Greetings,

New to this forum so go easy on me! I have a 2002 Chev ext. cab 4x4 with a 5.3L and 3.73 gears. Tires are 265/16s and only mods are a corsa catback exhaust and a "mystery" chip. I say that as i bought this truck late last summer and apparently it was chipped. The truck currently has approx. 240,000kms (150,000 mi) and has been mechanically babied since its been in my posession. Synthetics fluids in engine and in tranny. My problem is poor fuel economy. I get around 12-13mpg around town and 14-15mpg on the highway. In my opinion i should be getting way better fuel economy than that. The air filter is new and have run a can of sea foam through it. My next step is changing the plugs to E3s. No "check engine" light on so i can't really think of anything else. Ideas????

 

You might want to consider changing your gear and transfer case to synthetic you might pick a few tenth of mpg's that way.

That said 4X4's just are not the vehicle for fuel mpg. My neighbor had an 05 crew cab 5.3 exact same truck as mine execpt it was a Z71 and he was getting the kind of mileage that you are describing while average 18-19 daily driver and 20+ on the highway. I use synthetic oil in the engine and rear gears.

You just have a lot of driveline resistance with 4X4's so don't look for a big jump in mpg's but at $4.00 a gal. every bit helps

good luck
jvp

 

I'd also suggest cleaning the MAF and throttle body as well.

Take the MAF off and give the screen and sensor wires a good soaking with CRC MAF spray cleaner. Let it air dry. Do not touch the sensor wires with anything.

You can clean the throttle body with carb cleaner.

 

Thanks fellas. This is my 3rd GM truck (previous was a 2004 reg cab long box 4x4 5.3L and 3.73s and more recently a 2007 shorty 4x4 with same motor and gears) and oldest. I got around 15-16mpg bombing around town and at least 20mpg on the highway in both trucks (the shorty had MDS so was even better on gas) so am i expecting a little too much out of this truck? Would the higher mileage have something to do with it?

 

Yes, the older the truck gets and high mileage, the less efficient they get. Takes more power to move them along. That's why jvp is suggesting you go with synthetic oils in your drive train.

I don't think you are expecting too much with the mileage you're currently getting around town. Mines older and I get at least 14 or more if I keep my foot out of the gas.

As these trucks get older, sensors start to lose effiency as well such as O2, MAF, and MAP sensors. When I first bought my truck three years ago, I wasn't happy with the mpg either. Even though my sensors checked within limits with a scanner and no codes, I replaced them anyway and my mileage improved by a couple of mpg.

A problem I have right now is with the torque converter and going into lockup. Well, it doesn't lockup the converter even when the PCM commands lockup. That's having an impact on my mileage presently. I've replaced all the solenoids in the tranny but no change. Most likely suspects are worn out valve body or worn out boost valve. I plan to replace the tranny and TC this spring. That's what my tranny guy recommends.

 

Do not use the E3 plugs. Go back with Iridium plugs. To many people have complained and proven that the E3 plugs are no good.

 

Too late! Installed the E3s on sunday so i am going to run them for a bit to see, if any, there is a difference. I paid almost 80 buck for the set so regardless if my performance or fuel economy doesn't change i will more than likely leave them in.

 

Let us know how the plugs work for you. Did you put new wires on it also? And what brand?

 

Never thought of changing the plug wires but seems like an easy swap, no? Haven't run a full tank of gas since i've changed the plugs but the next fill i will figure out the difference, if any, in mileage. Back to plug wires, any suggestions on what/where to get?

 

you should also change the distributer cap and rotor while your at it i allways do that when i change my plugs and wires.
or just clean the cap and rotor reall good using the proper cleaning stuff