I have been fighting this problem for a long time. 1999 Ram 4x4, stock 318 magnum. 90% of the time it will have a dead miss on cylinder #5 for about the first 30 seconds when you first start it when the engine is cold. Outside temp or rain makes no difference. Miss is at idle and under load. Used a timing light to see if there was spark when this was happening and found no spark. Gradually it came back until it was steady and operating properly. I have cleaned injectors and throttle body. Intake plenum gasket has been replaced (that fixed the pinging problem). Several new caps androtors as well as plug and coil wires. Have re-routed all wires as per the TSB. Problem continues. Have run 20K plus miles on plugs and the plug is not fouled (stock champions). Figure it is not the coil since it is always #5 cylinder.Compression and injector should be good or would assume that it would miss at all times. PCM throws P0305 code and some times will run well on enough starts to clear the code, but it always shortly comes back. After the mis clears, truck runs like a champ. This all started aftera routine tune up. I have lived with this for a long time and kind of gave up on it for while and have done tune-ups at least twice since the problem first started. Remember this is only on cylinder #5. Any ideas?

 

I would check compression anyway.
Try switching the injector to another cylinder and see if the miss moves to that cylinder.

 

Read my mind why dontcha

How about looking down into the intake and see if anything foreign is down there. (with the TB off)
I check the compression first, but that's just me.

 

That's strange. I wonder if you have something wierdgoing on with the flexplate.

 

You know what I think it is the injector too. Odly enough this happends to my sisters 2002 ford taurus. I would have changed the fuel injectors around but on those damn fords the intake man. covers the injectors its too much work. But if you get yours going let me know.

 

OK, I guess I can swap the injector and check the compression this weekend. However, I fail to see how either would keep it from generating spark. Remember, when this happens there is no spark. This has been verified. If there was something in the intake it would always be there, not just when it is cold, and would not affect the spark. I have found where someone else is having this same problem on an AISE site, but since I am not AISE certified I can not view the full post.

Mopowar, how would the flex plate figure into this??

 

if it wasn't for the loss of spark, i would spout off a lot about other things. you've already done wires, cap, rotor, which is the path of the spark from the coil.

just a stupid idea... take a piece of rubber hose and split it lengthways and wrap it around the #5 wire. i don't know what that would accomplish, except provide more isolation for any kind of wierd cross firing thats going on along the path of the wires.

i'm stumped. i don't know of any control features that can control the spark on/off for a particular cylinder. i think the cam position sensor is in the distributor, but i can't see how that would have any effect as its purpose is to time the fuel injectors, not the spark.

 

I found a person on another site who had a similar problem, but their's missed continuously. Anyway, it all started when they put new plug wires on. They went back to Mopar originals and it went away. I have tried cheap wires, expensive wires and even made a set of accel's for it just like my drag car without success. Have thought about just shelling out the bucks for a cap, rotor and wires from the dealer......

 

the mopar wires are bosch , but thats odd , rare you hear something like that anything is possible..

 

I had several codes on the OBD scanner that stated multiple misfire and also #4 cylinder misfire, did complete tune up, no help, would miss just like you said. Cleared codes after tune up showed right back up.
May is suggest a couple things,
Pull out the O2 sensor closest to the engine, see if the performance or missing goes away or improves. Just check in PARK
My problem was a completely clogged catylitic converter, cut it open and could not believe my eyes.