crappy gas mileage.

[mr_jones71]

i just bought a 95 grand cherokee limited 5.2l full time 4 wheel drive. when i checked on the net it said that the averaged 14 in the city and 17 to 18 on the highway. mine on the other hand is reading 10.5 on the mileage read out in my overhed console. im planing on doing a tune up. plugs,wires,oil, and filters,to see it that helps. basically i was wondering if anyone has had a problem with this and how they got there mileage back up to normal.

[BenBB]

That could be right, it also has to do with how heavy you drive, because on the V8 that will be a factor. Other wise i would stick with doing the tune up too.

[gregmondro]

the v8 versus the i6 isn't a factor.

they both get shitty gas mileage lol.

check your tire pressure, also, when's the last time the o2 sensor was replaced?

[neon_rt]

The intake manifold gasket tend to leak hot air from the lifter valley onto the bottom of the intake manifold causing it to get very hot. This causes the computer to reduce ignition timing and richen the fuel mixture to prevent pinging. This also reduces gas mileage considerably, you may want to ckeck on the condition of the gasket/manifold when you are doing the tuneup.

[JDPascal]

Originally Posted by mr_jones71

i just bought a 95 grand cherokee limited 5.2l full time 4 wheel drive. when i checked on the net it said that the averaged 14 in the city and 17 to 18 on the highway. mine on the other hand is reading 10.5 on the mileage read out in my overhed console. im planing on doing a tune up. plugs,wires,oil, and filters,to see it that helps. basically i was wondering if anyone has had a problem with this and how they got there mileage back up to normal.

Hi mr_jones71

I have the same engine/power train as you.

The fuel mileage display can be reset by pressing and holding the buttons on the console for 3 seconds - check your owners manual.

I reset mine when going down hill with foot off the gas pedal. Makes me feel good about the 30+mpg it shows for a while. It feels better than watching and waiting for the mileage to improve from the 10 or 11 mpg too.

Resetting it while on a highway trip will give you a reasonable number to work from in about 75 to 100 miles. You don't even need a newly filled tank of gas to make it work out right. When I do this and travel at just under 2000 rpm on the tach, with the cruise engaged I consistently wind up with 19 to 19.3 mpg (US) on the avg mpg display after that distance. It is always reduced after I start in town and short trip driving and can get to as low as 12 or 13 - maybe less - if I don’t get out of town for a while.

I do keep up with the maintenance. I use regular champion plugs gapped to spec and change them every summer. The air filter is checked and intake housing cleaned spring and fall. I monitor tire pressures at least monthly and adjust to 36psi. Synthetic oil in the transfer case and diffs also help imho.

I use synthetic engine oil most of the time but haven't noticed how that might influence fuel economy. Some think there is an advantage there but I use it mainly because of quicker startup lubrication.

JD

[JeepForever]

Another post suggested that poor fuel efficiency can stem from a bad Oxygen Sensor. I just replaced mine last weekend and I haven't run a full tank yet. I'll report back with mileage after I've determined if it makes a difference. Supposedly with the O2 sensor it can go bad but not produce a Check Engine light because the computer doesn't know it's bad. It just thinks there's a bad fuel mix so it dumps more fuel into the engine. The computer does what it's programmed to do, and doesn't know that it's getting bad info (from a bad sensor). It took me about 15 minutes to replace the sensor.

[philipoc]

Can u describe where about the O2 sensor is found,and how to replace it?
My mpg is pretty bad also...

thanks people

[BenBB]

The most common that goes out, i think, is on the cat. converter, there may be another further up towards the engine but im not 100% sure. The last one i replaced was around 50-60 bucks. good luck.

[JeepForever]

The 02 sensors vary based on year. My '94 Jeep GC only has one and it's located before the CAT, close to the engine (follow the exhaust pipe toward the engine, in the exhaust pipe just a few inches from the CAT, closer to the engine). I was able to remove it with a crescent wrench, although it took some leverage and lube because it was really cranked in tightly. I unplugged the wire (about a foot up from the sensor), unscrewed the old sensor, carefully put the new one in, plugged it in, and took it for a test drive. I didn't even have to put the front wheels on ramps (although that would have made it a bit easier to get to).

So far my first tank of gas with the new sensor wasn't much better, but I was pulling trailer loads of firewood through some hilly roads. If I get the same (or slightly better) mileage towing heavy loads, I expect it will improve when I go back to normal driving.

[philipoc]

Thats great advice, thanks so much.
I'm driving a 93 gc limited. I'm assuming t he sensor can be found in a similar loction to the ones you've describe??
Thanks again..