Only getting 16mpg on the highway

[csprinkle]

Hello all,

 

I've noticed a slight decline in my gas mileage despite ditching the lead foot. I've been staying around 2500rpm on the highway and using cruise control when I can, but my mpg is still around 16. 99% of the time I am in rwd, so I don't think the 4wd system is really to blame here. I think my cats might be clogged because there's been a P0304 misfire code for a while now, dunno if that has anything to do in this situation. I've bounced around from Shell, Costco, Chevron, etc. over the course of a year and still saw the same results (all using premium/92 fuel).

 

Does anyone have any suggestions of where to start with tackling this sort of problem or should I just give it a rest? At the end of the day, I know it's a fuel-hungry V6, but I would expect a little more mpgs while driving like a grandma down the highway

 

Thanks!

[hawairish]

16 mpg on a misfire...I'd be happy to see that on my truck!

 

But ultimately, a misfire will absolutely affect mileage.  Since cylinder #4 (the "04" in P0304) is easily accessible on the engine (driver's side), you could at least swap the #2 and #4 coil packs to see if the problem travels, and pull the #4 spark plug to check its condition and replace if warranted.  Those two actions would at least rule out spark issues.

 

Air and fuel you can't really check without tearing down the top of the engine a bit, but maybe a borescope might show something.  In tracking down my own engine issues in recent years, a smoke machine proved super valuable in finding leaks.  Maybe run a fuel system treatment for a tank or two in case it's something with the injector.

 

Unlikely the code is tied to clogged cat.  Two other cylinders exist on the engine bank, so you'd throw a bank-specific cat or O2 sensor code instead.

[R50JR]

3 hours ago, csprinkle said:

Hello all,

 

I've noticed a slight decline in my gas mileage despite ditching the lead foot. I've been staying around 2500rpm on the highway and using cruise control when I can, but my mpg is still around 16. 99% of the time I am in rwd, so I don't think the 4wd system is really to blame here. I think my cats might be clogged because there's been a P0304 misfire code for a while now, dunno if that has anything to do in this situation. I've bounced around from Shell, Costco, Chevron, etc. over the course of a year and still saw the same results (all using premium/92 fuel).

 

Does anyone have any suggestions of where to start with tackling this sort of problem or should I just give it a rest? At the end of the day, I know it's a fuel-hungry V6, but I would expect a little more mpgs while driving like a grandma down the highway

 

Thanks!

Definitely try what Hawairish has recommended with the coil packs. I believe I was around 18 mpg when my pathfinder was stock. Now I am hovering around 13-14 mpg highway.