Looking for help in the right direction

Hey guys,

I've been lurking here for a little bit, but have had my 2001 3.4L V6 Tacoma since 142k miles. I'm currently at 225k miles and finally starting to see a slight decline in performance.

To put it simply, my Taco has started to experience a decrease in MPG recently as well as a somewhat noticeable decline in acceleration and general power. I've been researching this problem and working on diagnosing my truck for the past couple weeks, and tomorrow is another opportunity for me to attempt to fix my issue. The problem(s) can be described as: loss in MPG (I've historically always had 300-320mi till empty per tank but now have 260-280 at best), noticeably more difficult acceleration, somewhat of a body shake at higher speeds, an occasional clunk when shifting into gears but not common, and somewhat of a louder sound coming from the engine or exhaust. I believe I've narrowed down the possibilities, but would appreciate anyone's input for where to start first. I'm planning on doing the following work:

-Lift front end and spin wheels to check for stuck caliper
-Check spark plugs and lift each coil pack when running engine to check for difference in engine
-Tighten throttle body cable which does have slack
-Check for vacuum leaks with carb cleaner
-Check TPS sensor
-Repair quarter-sized holes in muffler and seal off potential leaks in exhaust
-Change fuel filter (already done)
-Run Seafoam spray (already done)

Tomorrow is car day for me and I'd like to figure out my problem but am wondering how much of my issue is inside of my head, if at all. I say this because I've recently bought a new truck topper, which is heavy, and have replaced brakes and rotors (potential caliper issue). I've also recently changed the transfer case transmission fluid, which really helped with hard shifting immediately, but I did not drop the transfer case to check the magnets for collected metal pieces. I've heard horror stories about replacing transmission fluid and am just paranoid that I damaged my transmission somehow, which I think would be the absolute last thing to look at in my case. I'm a little nervous to change the fluid again unless told otherwise. If anyone has any ideas on what could be the issue or where to point me I would greatly appreciate it. Thank you!

 

Clean MAF sensor? Air filter? Topper will definitely hurt mileage!

 

Do your list plus what Seagull said..... if those spark plugs are already over 80K minus well change them. (I'm planning to do mine at 90 or 100K)
I don't have camper but wheels are heavy and big 245-75-16 E load Keller AT , Line X bed , nothing else additional and I barely get the window sticker MPG 17 city and whatever Hwy .

Today I run up to the fuel light was on , I put 15.9 gallons 250 miles = 15.72 MPG so if you said you run 260-280 the best you're not bad at all because the Topper factor already mentioned.

Mine is 4WD don't know if yours is or not but I think 4WD is heavier.

 

I've already cleaned out the MAF and replaced the air filter a week or two ago when this became more apparent. Thanks for the information about your MPG; like I said before - I'm just not sure how much of this is inside my head. I'm only acting on it because historically, like literally every time in the past 80k miles, I've been able to pull 300 a tank. Just the past 3-4 tanks of gas have had a reduction, but would also align to when I picked up the topper . Mine is also 4WD and running new BFG A/T's at the same size.


Thanks for the responses, I'll do everything above and report back later with any findings / updates.

 

how is the motor mechanically? I would do a cylinder leak down before trying to fix something that is just normal wear.

 

I'd assume it's fine but then again I've never paid heavy attention to it. I'll look into doing a leak down test for sure though.

 

Alright, so I did end up doing a bit of work on my truck in the past couple days and have noticed an improvement of performance, and sound, after work + test driving. I will post back later if there is a more noteworthy increase / decrease in performance but for now I can tell there is a slight to moderate improvement in idle speed, shifting, acceleration and general sound. The work I did was the following (in no order):

-Repaired quarter-sized holes in muffler with a putty like substance and exhaust tape
-Cleaned the throttle body with cleaner and wiped it out
-Tightened throttle body cable for acceleration
-Tightened all drive belts to eliminate squeak upon start
-Checked both front calipers for stick with nothing found
-Checked / lifted coil packs to see difference in engine stability with nothing found
-Checked vacuum leaks with carb cleaner
-Filled coolant reservoir
-Did a good amount of cleaning between engine and exhaust

The main issue was a sudden decrease in MPG, which ended up being a whopping 1.25MPG loss in total (300 a tank vs 280 now) due to likely a combination of the above elements, winter gas and installing a new topper. Considering those factors and the fact that some of the issue was likely inside of my head to begin with - I'd say that I've done the best I can for the time being with the engine / exhaust sounding better. If any problems persist, or get worse, I'll troubleshoot further and re-post. But, I would consider this resolved for now. If anyone has any suggestions going forward, or comments, please mention them!

 

With 225k miles you might want to check your valve clearances. Maybe do a compression test too. You're probably ok, but it might be good to have the numbers recorded so in 50k miles you can compare.

Another thing is tires and the tire pressure can make a big difference in the feel of the acceleration and mileage. A few extra psi over the recommended pressures can get you a noticeable increase in mpg.

Also, check the tire pressure with multiple gauges. Some gauges can be way off and have you running lower pressure than you thought you were.

 

BFG A/Ts (E rated) are extremely heavy tires conpared to normal street tires...that coupled with the topper is to blame for the MPG drop, I would bet money on it because the same thing happened to me when I went with those tires and added a little extra weight. Went from nearly 300 miles a tank on average to about 250 if I'm lucky. Extra weight at the wheels kills the mileage on these trucks.

 

^^^

 

Update..

Driving style also has influence,
last tank I report 15.9 gallons 250 miles = 15.72 MPG , ( heavy foot , rushing at start point after light goes green)
this time truck did 263 miles \ 15.3 gallons = 17.19 MPG. ( driving like an Old man, not over the limit, releasing gas at long distance if light is red long ahead of you )

1.03 MPG more may not be a big deal so I go with the GO GO GO heavy foot and fast driving.

Any other update on your research ?

 

So far, I've run a couple of tanks of gas and have seen improvements. I believe the combined effects of replacing my fuel filter, cleaning MAF and throttle body, patching holes in exhaust AND (something that I haven't mentioned yet) changing my fuel from 85 to 87 has made improvements. I moved back to Colorado after spending some time in Indiana, where the lowest octane is 87, and haven't thought much about gas until last week. Colorado has a 85 octane gas, and is what I've been putting through my truck since I moved back and I've recently realized that the truck calls for 87 ... I'm almost through the current tank and am over 260 miles with just under a quarter tank of gas to go, so I believe this tank will exceed 300 miles.

 

LOL.... oh yeah 85 vs 87 I will be concern too. When I got the truck 1st thing I did was to run a bottle of Amsoil complete gas cleaner system since I didn't know what kind of Gasoline had been exposed, then from that point I only use Shell , Exxon, Chevron, Costo and just in case of extreme need because traveling then the Valero, All of them on the list of top tier Gas. A year ago I run the 44K BG services cleaning system at Toyota Dealer, plan to do it again every 30K miles