Strange drop in MPG

[Jeremy107]

265/75/17 tires 3” lift 80% highway driving I was getter nah around 320 miles per tank from tip top full to the last drop empty. The last few tanks I’ve been getting 270s, anyone have any ideas on the suddden drop?

Plugs and wires 6k miles ago, air filter and other regular maintenance done. Normal 5k syn oil changes as well.

No CEL, always run in ECT power and drive like a grand dad

 

[DaMonkey]

I think you'll get a handful of suggestions to replace upstream o2 sensor? that seems to be a culprit for mpg.

mpg can also change with seasonality with ethanol in gas but your drop is definitely big enough to be suspicious of anything else.

MAF is a spot to clean too.

 

[BamaDrewski]

I think you'll get a handful of suggestions to replace upstream o2 sensor? that seems to be a culprit for mpg.

mpg can also change with seasonality with ethanol in gas but your drop is definitely big enough to be suspicious of anything else.

MAF is a spot to clean too.

I 2nd the suggestion on the 02 sensor. (02 sensors rarely throw a CEL when they are failing/shot) However, I would recommend you replace the fore and the aft sensor when replacing any of them. I purchase mine from Amazon and they are DENSO and exact fit on a non-California, 3.4L 5VZFE. The Denso part number (for both) is 234-4162. I tried using Amazon's "part matcher" one time and it gave me two different part numbers for the 02 sensors. So, I wrote down the right part number in my maintenance records. If you have a Cali rig or a 4 cylinder, the part numbers are probably different.

 

[Jeremy107]

I 2nd the suggestion on the 02 sensor. (02 sensors rarely throw a CEL when they are failing/shot) However, I would recommend you replace the fore and the aft sensor when replacing any of them. I purchase mine from Amazon and they are DENSO and exact fit on a non-California, 3.4L 5VZFE. The Denso part number (for both) is 234-4162. I tried using Amazon's "part matcher" one time and it gave me two different part numbers for the 02 sensors. So, I wrote down the right part number in my maintenance records. If you have a Cali rig or a 4 cylinder, the part numbers are probably different.

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

 

[BamaDrewski]

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

I think it would be unusual if they did not fit and yes, both the fore and aft are the same part numbers. Through lots of experiences (bad experiences) I DO NOT TRUST Amazon's part matching "system". I would suggest you go to the DENSO website and see what they recommend and order that part number from Amazon. Good luck!

 

[19963.4lsr5]

Rock auto has the wire length I think. Then measure yours.


Sent from my iPhone using Tapatalk

 

[Kracker]

I had an issue with my 1998. Lockup was not occurring at 50 mph or so. Thus, not lowering the rpm to normal. Gas mileage was suffering. I am kinda handy but not a mechanic, by any means, but I replaced the shift solenoid, myself, and everything was just fine. However, I was getting a CEL which was diagnosed as a PO770 or 773 or something. I can't quite remember, exactly. I think you should be running around 2500 rpm's at 70 mph. Again, I am recalling from memory. You can research this on this forum if you think this may apply to you. Good luck.

 

[gamefreakgc]

Check into if your local county/state changed their fuel blends. In California, last year they added more ethanol to our fuel and everyone with an older vehicle lost about 10-15% of their MPG's. I dropped from averaging close to 18 MPG to 16.

 

[4-Ripcord]

Can almost guarantee it is either the PCV or upstream O2. PCV is cheap and easy to replace, O2 not so much.

Check out this post for a list of all items you can check to improve MPG:
Buyer's Guide: Tune -up pointers

 

[BamaDrewski]

Can almost guarantee it is either the PCV or upstream O2. PCV is cheap and easy to replace, O2 not so much.

Check out this post for a list of all items you can check to improve MPG:
Buyer's Guide: Tune -up pointers

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....

 

[p nut]

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....

OE O2 sensors as well. Do not go to Autozone to get Bosch units. Bite the bullet and go to Toyota.

 

[BamaDrewski]

OE O2 sensors as well. Do not go to Autozone to get Bosch units. Bite the bullet and go to Toyota.

In my experience, the DENSO 02 sensors from Amazon have worked fine. I might be wrong, but I believe the TOYOTA OE oxygen sensors are in fact made my Denso. The dealer wants over $100 ($116 at Toyota of Dallas NOT INCLUDING SHIPPING) for each sensor and Amazon has the Denso sensors for $46.48. Denso Part #234-4162 (Both sensors the same on the 3.4 non-California rigs)

I last replaced my 02 sensors in March of 2012 with the Denso's from Amazon and have had no issues....some 6+ years later.

I agree that if it is in the budget to go OEM but in this case, the saving of some $50 per sensor (a total of $100 savings) is a proven exception....(in my case anyways......)

With respect to BOSCH, it seems that anything BOSCH sells for our 3rd gen rigs is hated by our trucks. Made the mistake many, many years ago of trying to run BOSCH platinum plugs in my engine and it was a HUGE MISTAKE......never again!!!

 

[gamefreakgc]

In my experience, the DENSO 02 sensors from Amazon have worked fine. I might be wrong, but I believe the TOYOTA OE oxygen sensors are in fact made my Denso. The dealer wants over $100 ($116 at Toyota of Dallas NOT INCLUDING SHIPPING) for each sensor and Amazon has the Denso sensors for $46.48. Denso Part #234-4162 (Both sensors the same on the 3.4 non-California rigs)

I last replaced my 02 sensors in March of 2012 with the Denso's from Amazon and have had no issues....some 6+ years later.

I agree that if it is in the budget to go OEM but in this case, the saving of some $50 per sensor (a total of $100 savings) is a proven exception....(in my case anyways......)

With respect to BOSCH, it seems that anything BOSCH sells for our 3rd gen rigs is hated by our trucks. Made the mistake many, many years ago of trying to run BOSCH platinum plugs in my engine and it was a HUGE MISTAKE......never again!!!

You are correct, they are DENSO's. You can even buy them direct from DENSO if you really want to.

Bosch does make some great parts for other vehicles like BMW's, but they are not the original sensors for Toyotas like you said. Our vehicles use almost exclusively DENSO sensors.

 

[BamaDrewski]

You are correct, they are DENSO's. You can even buy them direct from DENSO if you really want to.

Bosch does make some great parts for other vehicles like BMW's, but they are not the original sensors for Toyotas like you said. Our vehicles use almost exclusively DENSO sensors.

Thanks for the tip. For the curious, the website to purchase direct is: DENSO Auto Parts

 

[p nut]

In my experience, the DENSO 02 sensors from Amazon have worked fine. I might be wrong, but I believe the TOYOTA OE oxygen sensors are in fact made my Denso. The dealer wants over $100 ($116 at Toyota of Dallas NOT INCLUDING SHIPPING) for each sensor and Amazon has the Denso sensors for $46.48. Denso Part #234-4162 (Both sensors the same on the 3.4 non-California rigs)

I last replaced my 02 sensors in March of 2012 with the Denso's from Amazon and have had no issues....some 6+ years later.

I agree that if it is in the budget to go OEM but in this case, the saving of some $50 per sensor (a total of $100 savings) is a proven exception....(in my case anyways......)

With respect to BOSCH, it seems that anything BOSCH sells for our 3rd gen rigs is hated by our trucks. Made the mistake many, many years ago of trying to run BOSCH platinum plugs in my engine and it was a HUGE MISTAKE......never again!!!

Not a direct experience with Toyota parts, but for my old Honda, which also used Denso and NGK parts, I've found in several instances where those parts were acquired at a parts store were found to be inferior. Either the part number was off by a digit or two, or the part itself was slightly different. This was especially true for the O2 sensor for my old Civic, which required a "wide-band" O2 sensor. Didn't work quite right. Bit the bullet and went Honda.

 

[Jeremy107]

I think it would be unusual if they did not fit and yes, both the fore and aft are the same part numbers. Through lots of experiences (bad experiences) I DO NOT TRUST Amazon's part matching "system". I would suggest you go to the DENSO website and see what they recommend and order that part number from Amazon. Good luck!

Got both these sensors in and just for the record these are the incorrect ones on the wiring harness end.

 

[Jeremy107]

Pic is from denso website but they both are listed downstream

 

[Jeremy107]

Downstream sensor replaced this weekend and from the first quarter of the tank seems to be back to where it was before the MPG drop but will need to wait until I run a full tank.

Correction downstream for 01 SR5 is Denso 234-4261

 

[BamaDrewski]

Downstream sensor replaced this weekend and from the first quarter of the tank seems to be back to where it was before the MPG drop but will need to wait until I run a full tank.

Correction downstream for 01 SR5 is Denso 234-4261

Glad you seem to be back on track with the mileage However, I am somewhat confused. Did you use the same part# sensor for the fore and aft positions? Also, is it 234-4261 or 234-4162?

 

[Jeremy107]

Glad you seem to be back on track with the mileage However, I am somewhat confused. Did you use the same part# sensor for the fore and aft positions? Also, is it 234-4261 or 234-4162?

234-4261 ordered and goes in no prob, also I know few said don’t pay attention to the amazon part match but it did verify it was the downstream. It is the threaded sensor, the upstream is held in by two 12mm bolts with a gasket and it is 234-9002