What the hell!??

C

calithirteen

New member
So I know this has been debated many times on here but I was just curious to see if anyone else has had this issue. My truck has never gotten that great of MPGs but I was very excited to see what would happen after fixing an exhaust leak and replacing both O2 sensors.

Low and behold, it has gotten WORSE!!!!! :mad::mad::mad: I went from around 15 mpg down to 11 mpg!!!

WTF!! Last year I did the sea foam treatment, tune up, maf sensor and throttle body cleaned, replaced a bad fuel injector as well as all of the fuel injector O-rings. Also, just replaced a bad u-joint and greased the entire driveline as well as replaced the fluid in the rear-differential. I am riding with 33" tires which i know hurts a little.

Should I replace the MAF sensor?
 
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How much have you driven since replacing? Did you pull the efi fuse to reset the ECM? The ECM needs to relearn after replacing parts like that.
 
S**T! I didn't! I was contemplating that. I did do that when I first got the truck 2 years ago. I'll give that a shot tonight and see how it goes. Thanks!

Any other suggestions?
 
Any check engine lights on? You did get the correct sensor for your vehicle right? Denso and not Bosch?
 
Robb235 said:
Any check engine lights on? You did get the correct sensor for your vehicle right? Denso and not Bosch?
Click to expand...

No CEL and fairly confident I used the correct Denso O2 sensors after all of the research I read on here. It's a non cali truck and the part number I used for both O2 sensors is 234-4162. I did have a CEL before the replacement which called bank 2 (if memory serves me correct) but I went ahead replaced both due to the age of the truck. After resetting the computer by pulling the terminals on the battery, the CEL went away and hasn't come back. I've driven well over 200 miles since the repair.
 
still burning up the gas

So I can't figure this out. I reset the EFI and noticed only a negligible gain in mpg. Barely 13. I know this truck has been know for it's whacky fuel gauge but for example, I am currently at half a tank and have barely 80 miles. When I reach E, I have hit roughly 225 miles for the tank.

Again to list all the recent mods:

new fuel filter,
greased driveline,
replaced rear differential gear fluid
new O2 sensors
patched hole in exhaust (welded in new piece of pipe by professional)
1.5" body lift kit
last spring I added 33" tires along with the tundra brake upgrade
last year, full tune up, cleaned throttle body, new air filter, cleaned MAF, replaced O rings on fuel injectors and 1 bad injector

Again there is no CEL on since replacing the O2s.

Any suggestions would help. Very desperate as the gas is just killing my wallet.
 
How are you calculating gas mileage? Are you just guessing the number of gallons used, or are you dividing the number of miles traveled between filling up by the number of gallons the car took to fill up? The reason I ask is because this will provide an accurate measurement of MPG, and some people have reported the 3rd gen to have inaccurate gas gauges certain years.
 
Also, the 33" tires will make your mileage traveled between tanks understated by about 7%. Just more food for thought.
 
I am calculating the MPGs by every tank I fill up. The amount of gallons used verse the amount of miles driven. I know about the whacky gauges as when I hit about 30 miles, I've supposedly used a 1/4 of the tank but it doesn't add up when I end up refilling it. I'm also aware of the effect of the larger tires can have, however, I have had them on since last March and was averaging around 13-15 local. As I mentioned earlier, since replacing the O2 sensors and fixing the exhaust leak, my mpgs have dropped to 11-13 local.

I noticed the change immediately after changing the O2 sensors as I expected a gain in mpg with that fix and instead the opposite happened. Do you think it's possible that the despite being Denso O2 sensors with the correct part number that they are not working correctly but somehow not throwing a code?:confused:
 
cold weather will drop the MPG. have you considered that. Also spark plugs will make a big impact on MPG. you can now buy the twin ground, dual platinum Denso plugs for our trucks whic will last longer than 50,000 miles
 
Gps

you have to calculate your miles via GPS! bc of your larger tires, your tripometer is reading low. i did the same thing after upgrading to 33's. run a gps and compare it to your tripometer and you'll see the difference.
 
I replaced the spark plugs last year with Densos as well as the wires so I doubt it is that. I know the cold weather does have an effect on gas but this seems extreme. Lastly I know the odometer will be off but the I only upgraded from 32" to 33" tires so again it shouldn't be this big of a difference.

Going to check under the hood and make sure the filter is ok and check all connections. I plan on doing another treatment of Seafoam sometime soon as well.
 
calithirteen said:
No CEL and fairly confident I used the correct Denso O2 sensors after all of the research I read on here. It's a non cali truck and the part number I used for both O2 sensors is 234-4162. I did have a CEL before the replacement which called bank 2 (if memory serves me correct) but I went ahead replaced both due to the age of the truck. After resetting the computer by pulling the terminals on the battery, the CEL went away and hasn't come back. I've driven well over 200 miles since the repair.
Click to expand...
Um, just to make sure we're not missing anything obvious you state you used the same part # for both sensors. Shouldn't they be two different parts? One an a/f sensor and the other o2?
 
"Um, just to make sure we're not missing anything obvious you state you used the same part # for both sensors. Shouldn't they be two different parts? One an a/f sensor and the other o2? "

My truck is non-Cali so it does not have the a/f sensor. Only 2 O2 sensors which are both the same part. CEL would be thrown if I had done that wrong!
 
Do they switch to that crappy oxygenated winter fuel in NY? They do it here in NJ around the middle or end of November. On my last two fill-ups the low level light turned on 20-25 miles sooner than when it used to.
 
Ed_C said:
Do they switch to that crappy oxygenated winter fuel in NY? They do it here in NJ around the middle or end of November. On my last two fill-ups the low level light turned on 20-25 miles sooner than when it used to.
Click to expand...

I believe they do. It's just weird how quick it happened. I feel like I was already running that winter mix crap but maybe not.
 
Are you sure you are calculating your MPG correctly with the larger size tires?

I put 32s on my truck and at 60mph im actually doing 68. I use a 1/4 tank in only 40 miles vs 60miles before.

I avg 14mpg per my odomoter and fuel used. HOWEVER if i use the correct millage im still getting 17. You have to remember you went from small tires to big tires and with 32s im off by 11% roughly.

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