Big Chief

I have a 2005 GC... owned since 2006. Never had any issues until now. I do regular maintainence... only 56,000 miles.

All of sudden I have a ridculous drop in mpg. I get 6 in city and 9 on highway. I noticed this about 3 weeks ago. I check this about every 1-2 weeks on the cluster, so it has not been that long.

What I have done already and what I have noticed:

No check engine lights. Motor starts and runs fine, except for a high idle in the morning at 1000rpm, then goes away with 10 minutes of driving. Transmission seems to shift fine also.

I replaced all 4 O2 sensors. I ran injector cleaner through a vaccuum line to clean the runners and injectors. I also pulled the intake box and scrubbed the throttle body and replaced filter.

Thoughts?

lookin2wheel

Check your oil for a gas small. If it is then you have a bad injector or several bad injectors dumping gas into the crankcase through the cylinders. I had this happen on an old Toyota Corolla I had. It was flooding the engine basically. Ran Ok but had crappy gas mileage and the oil was thinned with raw gas.

pwb

when you have bad MPG, stop the car, take out the fuelpump relay, wait 10 min, start the car, it should start and run for 1 sec. If it dont start then you dont have fuelpressure in your fuelrail and maybe a leak injector. I dont know if its possible to start a 2005 without fuel relay. But my 1993 4.0 did run for 1 sec without fuelrelay and after been shutdown for 10-15min, so that proved me that there couldnt be any leak injector or other leaks in the fuel lines. But i dont know if a 2005 engine is possible to test this way.

ActionJoe

hey i have pretty horrible gas milage as well im my 05 with 5.7l hemi
what you can try befor you pull stuff apart is resetting the gas milage.
to do this, go to the gas milage so it shows up under the rpms and press reset which is on the left side of the center controls area next to heat control. this should reset the gas milage and hopefully improve. take note that this is not always acurate, as it is an average and adds in the gas used when idling. Personally when i drive to school i can average as low as 8 mpg because im just inching forward for 10-20 mintues a day. GOOD LUCK

Big Chief

ActionJoe: I thought the gauge might have been faulty at first... Thats how I noticed all this started... I tracked my actual miles at fill up and quickly found, the gauge is accurate and working... I was actually only getting 6mpg for afew weeks till I noticed it.

Looking2Wheel: Wondered the same thing also... I changed the oil during all this, so it was fresh and I could monitor it easier. I doesnt seem to have any gas in it though. Atleast I am actually burning it, it appears. I have not checked the plugs for wearing yet though... thats my next task it appears.

PWB: This was an interesting test... Creative and Easy. I tried it 2 ways. First, the car has been sitting an hour... I cycled the key to try and "prime the pump"... then pulled the relay. Waited 10 mins and it "almost" caught and started. So I put back together, started car for 2 mins... then just pulled the relay (no priming this time)... waited 10+ mins... and the car actually started for a second. It barely held on, but it ran for about 1-2 secs. Put relay back in... and cranked right up.

According that test... It appears to be holding pressure. Regular and injectors would appear to be fine. I think I will try it again, and wait an hour maybe??

Otherwise, I am back to the drawing board now...

I heard someone say, there is a way to "reset" the computer??? Not the negative cable way... something more involved?

Thanks for your help guys,

Bustedback

Put a locking gas cap on your rig.

pwb

Have you checked all your vaccum lines? I had bad crankcase elbow and after i replaced both and the lines it seems to get better MPG, not much but arround 1-1,5. What is your color on the sparkplugs, if it get to much i think you would see it on them?

khunter0622

Big Chief, did you ever find out what it was? I am having the exact same issue. I used to get around 15mpg, now I am getting around 8mpg. Nothing noticeable happened. Newer plugs. Checked fluids. Checked for anything obvious. No check engine light. Nothing. Seems to drive exactly the same, no loss of power. Thanks

Big Chief

Sorry for the late reply... been out of town.

YES. I did find the problem. Absolutely ridiculous for Jeep to do this if you ask me though...

Is your ABS light also on? I bet it is... In all my life, I have always ignored this light on other cars because it wasnt worth fixing usually.

On the Jeeps, there are sensors on each wheel, which tie into the ABS light trigger. For some reason these sensors also tie into the computer for fuel consumption/distribution. I had a bad sensor on my rear wheel, took 30 minutes to replace it and $15.00 bucks... reset the computer and my problem was solved.

Good Luck,

dave1123

Huh! I'll have to check that out. The ABS light on my WJ comes on occasionally but will be off in a restart. Maybe that's why I sometimes get poor mileage. It usually happens after 3 hours of stop and go delivering newspapers. The VIC shows 11 mpg but 16+ on the highway.

Bakerbuilttracks

Same issue here also. Light came on and off randomly. Now it seems to stay on and the display says " service electric brake system". Since it is now staying on the lie o meter says 8-10 mpg when it used to say 18-20.

How did you determine which abs sensor was bad with out replacing all of them ?

Big Chief

It was dumb luck... After all the research and work I was doing trying to solve the MPG problem, I figured I should resolve that ABS CEL to start from a clean slate for troubleshooting.

After I realized the sensors were at each wheel, I pulled the first wheel (rear driver) and the broken sensor was obvious at that point. Completely snapped. I was about to pull all the wheels and check each sensor, but I only had to check the first wheel. 15 mins later it was solved.

Big Chief

Forgot to add... I was searching for info all over the net about the MPG issue and I had afew references to a speed sensor. Most speed sensors that I am familiar with are in/at the transmission though... Continuing in my research, I found the speed sensor for the Jeep were at the wheel(s). But most of my research also referred to a ABS sensor at the wheel(s).

By this point, I was just putting 2 and 2 together... and drawing upon any old car repair that I worked on in the past... I figured it was worth a shot and it worked.

As I re-think this more... I dont even know if all (4) wheels have a sensor or just the rear driver or rear wheels? Someone with more Jeep knowledge might be able to chime in...

All I do know is... it worked. Good Luck.

Bakerbuilttracks

I also have read the same thing. I went to the parts store yesterday and bought the only one they had in stk. It was the abs wheel speed sensor. It said there was one for the RR and LR can't remember if the there were applications for the front as they had 1 in stk and it was for the rear. LR and RR are the same part #. Im going to do some trouble shooting in the next few days and post back.

big_mike

Hey Big_Chief (or anyone else for that matter), I just graduated college last May and saved up for a while to buy an '05 Jeep Grand Cherokee. About a month into having this car, I'm getting the same problem you had - my mileage has dropped to 3.0 mpg, my ABS light is on, my display says "Service Electric Brake System" and my traction control light is on.

Since all four symptoms are the same as yours, I'm assuming I have the same problem. I took it in to a local mechanic who charged me $212 just to tell me my right front sensor was bad. If the part really does cost $15, I'd like to replace it myself, do you think that would be possible for someone that doesn't know the first thing about cars? I really can't afford the extra 200 he wants to replace it, and everytime I take it somewhere else, they're charging me a diagnostic fee of at least $150 before even getting to the problem.

Any help at all would greatly be appreciated. Even if you could just list out some steps for me to replace it on my own (and where I would even go about buying the sensor) would be beyond fantastic.

Thanks a lot, I really do appreciate it.