how does a tune effect fuel economy.

[wjurls]

Does the tune only effect fuel consumption (i.e. a richer or leaner condition )in open loop and WOT conditions or does it make changes througout the curve in part throttle conditions as well? I always understood that in closed loop operation (with the exception of WOT) the amount of fuel delivered is regulated by the feedback from the upstream O2 sensors and adaptive learning and therefore can't be chaged in the tune. Is this right? :shrug: My mileage has appeared to have taken a huge negative downturn. I have always averaged around 10MPG in mixed driving and the occasional romp but now it seems much worse even with gingerly driving.

 

[04MystiCobra]

It can have a huge impact on everything. If one thing is off in just the MAF transfer function table you'll be hurting in one way.
Tuning is not always done at wide open throttle. For example. If you buy an aftermarket mass air sensor you have to load up a new tune with the proper figures or your car will not idle, cruise or make effecient power. It may even blow the motor.

 

[WDW MKR]

Does the tune only effect fuel consumption (i.e. a richer or leaner condition )in open loop and WOT conditions or does it make changes througout the curve in part throttle conditions as well? I always understood that in closed loop operation (with the exception of WOT) the amount of fuel delivered is regulated by the feedback from the upstream O2 sensors and adaptive learning and therefore can't be chaged in the tune. Is this right? :shrug: My mileage has appeared to have taken a huge negative downturn. I have always averaged around 10MPG in mixed driving and the occasional romp but now it seems much worse even with gingerly driving.

While it is true the closed loop refers to feedback from the O2 sensors to make fueling adjustments, they can only be made +/- 25%. If your tune is not correct, changes in things like weather can required more adjustement than the O2 sensors can accomodate and the car will run like poo. You can change anything/everything in the tune with the correct software.

 

[S.V.T.]

that and with more boost comes more fuel ;-)
my fuel economy is shite!

 

[04CobraMatt]

Does the tune only effect fuel consumption (i.e. a richer or leaner condition )in open loop and WOT conditions or does it make changes througout the curve in part throttle conditions as well? I always understood that in closed loop operation (with the exception of WOT) the amount of fuel delivered is regulated by the feedback from the upstream O2 sensors and adaptive learning and therefore can't be chaged in the tune. Is this right? :shrug: My mileage has appeared to have taken a huge negative downturn. I have always averaged around 10MPG in mixed driving and the occasional romp but now it seems much worse even with gingerly driving.

Your right what you said, like WDW MKR said the computer starts with the MAF transfer fucntion and fines tunes with the 02 sensors. Custom tuners will fine tune your MAF transfer function so their is less correction going on. I dont see how it will make a Huge difference in fuel economy, but every little but helps. One thing is for sure, as someone else mentioned the second we increase boost, fuel consumption follows along closely.

 

[04MystiCobra]

I dont see how it will make a Huge difference in fuel economy

If the mass air transfer is screwed to begin with you'll have fuel issues.

 

[WDW MKR]

Your right what you said, like WDW MKR said the computer starts with the MAF transfer fucntion and fines tunes with the 02 sensors. Custom tuners will fine tune your MAF transfer function so their is less correction going on. I dont see how it will make a Huge difference in fuel economy, but every little but helps. One thing is for sure, as someone else mentioned the second we increase boost, fuel consumption follows along closely.

It certainly can make a big difference if the base fuel table or spark tables are adjusted incorrectly. Too much commanded fuel or too little commanded timing can make for poor closed loop fuel mileage. MAF Transfer isn't the only thing to worry about, though certainly the most important. As previously mentioned, it can drastically effect mileage if not adjusted to a point the O2 sensors can accomodate for. There are also little things that can make the car think it is running correctly when the A/F is actually off. Incorrectly adjusting certain scalars could also result in undesirable A/F being called for, especially at idle.

 

[wjurls]

Hey this is all great info guys! Keep it coming! There is a lot of stuff here that I wasn't aware of regarding tune but was always curious to know. It was tuned by Greg from RET and I have a stock MAS so I'm sure the tune is fine and the problem lies more with the bottom of my right shoe. Thanks!

 

[WDW MKR]

If you have a sudden change in fuel economy, the tune is normally the last place to look. I would be more suspect of failure or degradation of an O2 sensor, the MAF needing cleaning, failed IC pump elevating IAT2 and pulling timing, or even a faulty IAT2 sensor reading inaccurately high and pulling timing.

 

[wjurls]

The only reason I was curious about the tune was because it was just done 2 weks ago. It seemed that the first tank after tuning was normal but the next 2 went away rather quickly. I'm going to change the O2's as maintenance when I replace my midpipe soon anyway as I figure that it can't hurt. It has also been flippin' hot here the past few days which I'm sure doesn't help any.

 

[04CobraMatt]

It certainly can make a big difference if the base fuel table or spark tables are adjusted incorrectly. Too much commanded fuel or too little commanded timing can make for poor closed loop fuel mileage. MAF Transfer isn't the only thing to worry about, though certainly the most important. As previously mentioned, it can drastically effect mileage if not adjusted to a point the O2 sensors can accomodate for. There are also little things that can make the car think it is running correctly when the A/F is actually off. Incorrectly adjusting certain scalars could also result in undesirable A/F being called for, especially at idle.

pullied or not, how off could the lower part of the stock MAF transfer table be? I havent tried fine tunning mine yet but i will soon. And about timing, I was under the impression that .5 load and under shouldn't really be touched (or barely). Mine has been upped by 1*. Your feedback on this is greatly appreciated!

 

[WDW MKR]

pullied or not, how off could the lower part of the stock MAF transfer table be? I havent tried fine tunning mine yet but i will soon. And about timing, I was under the impression that .5 load and under shouldn't really be touched (or barely). Mine has been upped by 1*. Your feedback on this is greatly appreciated!

You're completely correct that most of these shouldn't happen, but they do. We're dealing with numerical changes in the 1000ths/10000ths when it comes to tweaking MAF Transfers and IAC tables. The slightest mistake in entering a value can throw the tune way off. Also, some tuner (absolutely no reference to RET) have back-door ways of accomplishing things. These methods can dial a tune for set conditions, but venturing outside said conditions (namely weather) can reveal a tune with values that max the O2 sensors.

And it's not the pulley that will effect your low-end MAF Transfer tuning: it's things like CAI, injectors, MAFia... things that effect air entry into the MAF or require adjustments to scalars that then effect the MAF Transfer indirectly.

I agree that low-end spark and fuel tables should more often that not be left alone. Mods like cams and changes to compression can often require changes in these areas.

 

[WDW MKR]

The only reason I was curious about the tune was because it was just done 2 weks ago. It seemed that the first tank after tuning was normal but the next 2 went away rather quickly. I'm going to change the O2's as maintenance when I replace my midpipe soon anyway as I figure that it can't hurt. It has also been flippin' hot here the past few days which I'm sure doesn't help any.

The computer will take a few drive cycles to settle in with parts of the tune like fuel voltage tables and LTFT. It is very possible that your tune is the culprit. You need to datalog before you'll know, as there is currently no SES light telling you 100% that it is a sensor gone bad.