Does your Jeep Wrangler sputter on acceleration? Do you have a strong gas smell inside the cabin? Does your Jeep feel underpowered and sluggish? Has your CHECK ENGINE light appeared with a few codes? If you answered yes to any of the above questions, you might find a solution in this article.
A sputtering Jeep Wrangler can be caused by any of the below bad components:
- Upstream O2 Sensors
- Valve springs
- TPS (Throttle Position Sensor)
- Spark Plugs
- Coil Rail
So there’s a host of possible causes why your Wrangler can become sluggish and sputter under load. The above-mentioned solutions will vary, depending on which year model Wrangler you own. The bad Valve springs, for example, are only related to the older model TJ’s, which were synonymous with this problem.
Various codes should appear, some of which you can safely ignore, as well as a CHECK ENGINE light. We’ll get into that in more detail a bit later.
Note: when self-diagnosing problems, be very wary of what advice you accept from the counter salesman, since most of them are not qualified mechanics and don’t always have your best interests at heart.
Now that we have that out of the way, let’s now look at a few possible solutions to your sputtering woes.
Sputtering On Acceleration (SOLUTIONS)
The below solutions cover a wide range of Wrangler models, which can include the 2.5 as well as 4.0 models ranging from the TJ and upwards. When replacing electrical sensors and other components, always insist on genuine Mopar parts for optimal performance. 3rd party components might be cheaper, however, they can cause additional problems later down the line, resulting in your vehicle not performing optimally. Sub-standard 3rd party components could even result in the issue not being resolved, even though the correct component was replaced. Remember, you buy cheap, you buy twice!
Ok, let’s get into it!
Upstream O2 Sensors
Let’s first understand what the function of the O2 sensors is, to properly diagnose the problem.
The Oxygen or O2 sensor is the sensor in your vehicle’s exhaust system designed to monitor how much unburnt oxygen is in the exhaust to allow the engine’s computer to adjust the fuel mixture accordingly. The O2 sensor gauges the fuel to air mixture and tells the computer to increase or reduce the ratios. The O2 sensor also assists in reducing the harmful and poisonous fumes from the motor into the atmosphere.
A faulty O2 sensor means the vehicle can’t properly monitor and adjust the fuel/air mixture accordingly and will result in strong gas fume smells inside the cabin. That indicates your Wrangler is running too rich in fuel.
You will experience the following symptoms:
- Runs fine when cold but sputters once it reaches operating temps
- Your vehicle will sputter on acceleration
- Strong gas fume smells
- CHECK ENGINE light will appear
- Fault Codes p0171 will be thrown out
If you want to determine which codes have been thrown out you’ll need to reset the engine’s faults. This is done by simply disconnecting the battery for 5 minutes. You then need to turn the key 3 times to read all codes.
Code is p0171 means bank 1 too lean, meaning the O2 sensor(s) are faulty and need replacement. There are 2x upstream and 2x downstream on each bank on the 4.0 wranglers. You want to replace the upstream sensors. The recommended sensors are the NTK O2 sensor and not any aftermarket or 3rd party sensors.
If you are going to self-diagnose your Jeep problems, it’s highly recommended to invest in an OBDII scanner to properly diagnose your problem, which can save you thousands in the long run.
Next, let’s investigate the valve springs.
Valve springs
Once again if your valve springs are shot, your TJ Wrangler should kick out a CHECK ENGINE light as well as a few codes. If the codes disappeared, you can call them up by doing the 3-turn sequence where you turn your ignition key from off to ON 3x ending it in the ON position. The computer will spit out all the relevant fault codes on your instrument panel for you to diagnose. Codes like 12 and 55 can be safely ignored.
If you get an error code you can check it here: Jeep Wrangler Error Codes
So after many years and many unhappy jeep Owners complaining about the same issue, jeep finally released a TSB (Technical Service Bulletin) addressing the issue of the bad valve springs on 97 models.
Insist on the OE Mopar valve spring replacement
TPS (Throttle Position Sensor)
If your Jeep seems to run normally under low RPM,s however when you accelerate to pick up speed the vehicle starts spluttering and feels very under-powered, this section is for you.
Possible culprits could be any of the following:
| 1 | Dirty throttle body |
| 2 | Faulty fuel pump |
| 3 | Bad TPS |
| 4 | CHECK ENGINE lights |
| 5 | Code P0123 (Throttle Position Sensor 1 Circuit High) |
| 6 | Code P0441 (EVAP Purge System Performance) |
| 7 | Code P0121 (Throttle Position Sensor 1 Performance) |
Before you run out and purchase a new fuel pump or throttle body, which can be quite pricy, start off by cleaning the throttle body thoroughly. It’s a worthwhile exercise that should improve performance as well as throttle response irrespective. There is nothing to lose by doing it.
Your fuel pump will give other tell-tale signs like loud buzzing noises coming from near the fuel tank.
A bad Throttle Position Sensor is more likely the case here since Code P0123 and P0121 indicates faults with the Throttle position sensor.
Do not cheap out on sensors and only Insist on genuine Mopar sensors for optimal performance and reliability.
Spark Plugs
A few years back I owned a little ¼ ton ford pickup. The vehicle suddenly developed a sputtering. After lots of head-scratching and troubleshooting, it turned out to be a crack in the porcelain of one spark plug. That’s when I remembered, a couple of months prior when I serviced the vehicle, I accidentally dropped one of the sparked plugs. It resulted in a hairline crack which I didn’t notice.
So obviously a badly worn or burnt spark plug will result in loss of spark on a cylinder resulting in a spluttering on acceleration. Also, a cracked sparkplug will lose a lot of spark to the cylinder, resulting in spluttering under load.
Coil Rail
If your vehicle sputters under light acceleration and low RPM but becomes increasingly bad the faster you drive, then you want to investigate your Coil Rail. Another tell-tale symptom is if the sputtering is in direct proportion to your RPM, i.e. the faster you drive the faster the sputtering.
We are quick to assume it’s the injectors, however, it’s very rare that Wranglers suffer from injector problems. The 4.0 Wrangler is not a very highly-strung engine compared to more modern high-tech vehicles.
Symptoms to look out for:
- CHECK ENGINE LIGHT
- Fault Code P0303 (Multiple Cylinder Misfire)
- Sputtering in sync with engine RPM
- Most apparent at 2,000 RPM
The Fault code indicates it’s a misfire on multiple cylinders. If you are 100% certain it’s not a clogged CAT or bad plugs then the only option in this instance is a bad COIL RAIL since it’s affecting multiple cylinders at once.
Resources
I must give kudos to certain Mr. Jerry Bransford. The man is a true legend in the Jeep community and has a wealth of knowledge he willing shares, helping thousands of Jeep Owners all around the world.
https://wranglertjforum.com/threads/tj-sputters-while-accelerating.17281/
Conclusion
So, we’ve identified multiple causes of a sputtering Jeep Wrangler. Some are year model-specific like the Valve springs which was mostly related to a batch of the 97 model range. There are other factors that could also cause sputtering and those include:
- Bad Fuel pump
- Clogged Fuel Filter
- Rusty Fuel Tank
- Vacuum Leaks
If there are no fault codes being thrown out, you need to drive it until it does. Usually, after 3 bad runs the computer will throw out a fault code, however, this isn’t always reliable. Do the 3x key turn dance to read fault codes on the instrument panel, alternatively invest in a decent OBD2 Scanner.