sudden fuel mileage drop

RenegadeT

RenegadeT

no shirt,no shoes,no dice
Moderator
Joined
Mar 24, 2005
Location
Stokesdale-Greensboro
I'm pretty OCD about tracking my fuel mileage, and was surprised to see a significant drop in my Jeep JL Wrangler Rubi, 3.6L V6/automagic tranny. I bought this used last year, been getting 16-18 mpg consistently regardless of hard/soft/no top, doors/doorless and with/without rear seat. Of course I'm ignoring Uwharrie trips where i do see a mileage drop.
So typically the dash shows 300 mile range after each fill up. Dec24, I was shocked when it showed just over 200 mile range, and my mileage tracker confirmed 13.4mpg for the last tank. Coincidence or not, I had NC inspection done Dec19, and at the same time, had them balance the tires. 2 weeks prior, I had rotated the tires myself and noticed a vibration above 65MPH; the tire balancing seemed to help, vibration was gone and I was happy. I can't imagine anything there that would've caused a this fuel mileage drop.
More info to muddy the waters...Thanksgiving wheeling trip, I pinched the RH exhaust downpipe. I think the engine has a littel stumble at idle due to it, but it didnt seem to impact fuel mileage thru December. I have a replacement pipe ordered, hopefully this is the culprit...but I'm not too optimistic.
I use regular 87 octane, never the cheap 86 stuff. Over the summer, I did hear some engine ping/knocking, so I tried 89 octane 3-4 times. Seemed to reduce pinging, with no change in fuel mileage. Google tells me this pinging is not unusual for this engine.
Any other thoughts?
 
20230105_222505.jpg
20221216_141907.jpg
 
was it a 1 tank anomaly that corrected itself or have you not gotten through another tank yet?

Were it me - and it was running fine otherwiese. Id get a couple more data poitns to just see if you got some crap watery fuel and it cleared up or if somehting had shit the bed.
 
I'll have to check the air filter, good call, thats quick and easy.
Besides a slight engine stumble that I attributed to the dented pipe, everything feels as it did before.
I don't track which gas station I go to, but its the same 3 or 4.
That app is called aCar, been using it for a while,. Seems OK, way better than the old 'write it on receipt and enter into Excel later' method. If I was more OCD or less lazy, I could enter the gas station info into the app; I leave it blank.
 
I wonder if they changed your air pressure when they balanced them?
If they lowers air pressure more resistance could lower mog
 
These new fangled vehicles make it impossible to ignore tire air pressure. The Jeep JL has a crazy high recommendation of 37psi (I presume to inflate the fuel economy rating), and the annoying TPMS light comes on at 32or33psi. Dash screen #2 is one button press away to show the tire pressure at all 4 corners (unless pressure is low, then it will pop up with an audible ding).
I do have a very slow leak on what was the right rear. I wheeled it over thanksgiving, then rotated it to the right front, and immediately noticed the vibration, prompting me to pay too much for tire balancing. I even asked tire shop to look it over. They couldn't find a leak, but did inflate all tires to exactly 37psi.
2 weeks ago, I replaced the valve core, it appears the slow leak is still there. I'm considering bringing it back, seeing if they'll pop that tire off, clean up the rim, and replace the valve stem, and of course rebalance.
 
If nothing else changed, my first thought was this:

Ron said:
I wonder if they changed your air pressure when they balanced them?
If they lowers air pressure more resistance could lower mog
Click to expand...

My lincoln drops 2mpg if I drop pressure from 40psi to 36psi.
 
UTfball68 said:
If nothing else changed, my first thought was this:



My lincoln drops 2mpg if I drop pressure from 40psi to 36psi.
Click to expand...
When that happens, do you just press a button and Matthew McConaughey hops out the trunk and pumps it up for you?
 
jeepinmatt said:
When that happens, do you just press a button and Matthew McConaughey hops out the trunk and pumps it up for you?
Click to expand...

Nah…that comes with premium package…all I get is an app that says ‘it’ll be alright alright alright’.
 
I check my mileage ever time I get gas in all of my trucks. The 98 S10 has 210k on the v6 and I thought the motor was dying the way it ran for a week a month ago and the mileage was awful when I got gas again. I put 89 in it and it's running fine now. I'm sure I got some shit gas.
 
They change gas in the winter months just like they do diesel fuel. That could be some of the issue.
 
Has your water temperature dropped and not running as hot as it was? If so you need to put a new thermostat in. These motors will run rich to bring up the temp to operating range and fuel milage will drop bad when the water temp is not in range.
 
LT1JEEP said:
Has your water temperature dropped and not running as hot as it was? If so you need to put a new thermostat in. These motors will run rich to bring up the temp to operating range and fuel milage will drop bad when the water temp is not in range.
Click to expand...

Probably runs lean to increase temp. Leaner is meaner.

But that's a good point. Thermostats (now) almost always fail open to avoid overheating. If it isn't getting up to temp, it definitely doesn't run as well.
 
Idk anything about the JL, so maybe this is useless, but I have a friend who's HHR SS dropped fuel mileage by 4-5 mpgs and the cause was a BCM. Idk how, but it's apparently known for that car, and he didn't suspect it until other issues popped up with lights. Once he changes the bcm, the mileage came back.
 
paradisePWoffrd said:
Idk anything about the JL, so maybe this is useless, but I have a friend who's HHR SS dropped fuel mileage by 4-5 mpgs and the cause was a BCM. Idk how, but it's apparently known for that car, and he didn't suspect it until other issues popped up with lights. Once he changes the bcm, the mileage came back.
Click to expand...
To that end...likewise no idea if there is any analog. But toyota had an issue at tone point on their flexfuel (IE e85 capable) engines where an ethanol sensor was too sensitive and would think you were running e85 when you were and would change the fuel and timing tables and it would obliterate mileage. It was so severe that when I bought my '15 I intneitonally paid more to have one shipped that wasn't a FFV...because reports had the already abysmal 12mpg down around 7.5.
 
Back
Top