Serious drop in gas mileage.

[PunkChachi]

Recently my gas mileage has plummeted. Today I went 90 miles and hit half a tank of gas. I don't drive aggressively and most my driving is only 5-10 miles at a time most in town, not tons of traffic. It has slowly dropped over the years, I use to get 18-20 city and 22 highway. It has been really bad every since my jeep sat for about a month a couple months ago. I have replaced all the spark plugs with recommended plugs properly gapped, replaced all the ignition coils and have run fuel system cleaner through it. The only other thing I can think to do is get a my injectors cleaned but my local Jeep dealer doesn't actually clean manually clean them they just run chemicals through it. Can anyone help me out?

 

[JeepinJarhead03]

check your front brake caliper sliders, one has a rubber bushing on the end of it that will swell and seize the slider causing the pads to drag

 

[renegade 04]

Sounds like a stuck caliper or even a stuck brake pad.

 

[Royy]

Since you mention it has slowly dropped over the years, it could be a combination of various things.
- Has the throttle body been cleaned recently?
- Is the tire pressure right?
- Is the air flow sensor clean?
- Are you using the recommended 5W30 engine oil, or a heavier weight oil?

Using a scanner, have a look at the fuel trim values. If those are too high, that could indicate issues with the fuel system, or a vacuum leak or O2 sensor problems.

 

[LibertyTC]

^all good ideas & suggestions!
Also try to eliminate any excess weight form the KJ!
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:gr_grin:

 

[rjkj2005]

You need an obd2 reader. Need to look at the fuel trim. If it's reading high you could have a vacuum leak or an exhaust leak scavenging out side air and fooling the O2 sensors into thinking it is burning lean and it is throwing fuel to it. In an attempted to richen it up.

Sent from my XT1585 using Tapatalk

 

[Dave]

^all good ideas & suggestions!
Also try to eliminate any excess weight form the KJ!
58938[/ATTACH]"]

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:gr_grin:

^^you too.....had to kick her off mine a couple of times .....LOL


Dave
ps.....didn't mean to help get off-track but the pic was too funny. It looks like members have given good things to check and I can't think of anything else to add at the moment. Let us know how you are making out.

 

[JasonJ]

Is there a squirrel nest under your air filter?

Seriously, I thought my air filter was pretty good by looking at it. I bought a new one because I had a 200 mile trip coming up... holding both new and old up to the light, I could see my old one (that I thought looked OK) really was about 50-70% blocked.

My fuel econ went up by 1.5-2.0MPG. I run this same trip routinely.... so I had a good history of comparison.

Other than that, definitely check out the brake caliper slides since you said it has been even worse after sitting... sitting and not being driven is the worst thing you can do to a vehicle.

 

[J33Pfan]

* if you can do your own work, take out your Fuel Injectors and sent them to a guy on Ebay to be rebuilt. you should have them back 2 - 3 days.

are you running different tires?

did you lift it?

winter fuels here on the East Coast are terrible for gas mileage. What octane are you using?
oh and did you install additional skid plates? (inside joke from a different thread)

 

[PunkChachi]

Thanks for all the replies I have Wednesday off so gonna dive into then.

1. Is it a challenge to take out fuel injectors, some of the videos I have seen make it look somewhat hard or maybe just delicate and can easily break things.

2. I haven't cleaned the throttle body or airflow sensor in maybe a year, I'll check that out. Oil is good too, using the recommended weight. Tire pressure is good all around, one of the first things I thought of and had the same tires on for about a year and a half. MPG were still decent when I switched them.

3. Air filter is fine too, relatively new...no squirrels, though I did recently pull out a dead mouse from my gf's heater blower motor. Poor fellow made a home and got sucked up into the fan when she turned the heat on. R.I.P. Phillip.

4. I'll check the brakes, is the rubber piece the part on the end of the rod that slides into the greased part? Should I drive it around for a few minutes to warm it up and check to see if it is swollen afterwards?

5. My friend has a OBDII Reader, might be a week or so before he can make it up this way to run it on my jeep though. How expensive is an OBDII Reader, think it would be a good investment and if so which would y'all recommend?

6. No extra weight that wasn't there before lol

 

[renegade 04]

One good thing to do is to take the serpentine belt off and check out each pulley and make sure they are good.

 

[LibertyTC]

The rear diff on the Kj likes new gear lube frequently too. Trac-Lok need LS additive and 75w-90 is the normal for non trailer use spec.
Have you had the rear diff cover off at all lately?
Is yours a 4x4? if so, maybe time to also get the transfer case & front diff serviced too.
Always see owner manual for specified oils/fluids etc.

 

[Royy]

5. My friend has a OBDII Reader, might be a week or so before he can make it up this way to run it on my jeep though. How expensive is an OBDII Reader, think it would be a good investment and if so which would y'all recommend?

You can get a simple one on eBay/Amazon for $20-30. There's plenty of different kinds out there, just make sure you get one that lets you view live data.

I'd definitely says it's a good investment. Whenever the check engine light turns on you can immediately check for codes, use freeze frame data to analyze what might have triggered the code, monitor stuff like engine and trans temp, fuel trims, etc.

And it's a great little tool to bring if you're ever buying another used car. In my experience, once pesky dealers see you pull out your scanner, they suddenly remember all the issues the vehicle they're trying to sell you has :laughing1:.

 

[tjkj2002]

Just be careful those cheap code pullers,even those that can display live data, will only display the very basic stuff and never the PID's you want or need to view.Not to mention there refresh rate is very,very slow compared to a actual bi-directional full function scanner.

 

[PunkChachi]

As far as my differentials go I had them regeared to 4.10 both front and rear when I had the transmission fixed last year about this time.

I always run 87 octane through it.

Quick update: I stopped at a lube shop on the way back, "DipSticks" they had a 2 step fuel cleaner for $40 they could run through. One went through the intake via an IV looking drip contraption, the second went in the gas tank afterwards. Had him do it took about 35 minutes. He said usually it kicks some black smoke out the exhaust but it didn't do it this time. Anyway got in it to leave started it up and check engine light came on, he had a reader but it doesn't show codes. Went to Advance Auto had it read, (unfortunately the guy wasn't the brightest bulb). Kicked out these codes,

2
9 <^Both of these say something about the VIN and not matching the engine computer...got these codes for the first time like 6 months had no idea what they meant. This is the second time getting them. Also they didn't have a Pxxxx code it was just two codes one said "2" the other said "9". Haven't found anything online.

P1684-Battery has been disconnected
P0300-Random multiple misfires
So I recently had disconnected the battery so maybe thats why P1684 was kicked out but idk about P0300.

As I was leaving the store I started it up and it was a hard start, took three tries. When it did start it shook and could feel the engine misfire again (check engine light blinked). Shut it off started it up and seemed okay. Zipped back home and have grounded it until I can figure it out. Had a few minutes, so I cleaned the air flow sensor and the throttle body. They didn't seem too bad. Hope this helps narrow it down cause I am once again stumped.

 

[tjkj2002]

After a service like that it needs to be ran kinda hard to burn off what it broke loose,could account for the p0300 code.


Oh and there is no "air flow" sensor of any kind in a KJ with the 3.7.

 

[Royy]

After a service like that it needs to be ran kinda hard to burn off what it broke loose,could account for the p0300 code.


Oh and there is no "air flow" sensor of any kind in a KJ with the 3.7.

I just assumed the little thing plugged into the air intake hose (right before the throttle body) was some kind of air sensor.
All the diagrams I can find online don't actually show a description for this part, do you know what it is?

 

[ltd02]

I just assumed the little thing plugged into the air intake hose (right before the throttle body) was some kind of air sensor.
All the diagrams I can find online don't actually show a description for this part, do you know what it is?

I think that's an air temp sensor.

 

[PunkChachi]

I think that's an air temp sensor.

Yup, just looked up a video. Inlet air temperature sensor, simplifies things I guess.

 

[JeepinJarhead03]

Thanks for all the replies I have Wednesday off so gonna dive into then.

4. I'll check the brakes, is the rubber piece the part on the end of the rod that slides into the greased part? Should I drive it around for a few minutes to warm it up and check to see if it is swollen afterwards?

the slider looks something like this, the rubber bushing over time swells from contaminants, heat, age, etc, etc, or use of non-synthetic caliper slider grease. It's a common issue that goes back something like 2 decades. if it's stuck you'll have a hard time getting the slider out of the caliper bracket, but it does indeed come out. Have ran into several folk who didnt even realize that slider was supposed to move

napa sells synthetic caliper grease for like 50 cents in those little plastic pouches.

if you decide to go bushingless, as long as you grease the sliders every 6 months you shouldn't run into an issue. that was basically the "fix" for the ford era's mistake of bushings on the caliper sliders

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