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Jeep Cherokee Sport 4WD P0171 & P0303: Fuel Pressure Low, Misfire in Cylinder 3 - Diagnosis and Fix

Model: Jeep Cherokee Sport Fault Code: P0171 Posted: 2016-06-08 10:33

My Jeep Cherokee Sport 4WD has started exhibiting poor idle performance, difficulty starting, and intermittent failure to start. During these issues, I noticed the gas pedal felt unresponsive—like there was no fuel pressure—yet no check engine light illuminated. After performing an oil change, replacing the oil filter and spark plugs with no improvement, I replaced the ignition coil. The symptoms persisted. Now, my OBD2 scanner shows two fault codes: P0171 (Fuel Trim Bank 1 Too Lean) and P0303 (Misfire Detected in Cylinder 3). I suspect a clogged fuel filter, but I'm unsure if this alone could cause these specific codes. The vehicle has a 4.0L engine, and I'm seeking expert advice on the root cause. I've tested fuel pressure using a gauge and recorded 20 psi. This reading appears low compared to specifications. Given that my Jeep's fuel system integrates the pump directly into the tank with no separate filter, I'm concerned about whether the fuel pump itself is failing or if there's another underlying issue.

Related fault codes

P0171P0303

Comments (5)

Anonymous 2016-06-08 11:03

This is a 4.0L Jeep Cherokee? First — check your fuel pressure using an accurate gauge and post the PSI reading. A vacuum leak after the throttle body could also be contributing, but fuel pressure should be your primary focus. You can borrow or rent a fuel pressure gauge for testing. Next, inspect the spark plug in cylinder #3: is it sparking? What does its appearance look like — wet, dry, black, or tan? For reference, see OBD-Codes.com/P0171. This engine is reliable — always use OEM parts and avoid modifications. Note: A key-on-off cycle may not retrieve all stored codes; use an OBD2 scanner with proper diagnostics to ensure full code detection.

Anonymous 2016-06-08 13:15

Thanks for the reply! Yes, it's a 4.0L engine. I've tested fuel pressure and confirmed it reads 20 psi. My current suspicion points toward a fuel delivery issue — either faulty injectors or a clogged filter. However, this model doesn't have a standalone fuel filter; the entire system is located at the top of the fuel tank. This makes diagnosing the problem more complex.

Anonymous 2016-06-08 14:19

I'll verify the specifications — but 20 psi seems significantly low, especially for a 4.0L engine. It's true that fuel pumps in this setup aren't easy to replace and often fail when the tank is full. Aftermarket pumps are generally not recommended due to compatibility issues and higher risk of failure. I'll retrieve the official fuel pressure specifications.

Anonymous 2016-06-08 14:25

Official specs: 49.2 psi ± 2 psi — in simple terms, you should expect around 50 psi. Your current reading of 20 psi is far below this range and strongly indicates a failing fuel pump. I recommend replacing the fuel pump with an OEM Jeep part — avoid aftermarket options, as they are often less reliable and may lead to further complications. On a positive note, the XJ platform remains one of my favorite vehicles — dependable, easy to maintain, and highly capable. If this is the only issue, it's definitely worth keeping.

Anonymous 2016-06-08 21:15

Thanks for the guidance, Kev! I was looking at a few aftermarket pumps at AutoZone, but now I understand — I should stick with an OEM Jeep fuel pump. Will do and appreciate your help!