13 jk

have a 08 jku,3.8,has 80,000 miles on,started setting code for #1 misfire
put a set plugs in it,still same miss,compression ok,injector has voltage on 1 side nothing on the other.
could the problem be in the computer?or could something be telling it to shut down that cylinder.
probed the brn yellow wire with a test lite hooked to ground injector seemed to start working,would that wire come straight from the pcm.thanks any help.

ronjenx

Misfire has a very long list of possible causes, because anything that affects crankshaft speed at any point in its rotation can set the code.
If a misfire is detected for a particular cylinder, the PCM will shut off that injector.

Here is most of the list of possible causes for misfire:

Visual inspection is first:

Turn the ignition off.
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ignition coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
- Internal engine component failures.

Then, test the following items:


(F342) ASD RELAY OUTPUT CIRCUIT

INJECTOR CONTROL CIRCUIT

COIL CONTROL CIRCUIT

IGNITION WIRE

SPARK PLUG

IGNITION COIL

FUEL PUMP INLET STRAINER PLUGGED

RESTRICTED FUEL SUPPLY LINE

FUEL PUMP MODULE

FUEL PRESSURE LEAK DOWN

FUEL INJECTOR

ENGINE MECHANICAL (see below)

POWERTRAIN CONTROL MODULE (PCM)


"Engine Mechanical", mentioned above, includes:

Check for any of the following conditions/mechanical problems.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
CAM LOBES - must not be worn excessively
CYLINDER LEAKAGE TEST - must be within specifications

VALVE SPRINGS - cannot be weak or broken

13 jk

got it fixed.turned out it was th njector,high resistance 70k,should be around 12-13k
put in 1 from the dealer(cheaper than aftermarket) runs fine now.fyi-when it was cold had a pulse signal to the injector,warmer it got the worse the miss.