Thanks for all the info everybody.
I used some lucas gas treatment and that seamed to get my gas millage back to where it was before but I will check it the way everybody said to.
Thanks,

 

Sean a good trick I have found for mpg with ethanol based fuels is to change the mv switch point from rich/lean. With high concentrations of ethanol at part throttle the egt's are moderately cooler thats the only thing i have seen that can affect the tuneup. Changing the switchpoints a bit to bias it towards lean will usually get the egt's up because its running at stoich it will help out with mileage and the function of narrow band sensors.

What I was getting at before is not that there arent tricks, its that they are marignally effective and there are not alot of them.

Something in my own experience has been what you actually get at the pump. What I mean by that is when I run shell gas I get the best mpg by looking at the gauge and by calculating. When I fill up at cheaper stations I find that they tend to have a froth that comes from the pumps, in effect selling you air, when you fill the tank it will have a head on it like a good beer. At the cheaper stations if you fiddle around and wait long enough you can get almost another two gallons in it from the first time it kicks off after the froth settles down. At the shell station I use if you try to pump more than after the second shutoff liquid fuel is gonna spash back at you.

I drive about 500 miles a week (100 a day) m-f same route and similar traffic every day. I have checked back and forth at different local stations for 5 tanks at a time or so. Logging knock retard mpg fuel trims and mpg. Shell is the all around best for my car i avg 23mpg driving 50/50 cty/hwy on thier fuel and no knock retard. Amaco and kroger 93 generally gets me about 20mpg and 2-3 deg of knock retard. The local dirtbag station nets me 18mpg and 6-8 degrees of retard.

Whats interesting is that if I just quit pumping at the first shutoff, I can get 70 more miles to a tank on the shell gas than I can any of the others. I attribute this to aeration of the fuel. You can also track the mpg right along with the fuel trims depending on the station it came from, takes about a tank or tank and a half of gas for it to take effect entirely.

Not really relevant to solving problems, just something i noticed doing TONS of driving buying at various gas stations.

 

Shell gas: is it up to 10% ethanol? I thought our local shell station wasnt b/c the cost is 10c more than other places but road thru the other day to get some and saw the sticker.

Wish my Buick had the switch points, we have gained 15%+ better gas mileage with these changes.

 

I think what i've been buying from shell is 10% ethanol. All I know is the car loves it almost as much as e85. It is a little more expensive, but when whats coming out of the pump is straight liquid instead of some two phase froth.. a few cents a gallon doesnt matter alot to me. It does seem more expensive at face value though, but when you consider i get more mpg out of it and my range with the car is farther to boot from a better fill on the gas tank. It has its up sides. In the end though you really kinda break even, but imo better mpg is nothing but better combustion efficiency which is a happier engine PERIOD.

What tricks have you been doing to up mpg Shon? If you pay attention to the lt1 pcm, there are different closed loop "modes" based on airflow and the o2 switch points are based on the modes. I'll just say my cammed car does not idle rich, even in closed loop but it did take me quite a few reflashes to get it all right.

 

Your math might be right but you are wrong about doing math,

My tank shows 5 gallons gives you almost 3/4 tank then everyything after that meaning the last 1/4 full = 10-15 gallons right? So how does that math work out in your situ?

 

I do agree that different forumlations (ie brands of fuels) burn differently in each car and you should find the one your car likes. And buying the 'more expensive' fuel does sometimes equate to better fuel economy so you do come out ahead.

I have not messed with the LT1 MPG tuning yet, but got a few customers that are going to want me to start playing with them so I will be burning fuel and time for them, but on the LSx stuff there are 'easy' tables to change to get the MPG up, telling the O2s what mV is stoich is nice. As for as my DD (buick) it really only has an stoich AFR and not much else to mess with so I have been messing with the AFR (14.7 stock) but knowing that is rich and best for emmissions I have been moving it up a little bit at a time to find the right number. 14.90 showed a nice increase in MPG, went from 23 to 27, then moved it into the 15.x range and it came back down to 25 (the sw does not log KR or O2s for some reason:HPT) so this is all my MPGs, and I have the PE enable at 95% throttle since I have not mess with that table but there are more tables I am going to start messing with, AFR is at 14.95 right now and MPGs seem to be doing well, 250 miles into the 3rd tank test.....spark tables have not been adjusted yet either. It would be alot easier if i could see the KR and O2 readings but I am having to go by the ST and LT FTs.

We do have a CTS V that is getting 27MPGs on the hwy, that is up 15% from where he was at and an 04GTO that is hitting 31MPGs on the hwy, he is very happy!!!

 

Alright i'll let one of my mpg tricks slip. I'm sure you're aware that 128 is stoich. I'm sure you're also aware in tuner cats you can adjust the max and min on the long and short term fuel trims. I usually use this to lean idle out by setting the maf or ve to create a lean condition without the aid of the trims and then let it ride on the blm limit. This will usually kick it into open loop at idle unless you turn off the codes for lean fuel system.

If you get all your blms close to 128 +- 4 or so. You can bracket a blm cell right around highway cruise, now this will be a small cell just say like 1700rpm-1900rpm or so and from map values of 35-45. You want to set it up so it pops out of this situation any time you're going up a hill or accelerating in any way etc you just want this when you're hanging around at 60 or 70... whatever your usually highway speed happens to be say on your daily commute. You can then set it to be up against the blm limit, and then you can basicly adjust a/f ratio to wherever you want it by how far off your maf or ve calibration is . Or if it pops into open loop on you (some cars dont if you turn off the dtc for lean fuel system), just command a leaner a/f there. I usually like to verify what i'm actually cruising at on the wbo2. Thats how i have managed to fool my lt1 into cruising as lean as 16:1. On the highway at 65mph my lt1 gets around 28mpg with the cruise on. As a side note if your car starts to missfire sometimes you can try some more timing advance, more advance usually makes an engine more tolorent of lean mixtures. Every engine is different though so i cant really tell you where to shoot for. Once you get it lean enough it starts missing back off some and add some timing right there and that should be about as good as it gets.

 

very good info! wonder how many will pick up on it???
I want to do an OL tune with a WB02 for a guy with a nice sized cam, so that in the MAP range of cruise it leans out but on the gas it goes to PE and does what it is supposed to do.
The MAF and VE tables are a nice thing to play with to get what you want, if you know what you are doing. especially on the MAF side.....

WS6: 28MPG from an A4/gears is good IMO, what gearing do you have? And have you tried to go leaner than 16:1, thinking a 17 or even more could be done.

 

Good point.
I will have to do it like everybody has told me to do and go by how much I put it.
Thanks,

 

I have 3.73 gears a 3000-3200rpm stall, high compression and a decent set of heads with a kinda large cam. The thing here is the change in air fuel ratio is not a huge savings. At 60mph lets say you use 30g/s or so by the maf reading. By using the air/fuel reading you can figure out fuel use rate by division. With a little bit of algebra and logic the fuel savings is going to be a function of air fuel ratio assuming it doesnt take more air to do the job running leaner (which is not exactly true fuel is power). when you go from 14.7 to 16 a/f ratio you're effectively going to use (14.7/16)*100 = 92% Which seems great, the catch 22 is that at 60mph. Using a spreadsheet I made awhile back to calculate instantaneous mpg from datalogs, the change will get you from 22.8 up to 24.8mpg sounds like a huge savings but is it really? Well if we say you drive that speed all the time with no stopping or acceleration with the cruise on etc. If you drive 15k miles a year like this with gas being $4.30 a gallon you save a whopping $230 wow somebody call Al Gore house 20 dollars a month and 53.5 gallons less!

I will also pass along if you're not running stock fuel injectors, and have an afpr crank the pressure up to about 60 and your atomization will be better Running a hotter coil and a .050 gap with a sorta hot plug will also get you closer. At the end of the day though i do not lose too much sleep over this. The best thing you can do for mpg is to keep your foot off the gas and drive slower.