So I am getting absolutely horrible gas mileage. Like I am talking 120-150 miles a tank. City and Highway. Does that sound right?
I did a complete tune up about 2000 miles ago. Spark Plugs, wires, cap, rotor, oil, seafoam and etc. I recently just had a muffler blow out so it has a new muffler as well. I am not very hard on it at all like below 3k RPM's at all times. What do you guys think?

Now that I think about I didn't gap the plugs. I can look it up but figure it would just be easier to ask.

1992 Jeep Cherokee 164k miles

Thanks in advance

 

definitly something wrong with how you installed the plugs.

 

It was this bad before the tune up... But just in case what normally could go wrong? Cause the order is right. I am pretty good with cars not just some kid that doesn't know what he is doin lol. I also have a 91 Camaro undergoing a difficult LS1 swap

 

OOOhhh put the LS1 in the Jeep!

There can be so much that causes bad gas mileage. The most common is in need of a Tune-up. Yours seems to be pretty extreme. Check for a hole in the gas tank LOL.

Are you lifted with bigger tires! May want to try running a can of Seafoam in with a full tank of gas,

Do you have anything causing drag on it. Alignment issues. Have ya thought about changing the timing chain...

There is a sensor I can't remember which one with out researching that will send more fuel to your motor if it thinks it is too cold or too hot or something. Map sensor or something. Sorry I can't help more.

 

Try getting your gas at a different location then you normally do.Also depending on where you live if it's winter and cold the gas companies use a winter mix in there fuels that does effect fuel economy.It's sounds like you may have other issues but this is a easy fix to try.

 

Any other ideas?


I always change gas stations and run premium BP gas twice a month

 

dragging brakes, low tire pressure/over size tires, coolant temperature sensor........
tell us more about your xj, what transmission? when did you last change differential fluids?
any driveabilty issues?

 

BTW the boat is too aerodynamic to cause gas mileage issues.

 

Brakes are fine. They kinda suck but I expect that from an 19 year old car. air pressure is good, stock tires. I think coolant sensor is good but I'll replace it along with the IAT tomorrow. Idk what transmission to be honest. M5 come to mind but IDK automatic though. I have never replaced differential fluid but the front does make noise when driving so I'll do that tomorrow too. Any tips for doin that? Any specific oil?

 

Bump

 

convertor may be plugging up only thing i can add

 

o2 sensors?


oh and spark plugs should be gapped 0.035

definitely check them...one of mine was off (too narrow of a gap) the rest were fine, but still should check.

 

I would check o2sensor. Hook it up see what computer says

 

Yeah, I would say front o2 sensor. Thats what controls the amount of fuel that the injectors spray.

 

Oxygen sensors have a finite lifespan of between 100k and 150k, depending on the efficiency of the engine. They can get "lazy" and contribute to a fuel/air ratio that is not optimum quite a bit before they actually set an OBD code.

If you do replace an oxygen sensor, stay away from no-name sensors and absolutely no universal sensors! Lot of crap sensors floating around e-bay, so buyer beware. I look for NTK or Bosch for oxygen sensors.

Gap for the plug is .035 Champion copper plugs are a good choice for your engine.

Calculate your gas mileage (miles driven divided by gallons consumed) for the most accurate gas mileage numbers. Get at least 3 samples before assuming anything.