Getting 8.5 mpg need help

[BlueCollarTahoe]

Ok, so you've got a 2004 Tahoe, which motor? 5.3 LM7 or L59 Flex? What rear axle ratio? Exactly what size tire are you running? What was stock size and what air pressure are you running in them?

Most importantly, you said you are running Shell, but what grade? Around where I live, Shell can always be counted on to deliver about the worst fuel economy as possible; even with their 93 octane gasoline.

Does your Torque Pro App show the alcohol content of the fuel?

5.3L v8 not the flex one. 17 tires. Nitto AT Grappler. air pressure is what it says on the door forget what it is right now. not sure about the real axel but the car is AWD if that tells what it has.is that true about shell? 87octane, regular. i thought shell was great actually. wow. what yall recommend then? and i dont think it shows that on the torque app.

 

[swathdiver]

5.3L v8 not the flex one. 17 tires. Nitto AT Grappler. air pressure is what it says on the door forget what it is right now. not sure about the real axel but the car is AWD if that tells what it has.is that true about shell? 87octane, regular. i thought shell was great actually. wow. what yall recommend then? and i dont think it shows that on the torque app.

Please be more specific with regards to the tires; What was the factory size and what size and type are the Nittos? For example, was the stock tire a 265-70-17 and a P-Metric? Are the Nitto's the same size and an LT tire?

If you have the LM7, it's unlikely then that the computer has an alcohol content setting.

Check your RPO sheet for the "G" codes for the axle ratios, you probably have GU6 for a 3.42 gear front and back. These trucks so configured were rated at 13 City and 17 Highway and 15 Average MPG.

 

[Doubeleive]

another thing to keep in mind is the awd trucks get a slightly lower mpg than the 2wd/4wd but it's shouldn't be severely different.

 

[bottomline2000]

I have the torque pro app and can get numbers at both idle and under load i just need specifics what to look for if someone can tell me what to watch for if it will give an idea where to start looking. i mean i know its a SUV and city driving kills mpg no matter what but damn if 250 to 300 a tank is really normal i would enjoy that better than the barely 200 i get now.

Does the app show long/short term fuel trims? If so, a screen shot of the left at idle and while under load would be a s start. Does the truck feel low on power?

I would pull the hose off the fuel pressure regulator and see if there is fuel in the line. If so, the regulator would be bad. I would also check fuel pressure and make sure you don't have a stuck injector or a weak pump. Just some ideas.

Sent from my SAMSUNG-SM-T377A using Tapatalk

 

[swathdiver]

Well, Jay didn't get back with us tonight. Jay, assuming that your original tires were 265-70-17 and P-Metrics, the air pressure for them will be around 30 psi on your door sticker. Now if those Nittos are and LT tire and you're running them at the same pressure, you're woefully under inflated and not even meeting your axle capacities. Somewhere over 40 psi and up to 50 psi is correct for an LT tire for your truck. This will bring up your mileage some if that is the case.

Now let's talk gasoline. It has been my experience for over thirty years and no matter the automobile driven that running higher octane fuels results in better fuel economy and fewer fuel system problems than low octane fuels. The difference in economy is at least 2 mpg and often much more. There are even differences between brands of 93 octane gasoline, some of which have degraded my mileage 6 miles to the gallon.

Several years ago I was running Sunoco's 93 in my Pontiac Montana and getting 16 mpg around town. We were given some gift cards from Shell and the best we could get was 13 mpg on their 93 octane fuel. And old boss challenged me to run cheap gas in this same Pontiac. Making deliveries all day with the motor running from 3AM to 3PM it averaged 12 mpg on Sunoco 93. Switching over to 87 for two tanks it plummeted to 8 mpg on the same route and routine and ran like crap to boot. This LZ9 loved to rev and got better gas mileage at 77 mph than at 70 or 75 mph. In fact, it got 21 mpg at 90 mph!

I've been running Mobil's Synergy, 93 octane since October when not using Ethanol. I switched over to it when we noticed our mileage beginning to fall when using Sunoco's 93 in all of our vehicles. We picked up 2-3 mpg in each of the autos switching to Mobil. Then on Easter weekend I had to run the tank down to switch from Ethanol to gasoline for some tests for BlackBear. Closest station was a Chevron so we filled up on that and where the truck struggled to get 15 mpg on the highway, it easily managed 17.5 mpg with an alcohol content of 20% on the highway. Refueling at the same station a week later now with an alcohol content of 11%, the truck's entire trip average was just over 17 mpg. Filled up the other night near home with Mobil 93 @ 5% alcohol content and the motor struggles to stay in the 16 mpg range and will only see 17 on the highway at no faster than 70 mph. The higher the alcohol content, the worse it is for fuel economy. The moral of this little story is that engines benefit from high octane fuels and in our area, Chevron is best.

It has been my experience that it costs more to use lower octane fuels than it does the high octane fuels in regards to gas mileage lost and in that they contribute to an engine running poorly and dirty.

You're going to have to see who has the best fuel in your town for your vehicles. It all comes down to cents per mile.

 

[BlueCollarTahoe]

sorry didny get back sooner was a hectic couple of days.

Please be more specific with regards to the tires; What was the factory size and what size and type are the Nittos? For example, was the stock tire a 265-70-17 and a P-Metric? Are the Nitto's the same size and an LT tire?

If you have the LM7, it's unlikely then that the computer has an alcohol content setting.

Check your RPO sheet for the "G" codes for the axle ratios, you probably have GU6 for a 3.42 gear front and back. These trucks so configured were rated at 13 City and 17 Highway and 15 Average MPG.

265-70-17 is the tire size of what was on there and what i got in the Nitto AT replacement. I had bridgestone Duelers HT. the RPO code shows i Have the LM7....the GT4 with G65 ( something about self adjusting). 13 is a long way from 8.5 mpg in city conditions.

another thing to keep in mind is the awd trucks get a slightly lower mpg than the 2wd/4wd but it's shouldn't be severely different.

yea i read that but even if its 11mpg thats still a ways from 8.5

Does the app show long/short term fuel trims? If so, a screen shot of the left at idle and while under load would be a s start. Does the truck feel low on power?

I would pull the hose off the fuel pressure regulator and see if there is fuel in the line. If so, the regulator would be bad. I would also check fuel pressure and make sure you don't have a stuck injector or a weak pump. Just some ideas.

Sent from my SAMSUNG-SM-T377A using Tapatalk

the app shows the following in this list at idle ( like 5 min idle) earlier:

intake: 5.1 psi
MAF: 5.4g/s
Revs: 542.8 rpm
speed: 0.0
load: 2.0%
STFT1: -1.6%
intake 73.4
throttle: 8.2%
boost: -9.6psi
f/t 1x1: -0.8%
f/T 2x1: 0.0%
02 1x1 : 0.7V
02 1x2: 0.5v
02 2x1: 0.1v
02 2x2: 0.7V
LPK (avg) 12.7l/100km
ltft1 : 0.0
ltft2: 2.3%
Stft2: -2.3%
FUel FLow: 33.7cc/min
Vol eff: 55.0%
fuel rem: 48.3%


now this is with the app..i have a plug in accel reader that seems to be instant but im not sure if i can drive with it reading the info. i will check but it measures the same things in a different order. i will check and list it here. not sure how accurate that torque pro is because if that last reading means fuel remaining then its way off. i only had about 1/4 of a tank when i took these readings. no where near half. i dont think this one has a regulator on the fuel rail. i looked at pics and didnt see what ive seen in youtube videos. the truck also has an air riad MIT intake. picks up good. when yall say under load can you explain what you mean exactly? is that highway driving at 65 for a set amount of time? if a stuck injector was the issue wouldnt it throw a code? i have no codes. whats the proper fuel pressure on these cars?

Well, Jay didn't get back with us tonight. Jay, assuming that your original tires were 265-70-17 and P-Metrics, the air pressure for them will be around 30 psi on your door sticker. Now if those Nittos are and LT tire and you're running them at the same pressure, you're woefully under inflated and not even meeting your axle capacities. Somewhere over 40 psi and up to 50 psi is correct for an LT tire for your truck. This will bring up your mileage some if that is the case.

Now let's talk gasoline. It has been my experience for over thirty years and no matter the automobile driven that running higher octane fuels results in better fuel economy and fewer fuel system problems than low octane fuels. The difference in economy is at least 2 mpg and often much more. There are even differences between brands of 93 octane gasoline, some of which have degraded my mileage 6 miles to the gallon.

Several years ago I was running Sunoco's 93 in my Pontiac Montana and getting 16 mpg around town. We were given some gift cards from Shell and the best we could get was 13 mpg on their 93 octane fuel. And old boss challenged me to run cheap gas in this same Pontiac. Making deliveries all day with the motor running from 3AM to 3PM it averaged 12 mpg on Sunoco 93. Switching over to 87 for two tanks it plummeted to 8 mpg on the same route and routine and ran like crap to boot. This LZ9 loved to rev and got better gas mileage at 77 mph than at 70 or 75 mph. In fact, it got 21 mpg at 90 mph!

I've been running Mobil's Synergy, 93 octane since October when not using Ethanol. I switched over to it when we noticed our mileage beginning to fall when using Sunoco's 93 in all of our vehicles. We picked up 2-3 mpg in each of the autos switching to Mobil. Then on Easter weekend I had to run the tank down to switch from Ethanol to gasoline for some tests for BlackBear. Closest station was a Chevron so we filled up on that and where the truck struggled to get 15 mpg on the highway, it easily managed 17.5 mpg with an alcohol content of 20% on the highway. Refueling at the same station a week later now with an alcohol content of 11%, the truck's entire trip average was just over 17 mpg. Filled up the other night near home with Mobil 93 @ 5% alcohol content and the motor struggles to stay in the 16 mpg range and will only see 17 on the highway at no faster than 70 mph. The higher the alcohol content, the worse it is for fuel economy. The moral of this little story is that engines benefit from high octane fuels and in our area, Chevron is best.

It has been my experience that it costs more to use lower octane fuels than it does the high octane fuels in regards to gas mileage lost and in that they contribute to an engine running poorly and dirty.

You're going to have to see who has the best fuel in your town for your vehicles. It all comes down to cents per mile.

i thought the cars had to be tuned for the best use of 93 octane? if shell isnt good what would be a good one? i have just about all the gas chains around. theres a mobil near by. alot of the gas stations have stickers that say 10% ethanol. is there a place i can compare this stuff? i also checked the tires seems the place put them all at 42 PSI on the new AT tires but i was also getting this before those tires.

 

[swathdiver]

Hi Jay, I reckon from your post that those tires are an LT tire and that at 42psi you're around the minimums for meeting your axle rating but I do not know the specifics for your truck. GT4 RPO code is 3.73 gear, excellent for towing and get up and go.

Twenty five years ago my cars made their most power on Shell's 93 octane gas. Today, not so much. I would recommend that you run a few tanks of say, Chevron's or Mobil's 93 and take note of your mileage, especially the second and third tank and then maybe switch to another brand if you feel it can be better. For a couple of years where I live it was Sunoco's 93 delivering the best mileage in our cars but for some reason things change. Is this a local problem or nationwide? I have no idea, which is why we have to see for ourselves where we live.

You might want to put another 6 psi in those tires too. If everything that's been changed is working good, then there's not much to improve upon here save for your driving habits and even then the motor could be just plumb wore out.

We used to pull our fuel rails and injectors and run them into jars and see that they all delivered the same amount of gas. A Tech2 can test individual cylinders via spark and fuel too.

I'm in a similar situation with my truck. While it had no official mpg ratings, it should get 14 City and 20 Highway. The only time I saw anything close to that was the first week after buying it, 17-18 mpg @ 78 mph bringing it home. Never again. Turned out to be a bad cat driving me nuts all those months. Replaced the whole Y-pipe and Cats with the Magnaflow and switched brands of gas. Funny thing, the truck gets about the factory ratings while on E85 but has a hard time getting close to its gasoline ratings. I finally saw an average of 15 mpg with 20% alcohol content and 17 mpg with 11% alcohol content and that was on Chevron's gasoline. Then I had to take on fuel quick and used Mobil's 93 and can barely maintain 16 mpg on the highway, let alone combined city driving. I also run AT tires @ 50 psi and have a 3.42 gear with a 6-speed transmission. I've been told the AT tires lose 1-2 mpg over highway tires. My only modification is a mild BlackBear tune with AFM turned off so that should be a wash.

So if you can get her back up to around 10-11 city and 14-15 highway, call it good.

 

[BlueCollarTahoe]

Hi Jay, I reckon from your post that those tires are an LT tire and that at 42psi you're around the minimums for meeting your axle rating but I do not know the specifics for your truck. GT4 RPO code is 3.73 gear, excellent for towing and get up and go.

Twenty five years ago my cars made their most power on Shell's 93 octane gas. Today, not so much. I would recommend that you run a few tanks of say, Chevron's or Mobil's 93 and take note of your mileage, especially the second and third tank and then maybe switch to another brand if you feel it can be better. For a couple of years where I live it was Sunoco's 93 delivering the best mileage in our cars but for some reason things change. Is this a local problem or nationwide? I have no idea, which is why we have to see for ourselves where we live.

You might want to put another 6 psi in those tires too. If everything that's been changed is working good, then there's not much to improve upon here save for your driving habits and even then the motor could be just plumb wore out.

We used to pull our fuel rails and injectors and run them into jars and see that they all delivered the same amount of gas. A Tech2 can test individual cylinders via spark and fuel too.

I'm in a similar situation with my truck. While it had no official mpg ratings, it should get 14 City and 20 Highway. The only time I saw anything close to that was the first week after buying it, 17-18 mpg @ 78 mph bringing it home. Never again. Turned out to be a bad cat driving me nuts all those months. Replaced the whole Y-pipe and Cats with the Magnaflow and switched brands of gas. Funny thing, the truck gets about the factory ratings while on E85 but has a hard time getting close to its gasoline ratings. I finally saw an average of 15 mpg with 20% alcohol content and 17 mpg with 11% alcohol content and that was on Chevron's gasoline. Then I had to take on fuel quick and used Mobil's 93 and can barely maintain 16 mpg on the highway, let alone combined city driving. I also run AT tires @ 50 psi and have a 3.42 gear with a 6-speed transmission. I've been told the AT tires lose 1-2 mpg over highway tires. My only modification is a mild BlackBear tune with AFM turned off so that should be a wash.

So if you can get her back up to around 10-11 city and 14-15 highway, call it good.

thanks for the reply, how did you know it was a bad cat? last time i went to the shop the mechanic said if it was a clogged or damaged injector a code would show...i assume he used his tech2 to check it he was sitting there for a while looking at stuff....i wanted the injectors cleaned and he asked why and went from there. the reprogramming he did was less than the injector cleaning so i dont think it was a flim flam type of thing and generally hes been really reliable before and the economy did get slightly better. on highway driving the estimator on the DIC if i clear it and drive all around on highway will hang out around 16/17. the city driving brings it all the way down to 8.5 id be happy with 11/15. cant really expect 2 much from a big SUV compared to smaller cars but cmon man lol im gonna switch to 93 premium at mobil next couple tanks see what happens. but im getting a feeling may be something off. i dont remember it being this low when i first got the truck and i did more city driving then. i honeslty remember thinking everyone says this is a gas guzzler this aint even bad.

 

[swathdiver]

Eventually mine was throwing a code for a bad cat on the right side and right before we replaced the y-pipe, started getting a code for the left one too.

A buddy of mine swears by these little bottles of Super-Tech fuel injector cleaner that you get at Walmart. Put two in my tank once and got 22 mpg driving home from the filling station. Come to think of it, I'm going to put some more in again since I'm running gasoline right now. No additives while running E85. Going to run down this tank of Mobil and switch back to Chevron and put a couple of those bottles in too.

 

[BlueCollarTahoe]

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