Lost 25% of fuel mileage, possible solns?

[IdahoJeeper]

Hi to all,
cruising the web looking for solutions to my problem and found AA. Read through the other threads but don't really see an answer...

Just bought my 96 Cherokee 5 weeks ago. 4.0L I6, auto tranny, 4X4. First few tanks of gas, got around 18.5 mpg. Recently, that dropped to 15 mpg. The driving style stayed the same. I have replaced oil and filter, plugs, air filter, cap and rotor. Ran a can of injector cleaner through it when I first got it. Have purchased a fuel filter and when time permits will install it. But I'm wondering...

Being a 36 year old teenager with a new set of hot wheels, I've leaned into the accellerator pedal a few times (trying to impress my kids - and myself). FEEL THE POWER! It seems lately like the auto-tranny isn't giving me the sharp shifts it did not long ago, and may be slipping. Is that even possible? ("Dammit Jim, I'm an electrician, not an auto mechanic!") I also saw something about the oxygen sensor in a different string... Any ideas would be helpful, I have a problem with throwing money at a mechanic without knowing it's nothing I can fix myself.

Thanks!

[gtmud]

I would recommend changing your tranny fluid and filter. There's a good chance that your filter is getting clogged. If you have a drain plug on your tranny pan your in luck, makesure that you have a GOOD pry tool handy, for some reason those darn pans all-but cement themselves to the tranny. It should take about 6 quarts of Dexron III. (consult your owner manual)I have done this at regular intervals to my 00', and have had great performance and reliability at 90K. WARNING: This can be a bit messy, so have a BIG pan to catch your fluid! Maybe while your under there, change out the T-case fluid too. Very easy, just remove the lower Hex plug, drain, recap, and remove the cap just above the drain plug and fill with(recommend Mobile one Synthetic)Dexron III. Good luck.NOT AS MESSY.

[IdahoJeeper]

Thank you GT, I went down and picked up new filter and fluid, also picked up an inline tranny filter. As soon as I can I'll get it changed out. Thankfully, I do have a drain plug in the tranny!

I am beginning to hear a kind of hissing sound when I put it in gear, and I noticed today higher than normal rpm's to get the same mph... like I said, I'm no auto mechanic. Hope this does it for me!

By the way, the inline filter is one directional. I assume I should install it in the cooling lines in the engine compartment. Do you know which one is the incoming line to the cooler, top or bottom?

[JDPascal]

I think gtmud mean't chrysler ATF+3 not dextron III.

If you put dextron in you will have shifting problems.

Check out the other transmission threads for yourself.

Chrysler's do not handle dextron or mercon ATF well.

JD

[hundahunta]

possible vacuum leak..!! visually check hoses and lines, check the line at the pressure regulator... good luck!

[capt. apathy]

the hissing sound would definitely make a vacuum leak a likely suspect.

another simple one that can screw up your mileage is the CTS (coolant temp sensor. the one under the exhaust manifold for the ECU, not the one in the head for the gauge).
mine was stuck and was constantly sending a reading of about 88F (even when overheating). this kept the Jeep in constant 'warm-up mode'.
as with most sensors on the Jeep, check the connection from the wiring harness to the sensor before replacing the sensor, more often than not unplugging and cleaning the connection fixes sensor problems without ever having to replace the sensor.

[IdahoJeeper]

Wow! all good info, thank you!

I thought I would have time to change the fluid and filter today (emphasis on thought). I know changing tranny filters is never fun, but this was my first time with a dipstick tube that entered the side of the pan. What a pain to get it off! I hope the upper part of the dipstick tube was supposed to stay with the Jeep! I didn't get it put back together (before I had to go to work) so I had to drive my '87 S-10 Blazer (ick).

I can tell you it appears the fluid definitely needed changed, just as brown as motor oil, and thick, no real burned smell though. What I could see of the filter screen did show some signs of plugging. How much metal is normal on the pan magnets? There was a little, mostly very fine but a few slivers...

I hope to get it back together tomorrow (also had the wrong kit), when I do, I will check the vacuum lines and electrical connections. Thanks to all!

[IdahoJeeper]

Thanks to all who responded!

A quick note to let you know that I think we've got it! This weekend I changed out the ATF, tranny filter, and fuel filter. Took it for a 200 mile drive through Northern Idaho, about 1/2 on dirt mountain roads. Filled the tank before I left and when I got back. I got right at 20 MPG! I'm pretty happy with that.

I read in the '96 owners manual, the dry capacity of the tranny is about 8 quarts, and only 4.2 gets drained at a change. I'm going to drain the oil and refill again, hoping to get more of the gunk out of the trans.

Can anyone tell me which of the cooling lines going to the radiator from the tranny goes into the cooler and which one comes out. I bought an inline filter and would like to get it on there soon...

[gtmud]

Glad to see that it all worked out! As far as your in-line filter, take off one of the lines at the radiator, have someone crank the engine, you will either see fluid coming out of the radiator, or the line. The rest is self explanitory. Good luck.
Oh, instead of the filter, might look into installing a tranny cooler, this will help extend the life of your fluid, and your tranny.

[IdahoJeeper]

Tranny cooler? Help me out, I've heard of it but don't know much. I assume this is outside the existing radiator oil cooler...