I am having similar issues to just like above and frankly am at a loss as to where to go next. Money is really tight, so having to do the work myself.
I have a 1998 Isuzu Rodeo 2.2l 4cyl, the person that started this thread. I too am getting the P0301 (Miss-fire #1 cyl) code in OBD. I can't figure out what is causing the problem.
I tell people, I am NOT a mechanic, but I have a mechanical mind, I can understand how things are suppose to work.
Background on this truck. Was driving it, started having issues with it cutting out, then dying. Found one of the spark plug wires arcing, so replaced the wires. Upon doing that, found that the spark plugs themselves were swimming in oil. Drove it for a couple of weeks anyway, figured I would look into fixing the leak. I knew I had an oil leak, but I didn't realize it was that bad.
About 2 weeks into it, on a drive home it was like someone flipped a switch. It started misfiring, losing power on the hills, under load, and running hot. I didn't let it boil over, needless to say it took 45 min to go 2 miles home.
1)I then replaced the valve cover gasket, cleaned all the oil out of the holes, replaced the spark plugs and wires again, just couldn't get the other ones clean enough to suit me. Also replaced the fuel filter.
Still miss-firing!
2)Next checked the compression on each cylinder, numbers were all consistent. Also performed a block test on the cooling system, looking for CO gas in the cooling system, negative on that as well, atleast it is not a head gasket!
3)Checked each of the fuel injectors with a resistance meter, found #1 value to be way off of the other three. Figured the fuel injector had gone bad. Had to order parts from off island, took almost 2 weeks to get a new injector. Replaced that a couple of days ago.
Still miss-firing! Still same code.
4)Ok, now I am wondering do I have an electrical issue? I picked up a noid light kit for checking the electrical connections to the fuel injectors. I am getting a consistent flash on #1 cylinder, grrrr...im a super frustrated right now.
**For a while before this all started, have been having issues with the truck running warm, especially pulling hills. I think the water pump is wearing out, so, when ordered the injector, I also ordered a water pump/ timing belt kit and serpentine belt, it's time to do that.** I think they are separate issues. Am presently running without the thermostat in the system.
I am at a complete loss right now as to where to go next! :Banghead