Bad Mpg Even After Tuneup?

Paint King · August 23, 2008

Not sure what else to do. 2000 rcsb z71 with 5.3 and auto tranny. Torsion lift and 285's. It's got fresh fluids, fuel filter, and plugs and wires. Getting 10 mpg in town and 13 on highway. I know with the bigger tires and little torsion lift would hurt but buddies 2001 gmc ext cab 2 wheel drive granted its different is pulling easy 15 or 16 in town and 22ish on highway.

I know the motors changed a little between '00 and '01. Could that be the issue? Should I spend the dough to have a shop run the scanner on it? Only thing I can think of is 02's but can't see that making a big enough difference.

Any sugestions? I actually went out and bought a motorcycle to help combat the mileage but another month or two and riding days will be few and far between.

Thanks,

Kyle

2000DV4.8 · August 23, 2008

Go to autozone or a similar parts store, most of them will scan for codes for free.

geektoad · August 23, 2008

I know the motors changed a little between '00 and '01. Could that be the issue? Should I spend the dough to have a shop run the scanner on it? Only thing I can think of is 02's but can't see that making a big enough difference.

your entire air/fuel map is based on data from the o2 sensors, so if they're messed up it can make a big difference. Though if they're that bad you should be throwing an SES light.

Paint King · August 24, 2008

I've scanned with the reader at parts stores but those only tell you what the CEL is for. I have no lights on. Just thought maybe it could be a soft code that only those fancy computer could pick up.

Paint King · August 25, 2008

Is my gas mileage fairly common? Or do you guys think there is a problem?

C6Racer · August 27, 2008

I used to get about 18 on the highway with my truck(see sig). I had been using 10W-40 synthetic oil along with Lucas oil sabilizer to quiet the noisy lifters. The last oil change I did, which was about 2 weeks ago, I decided to try a 5W-30 synthetic, making sure that it had the "Energy Conserving" label on the back of it and no Lucas. Boy, what a difference that made! I now get 22-24 highway mpg. The lifters are noisy now, but I'd rather save gas since I do a lot of highway driving. I also sprayed down the MAF with some MAF cleaner(duh), and that helped a little too. Also, remove your throttle body every 30k, or so, miles and clean it thoroughly. Remove the TPS and IAC valve before you clean it though. The first time I did it was at around 90k and my engine ran noticeably smoother. I've done it twice since and both times the throttle body was VERY dirty.

Having 4WD adds a lot of weight and drivetrain drag, however, so you definitely won't see the figures that a 2WD gets. Hope this helps and have a good one!

Paint King · August 27, 2008

Anyway a descreened maf could have something to do with this?

I run 5w30 mobil 1 synthetic. I haven't tried cleaning any of the parts you mentioned. Maybe I should look into that.

Kyle

Draenor · August 27, 2008

Anyway a descreened maf could have something to do with this?

Its a posibility. Your ECM may bee seeing 'too' much' air and is compensating by adding more fuel.

IMO descreening the MAF is a bad mod.

C6Racer · August 27, 2008

Anyway a descreened maf could have something to do with this?

Its a posibility. Your ECM may bee seeing 'too' much' air and is compensating by adding more fuel.

IMO descreening the MAF is a bad mod.

Yea, the MAF screen helps keep the air going in smooth as possible, as opposed to turbulent. If you don't want a screen I would suggest getting an MAF that is designed to work without one. Trust me, if it didn't need the screen, GM would NOT have spent the money to design and put it there.

Get some MAF cleaner and squirt those three resistor-looking things and the IAT (Intake Air Temp) sensor which is a little black blob that barely peeks out of a little hole on the inside.

No need for any scrubbing as the cleaner does a great job of blasting away any dirt, not to mention the damage that may occur to the sensor if you touch it with anything else. Cleaning just helps it monitor the air more accurately.

Paint King · August 27, 2008

Sounds like we might be on to something. I bought the truck that way and happened to notice it after removing the air intake several times for belt issues. I'll see if I can pick a salvage yard one up and make sure its clean and clean the other sensor as well.

Kyle

C6Racer · August 28, 2008

I would clean the sensor that you already have to see if it makes a difference BEFORE you buy any other parts. If it doesn't I would just keep it, unless you find a really, really inexpensive one.