My 2004 Grand Cherokee (4.0) is getting terrible gas mileage. It seems like the best I can do right now is 14mpg. That's driving 35 miles to work, all highway.

I think the bands might need adjusted in my tranny, but could it be killing the mileage that bad? It just seems like something is holding it back at highway speeds. The trans shifts fine, although it has slipped a couple times the last few weeks when it's cold - once it warms up, it's fine.

I can't figure out why the mileage has gotten so bad recently. I'm running stock size tires. I do have 112K on the clock, but the engine runs very smooth.

Any ideas on what I could check? I've Sea Foamed, changed the spark plugs, and cleaned the TB recently.

Thanks.

 

Are you looking at the overhead or are you doing the math at the pump? Your overhead is wrong. I have a 00 g.c. and the over head tells me that I am getting 12. mpg.

 

Even if he's going by overhead, he clearly has noticed a drop significant enough to cause concern and states he feels it holding back. Just because a guage is inaccurate does not mean it can't indicate a problem. If your speedo is ten mph off, and drops when you slow down, the number is wrong but you are still going slower than before (as an example).

Everything effects gas milage. It could be anything, including the trans adjustment. Start with simple maintence ie check your filters, plugs, tires, air pressure etc. Weather changes can affect air pressure.

 

tire size/speed/what do you carry?

 

Have u checked the overdrive\power switch? Sounds like overdrive is off.

 

Band adjustment will not help fuel mileage, basically band adjustment would only affect shift timing of 2nd gear. Front band is only applied in 2nd gear, rear band is only applied in Reverse or manual low/manual 1st gear. If the adjustment was out far enough to cause a major concern it would just burn and cause a concern much bigger than a fuel mileage complaint.

Other than checking obvious things, you might make sure your reaching operating temp (stuck/weak thermostat), if you have access to a scanner then make sure all sensors are indicating correctly. Check fro vacuum leaks, injector flush, complete tune up etc...