i recently got myself a 2001 GMC jimmy 4.3L.
i bought the truck cheep because it had a dead skip only over 2k RPM's the owner before me was my boss so i know what was done to it, new poppet's, lifters, MAF, MAP sensors ect..
he cleaned out the cat's as well because of a p0101 for MAF performance, so i buy this truck i do diagnoises(working for GM i got the dealer tools) i checked everything thinking that the exhaust was NOT plugged.
Well i got pissed off because i was going off what he diagnoised and i started from scratch and found out the drivers side bank had 5 psi back pressure at 2k rpm's at the HO2S sensor 1 location but zero PSI on bank 2 and nothing behind the cat's, so being a redneck i go get ye old cutty cutty and wow was i ever suprised when i found the pipe had internaly collapsed.
so i put a new ypipe and convertor's on it, ye old girl is running great!
but i did reset my fuel trim, nd well i got 275 km's from a full tank of fuel.
my question is what everyone else is getting roughly doesnt have to be exact per tank or MPG, i get better fuel eco in my 2006 half ton with an LS1 in it which i was going to turn into a wood's toy, but if this jimmy is that hard on fuel she's getting a Solid thrown under it!
Please let me know guys
Thank you very much!

 

I get about 15 mpg used to get about 10 until I changed the the o2 sensor before the cat

 

Sounds to me like your fuel consumption is a bit high. Right now in the winter I get around 460Km per tank of fuel, and am averaging between 15-16mpg based on my phone fuel tracker.

 

I am getting right at 18 miles per gallon. Stock GMC Jimmy Diamond Edition.

 

I get 17-22mpg in my stock 93.

 

Check out the Official MPG Poll.

 

bone stock, i get about 12 l/100 km and 400km on a tank (based on onboard). Seems 18-20ish is about right in the city depending on your habits.

 

Well thanks alot guys working for Gm i am pretty sure the O2 sensors are working properly. but if it keeps eating the fuel i will replace both sensor's for sure and go from there

 

My 1st gen 4.3 would get about 460km in the winter, and 520km in the summer per tank. I do about 50/50 hwy/city with it... Or even mostly highway.

You got some more diagnosing to do.