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

That's impressive. I'd be happy with 20 average. Wonder if its my automatics efficiency vs the manual? I also live somewhere that's all flat.

 

I took some time to enter summer (May to Oct) mpg for the truck into a spreadsheet;

Each black circle is a MPG calculated after a complete fuel-up, and the blue lines are the median (i.e., 50% of mpg records are above or below that value). I didn't do much quality control entering this, but should be good enough for my purposes.

The drop after 2009 makes sense, as this was the last summer before I moved west, where highway speed limits are 70-75 mph (instead of typically 55-65) and lots of gravel road miles. 2010 was a low mpg summer, and I think this was because 80% of those miles were gravel.

In a given year, I believe the points above the median are probably paved highway miles, and those below the median are gravel and city miles.

So noting all that, it appears that summer 2015 was the year when my mpg dropped off substantially. Average mpg is 1-2 lower than previous 4 years, and even in good conditions I get very few mpg over 25, compared with 2011-2014.

I've had the same summer tires from 2013-2015.

Seeing that the decrease in mpgs wasn't all that gradual, very curious about a compression check now.

Any other ideas on parts that could influence mpg like this without throwing the check engine light?

 

Got around to the compression check;
(dry, wet)
cyl 1: 174, 195
cyl 2: 160, 173
cyl 3: 159, 170
cyl 4: 157, 171

for 2.4 liter Haynes manual says;
"Standard" ...... 178
Minimum ...... 127
Max variation between cylinders .... 30

So by those standards, things don't seem too bad, although I don't have any previous experience interpreting these. Any thoughts?

 

They are all good numbers. When they start getting below 100......start thinking about either a rebuild or new engine.

 

Its been about 2 years since the last post so probably have enough mpg data to answer the question of whether new 02 sensors, MAF cleaning, and new spark plugs made a difference in fuel economy. The answer seems to be no. The vertical dashed line in the graph below is when I made these changes. The truck is now at 298,000 miles.


Seasons are color-coded. The definition for seasons was Nov 1- March 31 = cold season, April 1-Oct 31= warm season.
Tires have different shaped symbols, don't seem to be a confounding factor.

 

mpg you have to factor in the terrain and since we now have ethanol in our gas that too effects mpg. low rolling resistant tires seem to be a thing when it comes to mpg but not sure how much when its mounted on a truck. mix driving of city and highway is usually between. also weight.

 

Agreed - lots of factors affect mpg which I didn't record, that's clear in the variation within seasons. But there doesn't appear to be a difference in the average directly before and after the maintenance I did. My location and driving habits didn't change in that period. So based on this experience, I wouldn't recommend the preventative-maintenance I did to improve mpg.

 

But preventive maintenance is something I still recommend. Imagince an exhaust leak, not properly inflated tire, bad wheel bearing and air/fuel filter causing you to dump more fuel.

I at one point also was wondering why my, my dads now, old 4 cylinder tacoma wasn't getting good gas mileage back in the day. As i grew older I started to realize alot of factors were causing that and have learn to live with the +/-19mpg I got with it. If I were to drive straight highway and got 27-28 I'd be happy with it.

 

Agreed. I thought I might be able to find a "fix" because the drop in mpg seemed to happen "all at once" in 2015 with no change in driving habits/location. The change wasn't substantial enough to warrant "chasing" the problem, besides doing some overdue maintenance. In any case, I hope my experience will be informative for other owners of high mileage tacomas.

The graph below tells essentially the same story as the last one, but with a few more years data for context. This is my summer mpg (mostly highway) with a line that's kind of a moving average- note how the distribution of mpgs changed somewhat abruptly in 2015, and stayed down even after maintenance. (the change from 2009 to 2010 was probably due to moving to an area with higher max speed limits and more hills).

 

add another data point if possible... mileage

 

I like what you are getting at, but this is essentially the same graph as above because my mileage increased more or less linearly with time.

 

Two things that might affect fuel economy is battery voltage & valve adjustment. The computer likes 12.8-13.2 volts to keep all the sensors and ignition sensors happy.

 

I googled the battery thing a bit - seems like the mechanism there could be the alternator drawing more HP because aging battery is no longer holding its charge? Possible - my battery was pushing 7 years old, although it still seemed strong and wasn't really struggling with starting, even with temps in the 15-25 F range recently.

And valve adjustment -- another possibility - I never tackled this job in the ~230k I owned the truck.

Sold the truck last night so guess we'll never know...

 

The throttle position sensor came up when I googled gas mileage as a possible contributing factor.

 

As long as its tweak to factory, and your throttlebody is cleaned, should be fine. One thing I've read people do on ecomod is they use a boost gauge to check the vacuum. They try to keep it under I think +/-18 or 20. I could be wrong.

 

Very old trick, in fact some models of classic vehicles (Buicks, and a few other) used to have vacuum gauges with big segments that ranged from Good to Bad economy. Hell U-Haul still does it to this day to keep people from flooring the piss out of their rental trucks.

 

LIkes, wish there was one that said "dude wtf is you doin"