Sudden decrease MPG

So, I purchased a used 2008 Tacoma TRD access cab off road with 93k miles on it. I read the newbie guide and purchased a Scanguage II, did a synthetic oil change and put a drop in AFE high flow air filter. It had new spark plugs put in it at 90k miles. According to the scanguage I was getting around 24MPG for the first 5k miles. The two most recent mods I have done were the flyeyez lighting and redline plus struts. I don't see how those could possibly affecting MPG but I wanted to include them. After the strut install (hood struts; not the struts under vehicle) my MPG has dropped to 19MPG. Now, I realize that the hood struts have no bearing; or should have no bearing. At first I thought it might since I had not aligned the struts correctly during installation and my hood was not flush. But I have fixed that and still reduced gas mileage. I am really frustrated. I was so happy with the 24MPG average and I want to get back there. Was the scanguage just getting used to my vehicle?? I have no idea what could cause a roughly 20% drop in fuel economy so I am frustrated and grabbing at straws. I love my truck and I don't want to be irritated but I am atm.

Please help.

 

If you have never changed out the rear diff oil I can imagine what it looks like.

 

It was changed out at 70k. The owner was 68 when he bought it, 72 when he sold it. He wanted a 4 door truck for more easily getting things in and out of. All service records were immaculate. I have never seen; on paper, a more incredibly well maintained vehicle. All oil changes at 5k intervals. Spark plugs every 30k miles. Front, rear and transaxle were all done at 70k miles at the request of the original owner. I have been clearing out some trees from my father in-laws wooded lot around his cabin. Mostly oaks and all old growth. So I planned on switching out the rear/front/trans after I get done with clearing the rest of the downed trees out. It requires 4x4 to get in and out of and I figured they were getting a workout. I planned on using redline 75w90 gear oil but do you think the heavy lifting could have made it that rough? I have put about 1k miles on it since the work and it was getting good gas mileage up to this point.


In other words could that work have made the gas mileage drop?

 

Good to hear. Sorry can't help other than maybe make sure the spark plugs are tight. Carry on.

 

If you off road ck the air filter, the engine acts like a vacuum and can plug the filter quick......

 

Ranzid-
I've never gotten 24 mpg in my Access Cab TRD Sport V6. As for the mods you did, not one of them should cause a lack of mileage. It seems purely coincidental. Now, I'm wondering if:
You just did those mods and then winter hit. I know you're in TN but still- bear with me... there is a switch to "winter blend gasoline". And, keep in mind that when the temp drops, air compacts meaning that when aspirating, your engine is actually bringing in more air resulting in more gas burned to keep the air/gas ratio correct. It's like a seasonal cold air induction system. On top of that, if you get any snow/ice at all, your tires will slip a little and don't forget the morning "warming of the car" before you get in. Each of these will take a little more fuel and all together may contribute to noticeable MPG losses.

Is that what's going on with your truck? I cannot say. But this is what I'm thinking.

Oh- and your high-flow air filter??? More air=more gas burned.

 

Potentially winter fuel in your area and longer idle times to warm up your truck may contribute. GL

 

I just saw that your vehicle was owned by an older gentleman... I'd be willing to bet your driving style may be a little different. And I'd guess that it's probably a little more aggressive than his style- not saying you're an aggressive driver, but you probably don't drive like a 68-72 yo man normally does...

So all cars nowadays have this learning curve that they will go through. Once complete they actually try to predict your driving habits. This allows the engine and transmission to coordinate to provide less wear and tear and also better fuel economy. Ask anyone that has bought a new car- until it "breaks in" the mileage isn't as good. Well, there are debates on "breaking in" a car and what that actually means, but a good part of that is this adaptive system.

Put it this way- you don't want to take a car that's only been driven by grandma no more than 30mph and get on the highway expecting super performance. The car won't do it- at least not how you want it to. Drive that car for a little while and you'll notice how it changes.

So, since you've taken over ownership, your truck might be struggling to learn and adapt to your ways of driving. Couple that with the examples I've listed above and there goes some MPG for a little while.

 

How are you measuring mpg?, just with the scangauge or miles between fill ups divided by gallons filled. If it's not calibrated correctly the scangauge can over or under report mpg.

Most people with your truck aren't even getting 20 mpg.

 

+1

I get about 1-2mpg less with the winter fuel blend.

 

i think air temps have more impact then the gas. Last tank on winter blend i got 21 but we had mild temps. Last year same gas in much colder weather i got 19 on a couple tanks.

 

I get 13 mpg ( US )

 

I am believing that the winter blend has something to do with it.

 

I delt with these engine computers for years. They "guess" the amount of fuel being used based on an algorithm of sensor readings. They're not bad, but not 100% accurate either. Best way to get an actual mpg is to track mileage between fillups. That'll give you a good average number. Fuelly.com has a fun little UI to record your numbers to track.

 

If you have been hauling a lot of trees large loads it will decrease the MPG considerably...

 

shitty winter fuel

 

Possibly your driving habits changed. I recently took a big hit with mpg. Took a 7 hour trip and mpg went back up as good as I've ever had. Realized I'd been taking a lot of very short trips.

 

How long ago did you put the new filter in? A quick thing to try would be to simply disconnect the battery for a little while and let the ECU reset itself.

I've never seen 24MPG on my V6 4.0...best I've done is probably 22 and average is around 19-20 so I wouldn't be overly concerned.

 

First I would say forget about scangauge and check your MPG correctly. It is only guessing at it and not a true MPG reading. Second have you unhooked battery cables recently? If so you reset the computer and that can cause a sudden loss of MPG.

 

I'd like to see any source of information that describes accurately what happens with resetting computer after unplugging battery or vehicle learning your driving habits claims.

90%+ of my driving is closed loop feedback with the computer controlling to optimize emissions so unplugging the battery doesn't relearn how to run in closed loop. Only a small amount of time is open loop, that can't change mpg much.