KtrainHurricane

I just got through my first tank of gas and only made it 200 miles. My truck is a completely stock 1994 Xtra-cab v6 4x4 with an automatic and 145,000 original miles. I have BFG Long Trail 235/75r15 tires with good psi in them, and a very light foot. I mostly drive in the city - about 12 miles each way to and from work.

How is it possible that I am getting such poor mileage?! I know these motors have "bad" MPGs to begin with, but only ~12.5 seems a bit ridiculous. The motor has recently been "freshened up" with all new seals, plugs, wires, etc. If I cant squeeze a bit more out of each tank I am soon going to be homeless!

Yotalover01

The biggest reason I hear of the mpg blues is the o2 sensor! Try replacing it! I have a 1992 Xcab 3.0 manual trans with 32x11.50 maxxis mudders and I drive about 10 miles a day round trip and I average 15-15.8 mpg

Yotalover01

Also check your air filter make sure it's replaced regularly! And clean

niall

02 sensor is a good suggestion, i've had cars double their mileage with a new o2 sensor (not having even thrown a code)

Also check that you're VAFM is clean and operating correctly.

'85 Yota

I should probably change my filter soon. Been getting horrible MPG the last couple weeks.

Yotalover01

While your at it, change that fuel filter too! I'm not saying its part of the problem but a good clean filter that's not hurting your flow will definitely help your engine perform and run better!

KtrainHurricane

I know it's been awhile, but I have recently learned that my RPO code reads G254, which means I have 4.56 gears (right?). I discovered this because I am shopping for new tires, and was doing research on what tire size and what gears work well.

Could the fact that I have 4.56s on stock 28" tall (225/75r15) tires be the reason why I get such poor gas mileage? Do I have too short of gears for these tires?

I will note that the truck is a DOG. I hate the freeway on-ramps more than anything, because I become an instant hazard to everyone in the right-hand lane...shouldn't the shorter gears make my truck quicker? I floor the damn thing and still don't get to "flow-of-traffic" speeds by the time the lane merges!

SPARKS89

iTrader: (1)

4.56 gears will work well with a set of 31's. You can push it to 33's without much trouble. Not sure why you have 235 tires with 4.56 gears......sounds off to me.

Everyone's giving you good advice with what to replace/check. It's good to do those things when you buy a truck anyway.

The fact that you're only driving 12 miles (city driving, at that) to work tells me you're not giving the engine time to get to where it's getting good efficiency on such a short trip. Not much you can do about that.

a4runnerfreak

The 4.56 gars are the right gearing for the 28" tall tire, IF you had the manual tranny. In 91, the 4runner's came with the auto tranny, with both the 28" and the 31" tire packages. I had a 91 4runner with 31's, 4.56's and the auto. The proper gearing for the auto tranny is 4.88's. That's were you are losing some of your power and MPG. I now have a 94 4runner, with the 3.0 and auto tranny, but with the 4.88's, and get 16-17 MPG city, with 31's. Do the basics, plugs, wires, cap and rotor, air filter. Change your O2 sensor if it's been a while. Those thing will help SOME, but the 3.0 is not an engine known for power or decent gas milage......

KtrainHurricane

So since I have 4.56 gears with 28" tires and an auto tranny, what does THAT mean?

And I said in the first post that I had plugs wires, etc. replaced already. The truck also had a brand new exhaust (complete, from headers-back) put on right before I bought it, including a new O2 sensor. The air filter is also a fresh, OEM one. I understand that this isn't the most powerful or efficient motor out there, but 16-17 MPGs is a hell of a lot better than 12.5 MPGs...I have only been getting 200 miles per tank!

Here is one of the receipts for recent work that was done right before I got the truck:

wyoming9

iTrader: (1)

I have a short commute to work.

I get only 10 to 12 mpg.

I have the 92 4Runner 5 speed 3.4 that I just got all the issues sorted .

I am running the 235/75/15 tires Now mine is loaded down with a bunch of work tools also.

It does much better on longer trips but most in hills and back roads.

a4runnerfreak

My bad, I missed the part bout the plugs and wires and stuff.....kinda had 1/2 my attn on my 17 month old....lol. You are under geared for the auto tranny. Your options are to either re-gear to 4.88's, swap in a manual tranny, or buy a slightly bigger gas tank to get a lil bit more than 200 miles per tank. When I had my '91, I was LUCKY if I got just over 200 miles per tank....driving like grandma......lol. It's 1 of the natures of the beast with that year, unfortunately.
You can check out the classified section for some1 selling complete 3rd members for your 4runner, or send a PM to Deathcougar, a member here who works at Nix99, a toyota/lexus only wrecking yard, and see if he has some at his work. I think that might be the easiest on the wallet.......

Gamefreakgc

Your truck is old, it's not going to get great mileage unless you really work at it. It's Toyota's first attempt at a fuel-injected truck.

Check for vacuum leaks or damaged lines, also for exhaust leaks. If your oxygen sensor is getting unburnt oxygen downstream, it will compensate by pouring on gas, giving terrible mileage. I had that issue due to a valve that was stuck open during the compression cycle, a valve adjustment bumped me up from 13.5 MPG to 16.5. If you're looking to get better mileage, you have to baby this engine and clean/fix every issue.

Or, you can upgrade. My current setup with my truck gets me 17 MPG city and 22 MPG highway (just confirmed highway mileage again). The money I put into for the mods listed below will pay themselves off with fuel savings, since it's my DD.

a4runnerfreak

Gamefreak, this isn't Toyota's 1st attempt at an EFI truck, the 22re was introduced in 85. Ktrain, even brand new, the 91 4runner 3.0 V6 with auto tranny was only estmated 13mpg city.......

KtrainHurricane

4.88s are shorter than 4.56s...which would mean that the transmission would shift quicker, and be at a higher RPM in final gear when driving at highway speeds, right? If so, wouldn't taller gears be better? Or going with a slightly larger tire, so that the wheels don't have to rotate as much to game any given distance that my current ones do...?

FWIW, I have a pickup, not a 4Runner. Not sure if it matters, but a few of you have said "4Runner" specifically.

KtrainHurricane

So if I just brought it into my mechanic and asked, "do I need a valve adjustment?" is he going to look at me like I'm retarded? I really have no knowledge of these trucks, or vehicles in general for that matter...so issues like these I don't even try to do myself.


And all you really have listed in your signature is an intake and a cat-back exhaust, right? I was planning on doing the ISR mod soon anyway, and I have a big K&N lying around that I was going to throw on.

As far as the exhaust though - does a cat-back really make that much of a difference? I have always been told that your exhaust is restricted by its smallest part, no matter where it is located ... i.e. whether you have 2" in front of the cat and 2.5" behind, or 2.5" in front and 2" behind, or 2.5" in front and behind but the inside of the cat is only 2", it will all be the same = restricted flow to that of a 2" pipe (not sure if my explanation made sense, sorry). :confused:

RSR

Most folks who do cat-backs see 20% increase in MPG and 10% increase in HP.

What's your timing set at? It makes a huge difference on the 3vze. Set it to 12 or midway between 10 and 15 timing marks and give it go. Pull your EFI ECM fuse to reset before driving. Toyota recommends timing at 10 for emissions reasons, but it makes the 3vze a dog in the 1k to early 2k RPM range...

Have you had compression checked on your engine? If it's not compression, then it's mostly likely fuel, spark, or air that's causing.

On fuel, trying running a good injector cleaner like Redline or BG through. Replace your fuel filter. Maybe look at replacing your injectors with the new Flamethrower ones that are getting good reviews -- ideally after running intake and fuel injector cleaner through.

On spark, check and see what brand spark plugs were installed. OEM Toyota or NGK are best. Not Bosch. Same for wires -- OEM or NGK. Open your distributor cap and take a look to ensure your terminals and rotor are in good shape. Heck, it wouldn't hurt to pull a spark plug and look to see what color your spark is too. If your spark is red or orange, it's not getting hot enough. Bright white or blue you should be good -- if not hot enough, replace plugs and wires and cap and rotor and rechech... If not, it might be your ignitor... Also, inspecting your spark plugs will tell you how your engine is burning too. Lastly on spark, get the FSM and multimeter and check your distributor connections to see if factory spec. The crankshaft sensor on mine was shot and led to my engine running rich, but no error codes.

On air, you have two ends. Intake and exhaust.
On the intake end, use your multimeter to check the AFM. Change your air filter. Use your multimeter to check your TPS. Get a rag and some throttle cleaner and clean your throttle plate. Get some Seafoam spray or Amsoil intake cleaner to clean your top end. One thing I recently did that helped (plan to post a writeup this weekend as an addition to one of the ISR threads) is take 1/4" drill bit and drill about 20 holes below the drivers side headlight -- on the factory Toyota setup intake holes were only around headlight assembly with holes at sides and all indirect air flow; below is exposed directly to incoming air and those 20 holes add about an add'l 1 inch squared of air intake -- and then on the top of the air deflector/collector, I used some cold A/C line foam to seal the top that was open to the engine compartment so hot engine compartment air was sucked in and allowed some of that cold rammed air to escape. It definitely helps on highway hills. Probably a less than 5% peformance gain, but I'll take it for just my time. Btw, K&N intakes are bad news all around. The oil fouls your AFM all up and it allows a bunch of dirt and dust into and building up in your already restrictive plenum -- and most importantly, the cone filters without a cold air box, draw in the super hot air that's present in the engine compartment which kills power (for more info on intake air temp, look into why intercoolers are good to have with boost). K&N does have a dry filter affiliate/product that's both drop in or cone that's a better option than the K&N oil filter, but even then, you still need a cold air box and don't entirely remove the dirt issue... I'd stick with either Yota or Wix air filters in the stock setup. Several folks with next gen 4runners ran dynos w/ and w/o the K&N and found that the K&N cone actually led to a DECREASE in HP & torque. But YMMV.
Connecting the exhaust and intake, replace your PCV valve. Not sure on this truck, but on my wife's Honda, replacing a bad PCV increases highway mpg by 1/3rd. Also connecting the exhaust and intake, you need to have your valves adjusted. All techs HATE doing this on the 3vze, but it makes a huge difference if valves aren't properly seating. My truck hadn't ever had them done at 146k miles when I had my mechanic do it -- and he didn't want to do it either... All but one exhaust valve was out of spec, but no burnt valves...
On exhaust, the main things are, as noted above, the cat-back, the 02 sensor, and the catalytic converter. Look under your truck at your cat after driving at night. If it's glowing red, it's probably failed and needs replaced.
On the full potential of power from the 3vze exhaust, about 1/2 half of the performance increase can be had in the cat-back, 1/4 in replacing your Yota cat with a high flow aftermarket one (sell your yota one to pay for a new Magnaflow ceramic core -- almost covers entirely as there's a lot of platinum and other precious metals in it -- or 1/2 of a magnaflow metallic core, metallic being the more durable option for our 3vzes that tend to run rich which makes the cat run hot [ceramic core fails before metal for whatever reason]), and 1/4 in headers -- but much of the header increase can be had just from a crossover delete alone (or at least I think -- I posted my thoughts recently in a forum about someone looking to have a local tube guy build some headers for cheaper than currently available). And bear in mind the top of the line mandrel bent (this is important, mandrel, not crush bends) 2.25" aftermarket exhausts are actually optimized for the 22re, not our 3vze. You're best to go with a 2.5" exhaust on our engine (well you can really go 2.25" from cat back to exhaust tip due to exhaust gasses cooling and contracting for essentially the same performance and a little cost savings on tubing [same reason modern factory cars exhaust size decreases as it goes back], but through cat should be 2.5" for our trucks).
Lastly throughout on the air, the vacuum hoses and/or intake hoses having a hole in them can create all sorts of weird symptoms with stuff not working or unmetered air getting into the engine.

And the last thing to take a look at is your fluids. From tranny to differential to transfer to engine oil. On the 3vze w/ the auto, changing end of life fluids does a make a big difference in performance -- I don't know that my differential or transfer fluid had been changed either before I did it when first buying my truck. I noticed an immediate difference with changed fluids. I have amsoil in diffs and transfer, and Castrol Full Syn Ti for engine oil w/ the big Toyota filters -- I'm running the Japan-made Toyota Resin filters (99% of the 90915-20004 filters being sold are now made in Thailand too with same medium as the D1s and D3s; the Japan resin 20004s are the same size as the D3s but different filtering medium; the new Thais are a midrange size between the D1s and the D3s) but the YZZD3 or probably even better than the now crappy-ish Yota filters is the Purolator PureOne will help w/ oil flow too (TRD and the Mobil1 Synthetic Extended Performance are also good filters but much more expensive for same flow and filtering as the Purolator PureOne [buy on amazon btw for best price])... (On Toyota filters, now for the US market at least, they're nearly all made in Thailand, not Japan, and made with components that are of inferior spec to the Japan ones -- Toyota filters previously were reviewed and claimed to have superior performance specs throughout the interwebs to many of the aftermarket filters, but now that Toyota filters are now made in Thailand with cheaper components [we only have ourselves to blame; American consumers wanted cheap filters] it's now hard to justifying continuing with Yota filters, despite that product #s have not changed in line with production changes...)
And I plan to do my auto tranny fluids w/ Amsoil, but it's a pricey flush...
Amsoil does sell an engine flush that's good to run prior to switching to a synthetic oil in your engine to remove all the dino oil crud and buildup on the lower half of your engine -- they say it can be run in the tranny too, but I'm really hesitant to do so, and won't. I'm going to run it through my engine soon just b/c it's an 8 dollar cleaning, but the previous owner ran Mobil1 synthetic so isn't too terribly needed on my truck.

And don't forget to get out your grease gun and hit all the zerks on your driveshaft. Looking my rigs last owner's records, all of the quick oil places he went to marked the driveshaft as not done b/c it was sealed... Despite the fact that it wasn't. Lack of lubrication can reduce efficiency and rear wheel horsepower too, not to mention wear and tear.

One more thing that we don't know about your rig is that if you haven't gone manual hubs on your front end, do that ASAP. It's easily a 10-15% increase in mileage from that alone as well as significantly reduced wear to your front axles.

Hope this helps. Lots to do!

Gamefreakgc

The valve adjustment is a time consuming and tedious job. Most mechanics won't do it or know how to do it, they'll just tell you it's not worth it. I've heard of Toyota dealers turning it down as well. It's a lot of work so unless your engine wobbles a lot or is throwing a code 25 with no solution, I would not bother. It worked for me, but it's no guarantee that it will work for you.

The K&N filter helps improve air flow. These engines are like an asthmatic, the pipes are restricted and don't allow enough air for it to breathe. Any restriction you can remove to help more air flow, the better.

A cat-back exhaust is a proven upgrade, very common on most vehicles but especially effective on ours. By making larger piping from the cat and upgrading from the not-so-great stock muffler, you remove some restrictions which allows the engine to perform better. Magnaflow, Borla, and Flowmaster are all good mufflers. I did mine for $275 at a muffler shop in town. Search around for more info on this. You don't need to upsize every pipe to get a performance or MPG gain, this engine is so restricted that anything helps. By freeing up the end of the exhaust, you allow air to travel faster through the pipes, even though the headers and front exhaust are only 2" piping. You could try and replace the whole system, but then you are looking at $1000 to $1500...

I also modded the intake to 3" and replaced the air flow meter with a larger one from a Toyota Supra. More air in, more air out.

EDIT: Yeah what he said below. Unless you want to try a valve adjustment yourself, you're looking at $300-$500 alone in labor charges... I did it myself for $100 for parts but it took me a whole weekend to do it right.

RSR

P.S. Your Toyota mechanic will know what a valve adjustment is. It's just a 3-5 hour project and accordingly tedious for techs (and only the older/more experienced ones know what they're doing on the 3vze) and expensive for owners so it's not something that's done as often as it should be. But definitely, take it to a Toyota mechanic -- doesn't have to be a dealer, but a Toyota specialist. My older aged mechanic removed the cams to do it as it was faster for him that way...

The ISR delete leads to add'l throttle response, but really doesn't do a lot for seat of pants HP. And the supra AFM swap really needs the exhaust done first to see much gain in add'l performance. And you also need/want a wideband 02 sensor to properly tune.

And your gearing isn't ideal, but it doesn't explain your troubles. It's essentially a 7% difference between the 4.56 and 4.88 gears, which doesn't explain. If you were running 4.10s or something, I'd be more concerned here... 4.88s are ideal for 30-32" tires w/ autos, with 4.56 sufficing for below. 33s or larger with the auto, you should go w/ the 5.29s.

RSR

Not to derail the thread, but I strongly disagree with gamefreak on running a K&N cone filter in the engine compartment. Edited my first post above his to reflect why before I saw his comments.

But in brief, you want cold, clean air entering your engine. K&N cone filters open in the engine compartment do neither. The filter isn't the restriction. The stock AFM and intake piping are. The stock intake piping sitting right above your drivers side exhaust manifold also heats up your intake air -- a big benefit of the ISR delete is raising that intake pipe away from the manifold, and I would recommend either foil tape or high temp ceramic paint on your intake tube too to keep intake air as cool as possible.

The ultimate goal is to increase the amount of oxygen, not volume of air. Heat reduces the concentration of oxygen, which leads to not all fuel being combusted. Cool air with more oxygen combusts more fuel than hot air of the same volume. And cool air also helps to stop premature detonation of fuel. Hot air increases premature detonation/knocking. K&N cone filters just increase flow but isolated in the engine compartment not at a level that compensates for the significant increases of intake air temp (at 250* or whatever our engine compartment temperature is, you'd need to add considerable boost to compensate, and K&N's intakes don't add boost). Running your standard cold air intake with the two tweaks noted in my first post is a much better option. Definitely do the ISR delete too, but think twice about a K&N "cold air intake" -- a mistaken description for sure...