Bad misfire (cylinders 1 through 4), P0300
My wife's 2003 Dodge Dakota 4.7l 4wd quad cab (unknown transmission) suddenly started misfiring badly Friday. The only engine code is a P0300.
A buddy of mine that runs a local shop is coming by this afternoon to take a look, but I figured I'd toss this out to see if anyone had any experience/similar problems/advice/etc.
I spent a little while looking over it this weekend, and noticed that it SEEMS to be missing on cylinders 1 - 4; when I disconnect the ignition coils from those cylinders, it makes no impact on how well the engine runs, but when I disconnect one of cylinders 5 - 8 the engine suffers significantly and/or dies.
I actually disconnected cylinders 1 - 4 simultaneously and there was no difference in how the engine ran.
The coolant looks good, oil looks good. Plugs and coil packs aren't that old, maybe 10,000 miles, and the plugs pretty much look like new with ~.045 gap according to my crappy Autozone gap tool. Owner's manual doesn't appear to list the proper gap, the internet says .040 is recommended. I picked up a new coil pack and swapped it out across several of the suspected "dead" cylinders and it had no impact.
My spark tester won't work with the coil packs sadly, so I haven't been able to test whether those cylinders are getting spark or not.
A few things to add that may be related/unrelated:
Exhaust is clean, no steam/smoke, other than the expected strong smell of unburnt gasoline.
There also appears to be a sudden somewhat serious oil leak from the engine somewhere around the back, passenger-side valve cover, around cylinders 6 - 8 ; I've been losing oil slowly over the last few months, so it may just be that it's aggravated by the engine thrashing itself around currently. Over the course of running the engine for a total of an hour, it looks like maybe a quarter to a half a quart of oil was lost.
About two years ago I had a cut in the wiring harnass repaired inside the driver's side wheel well that was causing a fault in emissions and rough idle. It appears to be fine, though.
I recently replaced most of my emissions-related vacuum lines inside the engine compartment, and replaced the leak detection pump and the thing behind the battery with the two vacuum lines who's name escapes me at the moment. I'm pretty sure they're hooked up correctly according to the emissions diagram on the inside of the hood, and it's been weeks since I replaced them anyway, and I had no misfire problems during that time.
It has a small exhaust manifold leak on the passenger's side which I was hoping could wait until cooler weather to fix.
This occurred immediately after picking the truck up from having four new tires installed at a local place. Normally I'd find this suspicious, but for the life of me I can't figure out how having four tires installed would cause a problem like this. Once my buddy looks at it, I'm going to call the shop and see wtf might have happened to it, but I'd like to be armed with some information first.
Thanks anyone who took the time to read through all this, I wanted to be thorough in describing the problem.
Last edited by keenerb; 07-28-2014 at 11:04 AM.