outofrng623

Thanks for looking, sorry for another mileage thread...I have been reading around for weeks and troubleshooting with no luck. Any ideas would be appreciated, hoping maybe someone has been through this.
Purchased an 04 JGC V8 in August, was getting around 13-15 MPG, calculated by hand. In November I started noticing I was filling up a little sooner than usual, so I started keeping track. Week after week I was losing approximately 1MPG. Now one week to the next, I can understand a fluctuation, but this is crazy. Winter gas cannot be that much different and as I mentioned this wasnt a dropoff from 13 to 6, this got worse over time...From 11/20 I was getting 9.8 and over the last 8 weeks or so I am getting under 8. Have gotten as low as 5.75 and that week I was intentually babying the car. I have had about 3 stalls over the last two months and the truck has started right back up. I have done the fuel reg/filter 2x, first one WIX pushed 62 PSI, switched to Mopar, kicks around 57psi now. Plugs (champions), air filter, TB cleaning, IAC (mopar), BARRS headgasket sealer due to a slight coolant smell and some smoke, it did help that situation...O2 sensors done (mopar). Gas cap is the original, had aftermarket for a while and put original back as I understand that could have caused some problem...truck has new rad cap, new thermostat...TPS checked by me, backprobed, analog meter, smooth as it should be...I have tried fuel system cleaners, different gas stations, one of those compression oil additives...I am out of ideas.
If an alternator or battery is acting up, but not failing, could that cause this much of a drop in MPG?
New battery terminal connectors...
NO CEL light (and yes it does work).
A deep scan using Torque shows a non-monitored sytem check, 2 precat O2s switch a little slow, but fuel trims should make up for that (fuel trims are never out of whack)...I have also received a failed test on the purge system monitor due to an IAC shift, but cannot find any real information on that.
Also, did a vac test, stays smooth and steady at 18, drops, pops up and steadies out when reved, as it should.
Truck runs great, its still fast, no misfires, no sputters, I get a slight hesitation if going to WOT, thats it.

Any ideas? Thanks

eriejeep

Have you checked the entire fuel line system? may have a pinhole leak that only leaks when running. worth a shot...maybe run a air/fuel meter and see what that reads.

muffinman

Cat converter maybe? Mine did basically the same thing. Did not throw a code at all and ran pretty good except at wot. Did not want to pull past 4,000 rpm. Mileage dropped from 19.5 to 12 before I finally figured it out. Changed the main cat and it runs great and mileage is back to normal.

BearMBD

Is the jeep heating up to normal? If not, atleast in my case, the water pump went bad and would not let the engine heat up to running temps, which would kick the engine out of warm up mode and then save fuel in running mode.

outofrng623

Hi all. Thanks. Just saw that there were responses. Sorry for the delay.

Eerie, I have been under the truck a few times with it running, tracing the best I can, I am not seeing any leaks. File pressure was tested and is normal.

Muffinman, how did you determine it was the cat? I have no buildup smells and I thought there would be a loss in power if any were clogged. Also, my o2s are reading properly, which tells me the cats are ok.

Bear, it heats up normal, runs right about 203 F.

Thanks

muffinman

I tried everything else and finally just cut it off. I had no codes what so ever.I hooked it up to a scanner at Oreillys and everything showed normal. I thought it would read something about the 02 sensor if the cat was bad, but it did not. It ran normal around town. Just lost power above 4,000 rpm. You did say it has been stalling right? I am just guessing that yours "might" be the cat. I didn't mind replacing mine after 115,000 miles anyway.

outofrng623

It's only stalled two or three times. Once in drive at a light and once in reverse but sitting idle. Nothing since then.

I don't even recall hitting 4k on mind lol I think I'm taking a long drive tomorrow. Ill have to pay attention. Am I right in assuming you had the overdrive off?
Mine has 150k+ on it and my exhaust is starting to rot out, muffler is shoddy too...cats looked newer but couldn't say for sure. Maybe a whole new exhaust is in order.

I wonder if I pulled out the cats, ran a patch pipe...what may happen lol

dave1123

You're never supposed to mention removing the cats! However, I've removed the muffler, used a steel rod to break up the matrix, and checked if it had more power. It did, so I replaced it with a new one.

Case in point. My wife had a Dodge K car. Remember them? She was commuting home one day and the car just ran out of power. I went to bail her out and drove the car home. I felt like it was choking and I had to use a lot of throttle to get it up to 35 mph. I actually blew the EGR valve off the manifold before I got it home. I took the cat off and it ran fine. It was plugged SOLID! An air hose wouldn't even blow through it!

Because yours is getting worse over time, I would suspect that's your problem.

muffinman

I meant i took it out on the road and floored it. The trans will kick down and should pull to 5,000 plus if you want to. Mine got to 4 grand and just started surging and slobbering and not running well. Cut the cat off and it ran great. I DID replace the cat.

outofrng623

On a long run the other day, I went WOT, no spudders. I am having a compression test and smoke test done saturday. May get a smog test if he has the machine. Also going to check for exhaust in the coolant.
On a 140 mile trip I got 15MPG, steady driving. Should be higher, but it was better than seeing 6mpg.
I also changed the thermostat yesterday, apparently, although 3 months old...it was sticking. While it was on the lift I checked out the back near the evap canister. I have some wetness that does not appear to match up with the rest of the wetness. Hard to explain, I will post pic if I can. It had no odor to it though...Perplexed This is looking towards the back drivers side. Leak detection pump would be to the left I believe.

muffinman

Keep us posted, I am really curious about this. Don't know what your "wetness" is.

tiwvr1

Replace the 02 sensor, the pre cat one. Trust me, it wont always throw a code. Was the best improvement on mine for mpg. They wear out. I changed mine out because it was reading on the lean side with a scanner but it have black smoke at WOT. Fixed everything, and got 4 mpg increase.

outofrng623

O2s were done...

Heres a link to a forum I use more often. A lot more info about my situation there and maybe some ideas for those of you also having similar problems.

http://www.jeepforum.com/forum/f310/...-help-1490914/

outofrng623

Smoke test shower no leaks. Purge solenoid is at 25% but should max at 11%. So I'm now trouble shooting what triggers the evap purge solenoid such as CPS and MAP sensors. Updates are on the link above. Thanks.