Gas mileage issue

Howdy all. I am the original owner of a 2002 SR5 4runner. 159k miles. A few years back when camping in Utah, someone stole my catalytic converters. Didn't think much of it...had them replaced. Insurance covered it. All good. However, after moving back to lower altitude, lots of engine light warnings started happening. My favorite Toyota tech told me the fuel mixture was running super lean...this created some heat issues and caused some issues with the heads. Had them replaced. But now, my fuel mileage has gone to s**t (approx 12 miles/gal). Any ideas? Still related to the cats? Something new? Nothing shows when plugged into the computer. Let me know. Appreciate the input.

 

I can’t help you, but welcome to the forum.

 

Thanks.

 

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That's a weird story man. So it was running super lean so you had to replace the heads? So what was done to fix the super lean problem? New heads won't do anything to change a "super lean" problem. Pretty sure your engine uses an oxygen sensor (or two) in the exhaust to check the fuel/air mixture...so the throttle body measures the airflow then the oxygen sensor decides if the right amount of fuel is being added to the air. So I'd be thinking about cleaning the throttle body and checking/replacing the oxygen sensor(s) and I'd be looking for a new favorite tech if your current one can't explain what's going on. Just my thoughts.

 

I would have thought if something is that off, the OBD would throw some codes but you're saying none is displayed. You may need to have Toyota examine the car with the more capable OBD tool that they have. My other reaction is since the heads were replaced, have you done a compression check to see whether the work was done properly or not?

 

Welcome from Wisconsin! The stuff that Gumpus said makes sense, new heads I imagine because they were warped/cracked ? Did you drive it home after the Cats were stolen? Our '86 pickup was fussy that way. I drove it with an aftermarket exhaust system, no O2 sensor till I got town to replace it...... what a fuster cluck! Just wondered if your O2 sensor/sensors weren't damaged some how.

 

vehicles can be touchy at times...in regards to different sensors..etc

 

Thanks for all of the input. I did replace the up and down stream O2 sensors. I will look at timing, cleaning the throttle body, and any other sensor I can think of. Keep on keepin' on!

 

When you replaced the O2 sensors, did you use Denso sensors, or Bosch? Bosch are made for European vehicles, and Denso for Japanese, and never the twain shall meet. Bosch SAY they're suitable subs for the sensors on our trucks, but they don't seem to work just right for them.
Also, after you replace the sensors, with Denso ones, you really should reset the ECU. Pull the EFI fuse for a few minutes, or, what I do, is just pull the negative battery terminal. Give it about 5 min. then re-connect. Drive the truck about 30 miles, at various speeds. Then stop, let it sit for an hour or more, and do it again. That "teaches" the ECU what the new sensors are going to read, and what mixture to use.

Speaking of, the mixture is also affected by the engine's temperature. Thus, check the temperature sensor that feeds the ECU. It's different from the one that feeds the gauge, and different from the Cold Start Injector Timer sensor.

Make certain there's no vacuum leaks anywhere, and that the tube that feeds the Throttle Body from the AFM has no cracks or leaks of any kind. Make sure the IACV is closing down as the engine warms up. Ensure the idle is set right.
Test the TPS and AFM to make sure they're both reading right through their ranges.

All I can think of right off the top of my pointy little skull. Hope you get it solved!
Keep us up-to-date.
Pat☺

 

CODES! What CODES are you getting?

All of us can arm-chair-quarterback this all day long. But you need to tell us what actual codes you are seeing. If you are getting more than one, that combination can lead straight to the solution.

As mentioned, TOYOTA or TOYOTA OEM SUPPLIER (Denso/Aisin/etc) parts are the ONLY real deal. Everything else is just going to frustrate things.

Did they use OEM Cats when replacing? Cheap Chinese garbage will clog up and won't work for long. Some good youtube vids on replacement cats showing 1/3 the honeycomb material as the factory stuff. A few years is probably all they're good for. Do you lose power at higher RPMS?

 

Also, did you check with your dealer if the car uses O2 sensors or A/F sensors?

My 2002 4Runner uses A/F sensors.

If you bought the wrong ones from Toyota I think you would know since the connector is different. If you bought cheap ones to splice into the existing connector...you could have used the wrong ones. The dealer will take your vin and tell you for sure.