Multiple Misfire Codes and TPS codes

Hey guys,

I've been dealing with this for a long time. My XJ stutters and backfires then runs "fine" after. It still has some hesitation from starts.

As of right now my XJ is throwing 4 codes.

P0300 - random/multiple misfire detected
P0303 - cylinder 3 misfire
P0304 - cylinder 4 misfire
P0122 - Throttle/pedal position sensor/switch "A" circuit low

What I've replaced so far:
TPS (twice)
Injectors
Cap
Rotor
Spark plugs
Upstream O2 sensor
CPS
Ignition coil
Catalytic converter
Exhaust
Header

I can't figure out for the life of me what is going wrong. Compression checks out (a cylinders within 5-10%). I'm going to check again to make sure. I've also verified fuel pressure at the rail. No problems there.

I've also inspected the wiring harness following the TPS wires back behind the valve cover with no pinched wires or shorts.

Unfortunately my smog is due very soon and still can't figure this out.

My plugs are nowhere near as gummed up as this guys.
http://www.naxja.org/forum/showthread.php?t=1120175

Anything else I can try??

Genuine Jeep OBD sensors, or crappy Chinese "Lifetime Warranty" garbage ?

Basic Champion copper plugs, and NTK O2's, or one of the other brands/plug types that make a Jeep choke and gag ?

Tested the MAP sensor ? Tested the Coolant Temp Sensor (CTS) ?

P0122 Jeep - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes

- Faulty throttle position sensor
- Throttle position sensor wire harness is open or shorted
- Throttle position sensor circuit wire plugs poor electrical connection
- Failed capacitors in the Powertrain Control Module (PCM)
.

Tim_MN said:

Genuine Jeep OBD sensors, or crappy Chinese "Lifetime Warranty" garbage ?

Basic Champion copper plugs, and NTK O2's, or one of the other brands/plug types that make a Jeep choke and gag ?

Tested the MAP sensor ? Tested the Coolant Temp Sensor (CTS) ?

P0122 Jeep - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes

- Faulty throttle position sensor
- Throttle position sensor wire harness is open or shorted
- Throttle position sensor circuit wire plugs poor electrical connection
- Failed capacitors in the Powertrain Control Module (PCM)
.

Click to expand...

Sensors were from Oreillys, O2 sensor was NTK, champion plugs, CPS is the factory. I forgot to include the Coolant temp sensor was also replaced.

I'll have to test the MAP sensor, never thought about that.

As for the TPS. I verified the wires going back behind the valve cover. I added some dielectric grease to the connections.

Cheap crappy "Lifetime Warranty" parts are often out of specification, or even failed, right out of the box. Many times they have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep OBD sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

Dielectric Grease is not recommended to be applied to the actual electrical conductive contacts of the connectors because it could interfere with the electrical signals passing through the connector in cases where the contact pressure is very low.