Declining fuel economy in 2.4l 2wd 1st gen tacoma

I've noticed over the last year or two that my fuel economy has dropped off about 5 mpg on average. To the point I'm getting between 19-23 mpg, instead of 25-30. I'm up around 260,000 miles on this 2001 2wd 2.4l manual Tacoma.

I don't believe this is related to tires and I haven't done any mods to the truck.

I've recently serviced brakes (nothing stuck, wheel bearings seem good). I change air, oil (synthetic), and fuel filters at regular intervals. Spark plugs, PCV valve, differential and transmission oils, alignments also. O2 sensors are original, as are catalytic converters. No check engine lights. No indications of engine problems.

I understand an aging vehicle will lose mpg, but given how abruptly fuel economy has dropped off, I think this is related to engine/sensors. I would be grateful for some suggestions on what might be causing this change.
Thanks

 

You should do a compression check to see where the engine is health wise.

 

Have the exact same car except with the automatic 140k miles. My fuel economy has been very rough as well. I have done everything you have with the exception of the fuel filter and PVC valve. But I have changed both the upstream air/fuel ratio sensor and the downstream O2 sensor. I had the check engine light on for it but no change in mpgafter swapping them. My everyday fuel economy which is 100% city is around 17mpg. My most recent fuel up was 100% highway on a trip to the keys and I got 24.8 mpg which was the absolute best ive ever seen. I'm wondering if my fuel economy is due to the city driving or if its something we're missing.

Here's my mpg records:
http://www.fuelly.com/car/toyota/tacoma/2001/doorchore/355338

 

o2 original? I'd it is I'd probably replace it with an oem sensor. ..when was the last time you cleaned the mass air meter?

 

^^^
Yeah, that.

Changing your upstream O2 sensor (replace with OEM), cleaning your mass airflow sensor, and having your injectors cleaned and flow matched are the top three deeper things (beyond ordinary maintenance) for keeping fuel economy optimized. I saw about 1 MPG increase when I did each of those.

 

Thanks, for the advice.

I'm not sure when I'll get around to a compression test, but its on my list now.

Is it normal that the MAF sensor, 02 sensor, could be off without triggering a check engine light?

I took a look at the MAF sensor today and it was dirty. I'll report back on what improvement I get from cleaning it.

Any other things I might want to consider?

 

Why would it be OK to just replace the upstream sensor? They are pretty pricey, it'd be nice to only change one if the MAF cleaning doesn't do it.

 

The upstream O2 sensor's reading (along with the MAF sensor reading) is used by your truck's computer to calculate the air/fuel ratio that is provided by your injectors. If it's off, you could be running rich or lean. You can be off pretty significantly on either one and not set a code but still experience decreased fuel economy. That O2 sensor reads less accurately over time due to carbon buildup and wear and tear.

The cheapest solution I've found for replacing them is ordering the Denso brand one (same as OEM) through Rockauto.com.

The downstream O2 sensor's job is to determine whether your catalytic converter is functioning properly. It has nothing to do with fuel mix and therefore with MPGs. Unless you get a P0420 error code or fail a sniffer smog test, there is no reason to replace the downstream one.

 

Thanks, good price there, I ordered the sensor.

I'll see how this and the MAF cleaning improves mpg.

The injector cleaning you mentioned, what would that involve? This typically done at a shop? What cost could I expect?

 

Yes the mag sensitive gets dirty esp if you have a k+n style oiled filter

 

Indeed. I've used an oiled K&N filter for nearly the last 200,000 miles.

 

Why is no one pointing out that the OP could only be getting 25-30mpg if he had been driving downhill all his life?

If you searched before posting, you would find 19-23mpg is average to good mileage for your truck with typical use. As well your truck is 15 years old with over a quarter million miles on it. Just sayin.

 

True. That is why I posted the suggestion of a compression check.. If the O2 sensor is out of parameters........the check engine light will illuminate.

 

25-30 is about what I used to get in summer;
This is the truck's mpg ~140k (day of year 1= Jan 1; 200= July 18). Mixed driving, mostly highway.
I still keep track of mpg, thought I haven't made time to enter it in a spreadsheet the last several years.

So you disagree that the sensor (02 or MAF) could be off enough to affect mpg, but not throw a check engine light?

I agree that the compression check would be very informative (and I'll get around to it), but on the other hand, I'm not going to rebuild the engine...if compression is well below spec, then that's my lot. Regardless, I'll still consider other cost-effective ways to improve my mpg (like replacing the original 02 sensor/cleaning the MAF), before I eventually sell/scrap the truck.

Anyhow I appreciate everyone's feedback.

 

The 02 sensor should be replaced every 100k miles regardless if the engine light in on. So if you have the original, you are waaaaay over due for a new one. But I don't think that it is the cause of the MPG decline. A simple change in tire style, brand and size can drop the MPG's.

 

Changing tires definitely complicate things (as does tread wear). I've noticed this in my mpg records, even though I've kept the same size and similar style tire throughout the years.

I'll have the same tires on this winter as last, so should be able to observe what my little tune-ups do to fuel economy.

 

You have to pull them out, which is a bit time consuming but not too big a deal. There are services that will clean them all for around $100 if you send them off. If you can't be without your truck that long, you can order a clean flow matched set for $200 from LCE:

http://www.lceperformance.com/2RZ-Equalized-Fuel-Injector-Set-10-00-04-p/1062106.htm

 

I get 28 mpg on the road and I'm 4x4..I get 20 in town

 

I don't think any of this is possible without a Prius retrofit. The EPA numbers for a 2.4L 5-lug are 22/25mpg, and those numbers are known for being fudged toward ideal laboratory settings.

 

I don't care I knock down 400+ miles per tank of gas. .granted my mileage had dropped a little since coming to louisana because of all these hills. I drive like 60-65mph and that's what I get in the road with the 4 banger manual everything. I always leave my hubs unlocked as well