My MPG recently dropped quite a bit. i was getting 20-25MPG on my 22RE with a K&N Air Filter(cleaned regularly), new plugs, wires, distributor cap, rotor button, ECM computer, TPS, MAF, and a few other things. The last 2 times ive filled up i got 14-15MPG(worse than i was getting before the K&N). My check engine light will come on for a few minutes, and the only time i was able to check it before it shut off, it was Code 25 Air/fuel ratio LEAN and Code 26 Air/fuel ratio RICH. i dont know what could cause it to be rich and lean, maybe MAF? Any help would be greatly appreciated. Gas is way to expensive these days.

 

In Oregon they used to change the gas November 1st to 'oxygenated' gas with 10-15% ethanol to save the environment during the winter, now we have it all year and everyone's mileage went down.

Do they do that crap in Tennessee?

 

yeah we have 10% ethanol in the gas down here, but weve had that for about a year. some places still have ethanol free, but it costs about 10 cents more. the one time i used ethanol free, i got 24MPG.

 

The k&n might have contaminated the maf ,causeing the readings to be off. It is very easy to get a little to much oil on the filter when servicing it. This happened on my brothers gmc , the wire element was coated with oil .The Toyota maf may be a differant design.

 

O2 sensor could cause the rich/lean and hurt the gas mileage

 

1. Do a compression test. A sticking valve can cause this. If this is ok....

2. Check your spark plugs while you are doing the compression test. Any of them wet from fuel or have an unusual color?

3. Make sure your EGR isn't opening when it shouldn't. You can removed & plug the vacuum line going to the EGR to test this. You'll get a check engine light, but it won't hurt anything.

4. O2 sensor that's bad will cause terrible fuel economy. If it has more than 100,000 miles on it, time for a replacement. Denso or NTK ONLY~

 

@ TNRabbit- ill do the compression test when i get home. ill go ahead and do the 02 sensor just in case, it has 191,000 miles on it.

@swampfox- i just cleaned the air filter last night, and thats the first time ive cleaned it since the tune up 3,000 miles ago, so i dont think thats causing it, but ill keep that in mind.

 

These trucks don't have a MAF (mass air flow) sensor. It is a vane AFM (air flow meter) and isn't susceptible to air filter oil issues.

 

Thanks for correcting me ,I have not worked on one so I was not sure.

 

Definitely sounds like something involving the O2 Sensor, or some type of unmetered air issue.
Any new leaks develop around the intake?
Any exhaust leaks before O2 sensor?

 

---check your timing chain and guides---

my mpg went from ~22 to ~19 when the guide broke. simple to check. once the guide was replaced, it's back at ~22

 

now that i think about it i do have an exhaust leak at the manifold. ive got the donut gasket, but i havent had a chance to put it on yet. timing chain was replaced by PO at 180,000 it now has 191,000.

 

ok. just making sure

carry on...