2013 A4 allroad, 2.0 TFSI
See videos:
Cold start: https://www.youtube.com/watch?v=MCWngzwMGlM
Warm: https://www.youtube.com/watch?v=HM_RXmoIgGY
Edit: TLDR: The pops are intake backfires. Sometimes they're strong enough to blow off a loose charge pipe. If I disconnect the #2 coil, the intake backfires go away, and it's just normal dead cylinder symptoms. Tried swapping coils and plugs, compression and leakdown all good, timing chain marks line up. I'm stumped.
Every few times one of those ticks/jerks happens, it feels like a donkey kicked the car when you're sitting inside. You can see the whole car shaking in the second video. Not every tick is a strong jolt. Overall this is not at all like a normal misfire I'm used to. It almost feels like a cylinder is firing backwards, before it hits TDC. It's not on every revolution. It's only once every second, sometimes no jerks for a few seconds. Car has absolutely no power, can barely move. Putting the car into drive or reverse form park or neutral makes the shaking somewhat worse. At first I thought the tranny was out of oil and something binding inside, but it's very unlikely given that disabling cylinder #2 makes all the jerks go away.
If I disconnect the coil from the #2 cylinder, the jerks go away. It's then like a normal cylinder being out, like a dead coil. Much smoother and no noise. I'm quite familiar with these normal misfires.
Shuffling coils and plugs randomly doesn't change that #2 is the bad one. VCDS shows much higher misfire counts for #2, though it shows some for #1 as well. But I think that's just cross-bleed from #2 being so horrible.
Disabling any other cylinder makes the idle much worse and the jerks remain. So I'm quite sure it's #2.
Compression test 150 across all 4. Leakdown test 7% across all 4. Bore scoped the cylinders, all fine. Cranking with the plugs out is smooth, no noise.
So it's not coils or plugs, it's not pistons or valves.
Injector seems like the only possible culprit. I just replaced all 4 injectors a few weeks ago, because one was stuck open. No indication of a problem since, until my wife completely broke down yesterday going straight, slow, in a residential street. Car could not drive up an easy hill. Injectors are some no-name from O'Reilly, but they just looked like Bosch manufactured injectors, same markings as the factory ones, same manufacturing techniques, Bosch logo, everything.
I did the VCDS injector test, and I can't tell a material difference in the ticking sound between #2 and the others. Sounds the same.
I tried disconnecting the helper injector that's in the bottom-middle of the manifold. No change.
No codes in VCDS in any module other than random misfire and #2 misfire.
Cranking the engine with the plugs out spews the same amount of gas out the spark plug holes from every cylinder, and in the correct rhythm. Definitely not like the masses of fuel that was coming out when an injector was stuck open. Also no strange smell, like the masses of unburnt fuel when the injector was stuck open. But I can't think of what else it could be other than injector #2. I also don't want to rip everything apart and have it not be the injector, because it's more work than I have time for these days.
The only other thing is that I forgot to put back the intake butterflies when I replaced the injectors. But I didn't notice any effect for weeks, car drove the same as before, until it broke down yesterday. So I have a hard time believing it's the missing butterflies.
But the ticks/taps/pops do sound a bit like intake backfires. I don't hear much from the air filter area, but a bit around the intake manifold, and a bit around the turbo. Really hard to tell. The turbo piping muffles everything. I don't hear anything in the exhaust. I do feel the pops though when I squeeze the charge pipe, so I'm quite sure it's an intake backfire.
Could it be the timing belt skipped? Strange that it seems to only affect #2. But what else could cause intake backfires. My valves seal correctly according to compression and leakdown tests.
I even disabled the helper injector. I guess unless it's stuck open?? But I don't smell excess fuel, and disabling #2 stops the backfires.
Disconnecting the cam adjuster connectors makes no difference.
If I raise RPMs, the kicks get a bit stronger around 2000rpm, and I start getting exhaust backfires, I think. But around 4000rpm the kicks and pops go away, engine feels like a normal misfire, with minor exhaust backfires.
Sorry for the long description. But I tried everything I could think of, and nothing makes much sense. Hoping some of you have experienced something like this and can point me towards a fix.
Thanks a lot!
Bookmarks