help!!!!! lot of work mpg still bad

[booo66]

96 xlt cont trac 4dr 129,000 ..4.0
ive done everything i can think of... cleaned maf, throttle body, new air filter, new pcv, new fuel pump (needed), new fuel filter, new egr sensor , new bosch oil filter, went to mobile 1 syn (0-30) oil , 1 sea foam through the pcv and 1 in the tank , 2 or 3 gas treatments, stock tires to 45 psi (50 psi on the tire wall) (30-9.5 futera) they look pretty aggressive though...and 7 days ago new motorcraft plugs and wires (old autolite plugs looked great but were gaped at 44 ...new ones I gaped at 54) trans fluid looks and smells good (i dont know the history of the trans ive only had it about 8 weeks but it feels good) brakes dont seem to be hanging up ..... AND IM ONLY GETTING 12 MPG I THINK I LOST 1 MPG SINCE I DID EVERYTHING........... WHAT THE FLOCK IS GOING ON HERE ............it runs great now and i dont do that much hwy driving but this sucks for a v-6 ........I had a 91 before this with almost 300,000 on the clock and ran like **** but I was getting 14 mpg....... with the same type of driving ..cold starts kids to school, trips to the store etc...ive got no codes but the only thing i can think of is o2 sensors if so whitch one or is this the best im going to get here in chicago in the winter...........HELP is it the tires or something else........................

 

[Willard]

You say you have 30" tires, what gears do you have? That could be contributing to the gas mileage.

 

[Limited02]

Did you change the oil in the catalytic converters?

 

[booo66]

ls 3.73 and i didnt know about oil in the cat

 

[Willard]

Did you change the oil in the catalytic converters?

Stop being a smartass. Unless you are serious, in which case you are horribly mistaken.

ls 3.73 and i didnt know about oil in the cat

Since you have 3.73s you mileage shouldn't be that bad. Are you certain there are no codes? Even without a CEL triggered there may be codes stored.

 

[booo66]

just 401 and that went away after the egr sensor was changed

 

[Willard]

Hmmmm...the only other thing I can suggest is to disconnect the battery to reset the computer if you haven't. Hopefully someone else can chime in with a little more advice.

 

[booo66]

i changed the pos battery clamp do i have to do the neg to reset the computer

 

[Limited02]

Stop being a smartass. Unless you are serious, in which case you are horribly mistaken.

Easy partner, didn't mean to get your panties in a bunch! Yes, I was just kidding.

It is possible that one of the 02 sensors could be going bad causing your engine to run rich by feeding the engine a little extra fuel. Another thing to look into is the clutch fan. The one on my 89' mustang had worn out and locked up. I ended up changing to an electric fan and it ran stronger, smoother and the gas milage picked up some too. Your 96' is also heavier than your 91'. If you are like me and always out accelerate everyone from the stop light, then gas milage will go down the drain.

 

[IZwack]

Other thread deleted, booo66 - dont double post.

 

[Verno]

i changed the pos battery clamp do i have to do the neg to reset the computer

Whenever removing a battery connection to reset the computer the NEG cable is removed to disrupt the electrical path. In theory, removing either should do the trick; however, with todays computer controlled vehicles you should always remove/disconnect the negative cable.
As for MPG, mine is running 2MPG lower in the winter than in the warmer months most likely since I don't have to warm up motor/defrost/etc during non winter months. I know when I grew up in IOWA we always saw lower MPG figures over the winter months, and Dad's shop had lots of winter oil changes, cooling service then spring oil change & tune up service scheduled.

 

[Limited02]

Isn't also possible that in the winter, fuel company's blend their fuel a little different to compensate for the cold? TTherefore having a negative effect on gas milage?

 

[Willard]

Isn't also possible that in the winter, fuel company's blend their fuel a little different to compensate for the cold? TTherefore having a negative effect on gas milage?

That's a valid suggestion, however his mileage is worse than the gas causing it alone. In the middle of winter using winter blend fuel and driving around almost entirely in 4wd I can still manage to get 14 mpg or so. I've never gone below 14 that I can remember, and I've driven it with a half working transmission running on 5 cylinders.

 

[eXcali]

I think this is one case where I would look into the O2 sensors. As I said in the thread that got deleted, the life on these is supposed to be around 100k. I believe there's also a couple of ways to check them with a multi-meter and scantool. If it was out completely it should be throwing a code, but if just on it's last leg it could be causing it to run slightly rich. With an O2 issue you can see up to a 10-15% drop in MPG.

 

[booo66]

whitch o2 sensor do icheck there are 4 of them right

 

[jlsparky7]

Couple things you could try.

Extremely low or warn out differential fluid will make you take a MPG hit.
http://www.youtube.com/watch?v=CAiy8CN1JdE

Check for intake and exhaust leaks as well, both will MAJORLY mess up mpg.

Also compression test all your cylinders.

 

[jlsparky7]

whitch o2 sensor do icheck there are 4 of them right

Generally the 02 sensors before the cats are the ones that go bad first. Its a good idea to replace all of them at once though.

 

[Zero Signal]

I disagree with replacing all of the O2 sensors at once. You should have a total of 3 O2 sensors on your 4.0L. Two will be upstream of the cat, and one behind the cat. To just arbitrarily replace all three could run you $150-$180.

You can check their functionality with a digital voltmeter so you know which one, if any, need replacing.

I've cleaned O2 sensors with QD Electronics Cleaner in the past as a preventative measure.

The compression testing that was mentioned in another post is a good idea, especially considering the mileage.