Can a C3500 5.7L 4.10 beat 10 MPG?

[letitsnow]

I guess that, fuel economy-wise anyway, I'm jealous that my wife's 2015 Subaru Forester XT Touring with a 16 gallon tank can go way further than me, and she leadfoots the turbo!

I can beat the WRX in my avatar, and still get 25+ mpg! Sometimes it is over 30 mpg. Totally different animals though.

 

[454cid]

So 10 MPG is fairly consistent for just toolin' around town, it does marginally better on the freeway.

I haven't checked it in ages, but that's what my 454 used to get... 10-ish in town and 12.6 on the highway. RCLB 4x4 with 4.10's.

 

[Supercharged111]

Yeah, my 454 dually gets just shy of 11 highway. My 1500 gets 12-13 mixed, 13-14 hwy and it's a 5.7/4L80/4.10/9.5" diff like the OP plus it has a damn blower. 10 doesn't seem right.

 

[Darrin De May]

Yeah, my 454 dually gets just shy of 11 highway. My 1500 gets 12-13 mixed, 13-14 hwy and it's a 5.7/4L80/4.10/9.5" diff like the OP plus it has a damn blower. 10 doesn't seem right.

That's why I'm curious as to what kind of mileage other folks get running a similar setup. In order to pass smog this year and make the Service Engine light to go out I began going through the codes. It started with the two rear oxygen sensors, then the camshaft & crankshaft position sensors. Then it was the distributor cap & rotor, then the spark plugs & wires, with a thermostat & fuel filter thrown in for good measure. The light kept coming back on between these steps, and finally a new set of fuel injectors made the light go off long enough to pass smog and get my shiny new 2020 sticker. I would've thought that all of these nice new AC Delco parts would improve my mileage, but it hasn't made any discernable difference. Oh yeah, the light came back on a couple of days after my new registration arrived, and it's STILL on!

 

[Supercharged111]

What code is it?

 

[Darrin De May]

What code is it?

Not sure. I'm curious to find out, but since passing smog, it hasn't been as much of a priority. With all the new parts I've thrown at it, I'm wondering what could possibly be left!

 

[Supercharged111]

Just go to any parts store and use their POS scanner to tell you the code. That will help a lot in nailing down what's really going on. I recently **** out an O2 sensor in my dually and it MURDERED my mpg.

 

[Grimmcx]

Just to chime in, I have a 98' crew cab, long bed, 5.7 c3500. Just did a 800+ mile round trip pulling a loaded pop-up camper estimated around 3500lbs, 5 passengers. I averaged 14.29mpg one way and 14.56mpg the other way. This was driving between 65-70 mph, no a/c, and about 85% highway travel. All stock with the exception of the air intake resonators deleted and factory Duramax aluminum wheels on stock tire size.

 

[mykytiuk]

Yep!!! I agree with the other posts. ‘94 3500 4x4 crew cab longbox TBI 350 4.10 gears. 14 on the freeway(sometimes). 10 locally and 7 to 8 pulling 24 ft 4500 lb Airstream. Did the “Ultimate TBI Mod” and that seems to help for a little more power but haven’t had a chance check mpg on a longer trip. Thinking about a transmission controller to keep it in 4th gear more but not sure if it would help with mpg but should be easier on everything else. Slower gears won’t help unless you get the torque down low which TBIs are not known for, and the only way to do that is with a cam and aftermarket or Vortec heads. I’ve tuned, tweeked and tuned and tweeked somemore and unless you have a 1500 and only drive it with a tailwind and flat terrain this as good as it’s ever gonna do. Anybody that says they’re getting 16 to 18 with this heavy truck and no internal mods or maybe a lean of peak engine meltdown chip is FOS!!!

 

[Darrin De May]

Just go to any parts store and use their POS scanner to tell you the code. That will help a lot in nailing down what's really going on. I recently **** out an O2 sensor in my dually and it MURDERED my mpg.

I used the scanner at AutoZone initially, then the smog shop scanned it a couple of times when the damned light came on while I was driving TO the smog shop. I've been thinking about getting one of these $22 Bluetooth scanners that I read about on another thread. Are they worthwhile?

https://bafxpro.com/products/obdreader