1997 4Runner 242k
Engine pulled from truck and every single seal, gasket, line, timing belt is new and replaced @241k.
No lights, no codes, engine compression 180 across the board.
Truck is lifted 3 inches and running 255/80r17 STT Pro's. No armor.

Was towing a 12ft aluminum boat through rolling hills today and it feels very underpowered. Elevation 2170ft. Sometimes even hitting 70mph unloaded often requires a downshift. Are they just this under-powered, especially when on 33's?

What could it be? Fuel filter is new, injectors checked out, spark plugs are new, coils good, pvc is good. Exhaust is rusty af but I don't want to spend $$$ where it isnt needed.

I ran the truck after with the front O2 pulled and it was maybe a little bit better? Or it was the noise idk.

Cannot break 15.8 mpg on 91 octane.

Opinions?

16mog toeing sounds about right. The car is definitely under powered especially when towing.

I tow a lot as well and I’m eyeing a supercharger myself or just selling the truck and getting a GX

It's worse when I drive empty and I have a light foot. Mostly city driving as well. Something isnt adding up here. I had a GX 470 and it was too tippy for my liking. That v8 sucked fuel like this v6 lol. Sold it and bought a Navigator and haven't looked back.

When was the last time a tune up was preformed?

When was the last time you ran a good quality injector cleaner through it?


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These trucks suck at towing, the 3.4 v6 doesn't make much power for a 4000lb+ truck let alone towing anything. Honestly, there could be nothing wrong with your truck and your MPG sounds about right.

I tow a 2500ish lb boat/trailer and it absolutely sucks on the highway. Basically, any hill I lose considerable speed unless I turn OD off and hit the gas. Even on back country roads, I leave OD off otherwise I'll slow down quite a bit on long hills. I run 265/75/16's and have about a 2" lift, no armor. My engine is in tip top shape but its still slow AF.

Don't get me wrong, I love these 3rd gens but unless they are supercharged, the lack of power is the thing I hate most about them.

Have close to 10 years of towing a 18ft boat (approx 3,900lbs w/ trailer) with my 02 here's what Id recommend. Like everyone is saying these trucks came with 190hp back in the day and only a bit more torque, so they're not great for towing. Keeping the revs high is the only way i don't have the trans freak out and downshift into 2nd when towing uphill. Do this by hitting the ECT button and the OD off button. On the highway, I never tow above 65 and just run in 4th gear with OD off, gives me a bit more oomph when accelerating.

Like everyone said MPG seems spot on for towing. Try running some seafoam through it and checking to make sure your air filter, MAF, and throttle body are clean. I took off the plynem and went to town with some throttle body cleaner and it increased mpg on both hwy and city. Truck felt more willing to get up and go as well.

Whats your MPG without towing? If you're getting 16 or so city and 20-22 hwy I would say you don't have any major problems.

Hope this helps

Dude, the V6 4WD is RATED by the EPA at 16mpg city, 19 highway. (this is the 'adjusted' version that is more realistic, the window sticker does say something slightly higher)

16mpg around town is perfectly normal. Downshifting on hills at freeway speeds is normal.

Set the cruise at 65mph on a flat highway with no wind - you'll probably break 20mpg. But make sure you adjust for your tire difference in tire diameter (about 1mpg for you).

I think you are making unfair comparisons to modern vehicles - this truck was designed in the early 90's. The engine design is from the 80's (2VZ-FE came out in '88). And you have well over 200k miles on your >20 year old vehicle...

-Charlie

Par for the course on these trucks, nothing is likely wrong with yours.

What is your gear ratio? That has much to do with how it feels.

sounds pretty normal to me

when I hit the hillsn with a load, od off , not only for mpg, but lowers trans temp ( different thread about that) same as purposely going slow on hills, od off

Plenum, heads, TB, all cleaned when I rebuilt the engine.
Ill clean the MAF again, why not right?

Last mpgs:
MPG 80hw/20city ave 13.86 mpg
MPG towing 90hw/10 backroads 15.8 mpg

^^^^Doesn't make any sense to me^^^^

ECT is always on, OD was off when towing, mind you the boat and trailer weigh almost nothing, I can move both by hand on and off the truck; I tow it with an 06 outback and the car barely feels it lol. Truck was struggling with it at 55 mph on rolling hills.

19hwy would be ideal!

33's are very big to turn on the stock 4.10 gears. I'm assuming you have a 4WD rig, if not you have 3.9 gears which means you probably shouldn't have 33's on there lol. If you want some of that power back then you can regear to 4.88's, some even go for 5.29's but that might a bit much.

Some common items to do are cleaning the MAF sensor (there's a write-up showing with photos on where to clean it depending on what model you have), changing your air filter which sometimes gets forgotten, and replacing the front O2 sensor like you suspected. On 2nd Gen 4Runners the manual said to replace them every 90k miles, so if you have no clue how old it is get a new one.

Did you factor in the larger tire diameter and slower odometer when you got 15.8 mpg? It's 17 mpg's if you take the tire size into account. Both the tire size as well as the increase road height will affect your aerodynamics negatively, so highway miles will never be as good as they were stock. Also, there's no need to run 91 octane unless you have to. It primarily provides extra spark knock protection which a stock 5VZ-FE won't need. Supercharged, yes.

OP,
Yeah I would say that if the trailer isn't all that heavy than your fuel consumption and sluggishness is going to be coming from your larger tires. I would recommend turning ECT off when you don't need "power", it will likely improve your MPG. Like the other guy previously mentioned there's a whole thread about how running with OD off lowers the temp of the trans under normal op. and towing, so I would recommend you do that even with your light trailer.

Im no suspension expert and have not done any mods to the suspension on my rig, but I know that bigger wheels essentially is equivalent to gearing the truck down. Thus, the truck will have more strain on the drivetrain and make it seem as if it is down on power. They also can have the effect of lowering fuel economy as well. I would do some Google-ing or check out some other threads that talk about suspension to see if you can find your answer there, as I see no reason for this to be the faut of the engine from the information youve given.

Good luck!!

You never answered. What gears do you have?

4.10's will suck with 33's without towing, 3.9 more so. 4.30 was acceptable on 33's pulling 1500# mule 800# trailer OD off. Cruise set 65 not towing flat highway mostly 17-18 mpg with a tail wind corrected mpg's. Your pushing a large cracker box through the air your numbers sound normal.

4x4 with diff locker.

That doesn't answer the question directly, but I'm going to assume you mean you have a factory e-locker which would mean you most likely have 4.30 gears.