4.7L P0301 code, changed plugs and cylinder 1 coil
i have a 2005 grand Cherokee which i bought a week ago wit 105k miles, i keep getting a p0301 code every 2 to 3 days. all the spark plugs were replaced by our local jeep dealer about 2 weeks ago(a week before i bought it), and it still kept trowing a p0301 code after i got the keep, i ohmd out the coils and injectors, the injectors all ohmd out at 14.5ohm -/+2.0, and the coils all ohmd out at .04ohms +/- .2 ohms except for cylinder 1, which ohmd out at 1.8ohms. I ordered a new coil and replaced it, 2 days later, the code comes back.
One thing i should mention, the coolant level was right below the add level a few days ago, i topped it off and im currently monitoring the coolant level see if im loosing any, the dealer did pressure tested coolant system and couldn't find any kind of leaks when they replaced the plugs.
I guess im not sure how much of a leak into a cylinder i would need to get a misfire.
What do i try next?
I did that right now, i swapped cylinder 1 coil and plug with cylinder 2. and i also swapped cylinder 1 injector with cylinder 3. now ill go drive around and see if i can make it come back.
I also preformed a block leak test, the test calls for 2 minutes, i ran it for about 5 and it still tested negative, so that's a good sign. Coolant level hasn't gone down since i topped it off a couple days ago, there must have been air in the system when the dealer flushed and refilled it 3 weeks ago.
code p0301 came back again today. so if its not the plug, coil, and injector, then what is it?
One thing i did notice when i swapped the injectors, cylinder 1 injector was polished and looked brand new compared to the injector in cylinder 3 that i swapped it with. which makes me wonder if i don't have a valve problem.
Sorry to hear that your error came back. My Jeep has the P0304 error and is coming out of surgery later today (hopefully). I will get the full diagnosis when I pick it up today or tomorrow and will post--as I think your issue is very similar to mine. From what I've read, is you should check the exhaust and determine if it smokes a white, blue or black color...and also smell the smoke. The color and smell will indicate if coolant or oil is seeping into the engine. I had white smoke--which I bet you have--which indicates that it's coolant. I also noticed that my coolant bottle was low--just like yours. This leads me to believe that something that keeps the coolant out of the engine is worn. I'm not a mechanic and only understand this a bit because of my research over the last 2 weeks--but maybe its some gasket. Lastly, in my search for the solution they recommended having my heads redone. I have the 5.7l Hemi so there were two heads and they found only the one head in 3 cylinders to be somewhat problematic (I think they said valves or stems or the like). They fixed them and replaced the gaskets and I'll know more soon.
Hope this helps a little..maybe in just commiserating together.
I just made an appointment at our local jeep dealer, its going into the shop next tuesday.
Its not smoking at all, other then the white smoke/vapor when its cold in the morning which is what every vehicle does. I did a block test on it, exhaust in coolant leak, which tested negative for exhaust particles in the coolant. From the discussion i just had with the dealer mechanics, it doesn't sound like it has any kind of piston ring or valve problems. They suspect a cold start sensor or a crank sensor. It ONLY misfires once in a while during the first 10 seconds of the vehicle starting, then after a few seconds it runs smooth. I suspect a sensor or maybe even a coil or injector wiring harness. I just hope they can find the problem and its not going to cost me my other arm and leg to fix it.
just an update for you guys...the same day i made an appointment i stopped in at the dealer on the way home and they scanned the vehicle for codes since the light had been coming on and off, when they scanned it, they reset all the codes when they were done scanning. My appointment was four 4 or 5 days later, but the light never came back on. I called them a day before the appointment and they told me to cancel it, and wait till the light comes back on.
The only thing i did differently after they reset the codes again was pour in ANOTHER bottle of LUCAS injector cleaner/fuel conditioner, and started driving it like an American(not trying to keep my avg mpg over 16mpg) and needless to say, the code has not come back(knocks on wood). So im thinking/hoping it was just a carbon build up.
Yes you very well could have cleaned up the carbon out of tb etc, while I prefer the sea foam (it's free at work) but I changed my plugs last week has a p0301 cyl1 misfire, bought a new plug and coil just in case and put new plug into 1 cyl, then i sea foamed it through the brake booster vacuum line. Now i am running better and mpg better Carbon can cause your sensors to go crazy and intermittent codes, cleared with my obd code tool( but gave the computer time to read my habits and carbon free 07 gc with 103,000 miles) but it did work for me so I hope it cleared up yours, good luck