frustrating milage

[wightman]

I used to get about 14 mpg......I currently get 8mpg.

Things I've done in the last 7 months (in chronological order):

1) replaced gromets and vent lines to valve cover
-fixed leaking valve cover at same time
2) replaced exhaust manifold (cracked)
3) replaced t-stat and temp sensor
-temp sensor read 100 deg all the time (t-stat was actually fine)
3) ran a bottle of seafoam with about 10 gal of gas
4) 1/2 can of seafoam down throttle body
5) replaced spark plugs (propperly gapped)
6) replaced O2 sensor

While all these have smoothed out my idle, my jeep still gets 8mpg; and there's no gas leak, i know that much. I want to say that the milage has gone down since the use of sea foam, but I can't verify that (clogged exhaust?). The exhaust is about 4 years old (muffler and cat). The fuel filter is about 4 years also. Any suggestions? The strangest part is that my jeep still has the power that it did when I bought it....the exhaust really stinks though.

help?

[xeon]

Temp seems wrong... it should be at like 180 something or 210...
Replace that fuel filter.

Also, buy a Geo :bugeyed:

[LeadFoot]

Engine is not warming up to temperature...staying in open loop, which is the reason for the drop in mileage.

[wightman]

Perhaps I was misleading in my initial post. The temp was 100 degrees and i replaced the t-stat...that didn't fix the problem so I then replaced the temp sensor and it reads fine now. I actually went through two t-stats thinking that I bought a bad one, but it was definately the sensor causing the problem.

How could a bad fuel filter cause a drop in milage??? the fuel seems to be getting to the engine just fine. There's also no stuttering and it idles just fine.

[wcjp]

A bad fuel filter can easily cause bad mileage. A plugged filter can also take out a fuel pump. Your receiving fuel in the engine compartment. How much? 1/2?

A plugged filter can cause the pump to overwork. This will burn out the pump in no time.

Not saying the filter is the root cause. What type of thermostat? If you installed a high performance 180deg stat it could be your problem. The computer will stay in "open loop". This means it's ignoring most or all of the sensors and using preprogrammed parameters designed for cold start. This means more fuel and lower emissions. When in closed loop the computer monitors all sensors and dynamically adjusts to real time events.

The pickup tube in the tank could be partially blocked. I didn't see your signature. What mods are you running? Is the airfilter new or cleaned? What about the rotor, cap and wires? Did you use dielectric grease? Are the brakes dragging? Are the Ujoints throughout in good shape? Tire pressure? When is the last time you cleaned the throttle body? Are all engine accessories and pulleys moving freely? How old is the fluid throughout the entire drivetrain?

It's likely no one single thing is causing the event. It's likely you have two or more items in need of attention.

[wightman]

93 YJ, 4.0, auto TF999, 32" tires, 8.8, 4.10's, hardtop. Tire pressure is at about 27psi, u-joints are good, no dragging brakes, filter was cleaned 3 months ago, fresh oil throughout drivetrain, 195 degree thermostat....

Sounds like I should:
1) Clean the throttle body
2) Replace fuel filter (hopefully not the pump also)
3) New rotor, cap, and wires

[xeon]

Do a normal tune up. Which is rotor, cap, yada yada.

Replace that fuel filter. Cheap and easy. The t-stat should be a 180 right?

[wcjp]

One time I had a fuel filter that was new and bad. The pump sounded strange with the new filter. Bought another filter and noise went away. Remove the throttle body from the vehicle and use sensor safe carb cleaner/fuel injection throttle body cleaner. Also, don't use this stuff any where near the wife's flowers. The carb cleaner will kill anything.

[zman]

Any kids siphoning gas?

[jeepincj78]

If I am not mistaken there is two temperature sensors on that engine. One for the guage and one for the ECU. If the one for the ECU is reading wrong it will stay in closed loop causing the Jeep to run rich, evne though the Jeep is up to operating temperature according to the other sensor.

Frank :ijti:

[jwrape]

Where would this sensor be?

[jeepincj78]

I was refering to the 4.0ho. The sensor that tells the computer the temperature is on the thermostat housing itself.

Frank

[jwrape]

Originally Posted by jeepincj78

I was refering to the 4.0ho. The sensor that tells the computer the temperature is on the thermostat housing itself.

Frank

Oh your saying that the 2.5L only have one sensor?

[wightman]

Alright guys, every one of these things has been replace and/or cleaned except the muffler and cat. I'm still getting about 8mpg....this really sucks and it's getting very expensive to keep driving this thing.

My exhaust still smells like crap...like it's way to rich. I'm so confused, anyone else have any suggestions for improving milage?

[breakjeepparts]

if your cat has started to break apart it will def cause power problems meaning the engine will deliver much more fuel to try and compensate to no avail. Get under and give your cat a few good hits with your fist. If you hear anything inside rattle thats your problem. A bad cat will also present a gas like odor. Let us know. If it is your cat, don't replace with a factory one as you will pay 4x what you could pay. Just order the same size one from summit racing or something. Good luck. Went though this a lil while back.

[lessthanchris1]

you said muffler and cat were only 4 years old right? shouldnt be a problem...

hmm... I'm really out of ideas here...

Buy a locking gas cap, someone might be siphoning off you, only thing i can think of.... I mean... 8MPG is almost half 14 mpg... thats a HUGE drop...

with the temperature issue... anyone know how to tell if its in open or closed loop?

[savageracing]

Allright, instead of just guessing what is wrong like everyone else, I'm going to try to help you fix it, but 1st, we need to know what the problem is. You state the exhaust smells like crap, probably sulphur like? probably caused by a rich condition, but we don't know. So, find a shop with a 4 (or 5) gas analyzer. If they have a dyno that would be even better, but chances are they don't unless your state requires dyno runs for a smog. So assuming they have no dyno, get the 4 gas readings for idle and 2500 rpm's and post them up. Then we can see if it is rich, lean, misfiring, yada, yada, yada. Otherwise you are just doing the shotgun effect, throw parts at it until it's fixed.

[Rubicons_youngest]

kids are probally syphoning... i cant really think of anything taht will drop you 6mpg...

[mycj7]

Is the Manifold Air Temperature Sensor (MAT) working properly?