hey guys,i just got my fist blazer, could not beat the deal. i got a 98 4dr 4wd ls with the 4.3 vortech. it has 170,000 on the clock. only paid 1000.00 for it. as soon as i got it we tore the motor apart and found it had a bad rod bearing and rebuilt the bottom end. put everything back together and it appears to be kinda sluggish on the take off and then clears out. it smell rich and is only getting about 12mpg and i know it should do better than that. i also just got an obdII code p0442 which indicates an evap leak(small) and i am not sure how to go about diagnosing it. my main concern is the mpg i know it should be higher than that i cant figure it out. any help guys. thanks

 

Welcome!
Well, 12mpg seems about right, actually.
I filled my truck up yesterday, drove to college today which is approx. 13 miles both ways. That's a 26 mile trip, and on the way home I went to the gas station, filled the truck up again and it took 2 gallons. That's about 13 mpg.
The Blazer tends to be hard on gas. I mean, I was surprised it only took 2 gallons. I was expecting around 5. Much better than I thought.

 

No 12mpg is not about right. You were expecting it to take 5 gallons after a 26 mile trip? You do realize that's 5.2mpg, right? The worst I've ever gotten was 14mpg after romping on it quite frequently in 2WD in the snow for fun, and about 15 mins. total of 4WD when I started to slip. Factory quotes 15 city/21 highway. There are many threads on here about gas mileage. If you're only getting 13mpg (assuming your truck really was full when you filled up) then there are other issues to look at. As many on here have said before, never underestimate the value of a good tune-up.

To mystic, first off welcome! I'm assuming if you rebuilt the bottom end that you didn't open up the plenum at all, correct? Smelling gas sounds like too much fuel=fuel delivery issue. There are many threads on here concerning this, do a quick search and see what you come up with. I know I have read quite a few about the spider or 'nut kit' leaking and just dumping fuel but if you didn't take apart the top end of the motor then it shouldn't have been affected. This doesn't mean you don't have a leaky injector or something along those lines.

There are lots of knowledgable guys (and gals) on here that would be able to steer you in a better direction than I have, but just wanted to clear up that 12-13mpg is slightly below average and 5.2mpg is definitely not normal.

 

Haha, I know 5.2mpg is insanely low and I probably would only get that low if my gas tank was probably dropping gas on the road, but the way my gas gauge showed the needle moved quite a bit. And yeah, I fill it up 100%. Yeah, I read the city/highway mpg and I knew I was under 15 or 21 mpg.
One day I'll have to drive normally and not constantly floor it.
But I'm guessing the 2 door gets better mileage than the 4 doorr?

 

thanks for the replys so far guys. we actually had just the block with cam in it sitting on the stand. so yes, Tripleblackblazer, the plenum came off. i dont smell fuel very often just once in a while. i do still have the evap code will this affect my mpg in any way. i hate emission problems. the truck just feels very sluggish and obviously the low mpg is killing me. i am getting ready to drive from Va to MN and dont think this gas mileage will do me much justice. might as well drive the v10 superduty.

 

V10 Superduty?
I would love one.

 

Disconnect your O2 sensor and see if that makes any difference.

One other thing. Your gas mileage will be lower until the engine gets up to operating temp. If your driving in cold weather and it takes you 10 miles to get up to tmep, its not a very good indicator.

I would also run some seafoam throught he gas tank on your trip. That will help to clean out he fuel injection system. Track your mpg to and from your destination.

 

what will disonnecting my O2 sensor help me do or diagnose? what would i be looking for when i do this?

 

Fuel Pressure Regulator...could be leaking/ruptured...dumping fuel into the upper intake, killing mileage (my '96 gets almost 20 mpg with 108 on the clock). Was the upper intake clean on one side and kinda sludgy on the other? That's the visual tip off symptom. I'd replace it anyway if the clock shows 170K as you'd be overdue for a replace anyway. I think I paid $35.00 for the FPR at Autozone. Could also be leaking injector(s) or a bad spider.

At 170K, how about those intake manifold gaskets. They'd be long overdue for a replace (if they are originals)

The EVAP code is either related to the sensor on the engine (mounts to the intake plenum - not likely though) or the EVAP canister vent solenoid (located on the cross rail above the spare tire under the vehicle). Drop the tire, trace the fat vacuum hose from the charcoal canister to the solenoid vent, remove vent solenoid, replace with new (less than $50.00 at dealer, I could not get it at aftermarket stores, may need to pre-order part as it may not be readily stocked at dealer, FYI).

Another thing to keep in mind is that vacuum hoses do dry out and get dry rot/brittle over time. Check your vacuum hoses and replace as needed. Squeeze the hoses and look for harline cracking, replace anything even suspect. I did all mine (wasn't that bad) and the engine performance has improved greatly. Vacuum leaks, no matter how small, do affect performance and operability of quite a few components on the Blazers.

 

Disconnecting the O2 sensor makes the puter go into defualt mode. It will run, however your gas mileage will suck. If your puter is IN defualt mode that might explain your crappy gas mileage.