eight

So I've done some research on this and I've come up with nothing, either that or I am terrible at researching.

On my MY '07 with 223k, I've been getting random cylinder 1 misfires. It's always 1-3 counts, at start-up, never misfires after 3 seconds of vehicle being on, ALWAYS on cylinder 1. Have already swapped coils, plugs, and injectors. Always stayed on cylinder 1. It happens more often after I've driven the vehicle more than 10 minutes, stop the engine and let it sit for 20-30 minutes, then start it back up. Never consistently however. It's happened a couple times with it being dead cold but with 80-90 degree ambient temp. Pulled codes on several occasions, happens at 930-980 RPM with engine being warm (3-5 bars on dash).

I have seafoamed the car as a crap shoot and thrown fuel injector cleaner and engine cleaners in my fuel tank that we use for Audi carbon build-ups (I work at an Audi dealership) and it seems to make it a little happier. I've looked into the cylinders with a boroscope and cylinder 1 does not look any different from the rest of them. Wet and dry compression test yielded the same results, no different from the others.

It's also worth noting that this started happening shortly after my vehicle began drinking oil. No leaks are seen, not even any seepage. Tailpipe is clean, nothing out of the ordinary. That may be related since they both started happening near each other.

I've also entertained the idea that the injector is leaking only after the vehicle has been ran. I drove the vehicle for roughly 35 minutes, let it sit for 10 minutes, and started monitoring the injector from inside the cylinder for another 10 minutes. No drops coming from the injector, and just in case if I missed any, the top of the cylinder is dry.

I'm freaking stumped.. Hope someone here has seen this before. Maybe I'm going at this in the wrong fashion altogether..

I've thought of taking the valve cover off and looking at the top of the valves, there may be carbon build-up behind the valves which after so many miles, doesn't seem like a bad idea at all. But with carbon build-up, I should be seeing these symptoms on cold start.

Thanks for looking.

Slowcrash_101

Tight valves can cause a misfire, if they're too tight they'll burn and then you'll have to replace valves.

Also if you've ran synthetic oil you shouldn't see so much as varnish in the engine.

eight

Yea, I've always ran synthetic. Valvoline MaxLife for the daily and Motul for the track. Both being 10w-30.

I'm actually about to do another valve adjustment this weekend if it doesn't rain here in L.A. What do you recommend my spec should be? I have stock internals.

rmerchant3

If you are seeing an excess amount of oil usage, I would perform a leakdown and compression test. I have also seen alternators with an intermittent failure cause random misfires. You can usually tell by the dash lights flickering ever so slightly.

Slowcrash_101

Specs are on the hood, but if you need to know it's .008" - .010" on intake, and .010" - .011" exhaust. Insert feeler gauge until you feel some drag, on the intake side on the .008", and the .010" should almost not fit unless you force it. On exhaust side, just make sure the .010" feeler fits and has good drag, but the .012" feeler should not really fit without really fighting it.

Can be tricky to set clearance particularly in cylinder 4 since it's so cramped in there. One way you can make sure your settings are perfect are to compare the clacking noise a valve makes compared to a known well adjusted valve. On the intake they'll barely make any noise(still there) but since the exhaust valves are a little looser they will make a distinct noise if you move the rocker arm up and down. I use this in addition to the feeler gauge because if I left a valve too loose it will make more noise than one adjusted just right.