Question3.5 V6 has a rough idle, runs good otherwise. Codes were P0300 and P0305. Replaced spark plugs, checked coil paks, spark plug wires. Ohm meter checked OK. Put heavy dosage of injector cleaner in full tank of gas, traveled over 200 miles on highway trip. Check Engine light still ON. Codes read the same...P0300 and P0305. Gas mileage appears to be the same as before. Any ideas. ??
AnswerHi Ed,
The codes are based upon the detection of minor missing which causes subtle differences in the rpm as each cylinder fires to produce its rotational input (crankshaft speed sensor is the detector involved). The Chrysler troubleshooting manual lists the possible causes as:
secondary ignition wires, puel pump or fuel filter, injector harness connectors, ignition coil circuit, spark plugs, mechanical engine problem, contaminated fuel, water in fuel, PCM grounds, Injectors, Restricted exhaust, intake restriction, PCM, evap system, EGR system, Air gap at high rpm's, damaged sensor trigger wheel. That is quite a list!
Your mention of a rough idle would lead me to suggest that you start with the exhaust gas recirculation valve. It has a stem that is accessible between the vacuum actuator and the body of the valve proper in a flange are between the two. You will see the stem and notice that it has a slot into which you can put the tip of a screwdriver to allow you to move the stem back and forth. Check to see if the internal spring action moves it to a dead stop (valve close) and if it is sticky or sticking ajar you could spray some WD-40 on the stem where it enters the body and work it some to improve the closeability. A slightly ajar valve at idle can cause that sort of a miss that you describe. Other than that, going back to the previous paragraph:
The approach suggested is to check all electrical connectors and wiring, then do the tests in the following order:
secondary ignition
fuel delivery
engine vacuum
PCM power and ground connections
engine mechanical
The first one uses an engine analyzer scope to look at the high voltage pattern, then spray water on the cables to see if it changes. The possible repairs: individual spark plugs, coil or cable replacement
The second one involves pressure measurement and from there a variety of possible solutions
The third involves reading the intake manifold vacuum to see if it is steady at between 13 and 22 inches of HG. and if not the suspects depend upon the pattern shown by the gauge.
The PCM involves checking various wires at the PCM plugs
The last involves engine compression testing and a variety of other mechanical checks.
So I guess that beginning with the ignition wires makes sense unless you have a scope and the experience/knowledge at interpreting the patterns. You might try looking at the wires in the dark with the engine idling, then also spray some water mist on them to see in either case if you see arcing which would be a sign that the wires' insulation is breaking down. Then measure the coil resistances. If it passes that, then focus on the fuel filter and pump.
The code pointing to cyl #5 means the general problem is affecting that cylinder more than the others, but the approach to it is identical to that for the general misfiring problem, perhaps with a focus on #5. But the 0300 code is probably the controlling factor (involving multiple cylinder misfires rather than just one).
I can't give you any personal experience with this situation, unfortunately.
I'd be interested in learning what you find to have been the solution.
Roland
