Poor fuel mileage
12-22-2014, 09:54 AM
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Poor fuel mileage
Quick question:
09 LNF - 78000 miles
So, about 2 months ago, my fuel mileage started really suffering. It's continually gotten worse, and now it's real bad. Like, 23mpg at 72MPH, and 28MPG at 45MPH. Mods are in my sig.
I'm leaning toward it being an O2 sensor issue, but my AFR is 14.7 and Lambda is right around 1.00. I know 'winter blend' will lower mileage, but this is my 4th winter in MI and it's never been even close to this low. Car still runs fine and power is still there, no misfires, etc.
So, can it be an O2 issue even if the AFR and whatnot is where it needs to be?
09 LNF - 78000 miles
So, about 2 months ago, my fuel mileage started really suffering. It's continually gotten worse, and now it's real bad. Like, 23mpg at 72MPH, and 28MPG at 45MPH. Mods are in my sig.
I'm leaning toward it being an O2 sensor issue, but my AFR is 14.7 and Lambda is right around 1.00. I know 'winter blend' will lower mileage, but this is my 4th winter in MI and it's never been even close to this low. Car still runs fine and power is still there, no misfires, etc.
So, can it be an O2 issue even if the AFR and whatnot is where it needs to be?
12-22-2014, 10:16 AM
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These threads make me 
First off you're driving a performance car. If you want good gas mileage there's plenty of lonely Prius's in need of a driver.
Secondly, just because the afr is at what you are 'commanding' and there's no change in power doesn't mean it's not the tune. There's A LOT more to fuel than just what you are telling the afr to be. Especially since we are talking about highway driving in your post. I'd be willing to bet your STFT's and LTFT's are out of whack. Or I would at least start there instead of assuming it's a sensor. You're running a custom tune and the tunes can be more sensitive to weather conditions than the factory tune.
First off you're driving a performance car. If you want good gas mileage there's plenty of lonely Prius's in need of a driver.
Secondly, just because the afr is at what you are 'commanding' and there's no change in power doesn't mean it's not the tune. There's A LOT more to fuel than just what you are telling the afr to be. Especially since we are talking about highway driving in your post. I'd be willing to bet your STFT's and LTFT's are out of whack. Or I would at least start there instead of assuming it's a sensor. You're running a custom tune and the tunes can be more sensitive to weather conditions than the factory tune.
12-22-2014, 10:22 AM
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These threads make me
First off you're driving a performance car. If you want good gas mileage there's plenty of lonely Prius's in need of a driver.
Secondly, just because the afr is at what you are 'commanding' and there's no change in power doesn't mean it's not the tune. There's A LOT more to fuel than just what you are telling the afr to be. Especially since we are talking about highway driving in your post. I'd be willing to bet your STFT's and LTFT's are out of whack. Or I would at least start there instead of assuming it's a sensor. You're running a custom tune and the tunes can be more sensitive to weather conditions than the factory tune.
First off you're driving a performance car. If you want good gas mileage there's plenty of lonely Prius's in need of a driver.
Secondly, just because the afr is at what you are 'commanding' and there's no change in power doesn't mean it's not the tune. There's A LOT more to fuel than just what you are telling the afr to be. Especially since we are talking about highway driving in your post. I'd be willing to bet your STFT's and LTFT's are out of whack. Or I would at least start there instead of assuming it's a sensor. You're running a custom tune and the tunes can be more sensitive to weather conditions than the factory tune.
Now I remember why I stopped posting here. If you don't want to give useful info, then don't post. Simple as that.
Last edited by Speed_Thrills; 12-22-2014 at 10:22 AM. Reason: Automerged Doublepost
12-22-2014, 10:27 AM
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Florida winter...
72*
My fuel mileage is north of 30.
But that took a **** load of work on HPTuners to get it where it's at now. I HATED fighting with the short terms because the bastards kept zeroing out on me. I could never get the histogram tables to work for the fuel trims in HPTuners so I had to go in manually and adjust each and every block individually. Long terms much easier and never exceed +/-.8
72*
My fuel mileage is north of 30.
But that took a **** load of work on HPTuners to get it where it's at now. I HATED fighting with the short terms because the bastards kept zeroing out on me. I could never get the histogram tables to work for the fuel trims in HPTuners so I had to go in manually and adjust each and every block individually. Long terms much easier and never exceed +/-.8
12-22-2014, 10:28 AM
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Florida winter...
72*
My fuel mileage is north of 30.
But that took a **** load of work on HPTuners to get it where it's at now. I HATED fighting with the short terms because the bastards kept zeroing out on me. I could never get the histogram tables to work for the fuel trims in HPTuners so I had to go in manually and adjust each and every block individually. Long terms much easier and never exceed +/-.8
72*
My fuel mileage is north of 30.
But that took a **** load of work on HPTuners to get it where it's at now. I HATED fighting with the short terms because the bastards kept zeroing out on me. I could never get the histogram tables to work for the fuel trims in HPTuners so I had to go in manually and adjust each and every block individually. Long terms much easier and never exceed +/-.8
12-22-2014, 10:29 AM
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There's your problem.
Short terms are a pain in the ass and you're never going to get them steady below +/- 3. But as close to that is where you need to be. Your long terms can be much better. Mine usually sit at 0. But on longer road trips I will never see anything beyond +/-0.8. With some work you can get there.
12-22-2014, 10:33 AM
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There's your problem.
Short terms are a pain in the ass and you're never going to get them steady below +/- 3. But as close to that is where you need to be. Your long terms can be much better. Mine usually sit at 0. But on longer road trips I will never see anything beyond +/-0.8. With some work you can get there.
Someone said LTFT was based on the downstream O2.. any truth to that?
As soon as I get my truck back from the shop, I'm going to replace the upstream O2 anyway..
12-22-2014, 10:36 AM
#10
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if you aren't finding what you need to here and actually tune yourself, you might have some decent luck on the HPT forums finding specifics for what you need to zero in on fuel trims. i don't know much about it, but it's a start. Also, thetuningschool.com is/was actually giving out their tuning course online for free, you just had to register for it.
May be way more effort than you're looking, but if i had HPT i'd do it.
May be way more effort than you're looking, but if i had HPT i'd do it.
12-22-2014, 10:40 AM
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if you aren't finding what you need to here and actually tune yourself, you might have some decent luck on the HPT forums finding specifics for what you need to zero in on fuel trims. i don't know much about it, but it's a start. Also, thetuningschool.com is/was actually giving out their tuning course online for free, you just had to register for it.
May be way more effort than you're looking, but if i had HPT i'd do it.
May be way more effort than you're looking, but if i had HPT i'd do it.
12-22-2014, 10:55 AM
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How long has it been since your tune has been adjusted? And do you have any way to actually log your vehicle or are you basing this off of what was said to you by someone else? And how long were these logs conducted for?
Your fuel trims will go all over the place. In a nut shell the oxygen sensors monitor the exhaust gasses and report back to the computer any changes that need to be made to the tune. Either adding or taking away fuel. These are short term fuel trims. It's normal to see these numbers go plus or minus 3 as these change by the millisecond. But ideally you want as close to or under +/-3. Your long terms are based off of an average change of your short terms. So over time, if your short terms are indicating an average change of +3.5 then that is an indication your car is running rich. Or lean for a negative number.
I'm going to put money down your fuel trims are out of whack causing a change in fuel consumption. But remember, cold temps also effect this. And it's way more noticeable on custom tunes..
Your fuel trims will go all over the place. In a nut shell the oxygen sensors monitor the exhaust gasses and report back to the computer any changes that need to be made to the tune. Either adding or taking away fuel. These are short term fuel trims. It's normal to see these numbers go plus or minus 3 as these change by the millisecond. But ideally you want as close to or under +/-3. Your long terms are based off of an average change of your short terms. So over time, if your short terms are indicating an average change of +3.5 then that is an indication your car is running rich. Or lean for a negative number.
I'm going to put money down your fuel trims are out of whack causing a change in fuel consumption. But remember, cold temps also effect this. And it's way more noticeable on custom tunes..
12-22-2014, 11:21 AM
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My tune hasn't been adjusted for about 2 years. I'm basing all of this information on my Interceptor gauge - that's my only means of logging. I've been watching for a while and that's the changes I've noticed.
I know cold temps cause changes, but like I said, it's not even that cold (mid 30s) and it's never been this bad.. Even last year when it was -10 in MI, it wasn't like that.
I'm gonna replace the upstream like I said.. any reason to replace the downstream or no?
I know cold temps cause changes, but like I said, it's not even that cold (mid 30s) and it's never been this bad.. Even last year when it was -10 in MI, it wasn't like that.
I'm gonna replace the upstream like I said.. any reason to replace the downstream or no?
12-22-2014, 11:41 AM
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ive got my fuel trims under 1.0 so try adjusting your fuel trims, to get them as low as possible and maybe replace an 02 sensor as well. check your plugs and maybe try to seafoam the car as well.
12-22-2014, 02:12 PM
#20
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Do NOT listen to SL0baltSS aka DadsScionCanDoThis. He is notorious for bad info.
35mpg is only achievable under ideal conditions/and you're driving with gas mileage as priority over everything else. I've put more KM on the LNF than most. Many factors come into gas mileage. Weather, tires(condition,type,psi), gas blend(winter) road conditions, wind direction/speed, traffic, the driver, the car etc etc.
If you're mostly highway with little in town driving expect 28-32mpg.
If your mostly in town driving with little highway expect 24-28mpg.
If it's all idle/in town expect horrible gas mileage 20-25mpg.
If it's pure highway you shouldn't be under 30mpg.
35mpg is only achievable under ideal conditions/and you're driving with gas mileage as priority over everything else. I've put more KM on the LNF than most. Many factors come into gas mileage. Weather, tires(condition,type,psi), gas blend(winter) road conditions, wind direction/speed, traffic, the driver, the car etc etc.
If you're mostly highway with little in town driving expect 28-32mpg.
If your mostly in town driving with little highway expect 24-28mpg.
If it's all idle/in town expect horrible gas mileage 20-25mpg.
If it's pure highway you shouldn't be under 30mpg.
12-22-2014, 02:17 PM
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Do NOT listen to SL0baltSS aka DadsScionCanDoThis. He is notorious for bad info.
35mpg is only achievable under ideal conditions/and you're driving with gas mileage as priority over everything else. I've put more KM on the LNF than most. Many factors come into gas mileage. Weather, tires(condition,type,psi), gas blend(winter) road conditions, wind direction/speed, traffic, the driver, the car etc etc.
If you're mostly highway with little in town driving expect 28-32mpg.
If your mostly in town driving with little highway expect 24-28mpg.
If it's all idle/in town expect horrible gas mileage 20-25mpg.
If it's pure highway you shouldn't be under 30mpg.
35mpg is only achievable under ideal conditions/and you're driving with gas mileage as priority over everything else. I've put more KM on the LNF than most. Many factors come into gas mileage. Weather, tires(condition,type,psi), gas blend(winter) road conditions, wind direction/speed, traffic, the driver, the car etc etc.
If you're mostly highway with little in town driving expect 28-32mpg.
If your mostly in town driving with little highway expect 24-28mpg.
If it's all idle/in town expect horrible gas mileage 20-25mpg.
If it's pure highway you shouldn't be under 30mpg.
12-22-2014, 02:29 PM
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You might want to get those fuel trims adjusted.
I'm astounded at people riding around with fuel trims that out of whack. And I'm shocked you're not throwing a "too rich at idle" code... Assuming you don't have a CEL or if you do don't even bother to check it.
By the way, I wouldn't rely on your interceptor gauge alone for that. If you are tuned you need to be logging the car and going back to review your logs. You will be absolutely amazed at the nonsense you miss just by trusting an interceptor. Because let's face it, when you are WOT or in heavy traffic, you're not putting your eyes on that gauge long enough to retain any valuable amount of information. There's going to be a ton of peaks and valleys where your trims probably spike into the double digits or just plain zero out on you under certain driving conditions.
The cheap tuners way to fix things like this is "let's just command more fuel here and take fuel out there in this table".
Come on kids!
I'm astounded at people riding around with fuel trims that out of whack. And I'm shocked you're not throwing a "too rich at idle" code... Assuming you don't have a CEL or if you do don't even bother to check it.
By the way, I wouldn't rely on your interceptor gauge alone for that. If you are tuned you need to be logging the car and going back to review your logs. You will be absolutely amazed at the nonsense you miss just by trusting an interceptor. Because let's face it, when you are WOT or in heavy traffic, you're not putting your eyes on that gauge long enough to retain any valuable amount of information. There's going to be a ton of peaks and valleys where your trims probably spike into the double digits or just plain zero out on you under certain driving conditions.
The cheap tuners way to fix things like this is "let's just command more fuel here and take fuel out there in this table".
Come on kids!
12-22-2014, 02:30 PM
#24
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Yeah 23mpg is not right bro. Unless you're idling that car like mad in drive-thru's and traffic.
What type of tires you running and are they in good condition and at proper PSI?
Spark plugs? You're approaching gm recommended 160,000km change. (I've change mine every 75,000km cheap investment)
Last Oil change? Fresh oil can make a noticeable difference.
Driven with that zzp tune in winter before? Could just be geared towards making more power.
When have you last reset your fuel estimate? I always reset it every few tanks. And ignore results until you've put on 200km+.
What type of tires you running and are they in good condition and at proper PSI?
Spark plugs? You're approaching gm recommended 160,000km change. (I've change mine every 75,000km cheap investment)
Last Oil change? Fresh oil can make a noticeable difference.
Driven with that zzp tune in winter before? Could just be geared towards making more power.
When have you last reset your fuel estimate? I always reset it every few tanks. And ignore results until you've put on 200km+.