5.7 vortec mpg

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CRF450R

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So ever since owing this truck it's always bin hard on gas. My 1994 5.7 tbi 4l60 2wd extended cab would get 23.7 - 24.5 mpg at the cruise set at 110km/h ( live in Canada ). Note my mpg is in imperial mpg. My 1998 Z71 Silverado 5.7 4l60 gets 17mpg on the exact same highway trips once again cruise set at 110km/h and only a whippy 17 mpg I thjkt that's 14 mpg US. So I did plugs wires cap and rotor aswell as fuel filter and though it runs and idles nicer no mpg difference. After I deleted the cats did a full 3" true dual exhaust with a double H pipe and 3 in 3 out single chamber bottles 5" chrome tips I gained 1 mpg avarage as before the exhaust I got 15.5-16 mpg (imperial mpg) on the highway. I'm very fusterated about this and I also find it to be kinda gutless I find my 5.7 tbi had a bit more power and way better mpg it to had a full custom 3" true dual exhaust. My 94 had almost 400 000km on it when I sold it to a friend that is still running all original never opened motor my 98 at 350 000km should still be healthy I would of thought or is the vortec 5.7 not as good as the tbi everyone told my if I loved my 5.7tbi I'd love the 5.7 vortec I feel my 5.7vortec has les power and is definitely way way way harder on gas. Note I have no engine light on I've had this truck checked out by multiple shops thousands spent I'm getting very fusterated. Is this just as good as mpg a 98 Z71 5.7 get'? I know it's got 3:73s and a locking 14 bolt but really this crap mpg hell my 08 2500HD 6.0 vortec was doing 20mpg to 21 at 110km/h once again this is imperial mpg and had way way more power and just a way tougher truck then my old whippy 5.7 Z71 vortec.
 

Hobie

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Now a lot of people dont get very good fuel economy in a full size 4x4 truck, and being that you've already done a lot of work to it, it sounds like you may need to think about a tune on the ECM.

I believe blackbear makes an economy tune that they can throw onto a black box and send to your door, and also my 96 vortec 5.7 felt like a dog as well, until I actually changed to a larger throttle body.
You must be registered for see images attach

As shown here, the factory throttle plate actually has a restrictor on it that actually makes a huge difference in performance and drivability. You can either knock this restrictor off, or move up to a throttle body from a 454 vortec. Either way, your throttle response will greatly increase.

Another thing to look at is your air filter, it's a small thing that's commonly overlooked, and also replace the PCV while your under the hood, they are cheap, and can effect fuel economy, and I've found that I need to replace mine every other oil change to keep it working properly.

If you have access to a scanner, or even a bluetooth OBD dongle, go ahead and view your O2 sensor data as well as your long term fuel trims. They can tell you a lot about your engine, and how its performing. A negative fuel trim may indicate a leaking injector, while a positive fuel trim can indicate a vacuum leak. The fuel trim should be around 0%+/- 5%

And lastly, you said you replaced your plugs/wires/cap/rotor/fuel filter. What was the condition of them? How did the plugs look? And was the filter clogged? Anything fall out of the filter?
 

L31MaxExpress

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Bone stock the 97 G1500 Express conversion van I have would almost always touch 18 mpg on long trips even running 70-75 mph. 5.7/4l60E/3.42. The best mileage it ever got stock was about 19 mpg going through Kentucky and Tennessee. One tank went 550 miles on just over 29 gallons.

Biggest issues on the Vortecs. Carbon buildup in the intake, fuel pressure regulator and spider issues, and failing front 02 sensors. To me the Vortec engines always feel less torquey than the TBI engines but as the engine revs into the powerband the Vortecs extra midrange and top-end is easily noticeable.
 
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L31MaxExpress

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Now a lot of people dont get very good fuel economy in a full size 4x4 truck, and being that you've already done a lot of work to it, it sounds like you may need to think about a tune on the ECM.

I believe blackbear makes an economy tune that they can throw onto a black box and send to your door, and also my 96 vortec 5.7 felt like a dog as well, until I actually changed to a larger throttle body.
You must be registered for see images attach

As shown here, the factory throttle plate actually has a restrictor on it that actually makes a huge difference in performance and drivability. You can either knock this restrictor off, or move up to a throttle body from a 454 vortec. Either way, your throttle response will greatly increase.

Another thing to look at is your air filter, it's a small thing that's commonly overlooked, and also replace the PCV while your under the hood, they are cheap, and can effect fuel economy, and I've found that I need to replace mine every other oil change to keep it working properly.

If you have access to a scanner, or even a bluetooth OBD dongle, go ahead and view your O2 sensor data as well as your long term fuel trims. They can tell you a lot about your engine, and how its performing. A negative fuel trim may indicate a leaking injector, while a positive fuel trim can indicate a vacuum leak. The fuel trim should be around 0%+/- 5%

And lastly, you said you replaced your plugs/wires/cap/rotor/fuel filter. What was the condition of them? How did the plugs look? And was the filter clogged? Anything fall out of the filter?

I don't use a 5.7 Vortec PCV in mine. I run the 2001+ 5.3 PCV valve. The one that is a PCV valve housing with a fixed orifice drilled into it in place of the normal spring and valve. It cut my oil consumption in half and keeps the upper intake much cleaner.
 

Dre319

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My 98 K1500 has a 5.7 as well and gets about the same MPG.
I’m lucky to get 17-18 depending on how I drive on the highway and maybe 13-14 city.

Sent from my iPhone using Tapatalk
 

L31MaxExpress

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My 98 K1500 has a 5.7 as well and gets about the same MPG.
I’m lucky to get 17-18 depending on how I drive on the highway and maybe 13-14 city.

Sent from my iPhone using Tapatalk

With all the stop and go around here, I was lucky to get 11 mpg city.
 

CRF450R

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Now a lot of people dont get very good fuel economy in a full size 4x4 truck, and being that you've already done a lot of work to it, it sounds like you may need to think about a tune on the ECM.

I believe blackbear makes an economy tune that they can throw onto a black box and send to your door, and also my 96 vortec 5.7 felt like a dog as well, until I actually changed to a larger throttle body.
You must be registered for see images attach

As shown here, the factory throttle plate actually has a restrictor on it that actually makes a huge difference in performance and drivability. You can either knock this restrictor off, or move up to a throttle body from a 454 vortec. Either way, your throttle response will greatly increase.

Another thing to look at is your air filter, it's a small thing that's commonly overlooked, and also replace the PCV while your under the hood, they are cheap, and can effect fuel economy, and I've found that I need to replace mine every other oil change to keep it working properly.

If you have access to a scanner, or even a bluetooth OBD dongle, go ahead and view your O2 sensor data as well as your long term fuel trims. They can tell you a lot about your engine, and how its performing. A negative fuel trim may indicate a leaking injector, while a positive fuel trim can indicate a vacuum leak. The fuel trim should be around 0%+/- 5%

And lastly, you said you replaced your plugs/wires/cap/rotor/fuel filter. What was the condition of them? How did the plugs look? And was the filter clogged? Anything fall out of the filter?
I'm not interested in a tune I find on a gas truck there a waste of money I've had gas trucks dyno tuned with exhaust and intake mods to just have $700 less in my wallet. I think my next thing will be mpfi upgrade and new fuel regulator looks like a pain in the A$$ of a job. However I do find unless my truck is plugged in when it's cold outside and it's its sits overnight it won't start it just cranks over but if it's plugged in it fires up the second you touch the key. I was told it could be the temp sensor by the thermostat so put new one in no difference also had a shop do a fuel pressure test and said it was very good well within spec for the 5.7 vortec. So only thing I'm thinking is the fuel injectors and regulator. Why like to get to the bottom of this as I'm confident this truck should be getting better mpg and have more power then it does. And when I did the plugs they were bad it ran lot better after tune up just didn't change mpg at all it did look like I had a couple cyclinders running a bit lean there was touch of white on three plugs. And the truck also has all new 02 sensors.
 

Supercharged111

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You emptied your wallet for a bullshit tune. The Vortecs have a lot to give in stock form.
 

Hobie

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I'm not interested in a tune I find on a gas truck there a waste of money I've had gas trucks dyno tuned with exhaust and intake mods to just have $700 less in my wallet. I think my next thing will be mpfi upgrade and new fuel regulator looks like a pain in the A$$ of a job. However I do find unless my truck is plugged in when it's cold outside and it's its sits overnight it won't start it just cranks over but if it's plugged in it fires up the second you touch the key. I was told it could be the temp sensor by the thermostat so put new one in no difference also had a shop do a fuel pressure test and said it was very good well within spec for the 5.7 vortec. So only thing I'm thinking is the fuel injectors and regulator. Why like to get to the bottom of this as I'm confident this truck should be getting better mpg and have more power then it does. And when I did the plugs they were bad it ran lot better after tune up just didn't change mpg at all it did look like I had a couple cyclinders running a bit lean there was touch of white on three plugs. And the truck also has all new 02 sensors.
My truck used to be the same way, wouldnt start under 35°F without the block heater plugged in. My spyder assembly was pretty clogged. I should've replaced them with MPFI unit, but at the time I didnt know there was a replacement. But now that I have a #7 injector not working right, MPFI will be coming soon.

And may i ask what vehicle you had dyno tuned? I've seen a few 5.7 vortecs around here gain 40-50HP just from a tune, no exhaust, intake, ect.
 
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