03/07/2026
What's on the rack today?
Sometimes the real cause of an engine failure doesn’t show itself until after the engine is rebuilt.
Here’s a good example of how diagnostics can tell a story.
We just finished an in-house engine rebuild on this 2018 VW Golf Alltrack. The engine itself went together great, but it gave us a bit of a run for our money chasing a couple small oil leaks caused by sealant that didn’t bond correctly. After fixing those and confirming everything was sealed up, we took the car for a final test drive — strong power, smooth running, no leaks.
Feeling good, we headed out to deliver the car back to the owner (they live close so we occasionally do home deliveries).
And then… boom.
The engine suddenly developed a hard misfire on cylinder #2, which made the engine very unhappy.
Back to the shop it went.
Once inside we performed some quick “swap-nostics” (a favorite trick of mechanics). We swapped the ignition coil from cylinder #2 to cylinder #1 to see if the problem followed the coil.
It did.
That confirmed we had a failed ignition coil.
Now here’s where the story gets interesting.
When we originally tore this engine down, cylinder #2 had a burnt exhaust valve, but there were no obvious clues explaining why it failed. These 1.8L and 2.0L TSI engines (VW’s EA888 family) are generally very reliable, so something didn’t quite add up.
Then we remembered something the customer told us months earlier:
The car would occasionally run very rough, but if they shut it off and restarted it, the problem would disappear for a while. At the time, the vehicle never came in for diagnostics on that issue.
Fast forward a few months and the engine develops a permanent misfire that a restart no longer fixes — which is when the car arrived at our shop.
During teardown we also found something interesting:
• Two new NGK spark plugs in cylinders #1 and #2
• Two original VW spark plugs still in cylinders #3 and #4
• And the #3 plug was completely destroyed
That tells us someone had been trying to diagnose a misfire before the car came to us.
Putting the whole story together, the likely chain of events looks like this:
1️⃣ An ignition coil on cylinder #2 begins failing intermittently
2️⃣ The engine occasionally runs rough but resets after restarting
3️⃣ Over time the unstable combustion overheats the exhaust valve
4️⃣ The valve eventually burns and causes a permanent misfire
5️⃣ The engine comes to us for a rebuild
6️⃣ The original weak ignition coil goes back on the engine and finally fails completely during our final test drive
In the end, the root cause of the original engine failure was most likely a failing ignition coil that went undiagnosed.
The good news?
The rebuilt engine runs beautifully, and now it will also leave the shop with a fresh ignition system and a clean bill of health.
Diagnostics can be a puzzle sometimes, but when the pieces finally line up, the story finally makes sense.
— German Auto Services
