Gas milage
February 28th, 2021, 3:06 PM
#11
CF Veteran
The dash reading is an average. If you bought the van from a cable company then most of its life has been putt-putting through city traffic, waiting at stop lights and idling at job sites.
Hit the highway and cruise for at least a 1/2 hour to get a more accurate expectation of what you will get on your road trips.
Hit the highway and cruise for at least a 1/2 hour to get a more accurate expectation of what you will get on your road trips.
February 28th, 2021, 3:12 PM
#12
It IS an average. You just didn’t have anything to average because it was reset. Once again, the reading gets better WITH TIME. Every time you reset it, you throw away data and delay the process.
February 28th, 2021, 3:16 PM
#13
You won’t notice the 2 missing octane points.
February 28th, 2021, 6:21 PM
#14
Generally yes the fuel with the ethanol in it has less energy and the engine burns more.
However the flexfuel vehicle's computer systems are designed to compensate for this loss and maintain the efficiency. where if you use it in say a TBI-equipped van you get about 10% lower fuel economy as a result.
Seems like the 85 is 15% ethanol where most gas is 10% or even ethanol free.
I have always found it amusing that for all the upgrades and improvements the fuel economy has stayed roughly the same.
My 89 Suburban and 91 G20 each would get around 15, the 91 G20 would get 15 all day long whether you cruised 60 or 75 with it. The Suburban had a 2.73 rear so the one time I pushed it hard (75-80-ish) it actually averaged about 17. This with a TBI and the aero of a brick. My 2002s averaged about 15, the 2500 dropped off some but it had a bad temp sensor and some other fuel system gremlins, it got around 17 when I first got it.
Even the 1960 Pontiac I daily drove 25 years ago got around 17 out of a 389 with a 2bbl carb on it.
The only one that's different is the 1995 models and they're actually about 3 MPG worse, from what I could gather the federal emissions standards for trucks were tightened that year and GM basically detuned them to meet it because the OBD-1 was going away the next model year, it was cheaper to do it this way.
However the flexfuel vehicle's computer systems are designed to compensate for this loss and maintain the efficiency. where if you use it in say a TBI-equipped van you get about 10% lower fuel economy as a result.
Seems like the 85 is 15% ethanol where most gas is 10% or even ethanol free.
I have always found it amusing that for all the upgrades and improvements the fuel economy has stayed roughly the same.
My 89 Suburban and 91 G20 each would get around 15, the 91 G20 would get 15 all day long whether you cruised 60 or 75 with it. The Suburban had a 2.73 rear so the one time I pushed it hard (75-80-ish) it actually averaged about 17. This with a TBI and the aero of a brick. My 2002s averaged about 15, the 2500 dropped off some but it had a bad temp sensor and some other fuel system gremlins, it got around 17 when I first got it.
Even the 1960 Pontiac I daily drove 25 years ago got around 17 out of a 389 with a 2bbl carb on it.
The only one that's different is the 1995 models and they're actually about 3 MPG worse, from what I could gather the federal emissions standards for trucks were tightened that year and GM basically detuned them to meet it because the OBD-1 was going away the next model year, it was cheaper to do it this way.
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therewolf (March 1st, 2021)
February 28th, 2021, 9:05 PM
#15
The Gen V Vortec 4.3 (2014+ pickups) is supposed to make 297hp with 85% ethanol fuel. Compare that to the ~145hp Gen I model.
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therewolf (March 1st, 2021)
March 2nd, 2021, 7:00 PM
#16
Just an update in case anyone is interested; Filled the van up with regular gas yesterday, re-set the DIC fuel economy estimator and ran 75 miles worth of errands. Mostly rolling 45-55 mph back roads, some stop and go in town with traffic lights. Was interesting to watch the DIC number fluctuate up to 20mpg while gently rolling at 50 for ten minutes, down to 7 while in town at traffic lights.
Went back to the same pump, refilled to the same auto-stops, my math said average 15.2 mpg, DIC said 15.5 mpg. Pretty close figuring I only drove 75 miles and I'm happy with that number.
Went back to the same pump, refilled to the same auto-stops, my math said average 15.2 mpg, DIC said 15.5 mpg. Pretty close figuring I only drove 75 miles and I'm happy with that number.
March 19th, 2021, 12:56 PM
#18
Hi, my 2008 1500 Express with the go-cart motor 4.3l (according to MMJ) and 240k miles gets 15.4 mpg (empty) according to the computer and doing by hand. When I bought it in Florida back in 2015, was getting 20+ mpg on the way back to Ohio, 70-75 speed all the way on cruise control.
March 20th, 2021, 8:28 AM
#19
CF Veteran
Just FYI -
The flex fuel software only modifies spark timing and injector pulse width to achieve the most efficient burn for the ethanol content of the fuel. It cannot achieve the same MPG on rich ethanol blends as regular gasoline because, as you stated, ethanol does not burn as hot and has less energy during combustion. Every vehicle on the road today has flex fuel software already installed in the PCM - it’s just not turned on for some vehicles (how it’s decided which vehicle gets FF capabilities I couldn’t say).
That’s not to say that ethanol rich fuels can’t achieve the same MPG, but it requires specific tuning of the fuel injection and spark timing to make it happen. However since MOST drivers are looking for the cheapest place to fill up, usually the fuel in the tank is going to be an uneven mix of ethanol and gasoline. When I’m checking live data during diagnosis, I’ve seen alcohol content range from 10% to 75% and when I’ve thought it necessary to verify it, standard fuel sample testing supports the live data.
To really determine how a FF vehicle can do on ethanol vs. gasoline (or at least low content blends), the tank needs to be filled with the desired fuel at least twice to burn through the fuel already in it (unless you wanted to disconnect a fuel line and pump it out) and then at least 3 filling cycles performed to get the most accurate average. Then the process needs to be repeated for the other fuel for comparison.
Ethanol blends are labeled according to the content. E85 is 85% ethanol, E15 is 15% and the standard 10% in regular unleaded is E10 (though it’s not often labeled as such).
If you’ve been driving since the 60’s then you will surely remember “gas-a-hol” - that was the precursor to the ethanol used today. I know a few guys that kept spare fuel filters on hand and got quick enough to change them at a stop light because gas-a-hol would keep flushing rust out of the tank and plugging the filters.
The flex fuel software only modifies spark timing and injector pulse width to achieve the most efficient burn for the ethanol content of the fuel. It cannot achieve the same MPG on rich ethanol blends as regular gasoline because, as you stated, ethanol does not burn as hot and has less energy during combustion. Every vehicle on the road today has flex fuel software already installed in the PCM - it’s just not turned on for some vehicles (how it’s decided which vehicle gets FF capabilities I couldn’t say).
That’s not to say that ethanol rich fuels can’t achieve the same MPG, but it requires specific tuning of the fuel injection and spark timing to make it happen. However since MOST drivers are looking for the cheapest place to fill up, usually the fuel in the tank is going to be an uneven mix of ethanol and gasoline. When I’m checking live data during diagnosis, I’ve seen alcohol content range from 10% to 75% and when I’ve thought it necessary to verify it, standard fuel sample testing supports the live data.
To really determine how a FF vehicle can do on ethanol vs. gasoline (or at least low content blends), the tank needs to be filled with the desired fuel at least twice to burn through the fuel already in it (unless you wanted to disconnect a fuel line and pump it out) and then at least 3 filling cycles performed to get the most accurate average. Then the process needs to be repeated for the other fuel for comparison.
Ethanol blends are labeled according to the content. E85 is 85% ethanol, E15 is 15% and the standard 10% in regular unleaded is E10 (though it’s not often labeled as such).
If you’ve been driving since the 60’s then you will surely remember “gas-a-hol” - that was the precursor to the ethanol used today. I know a few guys that kept spare fuel filters on hand and got quick enough to change them at a stop light because gas-a-hol would keep flushing rust out of the tank and plugging the filters.
Generally yes the fuel with the ethanol in it has less energy and the engine burns more.
However the flexfuel vehicle's computer systems are designed to compensate for this loss and maintain the efficiency. where if you use it in say a TBI-equipped van you get about 10% lower fuel economy as a result.
Seems like the 85 is 15% ethanol where most gas is 10% or even ethanol free.
I have always found it amusing that for all the upgrades and improvements the fuel economy has stayed roughly the same.
My 89 Suburban and 91 G20 each would get around 15, the 91 G20 would get 15 all day long whether you cruised 60 or 75 with it. The Suburban had a 2.73 rear so the one time I pushed it hard (75-80-ish) it actually averaged about 17. This with a TBI and the aero of a brick. My 2002s averaged about 15, the 2500 dropped off some but it had a bad temp sensor and some other fuel system gremlins, it got around 17 when I first got it.
Even the 1960 Pontiac I daily drove 25 years ago got around 17 out of a 389 with a 2bbl carb on it.
The only one that's different is the 1995 models and they're actually about 3 MPG worse, from what I could gather the federal emissions standards for trucks were tightened that year and GM basically detuned them to meet it because the OBD-1 was going away the next model year, it was cheaper to do it this way.
However the flexfuel vehicle's computer systems are designed to compensate for this loss and maintain the efficiency. where if you use it in say a TBI-equipped van you get about 10% lower fuel economy as a result.
Seems like the 85 is 15% ethanol where most gas is 10% or even ethanol free.
I have always found it amusing that for all the upgrades and improvements the fuel economy has stayed roughly the same.
My 89 Suburban and 91 G20 each would get around 15, the 91 G20 would get 15 all day long whether you cruised 60 or 75 with it. The Suburban had a 2.73 rear so the one time I pushed it hard (75-80-ish) it actually averaged about 17. This with a TBI and the aero of a brick. My 2002s averaged about 15, the 2500 dropped off some but it had a bad temp sensor and some other fuel system gremlins, it got around 17 when I first got it.
Even the 1960 Pontiac I daily drove 25 years ago got around 17 out of a 389 with a 2bbl carb on it.
The only one that's different is the 1995 models and they're actually about 3 MPG worse, from what I could gather the federal emissions standards for trucks were tightened that year and GM basically detuned them to meet it because the OBD-1 was going away the next model year, it was cheaper to do it this way.
March 20th, 2021, 12:49 PM
#20
I've read that the injectors for FF engines are larger than non-FF injectors. So it seems it's not just about software. (it makes sensesince you need more volume of ethanol to produce the same power as gasoline). Also, my service manuals say that FF engines operate on lower fuel pressure (I don't understand why).
The Gen V 4.3L FF engine is able to make 297hp on E85 (12 more hp than using straight gasoline). Engines designed and tuned for ethanol are more powerful. (hence why racers use it). Of course you are burning a lot more volume of fuel, so it's costing you more money too.
The Gen V 4.3L FF engine is able to make 297hp on E85 (12 more hp than using straight gasoline). Engines designed and tuned for ethanol are more powerful. (hence why racers use it). Of course you are burning a lot more volume of fuel, so it's costing you more money too.