Would it be at all possible to change the stoich afr in HPT to say something like 15.3 and tune to that as you normally would? I've got a short stop/go drive to work and would like to get a few mpgs out of my GTP.
Would it be at all possible to change the stoich afr in HPT to say something like 15.3 and tune to that as you normally would? I've got a short stop/go drive to work and would like to get a few mpgs out of my GTP.
Open loop you could, if you are using your NB it will pull you back to stoich and won't work. You do not have control of the O2 switch point. NB's are no good for reading outside of stoich anyway. So, run open loop and you can do it.
2000 Trans Am WS6
changing stoich to alter your target AFR is like telling a pilot that the ground is 1000m higher than it really is, just so he can fly at a different altitude. it works..until you want to land.
if you want a different AFR, command a different AFR. stoich is determined by chemical makeup of fuel, and that's ALL it should reflect.
I assume what you're trying to do is lean back to a 16:1 or so AFR for very light throttle (Under .24gcyl)
Be warned though. Make sure your fuel trims are picture perfect before doing this without a wideband. You will lose fuel corrections.
If you still want to proceed, there is a easy way to do this.
Take a look at Closed loop enable temp and OL AFR adder
Last edited by Nixon; 02-29-2012 at 08:29 AM.
I do have a WB. I wouldn't be tuning without it. I don't think that I'll go as lean as 16.0, probably like 15.5. Anyone have any good threads saved for this type of tuning? I can still tune thefuel trims with the MAF in OL?
supposedly you can enable lean cruise with Tiny Tuner but I have never experimented with it....that is if you want to stay CL you could PM Bilemke he would know for sure
PB's 1/4 mi 12.21 117.75 trap ,1/8 mi. 7.779 93.99trap , 1.949 short time (FWD W body)
I tried messing around with TT and a bin and couldn't find anything dealing with lean cruise. I heard something about the PCM checking if it's a holden vehicle to activate it.
15.5 is about right though you could go as much as 16:1 without losing takeoff power.
I've heard of tiny tuner but I haven't ever messed with it. I shot bilemke a PM about CL. I'll look into OL tuning though and see what that's all about.
From some source I couldn't verify, 15.4 was supposed to be maximum fuel economy.
A point either way wont hurt.
Keep in mind the "loop" between the oxygen sensor and closed loop is based on the cross count voltage of the narrband O2, where the car "switches" from lean/rich/lean rich. Changing the stoich won't work because it doesn't have an effect on the PCM's traslation of what rich or lean really is.
As far as the 15.4:1, you're most likely better off at 14:1 because of the torque loss as you start leaning the mixture out.
In TT, look under Fuel > Open & Closed Loop > O2 sensor rich/lean threshold
If you scan the car in Open Loop with a wideband, you can get a pretty good idea what the narrowband outputs near stoic and leaner AFRs. You can dial the table it accordingly.
So the switch point from rich/lean is set in the narrow band sensor at a perfect burn (stoich) regardless of fuel used. That is why a different fuel can generally run with the same closed-looped system. If stoich of a fuel is 9.5:1 vs regular fuel at around 14.7:1, then a 12:5 reading from the wideband would be generally the same rich for each fuel. Right? A new thought for me, I thought that if the wideband was reading 14.7:1 and I was running a fuel with stoich of 9.5:1....then I would be WAY lean. Not the case, 14.7:1 is a perfect burn with any fuel in the tank (unless the meter has been adjusted to readout for the fuel). This is where that "Lambda" number comes in...1 is stoich burn and the change from 14.7:1 is calculated from the variance from Lambda.
The question still remains: what is the best way to change the closed loop/cruise AFR with just HPTuners (if possible with narrow band mechanics)? And what would be the expected gains in fuel usage/mileage if one was to change cruise from 14.7:1 to 16:1?
Thanks,
-Scott
The gain would be 10% fuel milleage. Thats what I run at light throttle. But to be honest you will gain allot more by having the TCM shift early and lock the converter at same time as shifting in combination with the 16.1
My city milleage went from 11.8 to almost 16 doing that. On the interstate you will only gain the 10% though. Others have gained some nice milleage by adding more EGR also, altho my truck doesnt have that to play with, so I cant help ya there.
2000 Regal GS ~ 3.25 Pulley ~ Headers ~ 3"ex ~ 1.85 Rockers
Sold 06 TBSS ~ Front Mount T88 ~ 0-30 in 1.17 ~ 0-60 in 3.0
Wanted ~ Engine-less 95/Older 4x4 ~ Jeep/S-10/Ranger for TT Project
I know that a lot can be gained with tranny tuning burning know nothing about that, I also dont have the EGR anymore lol.
Scott, let me try and calrify as I probably didn't use the right words:
You are 100% correct, O2 sensors output a voltage based on lambda sensed.
Just like MAF and MAP sensors have a transfer function, translating voltage to measured units, the PCM needs a transfer function for the O2 sensor mV to lambda measurement. However, O2 sensors have a "switching" type signal because they are usually used with comparators to build a delay type control loop. Normally, this loop has a reference voltage (or reference voltage thresholds) that act as the reference voltage in the loop.
The switching (cross counts) is a result of the PCM's control loop. If you command open loop, the O2 sensor voltage will stay constant as the car is ignoring the switch point thresholds and running whatever its told.
HPTuners doesn't have access to the tables, but Eddie Blanter's free Tiny Tuner does (atleast for some models).
If you can't change it from the PCM standpoint, Innovate's LC-1 does have a configurable narrowband output voltage curve where you could set .450-500mv at say 15:1, giving the impression of stoic.
Regarding mileage gains, as you lean a mixture, torque will eventually drop. This requires more pedal position, more fuel, and leads to decreased efficiency. Most textbooks cite 15.4 to be a breaking point where torque drops off enough to cancel out fuel savings.
Originally Posted by minimoe
last I knew (and played with) was that you cant change the command AFR just by changing the "command". The only way to control the AFR is to be in open loop (on the gtps anyway)...
so you would have to scan with the wideband and adjust your maf according to those outputs...
unless something has changed...?
2000 Trans Am WS6
I haven't played with switch points on the 3800s as much as the V8s but I never saw any change out the tailpipe on my wideband.
Plus you can change stoich to 15.5 and you'll still see 14.7 out the tailpipe if you're running closed loop because that's all the O2 sensor knows. Again, tested with my wideband out the tailpipe.
What I did wonder is whether the E85 O2 sensors can read beyond the 14.7 and whether installing one would allow stoich to be changed. I might test changing stoich on the next flexfuel vehicle I in-car tune.
Source:
page 16
http://books.google.ca/books?id=Mr-9...page&q&f=false
It is my understanding that it will not matter if Stoch it 14.7: or 30:1 for the fuel when the O2 is reading as the O2 sensor is reading +- Lambda.
"Lambda (λ) is the ratio of actual AFR to stoichiometry for a given mixture. Lambda of 1.0 is at stoichiometry, rich mixtures are less than 1.0, and lean mixtures are greater than 1.0."
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