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Unread 03-10-2013, 05:10 AM   #1
outofrng623
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Angry 6 MPG, out of ideas, please help.

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

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Unread 03-10-2013, 05:19 AM   #2
michiganmaveric
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Some one stealing your gas when you are parked. Fuel leak somewhere. Injectors leaking (does it seem like you have gas in the oil?).
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Unread 03-10-2013, 06:16 AM   #3
outofrng623
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Quote:
Originally Posted by michiganmaveric View Post
Some one stealing your gas when you are parked. Fuel leak somewhere. Injectors leaking (does it seem like you have gas in the oil?).

I have monitored the gas between leaving and getting back in day to day, does not appear that someone is stealing the gas...
I have not seen any leaks, have had it up on the lift and looked...Unless it's a pinhole and only happens at high pressure, I do not believe it's a leak.
No gas or coolant detected in the oil. Everything appears clean. Is there another way to check, any other signs if it were and would it essentially drop my mileage in half?

I also started to wonder if these AWD systems could bind up at all, essentially being in 4wd all the time...I do get some grab from time to time on turns at low speed, which to my understanding shouldnt happen...but, it does not "feel" like it's in 4wd all of the time. Quadratak 2
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Unread 03-10-2013, 08:55 AM   #4
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Hmm barrs head gasket sealer raises a red flag. You may have some serious issues if you had to put that in there. You should have it checked out. Are you losing coolant?

It's hard being right all the time.
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Unread 03-10-2013, 09:22 AM   #5
outofrng623
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Quote:
Originally Posted by chrism1367 View Post
Hmm barrs head gasket sealer raises a red flag. You may have some serious issues if you had to put that in there. You should have it checked out. Are you losing coolant?

It's hard being right all the time.
No longer losing coolant or blowing smoke. Did it at the first sign to avoide further issues.

Thanks, keep the ideas coming.
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Unread 03-10-2013, 09:23 AM   #6
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Also, I used the best one they make, head gasket and cooling system...Not the cheap one.
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Unread 03-10-2013, 09:42 AM   #7
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Im basically in the exact same boat and my issues started about the same time as yours. Ive also done all the same troubleshooting with all the same results. The only problem I know about is that my muffler is splitting at the seam with large holes. Cant imagine that would cause such a huge drop in mpgs though. Hopefully getting that replaced in the next week or two. Ill keep an eye on this thread and also let you know if I find out what my issue is.
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Unread 03-10-2013, 02:56 PM   #8
outofrng623
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I've had my mechanic check for vac leaks as well as testing the vac...sowed nothing. I've read around and I think I'm going to try spraying everything with carb cleaner. Carefully. Manifold, evap lines, etc. we shall see. Maybe it's a small leak in the manifold. Maybe it's a bad injector, something getting a bad ground, who knows. Just can't wrap my head around it. I hope I did it at some point and when I do I plan in creating a things that effect mileage thread lol
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Unread 03-10-2013, 04:58 PM   #9
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When your driving and watching the live data in torque what is your engine coolant temp?

Also are you in open loop or closed loop?
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Unread 03-10-2013, 05:14 PM   #10
outofrng623
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Driving highway it's around 160 if I recall. Idle 203 f max.

It goes into closed loop after about 1-2 after startup cold. Operates, or at least appears to operate correctly.
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Unread 03-10-2013, 06:07 PM   #11
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Quote:
Originally Posted by outofrng623
Driving highway it's around 160 if I recall. Idle 203 f max.

It goes into closed loop after about 1-2 after startup cold. Operates, or at least appears to operate correctly.
Replace the Thermostat. The V8 should get to just a hair below 210 rather quickly and stay there.
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Unread 03-10-2013, 06:16 PM   #12
outofrng623
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Thermostat was replaced about 3 months ago. Problem started before then. And would 7 degrees really make an impact?
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Unread 03-10-2013, 06:38 PM   #13
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Quote:
Originally Posted by outofrng623
Thermostat was replaced about 3 months ago. Problem started before then. And would 7 degrees really make an impact?
You say it runs around 160 at highway speed. That is way too cold and keeps it in enrichment.

If that is a OEM thermostat its broken.
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Unread 03-10-2013, 06:49 PM   #14
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On a 20 degree day doing around 70 I believe....its been a long time, that it was around 160. Ill take a run tomorrow and see where it's at to be sure.
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Unread 03-10-2013, 07:11 PM   #15
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Quote:
Originally Posted by outofrng623
On a 20 degree day doing around 70 I believe....its been a long time, that it was around 160. Ill take a run tomorrow and see where it's at to be sure.
My 04 with 4.7 shows 201 on the scan tool in most all driving conditions this past winter.
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