So you have a P0203 code or a P0303 code, here is some information for both
Check for a wiring rub through to the number three injector at the bracket for the throttle cable, if the injector connector is not turned towards the rear of the motor (2 o'clock position) and is facing up the wiring can chafe on this bracket causing the injector to not spray fuel at times or constantly
You can test the resistance of the injector coil with an ohm meter, and then test injector number 1 and 2 , they should all be almost exactly the same, this is the best way since resistance will change with temperature and this gives you a good base line to compare too
Also if it is worse after a hot shut down and a short soak you may want to try the bulletin
4.0L Rough Engine Idle After Restart Following A Hot Soak
Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked
engine. This condition may be most noticeable when the engine is restarted following a
prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF)
or higher. This condition may be consistent with short city stop-and-go driving trips and
can be aggravated by the use of fuel with a high ethanol content. Depending upon
various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.
This condition may be caused by heat from the exhaust manifold that following engine
shut down migrates to the area around injector #3 and causes fuel vapor to form
within the injector. This in turn may cause a momentary misfire of cylinder #3 until
the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3
temperature to a point below which the fuel will not normally vaporize.
Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves
about 1 in. in length.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the
injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o'clock
position (from driver's side of vehicle).
Let me know what you find and we can move onto more testing as needed
I checked the injector resistance, and it starts with a very high number, then steadily decreases. Both #1 and #3 do this. I've driven it more lately, and it seems like it runs smoothly for the first 5 miles after cold startup, then starts missing and the engine light comes back on. I cleaned the electrical connectors, but the problem remains. The connector is clocked at 2:00, and I was unable to find any cuts or cracks in the wires.
What are you getting for readings? for injector 1,2,3
You are testing across the two pins in the injector with the injector unpluged from the wiring harness?
If all of the injectors are giving you the same result, then most likley it is not an injector
P-0203 INJECTOR #3 CONTROL CIRCUIT
When Monitored: With Battery voltage greater than 10.4 volts, the auto shutdown relay
energized, injector pulse width less than 10ms, and engine speed less than 3000 rpm.
Set Condition: This trouble code takes .64 to 10.0 seconds to set when no inductive kick
is sensed 18ms after injector turn off, and with no other injectors on.
AUTO SHUTDOWN RELAY OUTPUT CIRCUIT OPEN
INJECTOR CONTROL CIRCUIT WIRING HARNESS INTERMITTENT
INJECTOR CONTROL CIRCUIT WIRING HARNESS OBSERVABLE
INJECTOR #3 DRIVER CIRCUIT OPEN
INJECTOR #3 DRIVER CIRCUIT SHORTED TO GROUND
POWERTRAIN CONTROL MODULE
Start engine, let idle for at least 20 seconds.
Key on, engine off.
With the scan tool, read trouble codes.
Is the DTC SPECIFIC GOOD TRIP counter displayed and equal to zero?
Yes Go To 2
No Go To 7
Disconnect the Injector #3 Connector.
Note: Check connectors - Clean/repair as necessary.
With the scan tool, actuate the #3 Injector.
Using a 12 volt test light, check the ASD Relay Output circuit.
Does the test light illuminate brightly?
Yes Go To 3
No Repair the open ASD Relay Output Circuit.
Note: The next steps require an analog voltmeter.
Connect the positive lead to a good 12 volt source(B+) and the negative lead to the
Injector #3 driver circuit at the Injector connector.
With the scan tool, actuate the #3 Injector and observe the voltmeter.
Does the needle fluctuate?
Yes Replace the Fuel Injector.
No Go To 4
Disconnect the Powertrain Control Module Connector.
With an Ohmmeter, measure across the Injector #3 Driver Circuit from the
Powertrain Control Module Connector to the Injector Connector.
Is the resistance below 5.0 ohms?
Yes Go To 5
No Repair the open Injector #3 Driver Circuit.
Using an Ohmmeter, measure the Injector #3 Driver Circuit to ground.
Yes Repair the Injector #3 Driver Circuit for a short to ground.
No Go To 6
If there are no potential causes remaining.
View repair options.
Replace the Powertrain Control Module.
Wiggle Wiring Harness from the Injector Connector to the PCM Connector.
Does the engine miss or stall?
Yes Repair as necessary where wiggling caused problem to appear.
No Go To 8
Ignition Off inspect the Wiring and Connectors.
Were any problems found?
Yes Repair as necessary.