Downstream Oxygen Sensor Questions (1 Viewer)

[landylover21]

Quick question guys:

My 98 has been getting horrible gas mileage lately (yes, even more horrible than normal) to the point where making trips around town uses an ungodly amount of gas (even starting it seems to use a lot). I checked and with some math I'm getting around 7 mpg, and that's driving somewhat tenderly. It doesn't seem to matter if it's short or long trips. I checked the thermostat and it seems to be operating correctly as it reads in the middle of the thermometer where it always has for the past 16 years; and I finally got a CEL two days ago. Pulled it with the code reader and got P0156 Bank 2, Sensor 2. This seems odd because I redid my exhaust including new cats and a Borla exhaust. I had the two upstream sensors replaced when I did this but the two downstream ones I saved a few bucks with and recycled my old ones. My 100 only has 80K on the clock and people say downstream sensors tend to last longer.

I've read that the downstream ones are only there to monitor whether or not the cats are doing their job (which they should be seeing how they're new OEM). Could this be the cause of my awful mileage? Is there anything I should check before ordering new sensors? I don't really feel like putting a lot of money into this if possible only because I spent so much money on this back in March so I'm kind of annoyed.

Sorry for all these questions, I love this truck, and in the 16 years my family has owned it, it has been a solid, reliable workhorse!!! I've searched but a lot of the o2 sensor questions stem from OEM vs aftermarket and the upstream sensors.

Thanks,

Rich

 

[White Stripe]

Downstream sensors won't affect fuel mileage. Upstream sensors can affect mileage, but will kick on a check engine light if thats the case. Mass air flow might be your culprit. However I do see you are in NY. I would check your brakes to see if they are dragging. If you do not lube your brakes properly in the NE they will stick after a few months in the winter salt.

 

[landylover21]

Thanks for the response. In regards to the MAF sensor, I clean it and the throttle body every time I do an oil change. I'll have my friend check my brakes to make sure they're not sticking, he has a lift so it'll be easier for him to do.

It's just strange because I know the consensus on this board is that fuel mileage will drop drastically before the engine throws a code, and its been like this for the past few months now and I finally got the P0156 the other day. I know these trucks are pigs by nature and don't mind paying the extra bucks for gas in return for safety and reliability but it has gotten to the point where I dread having to drive anywhere (luckily, I'm in walking distance to my work).

 

[pwcummings]

Probably too simple of a solution but I noticed a similar mileage drop when I accidently forgot to refill my tires after a wheelin session. Might check those tires. I usually keep my nittos at 50 psi for highway, 20 for wheelin. To look at them, it's hard to tell much of a stance difference between the wheelin mode and the highway mode, and I have got them down to around 15 psi before the tire pressure light activated.

Another problem might be bad gasoline?

More complicated culprits might be ecu troubles (although I would think you would see more codes than just the O2).

Might also be that the new cats that were installed are choking ur system, or just the piping or mufflers are doing the same. If you still have your old exhaust, I would put it back on and see if the mileage is affected.

Just some shots in the dark without knowing exactly how this problem began.


...via IH8MUD app

 

[landylover21]

pwcummings:

I usually keep my tires around 40-42 psi, will check in the morning.

I might switch gas stations for awhile and see what happens, only reason I'm going to this place is because my grocery store offers a discount at their gas station with their card. My old exhaust is looong gone, it rotted out which prompted me to just replace it with a decent quality catback that cost less than OEM.