Temps play a big role in my mpg.. now that it has been in the mid 30's at night compared to mid 50's two weeks ago i went from 20-21mpg to 18-20. i drive 85% highway and 15% city. nothing changes for me. the colder it is the more fuel you are going to burn and it doesnt necassarily have to do with the fuel itself. if you are getting 17+ on stock then you are ok i think.. these damned things arent known for gas mileage for sure.

 

The tires will make a difference. As stated earlier, your larger diameter tire will show a lower odometer reading. It will be just over 3% lower than what you are actually driving. So your 240 mile reading will be closer to 250, in actuality. Also, the change in tire size added some weight to the truck in the worst place possible. Not only does the engine need to move the extra weight but spin it as well. 6lbs per tire is what the difference is between the two revo sizes. So an additional 36 lbs to turn. Expect a slight decrease just for the tires. I'm sure it doesn't explain the full 50 mile per tank drop, but it will account for some of it.

My truck has 35's on it and my speedo and odo are reading 10% lower than actuality. Plus another 22lbs per tire over yours. If I calculated my mileage based on what I'm reading, I'd be getting 12-13mpgs, when in fact I am acheiving a whopping 14-15mpgs or about 200-215 miles per tank. 240 would be dream for me.

Cheers

 

so i searched through the forums and found some things i could fix before i take it to the stealership. i replaced the front O2 sensor, pcv valve, spark plugs and fuel filter- still craptastic mileage. i get around or just over 200 miles per tank. when i bought the truck about a year and a half ago- i was getting 312 miles per tank on the hwy... how i miss those days...especially with how we get raped at the pump's in Canada. suggestions anyone?


98' 4runner

 

Clean the injectors and the throttle body check air pressure in tires

 

oh yeah- forgot to add to my list of things done already- cleaned MAF, throttle body and air pressure is tip top.

 

would plug wires have a negative affect on mileage while still running smooth and seemingly normal?

 

Tires, new tires and accurate pressure helped me a ton!

 

Also replace the rear O sensor.

 

I changed my plugs (NGK worked better than Denso for me), replaced the wires (OEM from dealer), changed the fuel filter (OEM dealer), and converted to synthetic motor oil (Penzoil). The combination of these - although I can't say how much for each - has helped my mileage quite a bit. Good luck.

 

i have a 98 4runner which went from decent fuel mileage to crappy mileage a few years back. was like an overnight change. i have since replaced the usual suspects and it still has bad fuel economy. i was told by a shop that the cat might be plugged as its probably starting to rot. i pulled the O2 sensor and ran it around the block to notice if it ran any better, which i am not sure about. My question for you guys is, If i run a full tank of gas through the 4runner with the O2 sensor removed, am i going to have any problems (other than noise complaints from the neighbors). just want to see over the course of a tank if my mileage improves or not

 

Easy enough to pull the cat off (assuming it is the stock bolt-on type) and look through it. I had a clogged cat and you could only see though in the very center in an area about the size of a quarter dollar coin. Just hold it up to the light and look through the honey comb and see what it looks like. Granted you'll not be able to inspect the full face of the cat, only what you can see through the flanges, but they seem to plug up in the center last.

Running w/o O2 will make the ECU add more fuel to the engine to avoid it running too lean, so mileage will likely drop (if the sensor is good) or make little change (if the sensor is already bad), but it would be very unlikely to make it improve.

 

the cat looks like it is one piece that extends up beside the engine to meet the manifold... i could be wrong- will have to check again

 

Is there any rattling noise coming from the cats....cause that could mean that its time for a new cat

 

If the catalyst has broken it will rattle if you hit the case with a dead-blow hammer. Also when you go to give it gas the engine will bog down and have little or no power since the catalyst moves and blocks the exhaust. As others have mentioned, try to look at the catalyst if possible. If the cat is bad but isn't broken it will usually set a check engine light with a P0420 code. There are many other things that will affect fuel mileage too...fuel filter, tune-up, MAF, O2 sensors, etc. What kind of mileage are you getting?

 

alright- im at my witts end with my 98. this thing has been gutless with horrific mileage for 3.5 years now. i have chased all the usual suspects (see here)
https://www.yotatech.com/forums/f2/b...-money-154309/

and the cat is fine. when at highway speed and engine is under load (up hill or accelerating) if it does pickup rpms, its ever so minimal until it hits 3500 rpms and then its like a 2 stroke hitting the power band. If i staple the pedal to the floor it will scream and redline and only then it will respond cause it knows im pissed at this point or something. Any ideas.... besides sell it?

 

My MAF went but seem to read fine when the mechanic tried to diagnose my problem. My 99 was always slow to respond. The new MAF got it to respond much better, the engine sounds much better and it drives a lot better. Milage didn't get better as I just drive faster now

 

Have you with some help checked that your throttle linkage is adjusted correct.

Do you remember if anything happened when this all started??

I would guess you changed the air filter though it was not mentioned .

When you say you lost around 100 miles of travel per tank of gas .

Did you check the miles per gallon or just look at the trip meter when you put in gas.

I had a friend who had a sending unit going bad and thought her mileage was also going down hill .

With my big wide feet I sometimes press more on the transmission tunnel then the gas pedal and get to thinking the truck is running like crap.

I can throw a 1000 pounds in the bed and the climbing of hills is not effected . Stopping one has to be a little careful.

Good luck I hope you can figure it out

 

the thing pings like crazy under load- uphill or accelerating on the straights. noticeably gutless driving everywhere in all conditions.

 

I would kill for 500 kms per tank, even for 400. When I first got my 4R a few years ago I managed about 400-440 kms per tank on the highway. Scince the lift and tires (285/75 MT's). I now only squeeze 375 kms on the highway and 280-320 in the city. I have also done all the maintanence, plugs, filters etc......well at least it has power, coming from a previous 3.0 3vz...