Been chasing misfires on my 2007 Passat 2.0T for several weeks. Has 135K on it with the 6 speed. I've owned it for about 6 months and replaced some parts relative to the misfire codes. I clear the codes and sometimes it will be cylinder 1 consistently. I clear again and it may be 3 & 4 but not 1. Sometimes, it's all 4 cylinders. It may or may not trigger the CEL and sometimes causes flashing CEL (which I understand why) It is most predominant on /moderate to hard acceleration and is pretty smooth if you eased through the throttle. The strange thing is it seems sporadic....sometimes it will miss, sometimes it will not. I can't associate a bunch of common variables like weather, temp, city/highway, etc. except it seems to show up more upon driving from a cold start. It idles fine, no roughness or misfires.
I started with plugs and coils. The plugs were visibly bad so was a noticeable improvement but the missing continued. The clips for the coil harness connectors were broken so I soldered in new connector pigtails and used heat shrink to seal up the welds. Replaced the air filter as well. I also had a code for the VVT solenoid and found the connector broke on it so replaced it too. It was going through a lot of oil and found the PCV valve failing so replaced it. That issue is resolved. I removed the HPFP and replaced the cam follower. There was no visible wear on the original so assumed the cam was fine.
I had significant cam chain noise so figured maybe the slack in the chain was causing valve timing to change slightly under hard acceleration causing the misfire. I bought a new chain, adjuster gear, seals and tensioner and performed that repair. Noise is gone but still has missing issue.
I thought maybe a fuel pressure issue but it seems there would likely be CEL codes associated with rail pressure. I thought diverter valve but also appears low/no boost codes would likely set, not misfire codes..
The random and sporadic nature here has be baffled. It is most noticed cold under moderate/hard throttle but that's all I've got. I thought about carbon on the valves but might expect idling issues too. Clogged fuel injectors are also consideration but I haven't conceded to pulling it apart to check them. That said, has anyone had luck running an injector/valve carbon cleaner through the engine and if so, what is the most effective cleaner and method that yields the best results?
I did have it at the VW dealership for the fuel pump module recall and asked them to investigate the misfire. $160 later, they couldn't find anything. They too noticed the cam chain noise and suggested they repair it as a first step. Saved myself about $1200 and did it myself. Needed it for sure, but didn't resolve the misfire.
I'm not opposed to throwing a diverter valve at it just because it probably doesn't have the updated one in it but curios to see if anyone has experienced misfires and misfire codes due to a failed diverter valve.
Appreciate any expertise anyone can offer!
Edit: The misfire/surge/chug seems to occur at the time boost is starting to apply. It will miss or buck a couple of times and then come out of it as boost increases. At a certain point the miss/buck goes away and boost comes on hard. No whirring or whistling that I can hear. Diverter valve cause this? Or a vacuum leak somewhere? ANy common spots for a vacuum leak?
I started with plugs and coils. The plugs were visibly bad so was a noticeable improvement but the missing continued. The clips for the coil harness connectors were broken so I soldered in new connector pigtails and used heat shrink to seal up the welds. Replaced the air filter as well. I also had a code for the VVT solenoid and found the connector broke on it so replaced it too. It was going through a lot of oil and found the PCV valve failing so replaced it. That issue is resolved. I removed the HPFP and replaced the cam follower. There was no visible wear on the original so assumed the cam was fine.
I had significant cam chain noise so figured maybe the slack in the chain was causing valve timing to change slightly under hard acceleration causing the misfire. I bought a new chain, adjuster gear, seals and tensioner and performed that repair. Noise is gone but still has missing issue.
I thought maybe a fuel pressure issue but it seems there would likely be CEL codes associated with rail pressure. I thought diverter valve but also appears low/no boost codes would likely set, not misfire codes..
The random and sporadic nature here has be baffled. It is most noticed cold under moderate/hard throttle but that's all I've got. I thought about carbon on the valves but might expect idling issues too. Clogged fuel injectors are also consideration but I haven't conceded to pulling it apart to check them. That said, has anyone had luck running an injector/valve carbon cleaner through the engine and if so, what is the most effective cleaner and method that yields the best results?
I did have it at the VW dealership for the fuel pump module recall and asked them to investigate the misfire. $160 later, they couldn't find anything. They too noticed the cam chain noise and suggested they repair it as a first step. Saved myself about $1200 and did it myself. Needed it for sure, but didn't resolve the misfire.
I'm not opposed to throwing a diverter valve at it just because it probably doesn't have the updated one in it but curios to see if anyone has experienced misfires and misfire codes due to a failed diverter valve.
Appreciate any expertise anyone can offer!
Edit: The misfire/surge/chug seems to occur at the time boost is starting to apply. It will miss or buck a couple of times and then come out of it as boost increases. At a certain point the miss/buck goes away and boost comes on hard. No whirring or whistling that I can hear. Diverter valve cause this? Or a vacuum leak somewhere? ANy common spots for a vacuum leak?