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.

[Saddrs7]

Yeah, that could definitely be part of the problem. A loose bolt on the cam bridge, especially around the exhaust camshaft, can mess with things for sure. I mean, sometimes you’re sure you torqued something down properly, but it just doesn’t hold or maybe shifted a bit after. It’s good you caught it though. Replacing it just to be safe sounds like a smart move. Hopefully that sorts it out, but yeah, keep an eye on how it runs after. Could’ve been the main issue all along, you never know.

[Saddrs7]

Yeah, that could explain it. If the bolt was loose, it’s possible oil pressure was escaping at idle and only building properly once RPMs went up. Hopefully that was the cause.

[torkik]

Morning,
I started putting the timing and other components back together. Gave the engine a few test spins, then checked the cam-bridge bolts, the exhaust bolt was loose again. I know for a fact that I torqued them yesterday. So I re-torqued and gave another test spin, about a half of rotation on the crank, the exhaust bolt came lose again. Now just trying to figure out if its the exhaust camshaft or the cam-bridge causing the issue. Cam-bridge is from NAPA, Dorman part #635050. Wondering if this is the issue. I know Dorman is a hit or miss with parts.

[Saddrs7]

Man, that’s frustrating. Especially after torquing everything down properly,stuff like that can really throw you off. It’s weird that it keeps backing out like that after just a few spins. At least you’ve narrowed it down to the cam or the bridge, which helps a bit.

[Saddrs7]

I’ve heard mixed things about Dorman too, especially on critical parts like that. Might be worth swapping it out just to rule it out completely. Hopefully it’s not the cam itself.

[torkik]

Got it figured out, It turned out to be the Dorman cam bridge. The part was .2mm thicker (20.22) than OEM which is 20mm. it was enough to where the camshaft was recessed enough, not allowing the washer to come in to contact with the exhaust camshaft and not rotating with the camshaft like it is supposed to. It would just back off enough until it started to spin. I replaced the Dorman part with one from Pierburg (which is OEM with the Logo ground off). All is well now with it, drove it home yesterday and runs great. Thanks for helping out until I figured the problem out.