What's my 4.0's problem? - JeepForum.com
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post #1 of 76 Old 07-26-2017, 10:20 AM Thread Starter
kingcumonya
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What's my 4.0's problem?

Fairly new to me 98 grand Cherokee Laredo 4.0. 246000km/153k miles Problem is sometimes it doesn't seem like it has any power (engine power) I put my foot into it and it almost draws back instead of providing power to the wheels to take off. Here's what I've done since I've owned it in roughly a month:

-new plugs & wires cap and rotor
-oil change
-was sitting basically unused for nearly 3 years so fresh fuel and Lucas fuel treatment
-oil change
-changed coolant
-changed valve cover gasket was seeping. Oil leak is better but I think its still leaking from filter adapter (parts ordered)
-new battery and terminals
-new pads and rotors and fresh brake fluid

Starts and runs fine. I haven't taken it on any longer drives as it's mainly my around town daily driver till I get new tires and all the little things fixed.

What do you guys think it could be?

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post #2 of 76 Old 07-26-2017, 10:24 AM
LordHobbit
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Pull the throttle body and clean it well. Use Mopar CCC or carb cleaner/throttle body cleaner.

You're injectors may need a thorough cleaning also.

Plus it's a 4.0 so it is a bit weak. That's just what it is.

Your Jeep is a ZJ not an XJ fyi

93 red ZJ 190k 4.0. Spent more money than I should have ...

Isn't red the only color a vehicle should be?
If at first you don't succeed, use more speed.
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post #3 of 76 Old 07-26-2017, 10:40 AM Thread Starter
kingcumonya
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What is involved in cleaning the throttle body? Do I need replacement gaskets in order to take it off and clean it? That's one thing I haven't done yet that I thought I would need to.
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post #4 of 76 Old 07-26-2017, 10:50 AM
BorderWalker
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It's not all that involved. If you wanna get fancy, get a bucket and a tin of Acetone and give that Throttle body a bath in it. Otherwise some Throttle Body Cleaner will do well. Grab a small brush like an old toothbrush or one of the small brushes you can get at an auto store, spray some Throttle body cleaner or Acetone on the TB, and scrub with brush.

Make sure to remove the IAC and MAP sensor first though.

You honestly probably don't need a new TB gasket. It's recommended, but Throttle body gaskets are metal and I've taken off and reused mine plenty. If it's not scared or warped, it's still good.

a good clean out with Mopar CCC can work great as LH suggested, but is a big involved. I know @kg6mov has linked before in other threads to a great in depth writeup for using Mopar CCC to clean out the engine. I recommend cleaning the TB with Acetone or TB cleaner, then taking a can or two of Mopar CCC to the engine.

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post #5 of 76 Old 07-26-2017, 11:12 AM
kg6mov
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The whole enchilada on the combustion chamber cleaner is a good idea on an older motor: http://www.jeepforum.com/forum/f13/m...leaner-945851/

Check that the cat isn't clogged, and it may be worth it to do a new o2 sensor, the better the data from the o2, the better the PCM can run the engine. Check for the infamous 4.0 exhaust leak as well.

At the end of the day we call it the 4.slow for a reason though.


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1984 F250, 460 BB, T19, work truck/future tow pig
1987 Mercedes 300D Turbo, the diesel daily, 30mpg in style

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I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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post #6 of 76 Old 07-26-2017, 11:30 AM Thread Starter
kingcumonya
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How do I check the cat?
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post #7 of 76 Old 07-26-2017, 11:32 AM
kg6mov
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http://www.aa1car.com/library/converter.htm

On a 98 you can read the manifold vacuum over OBD2 with a scanner or a bluetooth dongle and an app like torque.


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1984 F250, 460 BB, T19, work truck/future tow pig
1987 Mercedes 300D Turbo, the diesel daily, 30mpg in style

Quote:
Originally Posted by Texas ZJ1 View Post
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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post #8 of 76 Old 07-27-2017, 06:52 AM
ZJDevilDog
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Change your fuel filter as well.

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post #9 of 76 Old 07-27-2017, 08:05 AM
GOLDWING
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Quote:
Originally Posted by ZJDevilDog View Post
Change your fuel filter as well.

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On the '98, the fuel filter is part of the fuel pump and is in the fuel tank.

GW

2 '98 4.0 ZJs
Hers is stock, mine, OME shocks, BB, Aussie, 2x6 sliders, 31s, etc.
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post #10 of 76 Old 07-27-2017, 11:59 AM
ZJDevilDog
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Quote:
Originally Posted by GOLDWING View Post
On the '98, the fuel filter is part of the fuel pump and is in the fuel tank.

GW
I didn't know that, thanks. Only ever changed filter on my old 95

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post #11 of 76 Old 07-27-2017, 03:05 PM Thread Starter
kingcumonya
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This weekend my plan is to clean the grounds. Replace the seals in the oil filter adapter and remove and clean the throttle body.
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post #12 of 76 Old 07-31-2017, 03:41 PM Thread Starter
kingcumonya
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Well my oil leak is fixed and I got the grounds all shined up. Didn't have time to tackle cleaning the throttle body though
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post #13 of 76 Old 07-31-2017, 10:09 PM
F1wanab
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Are you sure the transmission is using first gear? I mention this because I just had a problem with my 96 ZJ.... felt like the brakes were stuck when pulling away from a stop, and it took a few minutes for me to realize First gear was not working.
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post #14 of 76 Old 08-02-2017, 09:33 AM Thread Starter
kingcumonya
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Doesn't seem like a transmission problem as it doesn't happen all the time. It seems more like something sticking or maybe a sensor failing? On a happier note I found 4 good used tires for it yesterday and got them balanced and installed and it fixed the weird vibration I was experiencing.
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post #15 of 76 Old 08-03-2017, 09:08 AM Thread Starter
kingcumonya
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Finally had time to pull the throttle body off and clean it. Man it was black and gross. The Mopar CCC worked great and I definitely noticed a difference driving it this morning. Not sure if my problem is solved or not but it's another item off the to do list.
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