I have always had poor highway mileage with 33's and 5.29's on my 1990 4runner 3.0 5sp, usually about 15-16 overall. Recently it has dropped BIGTIME. I took a trip somewhere and basically drove 500mi in a day (100 in town, 400 fwy) and I calculated roughly 11mpg for the trip, 400 miles on a 34gallon fillup (i have 2 tanks). I usually tune it up every 75k or so, its probably been about 60k since the last cap/rotor/spark change, and the airfilter is a conical one that put in and doesn't look dirty at all. What else could have caused this? Its raining right now but when it stops i'm gonna go through and check everything, fuel leaks first, but what should I go to next? what would cause such a drastic drop in fuel efficiency? O2 hasn't been changed to my knowledge, about 205k on the dial now. Could it be that? EGR? thanks

 

Fuel filter, carbon build-up...

You could use Seafoam for the carbon build-up but I STRONGLY suggest that you do a search on it and read the entire thread started by Bamachem.

 

ignition failing part way causing engine to run rich?

Lamm

 

There are a bunch of ideas - seafoam, TPS, O2 sensor - search will provide the details.

Big one I realized was tire pressure now that it's colder. I would check that first.

 

You are running 5.29's with 33's powered by the 3.slow? Step up to 35's and I bet you mileage will be better. Your rpms must be well over 3200 at 65mph right? Talk about a revving time bomb.

 

just had it scanned, its clean, no codes.
no leaks, no clutch slip, no brakes sticking

bad batch of gas????

 

Fuel fitler and tire pressure would be the most obvious things that I would check first... When you filled it up was the tanker truck at the station, making a delivery of gas? When they deliver gas, it kicks up all the ÅÅÅÅ and sediment at the bottom of the holding tank and it can end up in you gas tank. :xmas12:

 

the 5.29s are your first problem. you have 33s 4.10 will work fine on 33s. my DD tacoma has 32s and i cant even tell a difference and my rock crawler on 35s has 410s and i can notice a difference but i still get 17 MPG.

 

how would a plugged filter make me use more gas? that would make it starve for gas and cause things like hesitation and such, i don't think its the ff. tires are at 36psi

and 5.29's are high but I need them for offroad. anything less would kinda make my 3.slo struggle a bit much

 

all the obvious culprits: dist cap/rotor, plugs, plug wires, clean air filter and throttle body, fuel filter, o2 sensor, TPS, techron concentrate for fuel injector cleaning -- or seafoam, but i've never done it myself -- or FP60 which is a good inexpensive additive that you add to every tank of gas, tire pressure...

are you running your _original_ cat and muffler? maybe a clogged cat is contributing to the problem but not likely the sole factor...

 

I pulled the cap off and it looks decent, as does the rotor. The platinum plugs come out unfouled and pretty clean as well. The filter is a 3" cone and is clean, wires seem fine. Had it scanned yesterday, no codes at all. Cat is original, and has borla muffler, I don't think its clogged. It idles perfectly fine, and runs well. I am stumped as to why it got this huge drop in mileage. I'll see how the next tank goes, maybe it was just a bad fill of gas.

 

yeah, it might just be some bunk gas.
platinum plugs, eh? those working out ok? i've heard bad things and always go with the ngk or denso myself.

 

denso makes platinum plugs... That's whats in mine.