what is too lean?

[smslyguy]

If at cruising speed can you have a 15 afr and at decelerating or let off have a 21.9 afr is this fine? I mean with no load to run 15 to say 15.5 a.f.r.??

[mr.prick]

Sounds like Deceleration Fuel Cutoff (DFCO) is enabled.

[smslyguy]

Sounds like Deceleration Fuel Cutoff (DFCO) is enabled.

that is correct. I was also playing around with lean cruise a little and was just woundering what to lean is? Is 15 to 15.5 afr to lean at cruising? and 21.9 on let off?

[odd boy]

15.5 is good fuel economy, I've seen a lot of engines run at 15.5 ~ 15.8 with GM stock tune. Make sure that there is no knocking at higher load (not WOT).

I'm assuming that you are using a WB.

[gmh308]

that is correct. I was also playing around with lean cruise a little and was just woundering what to lean is? Is 15 to 15.5 afr to lean at cruising? and 21.9 on let off?

No problem here aiming at 16.5:1 on cruise. Usually if it is getting too lean there will be some surge. Watch the cat temps. And like Odd Boy points out keep an eye on knock.

With DFCO operating, the fuel should be cut and your WB should max out. If you were 21.9 and not on DFCO you would probably get popping from the exhaust.

[smslyguy]

15.5 is good fuel economy, I've seen a lot of engines run at 15.5 ~ 15.8 with GM stock tune. Make sure that there is no knocking at higher load (not WOT).

I'm assuming that you are using a WB.

that is correct. but the w.b fluctates a lot from 13.8 to 15.2 at cruising speeds. i don't think this is normal is it?

[smslyguy]

No problem here aiming at 16.5:1 on cruise. Usually if it is getting too lean there will be some surge. Watch the cat temps. And like Odd Boy points out keep an eye on knock.

With DFCO operating, the fuel should be cut and your WB should max out. If you were 21.9 and not on DFCO you would probably get popping from the exhaust.

yes d.f.c.o is enable and i am maxed out on my a.f.r. gauge. So this is not to lean on let off? How much m.p.g would you say you gained from running that lean over stoich?

[odd boy]

that is correct. but the w.b fluctates a lot from 13.8 to 15.2 at cruising speeds. i don't think this is normal is it?

Ohh, it shouldn't be this way. It could be one of the following:

Is your car cammed?

Is there any exhaust leak?

Does the O2 work ok?

Is the setting of STFT and LTFT put correctly?

[gmh308]

yes d.f.c.o is enable and i am maxed out on my a.f.r. gauge. So this is not to lean on let off? How much m.p.g would you say you gained from running that lean over stoich?

And, it would be worth taking a log and posting up here to look at your 13.8-15.2 range. And to check the Fuel Sys status PID's. These will tell you whether you are in DFCO/CL/OL etc.

Also logging cat temps/knock retard/map/cylinder air etc will indicate whether you are getting into too much load to sustain the lean mix.

At most you would gain 5% improvement at 15.5:1 and 10-11% at 16.5:1. It is a gain of diminishing returns as the fuel decreases, but so does the torque decrease as combustion starts to get toward potentially unstable areas as AFR increases and you use more pedal to maintain cruise torque.

[smslyguy]

And, it would be worth taking a log and posting up here to look at your 13.8-15.2 range. And to check the Fuel Sys status PID's. These will tell you whether you are in DFCO/CL/OL etc.

Also logging cat temps/knock retard/map/cylinder air etc will indicate whether you are getting into too much load to sustain the lean mix.

At most you would gain 5% improvement at 15.5:1 and 10-11% at 16.5:1. It is a gain of diminishing returns as the fuel decreases, but so does the torque decrease as combustion starts to get toward potentially unstable areas as AFR increases and you use more pedal to maintain cruise torque.

here is a log of my gauge fluctuaing on the lc-1

[smslyguy]

Ohh, it shouldn't be this way. It could be one of the following:

Is your car cammed? no cam

Is there any exhaust leak?
no exhaust leak either.
Does the O2 work ok?the 02 do work i posted a log on here eirlier if you want to see the voltage switch. The w.b.is sensor 1 on bank 2.

Is the setting of STFT and LTFT put correctly?

How do you set these?

[gmh308]

here is a log of my gauge fluctuaing on the lc-1

Is this with the WB simulating an NB signal? And is the WB signal on the LC-1 an analog signal or digital?

[smslyguy]

Is this with the WB simulating an NB signal? And is the WB signal on the LC-1 an analog signal or digital?

one of the outputs, output 1 is simulating a n.b. out put two is going to efi live tunes.

[gmh308]

one of the outputs, output 1 is simulating a n.b. out put two is going to efi live tunes.

Your AFR is reaching 15.5 for only short periods like up to 1 sec as the STFT's cycle, and this may simply be due to NB sim output lag and the travel time from exhaust valve to sensor. It is only happening on the bank you have your WB plugged in to. On average at cruise it is 14.5.

It may be your WB just saying its lean, or actually causing it to be lean on that bank.

Pull the WB, connect the regular NB and log it again and see if your bank that had the WB is not seeing the lean spikes anymore.

[smslyguy]

Your AFR is reaching 15.5 for only short periods like up to 1 sec as the STFT's cycle, and this may simply be due to NB sim output lag and the travel time from exhaust valve to sensor. It is only happening on the bank you have your WB plugged in to. On average at cruise it is 14.5.

It may be your WB just saying its lean, or actually causing it to be lean on that bank.

Pull the WB, connect the regular NB and log it again and see if your bank that had the WB is not seeing the lean spikes anymore.

i have many runs without the w.b. in and there are no lean spikes with the factory o2's. infact when my mil light comes on p1153 the w.b. gauge reads 14.7 cosistantly. Don't know what's up with this?? Also then yesterday on the w.b. gauge in p.e mode i hit 12.2, which it is almost always at 12.7-12.8 in p.e. mode.

[gmh308]

i have many runs without the w.b. in and there are no lean spikes with the factory o2's. infact when my mil light comes on p1153 the w.b. gauge reads 14.7 cosistantly. Don't know what's up with this?? Also then yesterday on the w.b. gauge in p.e mode i hit 12.2, which it is almost always at 12.7-12.8 in p.e. mode.

With your long tube headers + your simulated NB signal, no doubt the PCM is seeing the O2 response curve/s as outside the normal operating envelope and then posting the P1153 DTC. This is an innovate unit right (based on your other thread?) so innovate support might have an answer.

Even though an NB sim output may be available on a WB controller, doesnt mean that the signal is exactly compatible with that of a normal NB, and that fact added to the travel delay in long tubes only adds time.

Your NB sim waveform from your WB controller tends to back this up. Its all over the place.

[joecar]

You could try this:

using LM Programmer software, for Analog 1 (the NB sim channel), raise the upper voltage a little, and bring the AFR span tighter...

(then flash it to the LC-1 and wait for it to finish flashing, then cycle power).

[gmh308]

You could try this:

using LM Programmer software, for Analog 1 (the NB sim channel), raise the upper voltage a little, and bring the AFR span tighter...

(then flash it to the LC-1 and wait for it to finish flashing, then cycle power).

Hey Joe. So you can tune these items to improve their compatibility? :)

[smslyguy]

With your long tube headers + your simulated NB signal, no doubt the PCM is seeing the O2 response curve/s as outside the normal operating envelope and then posting the P1153 DTC. This is an innovate unit right (based on your other thread?) so innovate support might have an answer.

Even though an NB sim output may be available on a WB controller, doesnt mean that the signal is exactly compatible with that of a normal NB, and that fact added to the travel delay in long tubes only adds time.

Your NB sim waveform from your WB controller tends to back this up. Its all over the place.

thanks for the reply:
I do have short tube headers not long tube, I don't know if this matter's at all or not.

[gmh308]

thanks for the reply:
I do have short tube headers not long tube, I don't know if this matter's at all or not.

Oops. My apologies. Ah the "S.T." Got it now. Shorties should be fine if your O2 is nearby. Looks like it is your WB running as NB sim then. Joecar's advice sounds good to go!

FYI LS1 lean cruise is around 16.5:1 at its leanest, and we have run leaner than that with no negative effects (17.5:1), though not sure if much leaner than 16.5 makes much difference to mpg numbers.

[macca33]

I thought I'd yet again tack onto the back of another thread I discovered.

I've just re-enabled DFCO in my tune and am a bit concerned about the AFR when the DFCO is active - I think it may be too lean.

I used DFCO sttings that I've hybridised from the stock GTS tune, as well as some other tuner files. The DFCO is working well - activating and deactivating when it ought to and I only get a slight burble just as it deactivates at the low-RPM cut-off, which is fine - it isn't too loud or bumpy in transition at any time.

Can someone please take a look and see whether it is safe to run out to that AFR, or whether it needs some work. Any assistance with just what needs to be altered would be greatly appreciated also!

cheers and thanks in advance

[WeathermanShawn]

Thats the whole purpose of DFCO. Essentially your injectors are 'turned off' during deceleration.

My AFR's do the same. Looks perfectly normal to me.

[macca33]

Thanks very much mate - I was concerned at the 24:1AFR, but, as you say, it will transition to a lean state due to no fuel and the low load on the engine probably means it won't detonate well there is no audible sign, nor KR in the logs and the transition back to accel is smooth.

The car drives very well with it engaged, so I'll try it for a while and if it remains as driveable as it is - still have to test some LOW speed car-park type driving - I'll leave it enabled.

cheers

[gmh308]

Thanks very much mate - I was concerned at the 24:1AFR, but, as you say, it will transition to a lean state due to no fuel and the low load on the engine probably means it won't detonate well there is no audible sign, nor KR in the logs and the transition back to accel is smooth.

The car drives very well with it engaged, so I'll try it for a while and if it remains as driveable as it is - still have to test some LOW speed car-park type driving - I'll leave it enabled.

cheers

24:1 might be the limit of the wideband. With DFCO activated, there is no fuel. Regularly run 16:5-17.5:1 at cruise. No worries.

[macca33]

Cheers mate - the WB02 runs to 25:1, so you're probably on the money there. I'm only commanding 15.4: or so in B3647 and it rolls down the highway without much fuss, returning respectable economy.