Can't get rid of cylinder 4 misfire

[Saucedup5051]

So I recently purchased a 2009 Dodge journey SXT 3.5 l it had been sitting in the guys backyard for around a year when I got it he was in a hurry to leave so I had to drive it home as it was what gas was in it have been there for a year everything else been there for a year not been touched so as I drove it home it overheated which he failed to tell me it had a problem with that nevertheless I found out I had a blown head gasket so I put Blue devil in it and it fixed it per se then it was the multiple cylinder misfire code I read up on and change the knock sensor fixed it for a little bit then the cylinder 4 misfire code came I've changed spark plugs coil packs switch them around then bought them  new I've did compression test leak down test they were fine I did what electrical test I could do that I knew how to do on wiring harness for the fuel injector coil pack anything that had to do with it clean the injectors switch them around put new o-rings in them several times I've looked for a vacuum leak still haven't found one that I could tell I put new intake gaskets upper and lower pretty much anything I could have done I have done other than take it to the dealership to have a diagnostic test done which is coming up in a few days but I would like to sit I figured out the problem and fix it myself but I'm at wit's end any idea of what may be wrong

[tsteves5]

It sounds like you've been pretty thorough.  I can't speak to the 3.5, but on the 3.6 I had a consistent misfire on a cylinder that was caused by the main wiring harness connector on the engine harness.  I've also had an issue where the computer was faulty and causing an injector not to fire.  Can you verify if the plug and injector are working properly, perhaps with an in-line spark plug tester and noid lights?

 

 

[Saucedup5051]

Yeah I was going to go and buy a inline spark tester and see what I was getting from that but the funny thing is about it that's really stumped me and I believe it's electrical and I want to say you're right on the harness it probably is but when the code is thrown I can have my computer with me wherever I'm at I can erase the code and it might not happen the rest of the day it might happen 10 minutes from then but since I've been putting 100% gasoline in it instead of the 10% ethanol have not had quite an issue since if that tells you anything

[John/Horace]

So you are running super test gas and it's slightly better. Interesting.  Ethanol is crappy on engines. Sometimes engine top end can have carbon deposits. There is a system called Motovac that hook's to fuel rail and runs engine on straight cleaner. Can fix crappy idle and emissions code issues. Not that expensive. If compression is within 10% of target in cylinder 4, might be worth trying.

[Saucedup5051]

14 hours ago, John/Horace said:

So you are running super test gas and it's slightly better. Interesting.  Ethanol is crappy on engines. Sometimes engine top end can have carbon deposits. There is a system called Motovac that hook's to fuel rail and runs engine on straight cleaner. Can fix crappy idle and emissions code issues. Not that expensive. If compression is within 10% of target in cylinder 4, might be worth trying.

So I took off the intake manifold upper and I cleaned it out real good decarbonized it whatever you want to call it I got all the oil which I didn't think it should have had any kind of oil or oily substance in it but it did I cleaned everything out of it real good put it back on with a new gasket and changed to iridium spark plugs instead of the OEM champion platinums and I thought for the first time since I've had it it was fixed did not throw a code all day didn't throw a code all night but then when sitting it idle in the McDonald's drive-thru it started to have a rough idle and then ding there goes the code but it wasn't a cylinder for this time that was a multiple random cylinder this fire but I was going to say also when I took the manifold off I looked at the valves or what was you know right there on top of the best I could and they were black inside there real rough feeling through the chamber that's going to leads down to the valves so maybe that needs to be cleaned and maybe that's what's throwing the code

[John/Horace]

Is valve cover leaking oil on to intake ? I guess it's engine blow by creating the oil film in the intake. Some carbon is often present on the exhaust valves. But too much and it can  affect seating of valves. Worn rubber valve stem seals will allow oil in as well, blue smoke puff on start ups too. Newer direct injection cars sometimes have carbon issues (cylinder heads removed to clean out etc). Carbon clogging the rings can also cause oil burning and potential cyl misfires.

Motovac is a brand of equipment, there are other systems for top end engine internals cleaning. Down stream cat could be messy as well. If engine internal components have too much wear the carbon will eventually come back I believe. Depends on how excessive oil consumption is.

Edited September 14, 2022 by John/Horace