Strange drop in MPG

[Mudeprived]

Checking the PCV is easier. Pull it off and shake it. If it rattles, its good. If not, spray some brake cleaner in it and shake. (It might just need a good clean out to get the ball inside to move freely) If you decide on a new PCV, please buy a Toyota OE PCV! They have the metal base and last a LONG TIME! The cheap aftermarket PCV's are G-A-R-B-A-G-E! The are usually all plastic and the engine heat (in my experience) has them fall apart in no time....Just my opinion from experience....

Not entirely true. I just pulled out my PCV a week ago and it rattled but it was not functioning. A new pcv solved many of my issues I was having.

To the OP, last year I sufferered a similar drop in mpg that caused me to run out of gas a few times (gauge is funky). I went from 305 miles per tank to barely hitting 250 and it happened right at the start of winter. It has still been piss poor up till today. I have not had the new pcv long enough to know if it was the cause.

 

[Jeremy107]

Not entirely true. I just pulled out my PCV a week ago and it rattled but it was not functioning. A new pcv solved many of my issues I was having.

To the OP, last year I sufferered a similar drop in mpg that caused me to run out of gas a few times (gauge is funky). I went from 305 miles per tank to barely hitting 250 and it happened right at the start of winter. It has still been piss poor up till today. I have not had the new pcv long enough to know if it was the cause.

This is good to know I replaced mine last week but it was aftermarket and literally 2$ at orilleys. Do you have the OEM part number for the PCV

 

[Mudeprived]

This is good to know I replaced mine last week but it was aftermarket and literally 2$ at orilleys. Do you have the OEM part number for the PCV

https://www.amazon.com/gp/aw/d/B00GJJNQB6?psc=1&ref=yo_pop_mb_pd_title

 

[TheDurk]

This is super helpful! Thank you. This came to mind for me as well but all previous cars if the o2 was bad it threw a code. Does 234-4162 work for both sensors upward and down stream sensors? Amazon says “doesn’t fit my 01” I indeed have a non Cali v6

No, you have a "Cali" type rig because all '01 and '02 4Runners have the Cali type system with a wideband Air/Fuel sensor up front, two catalytic converters and the threaded O2 sensor in back. The Feds moved to the Cali standards in 2001, so that distinction was done away with but you need to keep it in mind when ordering parts. The reason the O2 sensor did not fit in the harness is because the A/F sensors and the O2 sensors have different plugs so that people can't do what you tried to do. In addition,only '01 and '02 have the threaded rear o2 sensors, so the absolute worst thing you could do was take part number advice from someone with a non-Cali. rig from 2000 or before. Guaranteed not to fit front and back. The 234-4162 will not work in front or back on a 2001 because it is not threaded and is not an A/F. For a 2001, you want a 234-9002 (Cali-type A/F) in front and a 234-4261 in back (threaded O2).

ALWAYS check the Denso Find My Part site to get your p/n. The sensors vary by Cali/Federal, 4Cyl./6Cyl., 4WD/RWD, Auto/5speed, and year, so relying on another posters p/n's is a recipe for error unless you match ALL those things (with the exception of '01 and '02 which are all the same numbers I posted above).


Find My Part

Sorry I missed this thread first time around because some clarity was needed.

What is true is that the performance of o2 sensors CAN degrade with age without throwing a code. If mpg is down, and the front sensor has more than 85,000 on it, change it. The rear sensor you can leave until you get a code; they don't affect performance.

 

[Jeremy107]

No, you have a "Cali" type rig because all '01 and '02 4Runners have the Cali type system with a wideband Air/Fuel sensor up front, two catalytic converters and the threaded O2 sensor in back. The Feds moved to the Cali standards in 2001, so that distinction was done away with but you need to keep it in mind when ordering parts. The reason the O2 sensor did not fit in the harness is because the A/F sensors and the O2 sensors have different plugs so that people can't do what you tried to do. In addition,only '01 and '02 have the threaded rear o2 sensors, so the absolute worst thing you could do was take part number advice from someone with a non-Cali. rig from 2000 or before. Guaranteed not to fit front and back. The 234-4162 will not work in front or back on a 2001 because it is not threaded and is not an A/F. For a 2001, you want a 234-9002 (Cali-type A/F) in front and a 234-4261 in back (threaded O2).

ALWAYS check the Denso Find My Part site to get your p/n. The sensors vary by Cali/Federal, 4Cyl./6Cyl., 4WD/RWD, Auto/5speed, and year, so relying on another posters p/n's is a recipe for error unless you match ALL those things (with the exception of '01 and '02 which are all the same numbers I posted above).


Find My Part

Sorry I missed this thread first time around because some clarity was needed.

What is true is that the performance of o2 sensors CAN degrade with age without throwing a code. If mpg is down, and the front sensor has more than 85,000 on it, change it. The rear sensor you can leave until you get a code; they don't affect performance.

I was hoping I could dodge replacing the front on as it’s 120$ and a like 3 weeks till amazon ships!

This is very helpful tho thank you very much

 

[Jeremy107]

Two full tanks after the downstream O2 replacement and OEM PCV valve and still same MPG. Had the codes checked again and nothing. This is frustrating!

 

[T.A.Kirk]

Two full tanks after the downstream O2 replacement and OEM PCV valve and still same MPG. Had the codes checked again and nothing. This is frustrating!

Just a thought, but have you checked all your vacuum lines for frays and abrasions? One thing that will screw you up on these engines is if you've got a leak somewhere, and it may not even be consistent--I had a similar issue with my old 3VZE in my Truck, and that sucker eluded the mechanic and I for weeks. Took until I tore down the truck to re-do the valve cover gaskets for me to find the vacuum hose that had worn through, and it was basically invisible to a casual inspection--You had to disconnect that bastard and run your hand down it to find the spot, and then it was like "Damn... How'd I miss that?".

 

[Zorrota]

Two full tanks after the downstream O2 replacement and OEM PCV valve and still same MPG. Had the codes checked again and nothing. This is frustrating!

Unless I missed something earlier, it looks like you only replaced the downstream sensor. As mentioned, this does not affect mileage. You need to change the upstream sensor if it hasn't been changed. I've changed them in all my vehicles based on miles in service-never had a CEL-and fuel economy improved in every case.
Hope this is your problem.

 

[Jeremy107]

Unless I missed something earlier, it looks like you only replaced the downstream sensor. As mentioned, this does not affect mileage. You need to change the upstream sensor if it hasn't been changed. I've changed them in all my vehicles based on miles in service-never had a CEL-and fuel economy improved in every case.
Hope this is your problem.

I’m just confused as it is not throwing a code at all, shouldn’t it throw a code if the O2 is bad?

 

[Zorrota]

I’m just confused as it is not throwing a code at all, shouldn’t it throw a code if the O2 is bad?

If you get a total sensor failure or a broken wire, yes. If you just have degradation over time you won't get a code but you will see an improvement in drivability and economy with a new one. I change them at around 150K whether GM, Ford, Toyota, whatever.