2011 CCTA misfire and mechanical pop

[torkik]

Hey peps, got an 11 Audi A3 with CCTA few months back that needed an engine rebuild and I am excited to get this thing running.

Just got the rebuilt engine back in. Got the engine running, ran perfect for about 40 minutes then started to misfiring at idle on cylinder 1,4 then switch to a misfire to 2,3. While misfiring, you can give it a lil throttle (about 1300rpms) and it will clear up and run great but my concern is that when I do idle it up, there is a loud mechanical pop (to me it sounded like the timing chain tensioner but wasn't certain). It was rebuilt due to previous owner neglect, cracking some valves and damaged to the pistons. No damage to piston walls

Some of the new parts are new cylinder head, with all new head components (camshafts, cam bridge, valves etc.), new pistons with updated rings, new main bearings, oil pump, new timing chain (cams, balance shaft and oil pump chains). New plugs, coils, injectors, PCV system.

The only codes that I am getting are the misfires 1-4 and random misfire. Took the timing cover off this morning to inspect the timing chain, tensioners, all look good and still in time at TDC, Inspected spark plugs, piston heads with bore scope, all looks good with no damage.

Need some ideas on what this pop could be, any help would be apricated. Let me know if you need more info.

I have torn down a few of the CCTA's in some Volkswagens and rebuilt them with no issue, this one has me stumped.

[Saddrs7]

Hey man, thanks for the detailed breakdown,sounds like you’ve really put in some solid work getting that CCTA back in shape. It’s always exciting to hear it fire up after a rebuild, so I can imagine how frustrating it must be to run into misfires right after. That pop at idle definitely raises a red flag, especially considering everything is new and supposedly timed correctly.

[Saddrs7]

Given the way the misfires shift between cylinders and clear up at higher RPMs, it does sound like something related to valve timing or maybe an intermittent vacuum issue. Even though timing is checking out visually, I’d double-check the camshaft adjustment valves or the VVT solenoids,they can cause rough idles and misfires if they’re sticking or not getting proper oil flow, especially on a fresh build. Also worth scoping the intake manifold and runner flaps if you’re running the stock setup.

[Saddrs7]

That mechanical pop though,could be a sticking valve, lifter collapse, or possibly the balance shaft area if something’s not torqued quite right. Since it only happens at low RPMs and clears with throttle, maybe oil pressure at idle isn’t quite where it needs to be yet? Keep me posted, I’m curious to see how this one turns out.

[torkik]

That's what I was leaning towards, it being an oil pressure issue. After I made the post, I smoked the intake and vacuum systems, found no leaks. Almost everything in those system's are also new, including the intake manifold (stock). Sometime this week, I will pull the chains out and possibly the valve cover and take a look at the oil passages. Will also take a look at the cam bridge, as well as the control valve on the intake cam ( they are both new as well). Also, oil I used is 5w-40 Liqui Moly Molygen, with there Mos2 anti-friction additive.
I will update when I get it apart.

[Saddrs7]

You’ve done a solid job checking for leaks and replacing parts. It makes sense to focus on the oil pressure and inspect the cam bridge and control valve next.

[Saddrs7]

Keep me posted once you tear it down. Hopefully, it’s something simple and easy to fix.

[torkik]

Last night I was in the process taking the timing back apart, I found a loose bolt on the cam-bridge. The exhaust camshaft end bolt was loose, thought I did torque it down but was loose. I am thinking this may have been causing the issue but not certain. Any thoughts on it.
I am going to have it replaced, just incase.

[torkik]

Got it all apart, did not find any other issues besides the one bolt on exhaust cam end bolt on the cam-bridge. Going to put it back together and hope that was the issue. My opinion is that at idle, the oil pressure was escaping from behind the bolt/washer. Then when I idled it up, it builds enough pressure in the system to overcome it.
If there are any other opinions, let me know please. Always down to learn more about these motors.