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Why Is My Jeep Running Rough? Common Causes and How to Fix

Why Is My Jeep Running Rough? Common Causes and How to Fix

When your Jeep starts running rough, there are a few different reasons why that could be the case. Some of these common causes are easy fixes, while others are a little more complicated.

The most common reasons a Jeep runs rough is because of spark plug or ignition coil problems. Replacing those parts will fix most rough running Jeeps. Other common causes are due to a vacuum leak, a clogged EGR valve, or there’s an ECU malfunction.

Below you’ll get an overview of the most common reasons why your Jeep begins to run rough along with some solutions to the problem. Some of these Jeep fixes you might even be able to perform yourself.

Common Reasons a Jeep Runs Rough

If your Jeep is running rough, it’s not a problem you want to sit on for long. In some cases, running a Jeep with a rough engine can cause further damage to the engine system.

A Jeep can run rough due to the following common causes:

  • Vacuum leaks in the engine
  • Spark plug contamination or malfunction
  • Ignition coil problems
  • Clogged EGR valve
  • ECU malfunction

Fixing these problems involves repairing existing components for some causes, and replacing or reprogramming parts for others. It all depends on the underlying cause.

Here’s a quick video showing how a tune up can fix a rough running Jeep:

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Vacuum Leaks Cause a Jeep to Run Rough

Vacuum leaks are one of the more frustrating problems for mechanics to run into on a Jeep or any other vehicle since they can be difficult to track down.

Here are some of the symptoms you might experience if your Jeep is suffering from a vacuum leak in the engine compartment:

  • Engine hesitation and stalling
  • High or inconsistent idling
  • Check engine light on in the dashboard
  • Whistling, squealing, hissing, or sucking sound from the engine

Seek out any vacuum leaks in the hoses, seals, or gaskets of the Jeep and replace accordingly. Vacuum leaks typically aren’t difficult to repair, but they can be hard to find if they’re small.

If you can’t find the source of the vacuum leak, a mechanic can use a smoke machine to make the process less difficult.

Faulty Spark Plugs Can Cause a Jeep to Run Rough

Spark plugs are used in fuel-injected engines to start your Jeep. These small parts can cause startup issues as well as misfires in the engine that can make your Jeep run rough. 

If enough of your spark plugs go bad, the engine will eventually stall out. Symptoms of spark plug contamination or malfunction in Jeeps include the following:

  • Rough idle
  • Misfiring engine
  • Surging engine
  • Lowered fuel efficiency
  • Lack of power during acceleration

Spark plugs can also begin to malfunction due to oil contamination from an oil leak.

Spark plugs are easily contaminated with oil if your engine has an oil leak, and when one spark plug goes out it can cause the rest to misfire too.

It’s a smart idea to replace all spark plugs at once if you’re going to go through the trouble to replace one of them.

If the spark plug shorted out, the others are probably not far behind. If you’re paying someone else the labor to replace a spark plug, you don’t want to have to pay them twice. (Source: The Drive)

Ignition Coil Problems Cause Jeeps to Run Rough

The ignition coils in your Jeep are another component in the engine related to starting the vehicle.

These coils convert the Jeep’s battery voltage to a spark strong enough to ignite the engine’s spark plugs. (Source: AutoZone)

Ignition coil problems in a Jeep will show up with the following symptoms:

  • Difficulty starting the engine
  • Check engine light on in the dashboard
  • Engine backfiring
  • Lack of power while accelerating

The solution to ignition coil problems in a Jeep is to replace the faulty ignition coil during a tune-up.

In many cases, mechanics can change all of your ignition coils and spark plugs as part of a full tune-up to eliminate any running issues you may be experiencing with your Jeep.

While a Jeep can be driven temporarily with a faulty ignition coil, this can eventually cause damage to the vehicle’s catalytic converter. 

Clogged EGR Valves Can Cause Jeep Running Issues

An EGR valve is also known as an exhaust gas recirculation valve, and this component is responsible for recirculating part of the engine’s exhaust back into the engine chamber.

Symptoms of a clogged EGR valve in your Jeep include the following:

  • Smell of fuel
  • Engine stalling out in idle
  • Reduced fuel economy
  • Knocking noise from the engine

Clogged EGR valves can be repaired by spraying this EGR valve cleaner (from Amazon) into the valve and scrubbing away any build-up that accumulated.

ECU Malfunctions Can Cause Jeeps to Run Rough

The ECU is the Electronic Computer Unit of the engine, and this is a component that controls the amount of fuel added to the engine’s fuel injection system.

Here are some of the symptoms you might experience when your ECU is acting up on a Jeep:

  • Engine won’t start
  • Lagging and surging in engine while running
  • Problems with shifting gears
  • Poor acceleration and mileage

Depending on how the ECU is malfunctioning, it can affect the performance of the engine as well as the performance of the transmission.

In some cases, depending on the symptoms the Jeep is exhibiting, a faulty ECU can be mistaken for a transmission failure until the transmission is tested.

Unlike other running issues that can be resolved by a home mechanic, ECU failure is a digital problem.

If the ECU hardware is intact, the faulty unit usually has to be reprogrammed at the dealership using specialized equipment. This process is known as “flashing” the ECU. (Source: Foreign Affairs Motorsport)

How to Troubleshoot Jeep Running Issues

So knowing what the potential causes are, how should drivers troubleshoot running problems like a rough idle or stalling? Here are some of the things that a home mechanic can attempt to try and rule out some of the easier causes to fix:

  • Read the check engine light code. If your Jeep is throwing a check engine light in the dashboard, you can use onboard diagnosis to determine the cause.
  • Do a tune-up on your Jeep. Replacing spark plugs, spark plug wires, and ignition coils can clear up many running issues related to the injection system.
  • Listen carefully to the Jeep running. Strange noises like knocking or whistling can help you narrow down potential causes for a rough running issue.

At the end of the day, if you can’t determine the cause of your Jeep running rough, don’t be afraid to consult a professional.

Even if you don’t get your Jeep repaired at a car repair shop, it’s worth getting a mechanic’s diagnosis to pin down exactly what the problem is so it can be fixed.

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Many Jeep Running Issues Can Be Fixed at Home

While more complicated Jeep running problems that cause them to run rough may need the experience of a professional technician, some others can be fixed in your own garage.

If you’re interested in getting more hands-on experience in working on your Jeep mechanically, learning how to do a tune-up or spark plug replacement is a practical way to start.

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