Changed plugs, why is gas mileage still low?

[Bigham]

Have eddie bauer 99, 4.0 SOHC. with 184K.

Was averaging 17.6 before plugs then it jumped to 21+ after I changed out my plugs and wires. One plug was so bad the silver tip had broken off the top part of the plug that goes into the boot, cleanded air filter and MAF sensor. MPG went up by 4 MPG the first few days and now it dropped back to the same MPG as before the new parts.

I Have not changed the fuel filter or the PCV valve yet.

Am i missing something that would keep the MPG from increasing?

 

[Blee1099]

The fuel has a additive that is only used during the winter months.. That could account for the drop in mileage. Check things like air pressure on your tires.

 

[Bigham]

been staying on top of the tire pressure since i just installed two new tires. I still reset my MPG on thr trip computer every few days and still no change

 

[MountainSplorer]

well depending on your reset for the milage interval with time, your millage will vary a ton. if you reset ever 2 days vs 5 your driving on the last day is going to effect the gauge different because its basing it off 5 days or 2. Also your driving habits and if its city, or highway, and what gear and rpm your cruising at, will chage a lot.

I get 16.5 going 38-43 b/c Im in 4th at 2100 rpms and at 45mph i get 19-20 b/c I'm in 5th at 1500 rpms.

It also depends how long you cruise in those speeds and when. Are you basing this off consistent driving patters and normal same places you drive?

 

[yavapaires]

Quit relying on the trip computer for one thing. Fill up, record mileage, fill up record mileage, figure it the old fashion way. Will give you a better( more accurate) reading. Do that for a month or so. There will be a bunch of comments about this, but, disconnect the battery for 10-15 minutes, reconnect and go for a 15-20 mile drive. This will reset the computer and let it relearn your driving habits. I am not sure it will belp, but it will not hurt either. And it is cheap.

 

[SoNic67]

My on-board computer is wrong by 1-2 mpg, no rime or reason....

 

[Bigham]

I have the same driving habits, mostly highway to work (70%) and around town (30%) as always.

Guess I just expected an instant jump since the old plugs were in such horrible shape when I changed them.

Would changing the fuel filter and PCV valve make any difference?

 

[2TimingTom]

Would changing the fuel filter and PCV valve make any difference?

Possibly. But I'd only expect a dramatic increase if the filter was in really bad shape.

The best thing to do to an Explorer for an increase in fuel mileage is a 4 cylinder conversion. It's pretty easy to do too. You park the Explorer and drive a 4 cylinder instead.

I bought a $1500 Saturn SL2 and drove it instead of my V6 Explorer. In the 11 months I owned it (just recently sold it) I saved an estimated $778.29 in gas by driving it over the Explorer- and yes, I kept track of each tank and created a spreadsheet to total the savings. That equates to an average savings of $70.75/month in gas. Insurance on it was less than $30/month. So for me (the more you drive, the more you save) I was saving $40/month.

And the best part- I had 2 vehicles to choose from every day.

 

[SoNic67]

Yep, but you increased the chance to get killed by another driver (in an Explorer). I think to the extra money spend on gas as life insurance.

 

[2TimingTom]

^^Most likely true. Because at least around here, Explorers are driven almost entirely by brain dead soccer moms on their cell phone while doing 80 mph with blown shocks and under inflated bald tires.

 

[drbenz]

First do the the other things on your tune up list then if you have access to a scanner check the fuel trims if not pull the plugs and see if they are burning clean. Check for any air leaks in the intake (they are common) and as a last cheap resort, pull the battery cable for a few minutes to clear the computers memory and see if that helps. Past that parts will probably be needed (mass air sensor, o2 sensors, etc.

 

[dcdyd]

Couple weeks ago I cleaned MAF sensor on my 98 EB 5L V8. I am not sure whether the PCM is accurate for the mileage or not. But just from the display the milage increased from 14.5mpg to 15.8mpg. I don't drive on highway at all.

 

[Bigham]

I had cleaned the MAF before the plug change and did not notice any difference

 

[swshawaii]

Have eddie bauer 99, 4.0 SOHC. with 184K.

Was averaging 17.6 before plugs then it jumped to 21+ after I changed out my plugs and wires. One plug was so bad the silver tip had broken off the top part of the plug that goes into the boot, cleanded air filter and MAF sensor. MPG went up by 4 MPG the first few days and now it dropped back to the same MPG as before the new parts.

One important detail you left out was the brand of replacement plugs used.
As we've read in countless threads, the 4.0 SOHC is very finicky when it comes
to plugs and gap, which is usually .054. Many have made this mistake.
If you used anything other than Motorcraft SP500 or Autolite 103 Series, you
used a "replacement" that may not be the recommended or ideal heat range.
Providing everything was installed correctly, check your under hood decal or
owners manual to confirm the correct replacement plug model and gap. GL

 

[Bigham]

man, I aint going in there again to change the plugs. That is the reason that they got so bad in the first place. Took a lot of beer and bribing my buddy to get it done over two nights!

 

[swshawaii]

Judging by your reply, you did not use Motorcraft or Auotolite.
What brand did you replace them with, and what gap? Bosch? :thumbdwn:

 

[Bigham]

I think I had autolites but I cant swear in a court of law. I did not gap them, m friend did. I can assure you the gap on the new plugs was much smaller than on the old used up plugs

 

[swshawaii]

Not uncommon to have more than a .080 gap from severe electrode wear.
Rather than guessing any further, pull the most accessible plug, and see
what's in there. If they are Autolite, chances are you have another issue.

 

[Joe Dirt]

Agreed- pull an easy one and see what's in there.

I really don't think your mileage is that far off anyhow... You're within the margin of error due to windy days, more traffic lights, and general loaf-of-bread aerodynamic malaise...

 

[joe doe]

Possibly. But I'd only expect a dramatic increase if the filter was in really bad shape.

The best thing to do to an Explorer for an increase in fuel mileage is a 4 cylinder conversion. It's pretty easy to do too. You park the Explorer and drive a 4 cylinder instead.

I bought a $1500 Saturn SL2 and drove it instead of my V6 Explorer. In the 11 months I owned it (just recently sold it) I saved an estimated $778.29 in gas by driving it over the Explorer- and yes, I kept track of each tank and created a spreadsheet to total the savings. That equates to an average savings of $70.75/month in gas. Insurance on it was less than $30/month. So for me (the more you drive, the more you save) I was saving $40/month.

And the best part- I had 2 vehicles to choose from every day.

hahahaha......funny you should say that .i did the very same thing .bought a 2002 saturn sc2 3 door coupe .that thing gets 26-28 mixed city/highway and up to 31 highway miles per gallon .
while my ohv 2000 ex sport only gets 15 mpg on a good day .i am saving tons in fuel .but i still love my explorer and cant get rid of it .i just dont drive it as much .