How to Set Timing on 4.0 Jeep (10 Steps)

Knowing how to set the timing on a 4.0 Jeep is crucial to keeping the vehicle’s ignition timing in synch. For Jeep owners, correct ignition timing is essential for proper air-fuel mixture and keeping commutes and off-road adventures hassle-free. That said, this guide will cover the steps on setting your Jeep’s ignition timing properly.

When setting the timing on a 4.0-L Jeep, position the distributor correctly and align it with the rotor. Your Jeep’s model and the severity of the symptoms encountered will determine if you need to do more or less troubleshooting steps.

Here are the ten steps on how to set timing on a 4.0 Jeep:

1. Do the scribe mark.
2. Access the valve springs.
3. Line up the markings on the crankshaft pulley and the timing cover.
4. Install the rotor on the distributor.
5. Position the distributor into the engine block.
6. Rotate the rotor to the 4 o’clock position.
7. Ensure the distributor seats properly in the engine block.
8. Align the rotor blade trailing edge with the scribe mark.
9. Bolt down the distributor and connect electrical components.
10. Replace the valve cover.

An incorrect ignition timing brings with it a slew of issues, such as pre-ignition, hard-starting, bad fuel mileage, power loss, and overall poor performance – inconveniences that are guaranteed to ruin the joy of riding on the prestigious 4×4. If you want to keep these incidents to a minimum, continue reading this article.

How to Set Timing on a 4.0-L Jeep

Understanding the role of the distributor is vital in setting your ignition timing correctly. Although the ECM does the most when it comes to spark timing, the distributor generates the ignition signal and distributes the same to the proper cylinder. However, tinkering with it will not alter ignition timing. The latter task would require changing the position of the flywheel (view on Amazon) relative to the crank or moving the crank position sensor.

Having understood that, what this article covers is how to set timing on a 4.0 Jeep by ensuring the correct positioning of the distributor (adjusting the timing chain is a topic reserved for another article). The following steps cover the distributor removal and installation, regardless if it is undisturbed or not. Following them will tell you if the distributor (view on Amazon) is properly seated and help prevent heat consequences resulting from running the distributor retarded:

1. Do the Scribe Mark.

Note the terminal position for the #1 spark plug wire on the distributor cap and mark it on the distributor body.

2. Access the Valve Springs.

Remove the distributor cap and valve cover so that the valve springs are visible.

3. Line Up the Markings on the Crankshaft Pulley and the Timing Cover.

Using a 19-mm socket wrench, rotate the crankshaft until the pulley notch lines up with the “0” mark on the timing cover. When you do this, verify that the #1 piston is at TDC at the end of the compression stroke. You can confirm this by ensuring the valve springs on the #1 cylinder are relaxed and the valves closed.

Rotate the crank pulley another 360° should the valve springs appear compressed and the valves open at the end of the exhaust stroke.

4. Install the Rotor on the Distributor.

Check whether it is near the mark for the #1 plug wire terminal. If not, remove the bolt from the engine block and pull the distributor out until it rotates freely. Then, rotate the distributor body until the rotor lines up with a mark exactly 3 cm clockwise from the side of the cam position sensor’s rubber plug – just past the #1 plug wire terminal in a clockwise or advanced direction.

5. Position the Distributor Into the Engine Block.

Position the distributor into the engine block hole. Be sure the distributor gasket is installed.

6. Rotate the Rotor to the 4 O’Clock Position.

Visually line up the distributor housing ear with the clamp hole. Afterward, turn the rotor to the 4 o’clock position.

7. Ensure the Distributor Sits Properly in the Engine Block.

Slide the distributor down into the engine block until it seats, keeping the hold-down gear aligned to the hole in the engine block.

8. Align the Trailing Edge of the Rotor Blade With the Scribe Mark.

The rotor should be at the 5 o’clock point, with the rotor blade side lined up with the distributor housing scribe mark (#1 spark plug cable post location).

9. Bolt Down the Distributor and Connect Electrical Components.

Install the hold-down distributor clamp bolt and tighten to 23 Nm (17 ft. lbs.) torque, followed by the distributor cap. Next, connect the distributor electrical connector, install the electrical cooling fan and shroud (if applicable), and attach the battery cable up to the battery.

10. Replace the Valve Cover.

Once the distributor is securely bolted down, reinstall the valve cover.

Depending on whether you bought your Jeep brand-new or secondhand, you may require additional considerations, such as:

• Use of timing light to ensure the distributor is not installed one tooth out in the retarded/advanced direction (doing so will not start the engine)
• New gasket for the timing cover
• New front oil seal that fits into the timing cover

There would be no need for a timing gun when performing these steps since the tool is not used for timing adjustment. The distributor setup is done physically, while the ECU does the rest digitally. However, make no mistake – the rotor-to-distributor body placement is a unique step and is very important.

The positioning of the distributor is not something a Jeep owner can merely wing to set timing. You will need to pay close mind to where the rotor should be when the engine is rotated to TDC (Top Dead Center).

Furthermore, you will need a harmonic balancer puller to remove the crank pulley. This tool looks similar to a steering wheel puller and does not cause the crank pulley to come apart.

What to Do Without a Timing Light

If you don’t have a timing light like an Innova 5568 Pro Digital Timing Light (view on Amazon), follow these alternative steps in checking whether or not your engine is timing out. Note that these are only applicable if your distributor is not set up according to what is described in the service manual:

1. Turn the motor over with a large socket and breaker bar until your finger is in the #1 spark plug hole (pull all your plugs when doing this so that the motor can be turned more easily by hand).
2. Feel the pressure on your fingers as the engine comes up on TDC of the compression stroke. Have your buddy help you out on this step.
3. When your engine is at TDC on the compression stroke, verify that your TDC mark aligns with the pointer. Otherwise, it would mean the timing chain set is messed up. If so, look for the new TDC mark on your harmonic balancer and mark it well (this will come in handy later on).
4. Mark the distributor body where the #1 spark plug tower is on the distributor cap, then remove the distributor cap. The rotor should be able to go by the mark you just made on the distributor body. If not, your distributor is probably in the wrong.

Set the Alignment

Once you determine the distributor is displaced, pull it out (with the rotor in place). Align the rotor just before that mark on the distributor body, and align the distributor shaft with the oil pump slot to drive it. While you are at it, note the curved G-drive gear on the camshaft that requires being slightly backed off when placing the distributor in the engine.

Most manuals cover requirements for the gear setup and chain tightness. Likewise, they describe how to set up the 4.0-liter Jeep’s distributor and provide details on idle RPM respective to your specific Jeep model. If you find details in the manual inadequate, Jeep-dedicated forums are great repositories of information you will need to go about setting the timing on your 4.0 Jeep.

How to Install a Distributor

How severely off your ignition timing is may warrant installing a brand-new distributor. If you are treading this path, here are the steps to follow:

1. Before servicing your Jeep, refer to the precautions stated in your owner’s manual.
2. Set the engine at the Top Dead Center (TDC) of the #1 cylinder compression stroke.
3. Slot in the oil pump gear at 11 o’clock position.
4. Locate the distributor pin alignment holes in the plastic ring, and align the correct hole with the mating hole in the distributor housing. (Note: The distributor will rotate clockwise as the gears engage)
5. Position the base mounting slot at the 1 o’clock position, and install the distributor.
6. Ensure the centerline of the mounting slot aligns with the centerline of the clamp bolt hole.
7. Install the clamp and bolt. Tighten it to 23 Nm (17 ft. lbs.) torque.
8. Remove the locking pin.
9. Connect the CMP sensor connector, distributor cap, air cleaner tube, and negative battery cable.

Head’s Up!

Although setting the timing on a 4.0-L Jeep is pretty straightforward, new vehicle owners find some steps challenging, if not tricky. If you do not want to be caught by surprise the same way they have, here are some things to note:

Jeep Year and Model

Depending on your Jeep model, the timing covers could either have holes (so that the gasket threads in) or none at all. Because of this disparity, the oil-pan-to-timing-cover rubber gasket can be one of the most challenging things to work with when setting the timing of your 4.0 Jeep right.

Inspect the Tightness

Remember to inspect the tightness of the timing chain and gear wear the moment you take the timing cover off. Also, see if you have a stock or an aftermarket distributor – the latter reportedly have more issues than OEM ones.

Note Adjustment

If you had to adjust how the rotor on the distributor is installed, you would know you got it right if the hold-down ears of the loop for the distributor retaining bolt were on both sides of the threaded hole in the engine block. It is unnecessary to cut the hold-down ears to correctly position the distributor unless you are working with an aftermarket camshaft.

Follow the Manual

Strictly follow manual instructions, especially the marking on the distributor housing indicating the location of the left side of the #1 cylinder distributor cap post. Make sure the tail/backside of the rotor is exactly at or very close to that point.

You know you have done this correctly if the rotor goes by the #1 post at TDC. Otherwise, you would experience backfiring through the exhaust – a sign that your distributor is installed with one tooth retarded. Conversely, a Jeep that backfires through the throttle body (view on Amazon) means your ECU is working, and the engine is firing but at the wrong time. At this point, you simply need to reset the distributor.

Note New Symptoms

In some cases, getting the timing right does not fix the problem completely. You may encounter new symptoms like rough running and the like. If your Jeep exhibits these signs even after going through all the steps, you most likely have a throttle position sensor or TPS problem.

Beyond issues with the TPS, you may need to investigate a broader area encompassing your Jeep’s fuel and electrical/ignition system. For Jeeps with vacuum-controlled timing, doing other tests like fuel pressure (with and without a vacuum attached) and manifold vacuum would help narrow down the root cause.

On the other hand, ECM-controlled ones would benefit more from cleaning the IAC (specifically the gallery from the IAC cavity going into the throttle body, which can get clogged), dumping the learned memory in the ECM, or rotating the distributor shaft position clockwise one more tooth.

Note Assembly

How you assemble your vehicle’s top-end – particularly aligning the gears and chain – can sometimes result in a slightly off-base timing. This is worth noting, especially for Jeep owners who work on their timing problems in staggard. Tweaking the base timing is another way of setting your ignition timing right. However, it is a more challenging route to take – not the easiest to get done.

Replace the TPS if Hesitation Occurs

Getting hesitation when you hit on the gas does not automatically mean a bad distributor. After all, TPS is a sweep-type variable resistor. The “sweep” part of the sensor rubs against a resistor and moves from idle every time the vehicle accelerates, causing it to wear out faster. When this happens, replace the TPS first and go from there.

Ease does come with experience – and the same is true with resolving Jeep problems. I mentioned this because this is one fact of automotive life many of us tend to forget. Determining how to set timing on a 4.0 Jeep may be daunting at first. But really, it is relatively easy to get the distributor one tooth off. Plus, if you check the rotor positioning, spotting any misalignment is hardly a task.

Remember, you can only repeat the steps in this guide up until a certain number of times. If you are sure the distributor is in properly but still experiencing misfiring (even after a good number of attempts), perhaps it is time you look elsewhere for the source of the problem.

Conclusion – How to Set Timing on 4.0 Jeep

To recap, here are the 10 steps on how to set your ignition timing on a 4.0 Jeep:

1. Do the scribe mark.
2. Access the valve springs.
3. Line up the markings on the crankshaft pulley and the timing cover.
4. Install the rotor on the distributor.
5. Position the distributor into the engine block.
6. Rotate the rotor to the 4 o’clock position.
7. Ensure the distributor seats properly in the engine block.
8. Align the rotor blade trailing edge with the scribe mark.
9. Bolt down the distributor and connect electrical components.
10. Replace the valve cover.

You would know the distributor is correctly installed for your 4.0-L Jeep when the following conditions are met:

• The rotor points at the 5 o’clock position
• The alignment pin (or pin punch tool) is still installed to the distributor
• The #1 cylinder piston is set at TDC (compression stroke)
• The centerline of the distributor base aligns with the centerline of the clamp bolt hole
• The tail/backside of the rotor is on or just past the line once the distributor is fully inserted

If you followed this guide and instructions in your service manual to the T, all the above indicators should fall into place. You may occasionally have to pass up on some Super Bowl weekends, given the tedious nature of this task. But in return, you will have your 4.0 Jeep running like a champ in no time.