Ok so I replaced the plugs wires rotor and cap. Had the ecu reprogrammed , I have a Holley inileator ignition and a k&n filter. I baby the **** out of it and get 10MPG!!!?!?! So the only thing I can imagine is fuel pump? It usually takes like 8 - 10 cranks in a row ( one turn of the key) in my opinion that is a hard start. But will that make my MPG go down ???? I know I have 35" tires and 4:11 gears and push alot of air around but 10mpg .....? Any suggestions? I had it on the dyno and it gets 150 HP and 170flbs of tourqe at 5500 to the rear tires. Something is wrong here and I'm at my wits end and making me broke as I drive it to work daily.

I have looked through the posts as well but nothing really fits the description . Just sayin

I will try and do a fuel pressure test soon as well as a leak down test as well.

Oh I forgot to mention my truck is a 2003 blazer ls

Thank you all in advance

 

those power numbers sound about right, at the CRANK when its NEW the 4.3 puts out 190 hp and 200flbs of torque. so with age and at the tires those numbers arent bad. for the plugs, cap, and wires what brand did you use? (only use AC Delco).. For the fuel pump you could try the pressure test, you could also clean the MAF and the EGR and see if that helps anything.

 

Ngk was what was used. And it had 121 HP pre ecu tune . Also it has no hesitation or stumbles ... And a cat back with flow master exhaust

 

I'm gonna say that 10mpg with 35's is probably about right....... With 3.42's and 30" tires and no lift (save a torsion crank to fit the 30's) I'm getting 15. These engines are reliable....not efficient. (It's the rest of the truck that's not so reliable LOL)

 

I don't belive that 10mpg is the end result.
If that is the case then I better start looking for a 4.8L or a 5.3L to swap into my rig. I just can't wrap my head around the fact that 35" tires create that much rolling resistance. This truck only got 25km a tank more with the stock tires and 3:47's so it was terrible in the first place ... Still gotta do the fuel pressure test and leak down test. Bought a new fuel filter today and will install tomorrow.

 

Blazers aren't known for their fantastic mpg's my friend.

 

well.. stock it should get 20 on the highway. if you aren't getting that then theres a problem. right now my MPG is at about 13-14 and thats driving to school at 35 MPH or less and hitting every stop light on the way (my truck says my average MPH is like 11 or 12) so i have a lot of stop and go

so if you are getting 10 MPG in the city with 35's that would be a good number. but if you are getting 10 on the highway then thats a problem

 

Of course a stock Blazer (97) will attain 25mpg, flat terrain,no load,empty. Add all that plus the larger tires,Mike98Blazer is right:10 MPG is about right!

 

Ok I bought the tester today and the highest it got was 45 psi. I dOnt think it was right I will try again tomorrow. But when I turned the key on it went to 35 psi then cranked it and it went to 45 then when it was running maintained 45 untill revved and then it dropped to 30 !! I have a new filter I will put in tomorrow as well. But this truck only got 285 km to a tank of fuel driving mostly highway at 80-100kmh when it was stock. Now it gets 260 to a tank of fuel ( when the fuel light comes on) or about 71 bucks at 1.21 a liter of fuel. 87 octane.

 

I belive that it should be at 60psi dead headed and 55 running?? So if my test was right it is running lean.. And probably creating a bunch of problems as well as would explain the reason it's a bit hard to start in the morning or after sat for a while. Haven't had the time yet to do the bleed down test. Will do these test tomorrow