Thinking about replacing o2 sensor

[rustyboltz]

This past 2 years I have replaced and fixed most everything on my X and the MPG has not increased. The MPG has remained constant at 13 and I am wanting to get it up to where everybody else is saying that they are getting.
Anway, the only other part that I can think of that I have not replaced is the o2 sensor on my exhaust. It is at least 2 years old and probably is quite a bit older than that.
Would you recommend that I change it?

 

[wood1]

Only if it's no good. My '93 has the original O2 sensor(s) in it. Have you checked for codes? What have you replaced thus far? You have to approach any problem with a plan, it'll just cost you unnecessary money if you arbitrarily throw parts at it.

 

[Roadrunner777]

An 02 sensor can fail, producing codes. They also get old and react less quickly to changes in the exhaust stream. Unfortunately, OBD-IV, our engine system, does not give us information on this. You can see this on newer diagnostics with charts and all kinds of useful information, but our older system simply doesn't tell us. (Yes, maybe with an oscilloscope and some deep experience, not sure!).

Ok, this gets meaningful because the engine runs after warm-up, in closed-loop mode, meaning the O2 sensors feed back info to the fuel injection, basically fine-tuning the injection pulse. So, it is better to have O2 sensors that react quickly.

Will new O2 sensors help MPG? Maybe a little bit. Should you change them? The payback probably is not there. But, you may be the type of person that wants to change them just to have it out of the way. I'm like that.

You have already read plenty on MPG, I bet. So, very briefly: Driving habits, gearing, in/out of 4x4 mode, primary maintenance (plugs, wires, MAF).

After that, it may be advisable to figure out potential gain. Synthetic fluids should help, a little bit. What does it cost to convert to synthetics? A manual is more thrifty than an automatic. What does it cost to convert to a manual trans?

I'm doing my O2 sensors next year in search of a smoother idle (intake bolts, yes, I know), and frankly, just to get it in the books so I know what I am driving.

But, to me, a warm afternoon working on my truck, that's my candy, it's my therapy. So, that's just me. I just replaced my plugs with the factory spec Motorcraft double platinum, not the finewire, the originals. I have two more sets of those same plugs sitting on the shelf waiting for these to wear out in another 5 years. That's just how I roll.

 

[rustyboltz]

I bought the X 2 yrs ago and it would barely run. Since then, I have replaced the fuel pump and sock, fuel filter and FPR, flushed the engine radiator and heater, changed the thermostat, spark plugs (with autolite brand) 8mm spark plug wires re torqued the upper and lower intakes, replaced the cats, replaced all u joints and checked and topped off all fluids.
As I accomplished some of these things, she started to run better and better.
But I am still only getting 13 MPH. I have even checked the auto tranny that I have and it is good. I can do 60 mph at 1500 rpm. I can do 70 mph at 1900 rpm. I have read someplace that the o2 sensor can change the electrical signal to the fuel injector and I was thinking that maybe it might be getting too long of a electrical signal. For the past 6 months, I have not had a code. Ihave checked it every week and no code.
Maybe I should be happy with 13 MPG.

 

[wood1]

Clean MAF and replace air filter would be a good start.

 

[RangerX]

Accurate speedo/odo? A change in tire size or a regear will throw it off...

 

[rustyboltz]

I have cleaned the MAF and throttle position sensor several times recently. I have not replaced the air filter because it still looks white and clean. I have compared the speedo with my garmin and they are within 2 mph. I was thinking that maybe I should check the compression of the engine to see how much I have. The vehicle registers 136,000 but I have found out that the engine in it is from an van.

 

[Common Cents]

Since then, I have replaced the fuel pump and sock, fuel filter and FPR, flushed the engine radiator and heater, changed the thermostat, spark plugs (with autolite brand) 8mm spark plug wires re torqued the upper and lower intakes, replaced the cats, replaced all u joints and checked and topped off all fluids.

Did you replace the thermostat with a new one for the same temperature? Or when you "changed the thermostat," did you install one with a lower temperature rating than the original?

On modern, electronically controlled engines, cooler thermostats will often cause fuel economy problems because the engine computer tries to "warm up" the engine to full operating temperature and doesn't know that the thermostat has been changed with one 15 or 30 degrees cooler. This results in excessive enrichment, trying to "warm up" the engine.

Also, what is your methodology for measuring your fuel economy? Explain how you come your 13mpg figure? Often when discussing fuel economy issues, I'm amazed at the "creative" ways people come up with fuel economy estimates.

The 1993 is rated at 14 city/18 hwy for the 4.0 V6/automatic transmission/4WD model. 13mpg isn't that far off, really, especially after 18 years.

Fuel economy depends a whole lot on the driver and even on the driver's attitude. I have driven the exact same vehicle, under different conditions and with different attitudes, within a 24 hour period and had fuel economy measures that were significantly different. The most pronounced were some weekends back in the 1980's when I drove a small, economy hatchback. I could get 34mpg on a couple of tanks, and less than 12 hours later, get 7mpg (yes, that 07mpg) for a few tanks of fuel. Then at the end of the weekend, gas it back up and get 34mpg again on the way home. There were some minor changes to engine tuning settings (timing especially) between the 34mpg runs and the 07mpg runs, and also a big change in attitude. Also a difference in loading, with a much heavier load for the 34mpg runs (by over 600 pounds).

So, YMMV as always.

 

[Roadrunner777]

Mileage is a very common topic here... I'd suggest reading everything Aldive wrote here (he passed away a while ago, but he was absolutely devoted to mileage gains).

 

[rustyboltz]

The way I arrived at the 13 mpg was to just drive it like the normal person that I am and to set the trip odometer when I fill up. I then take the gallons and divide by the miles driven to arrive at that figure. I realize that my driving would probably have something to do with a few miles per gallon. I use this vehicle to drive to work and to drive around in. The only time I will use the 4 wheel is during bad weather that we have here. I thought that after 18 years of use/service, I was thinking that maybe there were some other parts that could be worn that if replaced could make it operate at its prime.
I have read all the threads in this forum and have learned alot and have used alot of the info.

 

[JTH1972]

I've been chasing a similar problem with my '94 for about a year now. I started with 17 mpg, but after a couple of months, it suddenly ran rough and dropped to around 13 mpg. I must admit, I haven't thrown as much money at it as you have. I did most of the basic things and decided that after that it wasn't a simple chase and beyond my diagnostic capabilities. Tested the FPR before replacing it ($60 tester vs $180 part) and that's about the furthest I got. Anything after that and I knew I'd be chasing a ghost and sinking a lot of money into something with no guarantee it would be fixed. Reset the computer ac ouple of times and it ran OK but not great. My FIL (with his freakishly acoustic ear) said he thought I was missing on a cylinder, but it wasn't running bad enough to be that obvious.

Yesterday, I finally (re: stopped procrastinating and got off my ass) got it into a shop with better equipment (and knowledge) and got them to stick it on their computer. Turns out my FIL was right! I had a dead cylinder from the coil. I've been running on only 5 cylinders without it being obvious. Apparently my Exp was the talk of the shop. No one had ever seen a vehicle run as smoothly as this one has on only 5 of 6 cylinders! They recommended replacing the coil and ignition module (which I'm working on). No guarantees this would be "the" fix, but it's an obvious problem and a place to start!

 

[Common Cents]

You're doing the math right on the mileage. Sorry to doubt you there, but I used to work in a dealership (Parts manager, before that service writer, before that tech) and I've heard every kind of mileage complaint you can imagine. In my experience, only maybe 1 in 5 people who I asked, "How many gallons did it take to fill it up? And how far did you go before you filled it?" could answer with actual numbers.

As for the 4WD thing, just having 4WD knocks off a couple of MPG compared to the 2WD models. Even if you never engage 4WD, you're still carrying around a transfer case (with some rotating parts in it even when it's "disengaged"), a front drive shaft, a front diff and housing, heavier front swing arm beams, possibly heavier front radius arms (I haven't compared them). It takes more fuel to move all that weight around. On top of that, I think the 4WD models had shorter final drive gears (higher numbers on the ratios), though I'm not 100% certain of that.

As for driving, pressing either pedal uses gas. Most people don't realize it, but if you can avoid the brake pedal, you'll use less gas. Whenever you use the brakes to slow down, you'll probably use the gas to get going again. Leaving more following distance, and coasting when you see a red light ahead that will be red when you get to it both save gas. Coasting to red lights saves a lot of gas.

On my 1994, I haven't driven it much. It's a 4WD model. I've been getting around 15mpg in mixed city/rural driving, and on the one long trip I've made, I got right at 20mpg, but that was on 2 lane back roads with the thing cruising at between 50mph and 55mph.

Also, I'm not sure my "miles" are exactly a mile. Not sure what gears I have, but I have 31x10.5 tires on it. That adds a couple inches to the tire diameter over the stock size. I doubt the speedo/odo has been corrected for this.