I have a big car show planned next weekend which I will miss unles I can sort this quickly.

[deano1712]

Check my logic then...

I couldn't see much info on narrowband voltages on the internet but the Innovate LC-1 setup indicates a standard sensor gives:
1.1v @ 14.08 AFR
0.1v @15.01 AFR
Is this data right? I have seen posts quoting 1v@14 and 0v @15.

The tune is shooting for 650 in closed loop plus a further 50 cold offset over 73 degrees ETC. This is 0.7v total, which would give 14.45 AFR if the figures above are correct. How does this fit with stoich? I had assumed it would be aligned with 14.7 AFR?

If I change the switching voltages to 433mV that would get me 14.7AFR.

[Russ K]

Change the O2 rich/lean to 450 mv, and the min rich/lean to 450 mv.

Russ Kemp

[deano1712]

Thanks for that Russ. I have changed the setting and it made it a bit better but the engine is still running 5% rich at idle. It seems I have small leaks in the headers around the collectors. The car passed emissions last year so I assume some cracks have formed since then. The headers were made by myself out of mild steel and were then ceramic coated. Whats the best solution - pull the headers off to see if I can fix them, or ditch the o2 sensors and go MAF open loop? I made the collectors myself - perhaps not the best decision I made on the conversion!

DSC02408 by deansie1712, on Flickr

DSC02287 by deansie1712, on Flickr

DSC02309 by deansie1712, on Flickr

[Gelf VXR]

Help! My car has just failed emissions test as part of its annual check (in UK) so its off the road while I get it fixed. Engine is a LS376/480 fitted to a BMW Z3. Its running in (pure) closed loop fine with small fuel trims. The tester was getting Lambda 0.95 to 0.99 - never over 1, at any speed. It needs to be in range 0.97-1.03 to pass. Its also possibly causing high CO - target is 0.5/0.3% idle/fast idle and these are not met. Values come right down when the engine is revved, when I assume the CATS get hot enough to work, but it soon goes over range as they cool off at idle. The exhaust outlet looks rich and its smelling rich too.

So the question is how can I adjust the settings to change the target stioch mixture? I cant see anything other than voltage limits for the o2 sensors.

Also from UK, also failed commissions like you have seen, both Innovate LC-1 wide O2 sensors were knackered (after 4 years), I use the NB output which you can tune the switch points to fine tune stoich for MOT or what ever AFR you like. No amount of fiddling with the switching points made a difference.

After replacements I tuned and passed MOT with 1.03 Lambda

[GPGTP]

I can't see your tune since I'm at work but I would suggest running it in open loop at idle so you can lean it out

[deano1712]

Also from UK, also failed commissions like you have seen, both Innovate LC-1 wide O2 sensors were knackered (after 4 years), I use the NB output which you can tune the switch points to fine tune stoich for MOT or what ever AFR you like. No amount of fiddling with the switching points made a difference.

After replacements I tuned and passed MOT with 1.03 Lambda

I was thinking of trying this but first I need to sort out the leak on the header. If I tune open loop the tail pipe analyser is going to read lean, since its sucking in fresh air. Next step is to try seal the headers with some furnace cement. The leak is right in the centre of the collector so virtuall impossible to get to with the welder. If I can seal up the leak I hope the o2 sensors will control to ~1.0. If not then its time to try NB emulation. Interesting comment about changing the switch point. I have changed it a few times and it doesnt appear to change anything.

[deano1712]

I got this sorted in the end after a lot of searching. I moved the injection timing back a bit at idle - around 10 degrees. The idle is a lot cleaner now and much smoother. I now have constant injection timing through 600-900rpm. The standard tune has it jumping around a lot which seems odd, and injects fuel in the valve overlap period so unburnt fuel can go down the exhaust. My tune originates from the stadard LS376/480 settings so its disappointing GM dont have this set up better.

Pics below show new settings, and also how the injection timing periods (at 850rpm) compare to the LS3 and GM hot cam profiles. With the timing retarded 10 degrees the exhaust valve lift with the hot cam is at a similar level.