First off I want to say high to all ,I'm new here to this site.Great site lots of info.
OK I bought this 01 5.2 4x4 last year for a fishing /hunting truck.No power ,terrible gas mileage , about 11 mpg.Did mods in this order,superchips(decent jump in power from being pathetic) fixed intake plenum with own aluminum plate,new 4 hole injectors from 50 motorsports,plugs,wires,cap,coil ,shorty headers, air intake.After all this ,very moderate gains in power and no gain in mpg.Is 11 mpg normal for a 4x4?
Last week I thought maybe the cat could be clogged. Cut it out (not clogged) and welded in straight pipe.Threw no codes until 150 miles. I thought this was strange. You would think it would throw a code rather quickly.O2 sensor possibly bad? Read where they can cause poor mpg. Is this really true?
I have been thinking long and hard on a 5.9 long block with RV cam from Carolina Engine. Been reading on how the 5.9 has way more power and torque than the 5.2. I just don't want to give up on the 5.2 just yet, it only has 103000 miles on it.
Cam swap is out of the question on the 5.2. I don't want to waste any money on parts that won't transfer too the new 5.9 long block.
Any ideas or am I expecting too much out of this 5.2?

 

11 around town really isn't all that bad...... especially in winter. What size tires ya runnin?

Do the non-fouler trick (article in faq section) on the rear O2 sensor. Should take care of your code.

The Rear O2 CAN cause poor economy, non-fouler might help with that too.....

Done a compression check?

 

A 5.9 will pretty much always get around 11 MPG. A 5.2 normally gets a couple more miles to the gallon, especially on the highway.

What kind of plugs are you using? My truck ran like poo until I got those crappy Bosch plugs out and put some good ole champions in em.

 

Tire size is 285/75/16.I will read faq on non fouler.
Plugs are Accel platinum from O'reilly.
Forgot to mention machined down tabs on throttle body and modded the runners in the keg. I own a machine shop so this was no big deal.
So the 5.9 would get worse mileage even with more torque?

If you drive the truck with no gas mileage in mind it runs better than when I bought it for sure.Its just amazing how much gas it sucks trying to be conservative with it.Put a boat behind it and it does not like it what so ever.

I come from the diesel performance industry so I'm use to a lot of power under my foot for very little money.I know I'm comparing apples and oranges but I'm just amazed how much of a pig my truck is compared to comments of other 5.2 and 5.9 owners.

 

103K miles?

You aren't going to get diesel power out of one of these guys.

Might wanna have a look at the timing chain and gears. That one change netted the most power of everything else I had done.

33" tires, and probably the stock 3.55 gears.... Re-gearing would get you some power, (perceived power.) oddly enough, it would prolly get you better gas mileage too.....

You own a machine shop? Where do you live?

 

Oh trust me I know it will never do what the mighty Cummins does. I just expected to see some mpg gains with what I did.
Why did the timing chain yield your results? It was that slack?

Houston area.

 

Damn. Too far away.

Yeah, the chains in these are the longest I have seen on an OHV engine. The stock, morse style chain stretches quite a bit, and you lose a lot of accuracy in the timing. Putting on a nice, tight, double roller, that is less prone to stretching, really woke my engine up. I had 170K on it at the time though.....

If you check some of the mileage threads that are going, you will find that right about 12 MPG around town is 'pretty good' for these trucks..... sad, I know.

 

I'm doing 11 highway.

 

if it makes you feel better i only get 13 doing straight hi way driving and i have a 2wd 318, 3 speed brick on wheels.

 

If I had a machine shop...I'd be thinking a stroker! (and I'm MUCH closer!)