Commanded AFR going out of spec

[Highlander]

Hello Guys,

I am having an issue where all of the sudden the commanded AFR will go from the 14.68 Closed loop into "open loop" and 15.69 or 13.59 AFR.

I have set all my open loop afr tables to 14.68 but I am still seeing those changes under unknown conditions...

I have seen this on 2 cars... The first one I didn't pay much attention and the second one... Well... it's time to chack...I have tried pretty much everything... It appears to be a random thing...

It will keep the last used STFT and LTFT and command a leaner 15.69 and/or a richer 13.59 on normal cruising... if you punch it, it will drop to PE normally... but still...

COT is OFF

Any ideas?

Thanks

[Highlander]

Anyone?

[CV8IIM6]

i'll try to find some info on it today but i've been told it's for emisions and something to do with "storing oxygen in the cats"?

[Highlander]

hm... so this is totally intended... Ross.. any way to get rid of this??? it will sometimes get the car a bit unstable to drive... If you are cruising its a bit ok... but... if you are stop and go it simply gets the car to hesitate a tad. This is a cammed car of course.

[GMPX]

I don't know what it is. Not something anyone else has complained of.
I seem to recall the LS1 did something similar when it thought the O2 sensors weren't responding, it would richen things up in an attempt to see a response from the O2's, maybe this is along similar lines.

[Highlander]

Well... thinking on that... since it first went leaner and then richer, I tried adjusting b1513 and b1514 to no effect as the car wouldn't go into closed loop. I tried inputing 1000 and 100 to see if it solved the issue and as I said, car wouldn't go into closed loop.

I had seen this with road dataloggin on another vehicle and didn't pay much attention. But now this one again... another LS7... So... I'll keep investigating... i'll try logging HO2S1/2 v and see if there is a pattern.

[CV8IIM6]

i didnt have time today to find documentation on this but my car does this regularly whilst cruising.
notice how the fuel trims even flatline while it commands 15.96 then 13.36
i definitely think its intended.

http://i449.photobucket.com/albums/qq213/CV8IIM6/AFRoutofspec.jpg

[GAMEOVER]

This is very interesting....

[Highlander]

You see ROSS!!! I am not inventing this :)

Thing is... that I am sure that once the fuel trims are "learnt" properly, you shouldn't have any issues. But while the learning process the car would hesitate when going leaner and richer at low speeds...

On my vehicles, I have seen them be a GOOD 2 to 3 miles on each before going back. This could work as a lean cruise actually. But it will revert to 13.3 negating the leaner effects.

[CV8IIM6]

Some info from a GM tech guild article on euro 3 emissions.

http://i449.photobucket.com/albums/qq213/CV8IIM6/OSC.jpg

[joecar]

The AFR cycle you see there may be the catalyst test being performed... that's exactly what it looks like...

The catalyst monitor transits the AFR and times the voltage response from front O2 sensor to rear O2 sensor (it does each bank simultaneously but independently)... if the response time is shorter than the prescribed minimum then the catalyst efficiency DTC is set (P0420, P0430)... then the AFR goes back to normal control.

The trims are just kept constant during the catalyst test.

[Highlander]

how do you shut it off?

[JAY4SPEED]

My '08 Trailblazer SS does a similar symptom. It is usually after an extended cruise at highway speeds then slowing to a stop like at a stop light on an off ramp. While sitting stationary, the engine will stumble and I'll notice on the wideband that AFR will go rich (12.5 or so) then swing lean (16.5 or so). It has done that since new with the stock calibration. I've caught it while logging as well and it's being commanded rich and lean when it occurs. I did notice that while staying in speed density open loop when doing my auto VVE and auto MAF that it did not occur. I was thinking it was some kind of O2 rationality test, looks like testing cat efficiency makes sense as well.

[joecar]

I believe the test can't be shut off in closed loop mode (even with DTC disabled, the test still runs, but its results are ignored).

I believe in open loop mode the test is never run.

[ssvolvo]

How about disabling {C1701} Catalyst Diagnostic Test ?

John

[joecar]

C1701 isn't in my file LS1 file.

[ssvolvo]

Sorry Joecar,

I was looking at my E38 stuff.

John

[JAY4SPEED]

How about disabling {C1701} Catalyst Diagnostic Test ?

John

I never noticed that. I'll have to give that a try.

[Highlander]

will do too.... maybe a custom OS to do a lean cruise?

[CV8IIM6]

I had C1701 set to disabled in my log from post #7.

Might have to adjust min and max temps (C1702 & C1703) to really make sure it's disabled.

[Highlander]

Revisiting.... Doing some more tests tonight... another LS7... same freaking issue.

[Highlander]

C1701 had a little effect on it. but not much. The tests appear to have been shorter. Still. Its annoying.

[Highlander]

ROss... PM Sent.

[Highlander]

Issue solved... C1709 on latest december 20 release! thank you ROSSSSSS

[alian]

Boy if only we could control this we could intruduce lean cruise in the e38 tuning.
Cheers Ian

[GMPX]

It would be fudged lean cruise, the lean cruise code was gone from the ECM's by the time the E40 hit the streets.

[mr.prick]

http://smiliesftw.com/x/myhijacked2.gif
I noticed Commanded AFR is not exactly the same as {B3601} & {B3618}.
The difference is very slight but it's still not what it should be. :bangin: