Help, 6 mpg!!! Why!!!!!?????

[Deuling]

Hi i have a 1985 chevy k5 blazer with a 305, Edelbrock 1406 carb, Edelbrock intake manifold, and an HEI distributor. Getting about 6 mpg city, maybe 10 highway. Im cuttin the cat off as soon as i get a muffler ordered to replace it,... Goes manifolds to Y, to cat, to another Y with fake duels out the back. I put in Bosch IR Platinums, heard they were best on gas, changed the oil twice since bought and put only 2000 miles on it. Halfa$$ed tuned carbs, no vaccum gauge so i just turned them in till it sputtered and back out till it was steady running. Running 2000 rpms at 60 mph with a 700r4, and i think 3.73's but could be different, thats just what the guy thought and i havnt looked but they seem to be most common. Um yah so any thoughts??? really love this truck but spending way to much in gas, where my 1993 GMC vandura with a 350 is getting 18 highway...... but that thing sucks in the snow lol.

Heres the thread i have on it.
http://coloradok5.com/forums/showthread.php?t=279028

 

[Hogback Fabrication]

It's the carburetor. It either needs a tune or better yet, switch back to a Quadrajet.

 

[Fordum]

Oh, where to start????

First, look hard and long at your right foot, and tell it "Bad Foot, not so hard....."

Next, take those platinums out and find someone you don't like and make him a present of them.
Put in some AC Delcos and that should get you an MPG or two. GAP them before you put them in.

Find someone who knows carbs or grab a book and get it tuned right. Make sure the air cleaner is clean, change to synthetic oil next time you change.

Smell your transmission fluid, if it smells burnt or looks dark, get ready for a rebuild.
Check air pressure in your tires. They should have close to the max in them until you are actually going off road.

All that should put you in the ballpark.

 

[4X4HIGH]

We need to know 2 things, gear ratio (not a guess but actual ratio) and also what size tires? If the gears or tires have been changed and the speed has not been recalibrated then you cannot use the odometer to calculate MPG since the speedo wont read correctly and would throw off any calculation you did.

 

[bailey9r]

more info...

How long have you had it?

Did it suck all along or did a change occur?

If new to you check timing and make sure vacuum is hooked to dizzy and is it from a timed port or constant.

Oh heck while your at it toss in a couple of pics ...(for good old porn and so we can see the 40" tires and get a clue).

 

[K5-Kelly]

Cat's probably plugged up, also could be a combination of things, dirty air filter is a good one but 6mpg sucks. Check your rolling resistance as well. Throw it into neutral while you got somebody behind the wheel on flat level ground try pushing it from behind, brakes could be dragging. I had that happen on my first K5 as I had contaminated brake fluid and both front calipers were dragging and didn't notice it right away.

 

[63chevyll]

you may have to jet the carb down? or your timing or timing advance is way off.

No lie,

I could get 10-11 MPG outa my 84 blazer in town driving once i changed my exhaust out,

it had a 700r4 and a crate 350 with a factory Q-jet

i was getting around 6 then added Doug thorly headers, dual 2.25 pipes no cats and some off brand flowmasters and gaind 4-5 more mpg's,

this was with10 inches of lift, 39.5's and 5.13's.

on the open road 15 mpg was eazy

 

[blazinzuk]

A solid tune on the carb is a good place to start.

RPMs sound good for decent mileage.

Driving habits can net you nearly 1 mpg usually.

A little more info on the truck would help.

And quadrajets get better mileage than most any other carb does

 

[4X4HIGH]

You would have to have 4.56 gears with 31" OR 4.56 gears with 33" tires to be spinning 2000 rpm's @ 60 mph in OD.

 

[diesel4me]

Any engine gets much less MPG when its cold out!--are you running a 195 T-stat??..have cardboard in frontof the radiator when it is below 20 degrees?..an engine needs to run hot to get the most efficiency..

The Edelbrock carbs I have ran all had issues with carb icing in cold damp weather,I think the fact I used a 1" adapter/spacer to bolt it to a Q-jet intake kept the casting of the carb too cold to efficiently vaporize the fuel,leading to a rich condition,and any mousture in the air formed frost on the butterflies ..my mileage was horrible on a 305 I had one Edelbrok on in the winter,till I disconnected the vacuum hose on the EFE (heat riser) valve in the exhaust manifold,that forces exhaust from the passenger side head to flow under the intake in the passages cast under the carb to pre-heat the mixture and prevent carb icing..having a stock air cleaner housing with all the pre-heating pipes intact and functioning is a must for best cold weather MPG...

All the other points made here about rolling resistance,the ignition timing,etc are all good ones..by advancing the timing (assuming you have HEI and not a computer) will usually increase MPG quite a bit,be sure the vacuum advance works and is hookedto the correct port on the carb (some vehicles do better with manifold vacuum VS ported),and I second ditching those platinum plugs,I've seen more Chevy engines run WORSE after installing them than any that ran beter or got better fuel mileage,I'd stick with Autolites or AC "regular" plugs...if you have tall wide heavy tires,those will kill MPG also!...

 

[Deuling]

We need to know 2 things, gear ratio (not a guess but actual ratio) and also what size tires? If the gears or tires have been changed and the speed has not been recalibrated then you cannot use the odometer to calculate MPG since the speedo wont read correctly and would throw off any calculation you did.

32 X 11.5 Buckshot Maxxis Mudders

 

[Deuling]

Theirs actually not a spot of rust on the body, its just got nasty snow on it and the muffler tips are cheapies. rusted up. But im gonna be puttin a new exhaust in shortly.

 

[Deuling]

more info...

How long have you had it?

Did it suck all along or did a change occur?

If new to you check timing and make sure vacuum is hooked to dizzy and is it from a timed port or constant.

Oh heck while your at it toss in a couple of pics ...(for good old porn and so we can see the 40" tires and get a clue).

Haha their you go put in a couple pics. Wish they were 40's then it would make some sense haha. Ive had it for about 4 months i think. Sucked the same fuel down from the day i brought it home. I just ordered an oil pan heater to help for cold starts. I do need to check timing

 

[Deuling]

Oh, where to start????

First, look hard and long at your right foot, and tell it "Bad Foot, not so hard....."

Next, take those platinums out and find someone you don't like and make him a present of them.
Put in some AC Delcos and that should get you an MPG or two. GAP them before you put them in.

Find someone who knows carbs or grab a book and get it tuned right. Make sure the air cleaner is clean, change to synthetic oil next time you change.

Smell your transmission fluid, if it smells burnt or looks dark, get ready for a rebuild.
Check air pressure in your tires. They should have close to the max in them until you are actually going off road.

All that should put you in the ballpark.

Haha i will try to teach the foot lol. But I dont really hammer on it that much, maybe a donut or 2 in the snow in the parking lot at work. But man those plugs really suck?? they were $8 a piece, everybody i had talked to said they got way better mileage with them, none in a 26 year old truck.... Um tranny fluid looks ok, it leaks out of the dipstick, need to get an O ring for it, but i keep it filled up all the time and looks fine on the stick.

I like to keep the tires at about 30-32 psi, helps in the snow alot, but still.

 

[4X4HIGH]

Doing the math given a TRUE 32" tire and if you're positive about 2000 rpm's @ 60 mph then you have 4.56 gears. I would pull the rear diff cover and count the teeth on both the ring and pinion gear then divide the ring gear by the pinion gear to see exactly what you have. This combo would definately be the culprit of your fuel mileage.

 

[blazinzuk]

a 32" tire is going to throw your speedo off a bit.

Got a GPS, use it to measure miles. Or to measure how far off your speedo is.

4.56s with 32s and your speedo is definitely not reading correctly.

 

[K5dreamer]

www.fuelly.com

im signed up and use it for both my truck and my jetta. the home page has lots of tips on how to drive, and tips for best fuel economy. The number one method to improve fuel economy is the "right foot mod" by far.

swapping out those 4.56 gears for a set of 3.73's would do ya good. ive got 33in tires, a TH400 trans, and 3.08 gears... and a diesel. so i get 15mpg around town, and 21mpg or so on the highway.

but with a 700R4, you should be doing well better than your current mileage. a carbed 305 with super deep gears is not a recipe for great fuel economy im afraid. try and find a TBI setup at the junkyard and upgrade.

 

[Deuling]

Doing the math given a TRUE 32" tire and if you're positive about 2000 rpm's @ 60 mph then you have 4.56 gears. I would pull the rear diff cover and count the teeth on both the ring and pinion gear then divide the ring gear by the pinion gear to see exactly what you have. This combo would definately be the culprit of your fuel mileage.

tag says 3.73. Dif code IG80, locking dif. I know it has a limited slip because both wheels spin when she breaks loose. I really dought the guy would have put different gears in

 

[Deuling]

www.fuelly.com

im signed up and use it for both my truck and my jetta. the home page has lots of tips on how to drive, and tips for best fuel economy. The number one method to improve fuel economy is the "right foot mod" by far.

swapping out those 4.56 gears for a set of 3.73's would do ya good. ive got 33in tires, a TH400 trans, and 3.08 gears... and a diesel. so i get 15mpg around town, and 21mpg or so on the highway.

but with a 700R4, you should be doing well better than your current mileage. a carbed 305 with super deep gears is not a recipe for great fuel economy im afraid. try and find a TBI setup at the junkyard and upgrade.

Tag says 3.73 in glove box, with limited slip. I dont think its got 4.56's in it.

 

[4X4HIGH]

tag says 3.73. Dif code IG80, locking dif. I know it has a limited slip because both wheels spin when she breaks loose. I really dought the guy would have put different gears in

I learned ALONG time ago to never ASSUME anything. When you assume it makes an ass out of you and me.

How do you know you're doing 2000 rpm's at 60 mph? Did you use a GPS or your speedo? If using your speedo it is not correct because of the tire size change.