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2000 Jeep Wrangler P0300/P0305/P0306 Misfire Only Above 2800 RPM - Diagnosis and Fixes

Model: Wrangler Fault Code: P0300 Posted: 2011-08-16 20:56

My 2000 Jeep Wrangler with a 4.0L inline-6 engine has recently developed a recurring misfire issue that only appears above 2800 RPM. The vehicle previously ran smoothly, but on Monday morning, the fuel gauge read empty and the car would crank but not start. After replacing the fuel pump (at 170k miles), I discovered the root cause was a faulty crankshaft position sensor (CPS). Replacing it allowed the engine to start again. However, shortly after, the check engine light triggered P0300 (random misfire), followed by persistent P0305 (cylinder 5 misfire) and later P0306. The misfires consistently occur above 2800 RPM as shown in freeze frame data. I replaced all spark plugs due to poor condition, then tried fuel system cleaner with Techron. This temporarily improved performance but eventually led to a return of P0300 and the reappearance of P0305 and P0306. I subsequently replaced the ignition rail (new MOPAR) in hopes of resolving coil issues between cylinders 5 and 6, but that did not resolve the problem. The engine runs smoothly at idle and can travel over 30 miles without codes when driven below 50 mph. However, once speed exceeds 65 mph or RPM surpasses 2800, misfire codes reappear—P0300, P0305, and P0306—randomly. The consistent occurrence above 2800 RPM raises questions: could it be weak valve springs? Or is there an air leak in the intake or exhaust system? I'm open to any suggestions based on known issues with this engine model and age. Has anyone else experienced similar behavior after a CPS replacement? Note: The issue began immediately after installing the new crankshaft sensor, which makes me suspect either the sensor itself (especially aftermarket models) or an underlying mechanical fault related to high-RPM operation.

Related fault codes

P0300P0305P0306

Comments (9)

Anonymous 2011-08-17 04:59

I recommend checking for exhaust system blockages. Aftermarket crankshaft position sensors have been known to cause misfires, especially under load or at higher RPMs—consider replacing with a genuine MOPAR or OEM sensor.

Anonymous 2011-08-17 08:48

The original CPS was a Borg Warner unit, which I believe was an aftermarket part supplied by Chrysler. At $45, it was affordable—but some users report poor signal quality in older Jeep engines. Try removing and replacing the sensor again to rule out installation or quality issues.

Anonymous 2011-08-17 11:28

That’s not accurate—Borg Warner wasn’t a primary supplier for MOPAR on early 2000s Wranglers. Wells brand sensors are generally more reliable and better suited to this engine platform, especially in older models.

Anonymous 2011-08-17 11:54

I’ll try switching to a genuine MOPAR crankshaft position sensor—paying the higher price for reliability. Since the issue started right after installing the new CPS, it’s plausible that the sensor is at fault. However, given the timing and RPM-specific nature of the misfire, I’m still considering other possibilities like air leaks or valve spring wear. I’ll test this in a few days and update with results.

Anonymous 2011-08-17 19:08

This issue may stem from improper air gap settings or poor signal quality in non-OEM crank sensors. If the engine ran fine before the no-start incident, then started misfiring after installing a new CPS, either the fuel pump or the sensor itself could be at fault—especially under high load and RPM conditions.

Anonymous 2012-12-27 18:21

I’m experiencing the exact same issue on my 2001 Jeep Wrangler 4.0L. Did you try switching from an aftermarket crankshaft sensor to a genuine MOPAR one? I’ve tried everything—no improvement yet—and am running out of ideas.

Anonymous 2012-12-28 09:20

gator13: Please start a new topic with detailed information. Specify the vehicle model, engine specs, modifications, and full history of repairs. Also confirm if it’s a stock setup and whether the check engine light is active during symptoms.

Anonymous 2013-02-17 22:43

I have a 2001 Wrangler with identical symptoms—misfires appeared after replacing my crankshaft sensor from AutoZone. I tried another sensor, but no improvement. Any other ideas or diagnostics that might help?

Anonymous 2013-02-18 09:57

rippersjc: Start a fresh topic and provide full details—engine type, transmission, any modifications, recent work history, and all diagnostic trouble codes (DTCs). Why was the crankshaft position sensor replaced? Also consider getting sensors directly from Jeep OEM sources for better compatibility.