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Dodge Repair/'04 Dodge Ram 1500 4.7L intermittent miss and P0300 code


My work truck is a 2004 Dodge Ram 1500 1/2 ton 2wd with a 4.7L engine.  It has had an intermittent miss for over a year now.  Right after this started we had a tuneup performed and 2 of the coil packs needed to be replaced because the broke upon removal.  A few months later we had a horrible miss that was traced to the coil pack on #5.  After that, the miss was intermittent.  There was a bad O2 sensor that was replaced about 6 weeks ago. We also had a bad fuel pump replaced about the same time.  The latest diagnostics showed a complete loss on 1,3,5,7 when it happens but it only lasts for a few seconds, not long enough for the scanner to track it down.  The ECM for this year doesn't store the misfires for each cylinder, just the general P0300 code.  Any place we take it doesn't seem to be able to track it down and we don't want to end up paying thousands in diagnostic time for them to eventually track it down.  I am wondering if it might be a wiring harness that has rubbed through somewhere either for the O2 sensors or the coil packs or even the injectors that would cause them to momentarily short and cause the miss to happen for the few seconds it lasts for.

ANSWER: Hi Frank,
The injectors and the coils all need a solid 12v supply from the automatic shutdown relay.
If the right side bank is momentarily shutting down then there well could be a loose connection at the splice which carries the 12v to those injectors/coils on the right side.
The 12v comes in on a brown/white wire to a splice located at the rear of the engine above the valve cover on the right side where if feeds the 5 and 7 units and also a wire that feed a splice that feeds the 1 and 3 units located further along that right side. So if the entire right side is dropping out I would check that rear splice where the right side branches off from the left side.
I am surprised that the ecm doesn't show individual cylinder misses. Maybe the miss is indeed for all 8 cylinders and is due to a problem with the incoming brown/white wire from the ASD relay to the splice I have described.

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Yeah this ECM doesn't track the individual cylinders which makes it tough to track this down.  Also, when you say right side bank are you referring to the right side when facing the engine from the front of the vehicle (which would be the drivers side of the truck)?  I have a feeling that is probably the case with the bad connection.  Also, can you tell me where the power harness for the blower fan (a/c and heater) runs in the engine compartment, I also have an intermittent loss of blower fan operation, but not at the same time as the miss.  And, the blower fan can remain dead for a few minutes to half a day.  It too is totally random when it occurs.


ANSWER: Hi Frank,
No the splice in question is on the passenger side of the engine, at the rear just above the valve cover according to the diagram. Just trace back from the cyl 7 plug/coil and you will find it.
On the blower fan, I would suspect the resistor block is opening up. When that happens you will lose all the slower speeds but the high speed will work. If that is the case, then you will find it under the dash at the right hand end of the HVAC on the underside. The blower motor harness plugs into it.

---------- FOLLOW-UP ----------

QUESTION: Nope, the entire fan dies, no speeds it has lost power, both the connections at the resistor block and the fan are ok.  Does this harness run out into the engine compartment or does it run strictly inside the dash?

The blower is powered from a section of the ignition switch which gets its power for that section via fuse 4 (40 amp) in the main power box. So either that fuse is flakey, the ignition switch section is flakey, or the blower could be flakey, or the wiring. You would need to check it out when it isn't working.  

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Roland Finston


Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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