hey guys, so ive owned my 1993 toyota 4runner 3.0 auto for almost a year now and i love it, i just hate the mpgs, im getting about 11 city which is horrible for a v6. it does have a 5in lift on 33 inch tires but i know i guy with 37 inch military tires that is getting 15 city! i have a cold air intake and a magnaflow exhaust but i dont know why im getting bad mpgs. i also just replaced my plugs, wires and cap plus my pcv valve and plenum gasket and i thought it would help but it didnt? whats going on? it does have a cel light that reads code 25 which is lean but i cant figure out why and if thats the problem??

Hi
have you corrected milage for oversize tyres. code 25 is related to o2 sensor. further details to check if not o2 sensor is the whole fuel system start at fuel pump finish with injectors or vice verser. would change o2 sensor first use denso only. then move on to other checks. Spark plugs
will tell you how lean you are runnning

Hi
pervious posting is correct but smartphone makes it difficult to edit. code 25 is an open circuit in o2 sensor basicly it has failed and needs replacing or there is a break in the wiring.

Oh I bad 02 sensor would kill my mileage. I'm not totally for sure if any 02 sensors have ever been replaced. The one before the cat has its plastic meleted together from the exhaust pipe so its going to be really hard to get off.

are you running stock gears? your rig has the aerodynamics of a brick wall, don't hold your breath for great gas milage. if unsure of the age of that o2, replace it. how about your tune up parts?

it will vary greatly with your driving style as well. If you're driving like a granny your fuel economy will go up. If you're trying to race off of every red light I'm impressed that your getting 11

The miss conception a lot of people think is because the 4runner is a smaller vehicle than large trucks or SUVs and it has a V6 it should get great gas milage. It is geared pretty low and the milage isn't that great but, I can live with it because I can go a lot of places without worrying of getting stuck on the beach. I have even pulled a lot of 1/2 and 3/4 trucks out of the sand.
Work on your code 25 and see if it improves some. I have 31" tires and I'm averaging about 15 to 17 MPG.

Previous owner told me the gears were 4.30 but I don't know for sure

You should have 4.56 to 4.88 (4.88 preferred for auto) and 33's.
Fix the code first.

Okay I'm going to did the code but I don't know for sure if its the 02 sensor. O'Reilly sells them for a 100 bucks a pop which is rediculous. There are an up stream and down stream sensor right?

chefdave: are you confusing that with code 21 (which is a break in the O2 heater circuit)? http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf

Code 25 is a lean malfunction, which could be the O2 sensor, but there are plenty of other possibilities. First thing to do is check the operation of the O2 sensor. http://personal.utulsa.edu/~nathan-b...01heatedox.pdf You'll need a multimeter. Would you spend $100 for an O2 sensor without using an $8 multimeter first?

Another likely cause of a lean malfunction is vacuum leaks. I'm told you can easily search for those with an unlit propane torch.

Only on California trucks, but you don't have a problem with the downstream sensor. That would give you a code 27.

Let us know how this turns out.

Hi
thanks for pointing out my error. on op first or second posting hes says his o2 sensor has melted plastic from connector. my 1989 3vze pick up is california spec and i
have only one o2 sensor. ummmm i think i need to do more research. if new o2 sensor is
required try places like jc witney
and rock auto both stock denso o2 sensors for a lot less than $100

Continuation of previous post.
You can buy and have delivered for a lot less than $100. Agree that o2 should be tested.

The O2 sensors are cheaper at Rockauto.com. You'll just have to wait on shipping.
Just like the previous post said code 25 can be caused by multiple things.

Hi
according to my haynes manual code 25 is related to injector circuit; injector; fuel line pressure; ignition system; oxygen sensor circuit; oxygen sensor; air flow meter; water temp sensor; ECU.
that covers quite a bit hope it helps. as a previous poster has mentioned a multi meter would be a wise investment. tests for all these listed above items should be found on this forum.

I will be testing my 02 sensor this weekend. I replaced every vacuum hose on the engine and the plenum and throttle body gasket plus a leaking valve cover gasket so I'm going to rule our a vacuum leak.