Engine Misfire

rolledover

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How many miles do you have on the engine? I had a very small shake at idle (No CEL, no misfires) but it has since gone away. I'm running a few bottles of Sea Foam through my fuel system and might do the intake version as well... but having a valve stick sucks... I'm at 94k miles.
I was at about 150k when it started, am at exactly 168k when I started tearing it apart a few weeks ago. I ran a few bottles of BG 44k through the fuel system when this first started, used the CRC GDI Intake cleaner stuff, pretty much tried everything cheap before getting a leak-down test to confirm my worst suspicions. This went on for over a year before I decided to fix it properly. The shop that did the leak-down quoted me 7k to do this job.
 

pete0rz

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I have a quick update to share (via indy shop tech) and will know more re: options Monday. Didn't take tech long, in the engine tear down, to find cause of the misfire: 1 of the intake valve seats is completely gone / burned out (in #5) and tech advised that the (passenger side) cylinder head will need to be replaced. In video shared with me tech commented: that issue wasn't detrimental to the cylinder block per se and while there's no obvious mars on cylinder walls, there were a couple overheat (dark) marks on the block. Tech commented that some cylinder cross hatch was still present, but also saw some scratches, probably due to sealant loss. Btw, it was hard to tell if the scratches present were in the head or the block, but the overheat marks were adjacent to those. Towards end of video tech showed the spark plug electrode which was white, indicative of running lean, but that no pieces of ceramic were peeling off or present in the cylinder. I've run 93 and at times 91 (when 93 wasn't available), but nothing else so unsure why a lean condition would present.

Wondering if folks who've had cylinder head replaced could comment on engine afterwards. Will replacing head (will probably do timing chains too) buy me another few years of engine life? Again aside from the rough idle, 305/316 coupled with an occasional 305 misfire, no other DTCs were present.
 

johnr7255

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New member. I have 156K on mine. 2010, 5.0 engine. Have exact CEL as you (#5). I bet I have a similar issue. I will have a leak down test performed. Also have been loosing coolant. about 2 quarts a year.
 

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