In 1990, development of a successor to the YJ began in Chrysler's "Jeep-Truck Engineering Pre-Program" department under Bob Sheaves and TJ program director, Craig Winn. Mules based on the YJ were built from 1990 to 1993, when formal approval was given for the TJ development program at a 0 million budget. From 1991 to 1992 designers worked at the new Chrysler Technical Center, building on various design proposals. In late 1992, Michael Santoro's TJ proposal was chosen by Tom Gale, Lee Iacocca, and executive management. In May 1993, now with engineering and supplier input, Santoro's final Wrangler production design was frozen at 32 months ahead of initial assembly. Verification prototypes using production bodies were built from early 1994 and tested through late 1995. As YJ production ceased in December 1995, the last pre-production TJ examples were assembled, with start of series of production in January 1996. Unveiled on January 2, 1996, at the 1996 Detroit Auto Show as an early 1997 model year introduction (1996 model year skipped), the TJ was an evolutionary update. It later arrived in Jeep showrooms in April 1996, after 6 years of overall investment and 36 month production development phase.Instead of leaf springs, this updated Wrangler featured a modern coil-spring suspension, front and rear, based on that of the Jeep Grand Cherokee, for better ride and handling, and a return to the classic CJ's round headlamps. The engine is the same 4.0 L AMC 242 Straight-6 used in the Cherokee and Grand Cherokee. A 2.5 L AMC 150 Inline-4 engine was available on entry-level models until 2002. The 2.4 L DOHC 4-cylinder engine previously used on the Chrysler PT Cruiser replaced it for 2003.A right hand drive version of the TJ was available for export markets, and was also offered for sale to U.S. rural route postal carriers. The version offered to U.S. postal carriers was only available with an automatic transmission.

In 1998 (MY1999), the fuel tank became standard at 19 U.S. gallons (72 L; 16 imp gal) capacity. There were some changes between the 2002 and 2003 years. From 1996 to 2002, the side door mirrors were black metal framed mirrors; and from 2003 to 2006 they were plastic molded mirrors. The fit of hard and soft tops is slightly different, and the fabric and colors available changed from 2001 to 2003. In 2002 (MY2003), the 3-speed automatic transmission was replaced with a 4-speed automatic with overdrive. The overdrive can be turned off with a dash switch. The radio bezels went from a rectangle in 2002 to a rounded-edged rectangle for 2003. The sound bar inside was changed to sound pods. The interior seats also changed design, going from a rounder model to one with a distinct separation between back and headrest areas. The standard skid plate was also revised for 2003 to make room for the Rubicon's bigger NV241OR transfer case. The change from the 30/32RH to the 42RLE also gained an additional skid plate. This version of the Wrangler is also notable for being the last production vehicle to use AMC-related parts. The AMC Straight-4 engine was retired after the 2002 model year, and both the AMC Straight-6 engine and the door handles (the latter of which first appeared on AMC vehicles in the 1968 model year) were retired along with this generation in 2006. Like the YJ Wrangler, the TJ Wrangler used both the AMC passenger car door handles as well as the larger door handles off the AMC-built Jeep CJ for higher-end models.

 

### Tools Needed:
1. **Jack and Jack Stands** - To lift and secure the vehicle.
2. **Socket Set** - 10mm, 13mm, 15mm, and 18mm sockets.
3. **Ratchet and Extensions** - For better reach.
4. **Wrench Set** - Similar sizes to socket set.
5. **Pry Bar** - To leverage and remove components.
6. **Torque Wrench** - To ensure proper tightening.
7. **Hammer** - For tapping stubborn bolts or bushings.
8. **Ball Joint Separator** (if needed) - For separating joints without damaging them.
9. **Grease** - For new bushings.
10. **Replacement Trailing Arms** - Ensure they are the correct parts for your Jeep Wrangler TJ.

### Safety Precautions:
1. **Work on a Flat Surface** - Ensure the vehicle is on a stable and level ground.
2. **Use Jack Stands** - Never rely solely on a jack; always use jack stands for support.
3. **Wear Safety Gear** - Safety glasses and gloves are recommended.
4. **Disconnect Battery** - To avoid any electrical issues while working under the vehicle.

### Step-by-Step Replacement:

#### 1. **Preparation:**
- Park the Jeep on a flat surface and engage the parking brake.
- Disconnect the negative battery terminal to prevent electrical issues.

#### 2. **Lift the Vehicle:**
- Use the jack to lift the rear of the vehicle.
- Place jack stands under the rear frame to secure it.

#### 3. **Remove the Wheels:**
- Use the socket and ratchet to remove the lug nuts.
- Take off the rear wheels to access the trailing arms.

#### 4. **Locate the Trailing Arms:**
- The trailing arms are located behind the rear axle, connecting the axle to the frame.

#### 5. **Remove the Old Trailing Arms:**
- **Upper Bolts:** Start by removing the bolts at both ends of the trailing arm using the appropriate socket and wrench.
- **Lower Bolts:** Repeat for the lower bolts. If bolts are stuck, use the hammer to tap them gently, or a pry bar for leverage.
- **Ball Joint Separator:** If necessary, use this tool to separate any ball joints without damaging them.

#### 6. **Inspect Components:**
- Check the bushings and mounting points. If they are worn or damaged, you may need replacement bushings or mounting hardware.

#### 7. **Install New Trailing Arms:**
- Align the new trailing arms in place.
- Insert new bolts (if required) through the mounting points.
- Hand-tighten the bolts first, then use a torque wrench to tighten them to the manufacturer’s specifications (usually found in the service manual).

#### 8. **Reinstall the Wheels:**
- Put the rear wheels back on and hand-tighten the lug nuts.
- Lower the vehicle off the jack stands using the jack.

#### 9. **Torque the Lug Nuts:**
- Once the vehicle is on the ground, use the torque wrench to tighten the lug nuts to the specified torque setting.

#### 10. **Reconnect the Battery:**
- Reconnect the negative battery terminal.

#### 11. **Test Drive:**
- Take the vehicle for a short test drive to ensure everything is functioning correctly.

### Common Pitfalls to Avoid:
- **Over-tightening Bolts:** This can strip threads or damage components.
- **Not Using Jack Stands:** Relying only on the jack can lead to serious injury.
- **Forgetting to Inspect Other Components:** Always check adjacent parts for wear while you have access.
- **Ignoring Torque Specifications:** Always follow the manufacturer’s guidelines for torque settings to avoid failures.

### Replacement Parts:
- Ensure that you have the correct trailing arms for your specific model.
- Consider replacing bushings if they show signs of wear.
- Inspect bolts and hardware; replace if corroded or damaged.

By following these steps and precautions, you can successfully replace the trailing arms on a Jeep Wrangler TJ.
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### Valve Springs in a Jeep Wrangler TJ: Detailed Explanation

#### Overview

**What are Valve Springs?**
Valve springs are components of an internal combustion engine that help control the opening and closing of the engine's valves. In the Jeep Wrangler TJ, which has a 4.0L inline-six engine, valve springs play a critical role in the engine’s performance.

**Why Replace Valve Springs?**
Over time, valve springs can wear out or lose tension, leading to poor engine performance, increased emissions, and potential engine damage. If a valve spring breaks, it can lead to a misfire and severe engine issues.

### Components of Valve Springs

1. **Spring Body:**
- The main coil structure made of high-carbon steel. It stores energy when compressed and releases it to close the valve.

2. **Spring Seat:**
- A flat surface at the bottom of the spring that sits on the cylinder head. It provides a stable base for the spring.

3. **Spring Retainer:**
- A cap that holds the valve spring in place on top of the spring. It secures the spring to the valve stem.

4. **Valve Stem:**
- The part of the valve that extends into the engine. The spring pushes against the retainer, which in turn keeps the valve closed.

5. **Keepers (or Collets):**
- Small, wedge-shaped pieces that lock the retainer to the valve stem, preventing the valve from popping out.

### Theory Behind Valve Springs

**How the System Works:**
- When the engine is running, the camshaft rotates, pushing against the lifters that push the pushrods, which in turn actuate the rocker arms. The rocker arms open the valve by pushing on the valve stem.
- The valve spring compresses during this action, allowing the valve to open. Once the camshaft moves past the high point (the lobe), the spring pushes the valve back to its closed position.

**Analogy:**
Think of the valve springs like a trampoline. When you jump on it (open the valve), the trampoline compresses (the spring compresses). Once you jump off (the camshaft rotates past the lobe), the trampoline springs you back up (the spring pushes the valve closed).

### Signs of a Failing Valve Spring

1. **Engine Misfire:**
- If a spring loses tension or breaks, the valve may not close properly, causing a misfire.

2. **Rough Idle:**
- A weak spring can cause uneven valve timing, resulting in a rough engine idle.

3. **Increased Oil Consumption:**
- If the valve does not seat properly due to a weak spring, it can lead to oil leaking into the combustion chamber.

4. **Loud Noises:**
- A broken spring can create a noticeable tapping or rattling noise from the engine.

### Replacement Procedure

#### Tools Required
- Socket set
- Torque wrench
- Valve spring compressor
- Screwdriver
- Pliers
- Clean rags
- Gasket scraper (if needed)

#### Steps to Replace Valve Springs

1. **Preparation:**
- Disconnect the battery and remove any components obstructing access to the valve cover (like air intake hoses).

2. **Remove the Valve Cover:**
- Unbolt the valve cover and carefully lift it off. Clean the surface before reinstallation.

3. **Remove the Rocker Arms:**
- Use a socket to remove the bolts securing the rocker arms. Keep track of the order for reinstallation.

4. **Use the Valve Spring Compressor:**
- Place the valve spring compressor over the valve spring. Follow the manufacturer's instructions to compress the spring.

5. **Remove the Keepers:**
- Carefully remove the keepers (collets) using pliers. Be cautious as they can spring away.

6. **Remove the Spring and Retainer:**
- Once the keepers are out, release the compressor to remove the spring and retainer.

7. **Install New Springs:**
- Place the new valve spring and retainer in position. Use the compressor to hold them in place.

8. **Reinsert Keepers:**
- Carefully reinstall the keepers while the spring is compressed. Make sure they fit snugly.

9. **Reinstall Rocker Arms:**
- Carefully put the rocker arms back in place and torque them to the manufacturer’s specifications.

10. **Replace Valve Cover:**
- Clean the gasket surface, apply a new gasket if necessary, and reinstall the valve cover.

11. **Reconnect Battery:**
- Reconnect the battery and start the engine to check for proper operation.

### Conclusion

Replacing valve springs is crucial for maintaining engine performance. Understanding how they work and recognizing signs of failure can help in timely repairs, ensuring a smoother, more reliable Jeep Wrangler TJ. Always follow safety precautions and refer to a repair manual specific to your vehicle for detailed instructions.
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### Throttle Cable on a Jeep Wrangler TJ

**Overview:**
The throttle cable in a Jeep Wrangler TJ connects the accelerator pedal to the throttle body, controlling the engine's air intake and thus the power output. When you press the accelerator pedal, the throttle cable pulls on the throttle body, allowing more air into the engine and increasing power.

### Components of the Throttle Cable System:

1. **Accelerator Pedal:**
- **Description:** The part you press with your foot.
- **Function:** When pressed, it pulls the throttle cable.

2. **Throttle Cable:**
- **Description:** A flexible cable that runs from the accelerator pedal to the throttle body.
- **Function:** Transfers the force from the accelerator pedal to the throttle body.

3. **Throttle Body:**
- **Description:** A component on the intake manifold with a butterfly valve inside.
- **Function:** Controls the amount of air entering the engine based on cable tension.

4. **Cable Housing:**
- **Description:** A protective sheath that encases the throttle cable.
- **Function:** Keeps the cable safe from wear and tear while allowing it to move freely.

5. **Return Spring:**
- **Description:** A spring located on the throttle body.
- **Function:** Pulls the throttle back to the closed position when the accelerator pedal is released.

### Theory Behind the Repair:

Over time, the throttle cable can stretch, fray, or get sticky due to dirt and grime. This can lead to poor throttle response, where the engine doesn’t react quickly to your pedal inputs. Imagine a rubber band that has lost its elasticity; it won't snap back quickly when you let go. Similarly, a damaged throttle cable won't efficiently transmit your foot's movement to the engine, resulting in sluggish acceleration.

### Common Issues:

1. **Cable Fraying:** This can cause sticking or complete failure of the throttle.
2. **Binding:** Dirt or corrosion can cause the cable to bind, making it hard to accelerate smoothly.
3. **Stretching:** A stretched cable can result in a delayed throttle response.

### Repairing the Throttle Cable:

#### Tools Needed:
- Ratchet and socket set
- Screwdrivers (flathead and Phillips)
- Pliers
- New throttle cable

#### Steps to Replace the Throttle Cable:

1. **Disconnect the Battery:**
- **Why:** Prevent electrical shorts while working on the vehicle.

2. **Remove the Old Throttle Cable:**
- **Locate the Accelerator Pedal:**
- Find where the throttle cable connects to the pedal.
- **Unclip/Unscrew the Cable from the Pedal:**
- If there’s a clip, use pliers to gently remove it. If it’s screwed in, use a screwdriver.
- **Follow the Cable to the Throttle Body:**
- Look for a bracket or clip securing the cable to the firewall or intake manifold.
- **Unfasten the Cable:**
- Remove any clips or screws holding the cable in place.

3. **Install the New Throttle Cable:**
- **Route the New Cable:**
- Follow the same path as the old cable, ensuring it’s not pinched or kinked.
- **Attach to the Throttle Body:**
- Secure the new cable in place, ensuring it moves freely.
- **Connect to the Accelerator Pedal:**
- Attach the cable to the pedal and secure it.

4. **Check Cable Tension:**
- Make sure there is slight tension when the pedal is idle but not overly tight.

5. **Reconnect the Battery:**
- Reattach the negative terminal.

6. **Test Drive:**
- Check throttle response. The engine should respond promptly to pedal inputs.

### Conclusion:

Understanding the throttle cable's function is crucial for maintaining a responsive engine. By following the steps outlined above, you can replace a faulty throttle cable and ensure that your Jeep Wrangler TJ accelerates smoothly.
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