Bad Mileage (200kms to a tank)

[badwithcomputer]

My Jeep's engine has never really given me any grief at all since I've bought it. I replaced the plugs and changed the oil regularly in the last 5 years and that's all it has seemed to have needed.

Now I am getting abysmal mileage. I have a check engine light on, which traces back to "fueling with the gas door open" which I did one day not thinking trying to finish off a gas can. I don't think that could cause any major MPG issues?

I can spin all 4 tires freely so no sticky calipers, the Jeep idles fine and doesn't smell rich. My speedo is within 10km/h of gps (to the plus side) So I'm actually getting worse than 200kms to 58 litres (most recent fill).

The only thing I can think of is my exhaust. When I had it done back in the summer he had to downsize the tube to 1.75" in a small section to clear my cross member, but at the same time I also eliminated that "extra" cat (4.0L). My mileage didn't seem bad (actually it improved greatly after removing that extra cat) back then though or I would have posted here pronto or taken it back to the muffler shop. The Jeep almost feels restricted though when I drive, like my foot is further into the pedal than it used to be. Feels like I am constantly driving up hill but it never fails or falters like you think it would if there were some kind of issue.

What should I start checking/cleaning?

Specs Below:

2002 TJ 4.0 5 Speed
4.56
35" AT's at 25psi
134,000kms
Reusable drop in K&N and I do clean it once a year.

[Old Yeller]

I would be looking into your engine light again. Since it is already on, you cannot tell if you get any additional codes. Read it again, and I'm willing to bet you now have O2 sensor issues. Depending on the sensor, it will throw you jeep into a default limp mode, and greatly affect your gas mileage. I'm unsure what else would give you such a big hit, so start there.

Rob D

[gonejeepn]

go with the O2 sensor, also check ur cat if it is still on there. it pluging up could also give you bad mileage.

[badwithcomputer]

I'll do the key thing again to make sure. Was talking to Bubba last night and he gave me a list of things to check as well. I have 108kms on this tank and she's passed the 3/8ths mark lol I think there are 3 cats on the '01 and up 4.0's? 1 of which I have eliminated the other two are up by the manifold, I'll leave those for last, I can't imagine those being clogged though? You never know! I also thought "limp mode" meant that it knocked the rpms down significantly? I can accelerate right up to the red line without hesitation, it's just godawfully slow getting there.

[C Monster]

my jeep is this way to ,very bad on gas
I can only get 70 km per tank than the fuel and the light comes on and it's on E
and when fill it up it only holds $20 dollars

it's my fuel gauge I can drive 400 ++ km with the gas light on

[badwithcomputer]

When mine get downs to the E it's usually around 55 to 58 litres to fill, as much I was hoping that was my issue.

[justajeep]

I put new front pipes on a JK a couple weeks ago, one of the cats right off the manifold was all broken up inside.

[jamesc]

Any chance the clutch on the cooling fan is stuck (assuming you haven't switched to an electrical fan)? Had that happen to me a couple times and my mileage plummeted when it did. You'd hear it, the engine sounds like a big rig lol.

James

[badwithcomputer]

P0456 is the only code coming back - something to do with very small evap leak.

As for the clutch fan.. wouldn't that just cause it to spin at one speed? It's attached to that big bottom pully, I don't understand the workings of how that could cause it, educate me please! 196kms and gas light almost on!

[dartjeep]

That evap code... is that a vacuum leak? Asking because the evap system is tied into the vacuum maze of hoses, isn't it? That would cause crappy mileage.
Excuse my ignorance if it's not connected to that system. Just throwing out ideas.

Also, winter gas. My Jeep gets terrible mileage this time of year. I don't even track it, it's that bad.

[The Garagemahal]

Sounds like plugged cat
Ignore the evap

[C Monster]

Did that flapper valve stick closed in your muffler

[badwithcomputer]

Dec 16, 2013 23:19:37 GMT -4 C Monster said:

Did that flapper valve stick closed in your muffler

Actually that could be entirely possible. I will add that to my list!

[Creepy]

Dec 16, 2013 23:19:37 GMT -4 C Monster said:

Did that flapper valve stick closed in your muffler

What's this now? I basically have the same thing going on....just never replied to the thread. stock exaust, O2 codes, etc. lol I just keep putting gas in it.

[badwithcomputer]

The muffler I have is a straight though design with a "valve" on the inside that opens and closes (but not completely) depending on exhaust pressure. It worked great when I had no tail pipe and it just dumped after the muffler. since I added the tail pipe it sounds like absolute shit. It very well could be stuck in the closed position which would limit the exhaust gas from passing by a considerable amount.