Poor highway mpg

S

Sr Auron

New member
I can seem to find a thread on this so if there is one, point me to it.
My highway mpg is worse than my city. My city is actually good at 16.5, but highway is maybe 14.6.
It's completely stock and I've only had it 2 weeks, so I don't know much about it. After changing plugs I reset to EFI as well.

If you think it matters, I also have a check engine code P0456.
 
Register to hide this ad
V6 or V8 ?

I can tell you my V6, with winter gas blend I get around 17.5 country driving and 18 highway traveling around 70~75mph

Summer gas gets better overall mileage, 19 country and around 22 on the highway.


Your code could be a gas cap or other small leak in the evap system. Probably evap system, as the cap sets other lights.
 
Sr Auron said:
I have a scan tool, what numbers should I check that could clue me on the issue.
Click to expand...

Maybe check your fuel trims if your scanner can look at that live. That should tell you if the engine is running lean or rich and when.

ScannerDanner on youtube has some great videos explaining fuel trims if you aren't familiar with them.
 
I know in the summer when mine were working well

My 03 would get 21 MPG

My 08 would get up to 24 (currently running about 21)

The usual stuff for MPG is the air intake filter, spark plugs/coils, consider a fuel and exhaust cleaner. Otherwise, I wonder if its a cooling issue with your engine - if it is getting too hot, something rubbing on your wheels/ calipers/breaks creating drag
 
Since we're throwing ideas into the pile. maybe it's not shifting into overdrive or the torque converter isn't locking up properly.
 
Montego Murph said:
Since we're throwing ideas into the pile. maybe it's not shifting into overdrive or the torque converter isn't locking up properly.
Click to expand...

That should be easy to check. Just count the shifts as you accelerate onto the highway. Or see how high your RPMs are at >60mph.

If the torque converter isn't locking up would that cause the "rumble strip" issue? I would think that would be easily noticeable too.
 
Frozen caliper(s) will haul down the fuel mileage noticeably. So will dirty MAF sensor and TB. I had dropped off from 22mpg highway to 19mpg, cleaned the MAF and TB, changed out the plugs just because, air filter was fine. Mileage slowly climbed back up to ~21mpg where it remains now (the dreamometer shows around 23mpg to make me feel better :) ). Easy to check the calipers if you have an IR thermometer - drive without doing much braking and then measure the temps of the rotors all around - you may find one or two significantly hotter than the others (significant being a couple hundred degrees difference in my case).
 
tom4416 said:
Frozen caliper(s) will haul down the fuel mileage noticeably. So will dirty MAF sensor and TB. I had dropped off from 22mpg highway to 19mpg, cleaned the MAF and TB, changed out the plugs just because, air filter was fine. Mileage slowly climbed back up to ~21mpg where it remains now (the dreamometer shows around 23mpg to make me feel better :) ). Easy to check the calipers if you have an IR thermometer - drive without doing much braking and then measure the temps of the rotors all around - you may find one or two significantly hotter than the others (significant being a couple hundred degrees difference in my case).
Click to expand...

Do you happen to know what type of plugs you had and what kind you have now? I was reading through some threads on here yesterday and a couple people said they switched to iridium and noticed a drop in mpgs.

I switched from copper to iridium a few thousand miles ago and noticed my mpgs dropped. It's either that or one of my calipers is sticking. I'm planning on replacing the calipers then waiting a couple thousand miles to see if the fuel economy improves. If it doesn't I'll switch the plugs back to copper and wait again. If that doesn't do it I'll try the MAF and TB. I would just do it all at once, but I really want to know which is causing the drop haha.
 
Thanks for all the input. I just cleared my codes to see if they come back, after a few adjustments. I'll have to grab mass airflow cleaner as well. How much does the pcv valve play into mpgs?
 
Sr Auron said:
Thanks for all the input. I just cleared my codes to see if they come back, after a few adjustments. I'll have to grab mass airflow cleaner as well. How much does the pcv valve play into mpgs?
Click to expand...

PCV valve should have very tiny effect on measurable MPG. Maybe check highway RPM's, tire pressure, and brakes of course
 
You must log in or register to reply here.

Members online

Total: 391 (members: 3, guests: 388)

Forum statistics

Threads
278,307
Messages
3,554,054
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top