I have posted this on the Dodge forum, but I think the level of expertise is higher here. I have two 2005 Dodge Magnum RTs - Both have the same issue. Sometimes a misfire at idle, and surging and an occasional misfire under part-throttle acceleration. Periodically the check engine light will come on for a few days then go out. On one car I was able to get a read on the MIL and it was P 300 - random misfire. The garage that scanned it suggested O2 sensors, which with 134,000 miles I felt couldn't hurt. It made no difference whatsoever. I then replaced the plug wires with top-quality units, checked and cleaned the PCV valve. and inspected the plugs. They were not old and were in great shape. the throttle body was filthy, and I removed and cleaned it, and replaced the O-ring that seals it. All of the above made absolutely no difference. I'm not going to do any more diagnosing by parts replacement. It obviously could be a coil, but if it were only one coil, I would think that the code would be for two specific cylinders. Anyone have any ideas? One guy on the Dodge forum suggested cam/crank sensors, but said that if either were bad I would probably have an extended crank to start. Both cars start instantly.
Buy a can of BG44K & good dry gas. The 44K will clean the injectors & the isopropl dry gas will displace moisture. Use with at least a half tank of fuel. Run it a couple times if nec. LOTS less costly than replacing parts. IF it turns out to fix the problems you didn't even need to get your hands dirty & it costs much LESS than replacing parts willy/nilly.
I would not have guessed o2 sensors, but modern cars, who knows? I’m surprised the Mopar crowd hadn’t seen this a thousand times if you have it twice. Maybe crank trigger, maybe wiring to it, maybe a ground problem somewhere? Patrick
Actually they have. The problem is that the replies are all over the place, ranging from cam and crank sensors, bad coils, plug wires, broken valve springs, bad valve seats, blown headgaskets, PCM, intake leaks, variable displacement harness... You get the idea. Interestingly, no one mentioned dirty injectors. I just ordered two cans on Amazon Prime. Thanks for the tip, Tom.
I used to frequent a Ram forum when I had my '04 1500. The early Gen II Hemi's (usually '03-'04, but I've heard of it happening later as well) had sporadic broken valve spring issues. From what I can recall, the problem could present itself as a minor miss, or make the engine not run at all. Might be worth pulling the valve covers - they were relatively accessible from what I can remember. Only other Hemi specific things that come to mind are plugs/wires/coil packs, and the coil pack wiring harness. For whatever reason these motors seemed to prefer a standard run of the mill plug. Guys that used exotic stuff like platinum, special ground strap designs, etc, reported weird issues similar to what you are experiencing. Same thing with low resistance performance plug wires, or aftermarket performance coil packs. I've also heard of the coil pack wiring harness getting chaffed from the way it was run under the engine cover/around the intake. Start with the injectors, hopefully that clears it up!
Could also be a bad ignition control module. They were also known for dropping the valve seats out of the aluminum heads. MANY factory/dealer engine replacements.
Yes Tom, I knew about the valve seats, but if one seat were loose, I'm guessing that the code would be cylinder-specific instead of "random". The same thing (I would think) would be true of coils. I think the chances of having all of the coils going bad at the same time would be slightly less then my chances of winning $400,000,000 in the lottery. As I said earlier, if it were one coil, I would think that the code would identify the cylinders. I like the injector idea. They have all been in the engine for the same amount of time, and all have handled the same amount of fuel (not exactly true with the variable-displacement feature) and the car doesn't use a fuel filter.
My ‘07 Tahoe had one broken valve spring which caused a bunch of odd symptoms at idle but, like you suspect above, set a specific cylinder misfire code (number 7 in my case). Patrick
The seats DON'T normally get loose, they fall out & it usually goes through the piston top. NO WAY you can tell this short of removing the heads or IF it does become dis-lodged a replacement/rebuilt engine. The later engines have had the updates. Just a FYI. IF you do decide to change a coil for some reason go OEM ONLY. Aftermarket coils have a tendency to "Fry" the ignition module causing MANY other problems.
Tom, as a matter of course I like factory parts unless I am pretty sure that something aftermarket is better (such as your pistons and starters). I suspect strongly that if a valve seat had fallen out and gone through the top of a piston, there would be symptoms that are a lot more serious then what I have. I still like your injector theory.
