God Awful MPG

[mastermoose]

So I have a 1998 explorer with the 4.0 sohc with 120k miles on 33s with I think 3.73 gears. I get like 7 miles to the gallon with city/ highway driving. I don't drive the truck that often but Jesus when I do its like burning money. I never regeared because I'm putting one tons in it anyways, but does anyone have any advice to solve this? I have a vacuum leak at the vacuum ball so I gotta fix that. It has a cold air intake and a stock muffler. Should I change spark plugs? Fuel filter? Sea foam? Any help would be greatly appreciated.

 

[FPGT24]

The 33's are a big part of the problem! With 31's on my 98 SOHC i was getting a pathetic 14mpg average. So that is likely the biggest cause. However, I'm sure some new plugs/wires would be of some benefit. Check your intake plenum gaskets, the way to tell if they are going out is a tough time getting the engine started when its cold or if it has a rough idle, and sometimes a CEL "lean" code.

run a few bottles of Marvel Mystery Oil through the fuel system and try a bottle of seafoam (or at walmart you can get a walmart supertech brand of it for less than 5 bucks and its GREAT stuff) through the vacuum line on intake from the brake booster.

 

[Glacier Explorer]

How are the pressures in your tire? Too low and it could cause a lot of added friction. I am only on 31s with 3.73 gears and 4.0 SOHC at 204k miles, and I still get 15 city, 18+ highway. Pulling an enclosed trailer brings me down to about 12, and that is with OD off too. Definitely check you plugs and wires. Check the tire pressure. And check to make sure you don't have a seized caliper or stuck e-brake. Is it throwing any check engine codes?

 

[mastermoose]

No codes. It does idle really low (~500 rpm) and kind of funny (it will rev itself up to like ~750 rpm and then drop back down to 500 on occasion) but I think that's from the vacuum leak

 

[FPGT24]

Intake plenum gaskets are probably shot, which would be a vacuum leak. Change them. They are cheap, and it's easy.

 

[mastermoose]

I was really hoping you'd tell me I just had to hit something with a hammer or fix a wire or something, but this is simple enough too. Thanks for the advice! Ilol get it done this weekend.

 

[FPGT24]

No prob. Let us know if its changes anything.

 

[Spoon91]

Have you looked for a large hole in your gas tank?!?!?
Dang Brother my '97 2WD 5.0L with 3.73 gears, 3in lift and 33's gets 14/15 City/Highway.
I would B!t€h about my MPG before Reading your post.....I'm going to go home and give my old girl a big hug and kiss for doing so well LMAO.

 

[FPGT24]

Have you looked for a large hole in your gas tank?!?!?
Dang Brother my '97 2WD 5.0L with 3.73 gears, 3in lift and 33's gets 14/15 City/Highway.
I would B!t€h about my MPG before Reading your post.....I'm going to go home and give my old girl a big hug and kiss for doing so well LMAO.

Damn son. My 5.0 only gets 14mpg on a good day! Its mostly stock except for lift shackles.

 

[1997XLTRollover]

7 is pretty bad. Your tires are certainly what killed most of your MPG, but you should be getting at least 9-10.

 

[mastermoose]

Yeah it's pretty awful having to hit the gas station everyday. Hopefully tracking down the vacuum leak and doing the intake gaskets helps

 

[1997XLTRollover]

Yeah it's pretty awful having to hit the gas station everyday. Hopefully tracking down the vacuum leak and doing the intake gaskets helps

Oh I hear ya. I get 9 MPG in the winter months. That vac leak will probably bring back some power and MPG if it's bad enough.

 

[Fredness]

Wife is getting 12mpg on E85, 32's and 4.10's [Edit: on a 4x4].
Yeah, 2nd the intake seals - PM me your snail
mail - I have a set I'm not going to use and it's costs more to mail them back than I paid for them....

 

[1997XLTRollover]

Wife is getting 12mpg on E85, 32's and 4.10's.
Yeah, 2nd the intake seals - PM me your snail
mail - I have a set I'm not going to use and it's costs more to mail them back than I paid for them....

Even with 4.10s you're getting 12? That doesn't sound right either haha. Did you ever calibrate your Speedo after the 32's?

 

[CDW6212R]

Fix the vacuum leak or leaks, that is huge because it screws with the computer and air/fuel ratio. A tiny leak wouldn't affect the idle or mileage, but it sounds like more than a tiny leak.

The computer usually throws an error code when the intake gaskets leak enough, and that often doesn't affect the mileage(when it's enough to create the error code(light one)). So if you don't have a lean 0171 code etc, the gaskets probably aren't that bad.

Give it a thorough tune up, it's something in there or the vacuum leak, or very heavy wheels and tires. What does the wheel and tire weigh? Stock is in the 55lbs range, if you have 75lbs then that's a bunch harder for the engine to accelerate.


The 33" tires do hurt the mileage some, but that's minor compared to the loss you report(7mpg versus high teens it could get). Divide 33" by 30", and multiply that by the gearing in the diff. That's ideally what your gears should be with those tires. For a 3.73(you might have 4.10's(most 4WD SOHC's had those)), I get 33/30*3.73=4.103 gearing. The 33's aren't that bad for gas mileage, unless the truck had 3.27's etc. Check your door VIN tag, what's the "axle" code?

 

[Fredness]

Even with 4.10s you're getting 12? That doesn't sound right either haha. Did you ever calibrate your Speedo after the 32's?

E85 (Ethanol) is a 30% ding in MPG (the wife driving is another 30% ding) - I routinely get 18-21 when I drive on E10 (Gasohol).

[Edit] Speedo calibrated to a gnats nard using GPS and revs per mile in the tune.

 

[CDW6212R]

E85 (Ethanol) is a 30% ding in MPG (the wife driving is another 30% ding) - I routinely get 18-21 when I drive on E10 (Gasohol).

That's a good name for this crap we're all forced to use now. Let's force the use of corn for our vehicle fuel, and thus force all food prices higher(corn is in most foods). Thanks for that dumb idea. I've had to R&R two gas tanks in the last ten years because the gas is no good after a couple of years. I fortunately have a pure gas gas station nearby, I often go there when the price is within 20 cents per gallon. Right now it's $2.05, with fake gas at $1.96 or so around town.

 

[1997XLTRollover]

E85 (Ethanol) is a 30% ding in MPG (the wife driving is another 30% ding) - I routinely get 18-21 when I drive on E10 (Gasohol).

Ahhh ok I had a feeling that was the case.

 

[FPGT24]

Theres only one REAL gas station in my area that has actual 100% real gasoline, but they are nearly a dollar more a gallon than the ethanol mix so it isn't worth it. Ethanol = destruction of older cars PERIOD.

 

[CDW6212R]

The real gas is so rare it is like a different product. I say that because what that means is the pricing will fluctuate differently than the other gas. I asked this place near me why there's is sometimes $0.20 per gallon different, and other times it may be $0.40 more. The pricing is not tied to other gas prices, it sounds like they make batches less often, and depending on conditions at that time, the prices will wildy change.

So keep an eye on all stations to find the pure gas, and then watch those prices very carefully. They may sometimes be well worth it to buy the real stuff. Mine here has been as close as 5 cents different for a couple of weeks. The gas station doesn't control it, and it looks like for now they don't change the pure gas price based on the how the rest is priced.