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Hello all. I haven't been a Chrysler owner for a while, so long that my username went invalid! But my son's girlfriend drives a 2000 300M, so I'm back at Allpar for help. I remember this forum being very helpful when we had a Chrysler minivan. The 300M has about 120k miles.

The issue we're having is with injector/cylinder 4, codes P0204 and P0304.
I'm posting to ask if it is typical for the 3.5L V6 Chrysler engine (or other) to exhibit this behavior for a bad injector: runs very rough when cold, but when warm runs like a champ.

After limping the car over to our place, I used a screwdriver between my ear and the running engine to listen to each injector. They all made a similar tick-tick-tick sound, so I know #4 is actuating, and it sounded like all the others. I'm not sure what prompts the fault code but it must not be failure to actuate.

We checked the plugs, which appeared to be the original set. #4 was not fouled in any way. The gap was huge on all of them, so we re-gapped to 0.050 (I think that is correct--I also saw 0.035 somewhere, but I think the 2000 engine requires the larger gap.) New plugs were ordered immediately. We reset the codes and thought maybe it was just something clogging the injector. Fuel injector cleaner was added to the gas tank.

Next morning, car was back to rough running, and CEL was back on. I guess we didn't get lucky.

Is it worth trying to clean the injector(s)? We have a used set from the junkyard that are clean and operate when tested. The effort to change injectors is not small. Trying to decide if we should:
A. Replace injector 4 with new or used
B. Leave the others alone or clean them while we're in there

We will of course replace the plugs at the same time. Any advice will be appreciated.
 

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Welcome back. I suspect that the P0304 (#4 misfire) is because of P0204 (#4 injector circuit).
Solve for P0204 shown on p. 121 in the '00 LH Powertrain Diagnostic Procedures manual here:
http://oskin.ru/pub/chrysler-dodge/...d/LH_Powertrain_Diagnostic_Manual/ELH_PWR.PDF
In the 'Possible Causes', the issue can be the ASD (+12v) supply wire to the injector, the return wire to the PCM, the injector itself or the PCM (internal driver).
If you can eliminate these possibilities one-by-one, you should arrive at your answer.
For an injector test, you can swap #4 with an adjacent injector on the fuel rail. Note that if you disturb the fuel rail to swap injectors, it may start fuel leaks because of old brittle rubber o-rings. You may want to replace the o-rings if you remove the rail for this service. The intake manifold gasket may or may not be salvageable after 16 years.
Sometimes, but not always the injector ohms test will show higher or lower resistance than normal (compared to the other 5). The PCM tests the injector by looking for the voltage 'kick' when turning off the coil rather than an injector coil resistance test.
Check the wiring harness on top of the engine for rub-throughs or breaks. Engine heat and vibration over the years may have damaged the wiring. You likely don't have a DRBIII, but a volt/ohmmeter should be able perform most of the important tests.
A simple schematic is shown on p. 369. Injector #4 connector pinout shown on p. 350.
DGn/LGn should be 12 volts in, LBu/Br should be the return to the PCM which grounds the injector momentarily for the timed squirt.
PCM pinout is on p. 363/364.
The injector to/from wiring needs good continuity from end-to-end with no short to ground or opens.
 
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