Hey All,
I have gained a lot of useful information on this site and would like to share my current situation in order to receive advice and to help anyone with similar problems. I have owned my 01 Sport for about 10 years and have performed almost all maintenance and repairs. It has run great with minimal issues, any that did arise I was able to easily diagnose and repair with the help of this group.
I have recently been dealing with a cylinder 1 misfire, P0301. Starts fine, idles fine, and runs well as long as RPMs are over 2000 or engine is cold. Throws flashing CEL if coasting or running around 1500 rpm or less.
I am starting my diagnosis with the usual suspects, fuel, spark and air.
Fuel:
Tested pressure at fuel rail, 55 psi. Too high, also had long crank issue so I figured bad regulator or check valve. Replaced fuel pump (Delphi), pressure now at steady 49 psi with no issue holding pressure at rail when engine is off.
Still having misfire.
Removed fuel rail and injectors, visually inspected injectors (original mopar), no cracks or bulging, cleaned external surfaces and replaced o-rings. Swapped No.1 injector with No.5 injector. Verified injector pulses with test light, replaced injector harness to ensure good connection.
No change.
Camshaft sensor alignment seems good, verified cylinder 1 compression stroke TDC against alignment holes in OPDA. (Don't have access to scanner to 0 it out)
87 octane ethanol free gas.
Spark:
Had similar issues a few years ago. I discovered that after replacing the coil rail, (Delphi) spark plugs, (autolite XP985) crankshaft sensor, camshaft sensor and TPS. (all Mopar) that the battery was toast, it started the Jeep fine and ran ok, but failed under load. After installing a new Napa AGM battery, it has ran almost perfect for the last two years. After the current problem started and after checking the battery. I have again replaced coil pack and spark plugs (Autolite APP 985 gapped to .035). Old plugs looked good and I am keeping them as spares as well as the old coil pack. I also traced the wiring for the ignition coil drivers back to the pcm harness for continuity, not sure if this rules out a short, but it definitely gets signal. ( I did the same process for fuel injector grounds also).
Battery and grounds check out at this time.
Air:
Vacuum reading 12 inches steady at idle.
Removed and cleaned throttle body, replaced gaskets and IAC valve. No noticable change in RPM when applying propane or aerosol around intake.
Dribbled water through air intake and also did seafoam intake treatment to help with possible carbon issues.
It now purs like a kitten until it warms up. Then bam misfire cylinder 1.
I replaced both the down pipe(2 little cats) and the main cat about three years ago. All 4 O2 sensors are NTK with about two years on them.
It's going into the shop on Monday for compression and leak down tests. I think it might be a blown head gasket or cracked head at this point. It has been drinking a little coolant. Also not ruling out PCM or wiring harness, just want to rule everything else out first. If anyone has any ideas or tips please share. I will post updates when they are available.
I have gained a lot of useful information on this site and would like to share my current situation in order to receive advice and to help anyone with similar problems. I have owned my 01 Sport for about 10 years and have performed almost all maintenance and repairs. It has run great with minimal issues, any that did arise I was able to easily diagnose and repair with the help of this group.
I have recently been dealing with a cylinder 1 misfire, P0301. Starts fine, idles fine, and runs well as long as RPMs are over 2000 or engine is cold. Throws flashing CEL if coasting or running around 1500 rpm or less.
I am starting my diagnosis with the usual suspects, fuel, spark and air.
Fuel:
Tested pressure at fuel rail, 55 psi. Too high, also had long crank issue so I figured bad regulator or check valve. Replaced fuel pump (Delphi), pressure now at steady 49 psi with no issue holding pressure at rail when engine is off.
Still having misfire.
Removed fuel rail and injectors, visually inspected injectors (original mopar), no cracks or bulging, cleaned external surfaces and replaced o-rings. Swapped No.1 injector with No.5 injector. Verified injector pulses with test light, replaced injector harness to ensure good connection.
No change.
Camshaft sensor alignment seems good, verified cylinder 1 compression stroke TDC against alignment holes in OPDA. (Don't have access to scanner to 0 it out)
87 octane ethanol free gas.
Spark:
Had similar issues a few years ago. I discovered that after replacing the coil rail, (Delphi) spark plugs, (autolite XP985) crankshaft sensor, camshaft sensor and TPS. (all Mopar) that the battery was toast, it started the Jeep fine and ran ok, but failed under load. After installing a new Napa AGM battery, it has ran almost perfect for the last two years. After the current problem started and after checking the battery. I have again replaced coil pack and spark plugs (Autolite APP 985 gapped to .035). Old plugs looked good and I am keeping them as spares as well as the old coil pack. I also traced the wiring for the ignition coil drivers back to the pcm harness for continuity, not sure if this rules out a short, but it definitely gets signal. ( I did the same process for fuel injector grounds also).
Battery and grounds check out at this time.
Air:
Vacuum reading 12 inches steady at idle.
Removed and cleaned throttle body, replaced gaskets and IAC valve. No noticable change in RPM when applying propane or aerosol around intake.
Dribbled water through air intake and also did seafoam intake treatment to help with possible carbon issues.
It now purs like a kitten until it warms up. Then bam misfire cylinder 1.
I replaced both the down pipe(2 little cats) and the main cat about three years ago. All 4 O2 sensors are NTK with about two years on them.
It's going into the shop on Monday for compression and leak down tests. I think it might be a blown head gasket or cracked head at this point. It has been drinking a little coolant. Also not ruling out PCM or wiring harness, just want to rule everything else out first. If anyone has any ideas or tips please share. I will post updates when they are available.
