bad gas mileage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**StingRay** · 02-03-2009, 11:42 AM

I've got a 92 RCLB K1500 with about 110k miles. It has a new fuel pump and filter, new AC Delco 02 sensor and CTS, recent cap, rotor and plugs, new air filter and timing has been set. I have run sea foam through it and used it in the tank as well. It has a rebuilt 700r4 and has 342 gears with p265 tires. Highway cruise RPM is about 1700 at 60 MPH, Compression is good on all 8 cylinders, it idles smooth and starts flawlessly. I have only been getting about 10 MPG with it and I drive mostly highway. From what I understand some of you guys are getting into the 20's with these trucks. Has anybody got any thoughts on what else to look at?

piecesparts · 02-03-2009, 05:02 PM

I have a 91 SWB regular cab, with a 350 and 700 R4 tranny and 3.42 gears. I run a set of 275/50/17 tires on the truck and get 20 MPG pretty regular out of it. I used to get around 17 MPG out of it, when I first purchased the truck. I took the tranny apart some time ago and built it up to sharpen the shifting and response. I also run a TB spacer with a set of shorty headers and 2 1/2" dual exhaust outlets. I put a standard 14" X 4" high round air cleaner on my TBI unit instead of the air cleaner and snorkel tube. I also put in a set of dual electric fans and got rid of the factory driven clutch fan (that gained a good 1 MPG).

The one thing that you might look at is the EGR solenoid and see if it is not cycling the EGR valve slightly and allowing the exhaust gases to leak by when they shouldn't be. That may be affecting your gas mileage some. It is possible that your RPMs might be too low for daily driving and you are working the engine to get up into the operating band. Just a thought---my truck runs a little higher in RPMs at 60 MPH.

worley91 · 02-03-2009, 06:48 PM

Yes when I unhooked my EGR pump it knocked my gas mileage from 17 to 15. Keep in mind mine is 4 wheel drive with 285-75-16 and mine is a 5 speed but the EGR will affect your mileage.

**StingRay** · 02-03-2009, 10:08 PM

I've been wondering if maybe a 373 wouldn't be a better gear. It does work pretty hard down at those RPM's. I was under the impression these TBI's were built to lug at low RPM's though.

66truckin · 02-04-2009, 01:05 PM

I don't think your going to notice much difference going from 3.42 to 3.73.

02-03-2009, 11:42 AM	#1
StingRay Senior Member Join Date: Mar 2000 Location: Saskatoon,SK,Canada Posts: 2,498	bad gas mileage I've got a 92 RCLB K1500 with about 110k miles. It has a new fuel pump and filter, new AC Delco 02 sensor and CTS, recent cap, rotor and plugs, new air filter and timing has been set. I have run sea foam through it and used it in the tank as well. It has a rebuilt 700r4 and has 342 gears with p265 tires. Highway cruise RPM is about 1700 at 60 MPH, Compression is good on all 8 cylinders, it idles smooth and starts flawlessly. I have only been getting about 10 MPG with it and I drive mostly highway. From what I understand some of you guys are getting into the 20's with these trucks. Has anybody got any thoughts on what else to look at? __________________ Saskatoon, Saskatchewan Canada Last edited by StingRay; 02-03-2009 at 11:43 AM.

02-03-2009, 05:02 PM	#2
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: bad gas mileage I have a 91 SWB regular cab, with a 350 and 700 R4 tranny and 3.42 gears. I run a set of 275/50/17 tires on the truck and get 20 MPG pretty regular out of it. I used to get around 17 MPG out of it, when I first purchased the truck. I took the tranny apart some time ago and built it up to sharpen the shifting and response. I also run a TB spacer with a set of shorty headers and 2 1/2" dual exhaust outlets. I put a standard 14" X 4" high round air cleaner on my TBI unit instead of the air cleaner and snorkel tube. I also put in a set of dual electric fans and got rid of the factory driven clutch fan (that gained a good 1 MPG). The one thing that you might look at is the EGR solenoid and see if it is not cycling the EGR valve slightly and allowing the exhaust gases to leak by when they shouldn't be. That may be affecting your gas mileage some. It is possible that your RPMs might be too low for daily driving and you are working the engine to get up into the operating band. Just a thought---my truck runs a little higher in RPMs at 60 MPH.

02-03-2009, 06:48 PM	#3
worley91 Big Boys With Big Toys Join Date: Nov 2008 Location: Seneca Illinois Posts: 142	Re: bad gas mileage Yes when I unhooked my EGR pump it knocked my gas mileage from 17 to 15. Keep in mind mine is 4 wheel drive with 285-75-16 and mine is a 5 speed but the EGR will affect your mileage.

02-03-2009, 10:08 PM	#4
StingRay Senior Member Join Date: Mar 2000 Location: Saskatoon,SK,Canada Posts: 2,498	Re: bad gas mileage I've been wondering if maybe a 373 wouldn't be a better gear. It does work pretty hard down at those RPM's. I was under the impression these TBI's were built to lug at low RPM's though. __________________ Saskatoon, Saskatchewan Canada

02-04-2009, 01:05 PM	#5
66truckin Registered User Join Date: Jan 2009 Location: Springfield, IL Posts: 185	Re: bad gas mileage I don't think your going to notice much difference going from 3.42 to 3.73. Last edited by 66truckin; 02-04-2009 at 01:07 PM.



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