2001 Jeep Grand Cherokee 4.7L: Diagnosing P0202, P0175, P0300, P0301, P0302 Codes and Rough Idle/Stalling Issues

Are you using an OBD-II scanner? The 'key dance' (on-off) trick may not capture all stored codes. Allow sufficient runtime to reset the system. Use a scanner to monitor fuel trim values and pre-cat oxygen sensor readings. Without a scanner, test fuel pressure with a gauge—observe any drop during key-off engine operation. A rich condition could stem from injector #2 staying open (P0202 and P0175). Check spark plugs 1 and 2 for signs of fouling. A noid light is recommended to verify injector circuit functionality at cylinder #2.

Thanks for the response—I’m planning to get a fuel pressure gauge soon. When I replaced the coils, I checked the spark plugs and found them in good condition. I was told that a quick drop in fuel pressure points to a failing fuel pump, while a slow drop suggests an injector issue. Is this accurate? Sorry for the delayed reply—I had to go out of town.

"Quick pressure drop indicates fuel pump failure; slow drop suggests injector issue." This is only part of the picture—consider all symptoms: rich mixture, fouled plugs, fuel in oil, normal operation at startup but poor performance later, multiple misfires on start-up, isolated misfire in one cylinder. Also consider rail pressure regulators and check valve issues within the fuel system.

I haven’t tested fuel pressure yet. I’ve decided to take the vehicle down the block to see if any new codes appear. The engine runs roughly, but when I release the accelerator pedal, it stalls completely. I also hear a knocking sound from cylinder #2—could this be related to a PCM malfunction or mechanical failure in that cylinder?

I meant the stalling issue—not the knock.

A PCM issue is possible, but don’t jump to conclusions. All symptoms point toward cylinder #2: misfire, rich condition in bank 2 (P0175), and P0302. Likely root cause: a wiring or injector circuit fault at cylinder #2. This may be causing the misfire and rich mixture. Also note that P0301 and P0302 contribute to the overall P0300 (multiple misfires). I recommend testing fuel pressure under KOEO conditions and inspecting the wiring at injector #2. A thorough diagnosis is essential.

Quick question: If injector #2 is faulty, would that cause stalling or just a rough idle? I’ve borrowed a cylinder compression tester and was planning to check cylinder 2. I’ll be unable to get the fuel pressure gauge until tomorrow.

I truly appreciate all the detailed input and troubleshooting tips provided—this has been very helpful in guiding my diagnosis.

Code P0202 does not indicate a faulty injector—it refers to an 'injector circuit' fault. A noid light makes this test straightforward; alternatively, use a multimeter or test light. Are you comfortable using these tools? Compression testing is always valuable—consider including cylinder #1 since it also shows a misfire code (P0301). While the plugs are out, they appear dry and not fouled—Champion brand, as I recall. Never assume that an OBD-II code directly points to a part failure—that’s what auto parts stores sell you.

No compression reading from cylinder #2.

I was told that this engine model is known to develop a follower (rocking arm) failure. Could this explain the lack of compression in cylinder #2?

Open the valve cover and inspect—remove the valve cover and check for signs of wear or damage. A visual inspection can reveal issues like a broken rocker arm or bent valves. Here’s a helpful video reference: https://www.youtube.com/watch?v=ksrDE2zjC34

After finally removing the valve cover, I found a worn rocker arm (follower) from cylinder #2. I purchased a new lifter, but now it appears the valve may be stuck—rockers slip easily and show excessive play. Is it possible that a weak valve spring could cause this kind of failure?