Fuel economy - bad to worse

Hi, my 01 TJ (4.0L Auto) seems to have lost whatever fuel economy it had before. Lately, I can only do about 300kms on a full tank. I am running 265/70R16s and an OME lift. These mods did not change the fuel economy when they were done two years ago. Could it be that the O2 sensor has gone bad? There are no error codes or check light coming up. Every thing else feels/runs fine. Any ideas?

Thanks TW

Reply to
TW
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Tire pressure, air filter, spark plugs, dragging brakes, diff lube, ATF...to start..

Reply to
billy ray

Billy,

Tyre pressure checked every week (running at 30psi), air filter replaced Dec '05, spark plugs replace d Dec '04, front brake pads replaced two weeks ago, diff oil changed Dec '05, ATF changed Dec '05. Any other ideas?

Thanks TW

billy ray wrote:

Reply to
TW

Your new brakes aren't dragging are they?

What about the parking brake? some times the cables seize...

Check the plugs... although if they were mis firing regularly you would get a p030x code..

Pull off the intake resonator and take a look at your throttle body, It might need a cleaning with spray cleaner and an old toothbrush.

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The injectors might be a bit sticky, a can of Seafoam or Techron in the gasoline might help

Be careful if you go to buy Techron. They make Techron Cleaner (pure stuff) and Cleaner with Techron (diluted stuff), you want the pure stuff. Both retail about $6-$7 (us) per bottle

You don't let your wife or teenage daughter drive it do you?

Do you have neighborhood youths who might be siphoning it out?

What about a gas tank or gas line leak?

Have you changes *brands* or octane of gasoline? It can make a difference.

The last thing that comes to mind at the moment (it is 3:30 AM here) is driving style....... has that changed? It can alter your mileage 30-40% per recent tests.

Reply to
billy ray

Reply to
L.W.(Bill) Hughes III

O2 sensor drift can cause lower milage. I have noticed that as well. The problem is the drift is so slight it's hard to tell without being anal with the records.

For example. :)

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The pdf is just a chart of date/mpg and date/fuel cost.

the spreadsheet has all sorts of stuff in it. Need to update a few things.

Reply to
DougW

Tune up time?

Lots of folks forget about the distributor cap and rotor....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

It could be the recent change in the fuel formulas. Don't know if you are running the same thing we are here in the states, but the new fuels decrease your mileage and sometimes as much as 5mpg like it did in our Liberty.

Kate

Reply to
Kate

An 01 TJ is distributorless there oh great "technician"

Reply to
Simon Juncal

That's right, losers always come out with the insults. Calling me a 'technician' now, ouch that hurts....

Mike

Reply to
Mike Romain

What in the world are you saying here?... On the first score, you started with the insulting in the other thread, on the second score: do you not understand what sarcasm is?

You're a great help to a lot of people here over the years, I've nothing against you personally except for the kooky fact that you think the Carter BBD is better then anything created after it, inlcuding fuel injection and several other much better working Carbs, like the popular motorcraft and weber 2bbl swaps.

Reply to
Simon Juncal

Reply to
L.W.(Bill) Hughes III

New Zealand uses RON Octane ratings, we have 91 (regular) and 95 premium. Owners manual says to use 91, which is what I use. Normally I go to Shell, Mobil or BP. At this stage, we don't use alcohol in our fuel. I will try to stick to one grade from one supplier and then switch and see if that makes any difference.

TW

L.W.(Bill) Hughes III wrote:

Reply to
TW

Brakes were done two weeks ago, fuel economy went south about 3 months ago. I might change the plugs and air filter and see that makes any difference. Cleaning TB is also a very good idea. I have a locking fuel cap.

Thanks for all the good ideas. TW

PS: no teenage daughters > Your new brakes aren't dragging are they?

Reply to
TW

It has fuel injection with no distributor (uses three coils on the rail). Total mileage done so far, 63k kms since new.

TW

Mike Roma> Tune up time?

Reply to
TW

It could be that, I will try switching it to a different rating and company and see if that makes any difference. NZ uses RON, where regular is 91 and premium is 95. I use 91 from Shell, Mobil or BP.

Thanks TW

Kate wrote:

Reply to
TW

Well, I was never anal with my record keeping. But I do know that I used to get around 425 kms per gas tank, which is now down to around 300 kms. Do you think that could qualify as O2 sensor drift?

TW

DougW wrote:

Reply to
TW

We used to use RON here, .... before unleaded gasoline came out. The typical values were 94-95 for regular and 100-105 for premium as I recall.

Nowadays we use (RON + MON) / 2 and typically have values of 87 for regular,

89 for mid-grade, and 91-93 for premium. (octane requirements vary with altitude)

MON measures high speed knock and RON measures low speed knock and the rating formula change was supposed to give a more accurate overall report.

However...... at the same time the rating formula changed people started having drivability problems with the gasoline that the manufacturers claimed had not been altered.

I think most people assumed that the new measurements was an attempt to hide that for the first time gasoline quality was taking a step backwards..

Reply to
billy ray

Did the mileage drop happen at the same time as the start of 'Winter Blend" gasoline?

Reply to
billy ray

Yes, easily. Alas there is only one real way to test an O2 sensor, and that is with an expensive test rig or a datalogging scope. :/ On the bright side if you put a new one in there and nothing changes, you then have a spare.

Also, any cracked hoses, especially between the intake rail and MAP sensor. You will know this when the vehicle refuses to accelerate well unless you go wide-open throttle. Easy enough to find with a can of carb cleaner. spray and listen for engine stammer.

With the coil system you have it's important to keep the plugs gapped identically and clean. one plug out of whack will cause the sister plug to have problems.

Another thing to be on the lookout for if you have spark problems is the rail shorting out. I've seen one where the rail arced out internally and was frying coils. (doubt you have this problem) But it's still worth knowing. Another reason to keep up with the spark plug maintenance.

Reply to
DougW

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