Misfire Issue And Slight Knocking Advise Needed Please

[sidewayzgt]

I have a 2000 S4 Stage 3 and am having a small issue. When I first start the car in the morning and drive for the first 10-15 minutes everything is perfect, the car drives and idles fine. After the 15 minutes, it develops a slight misfire and what sounds like a slight knock. I have no check engine light on at the moment but I did try and get it smogged the other day and 5 minutes in to the process the CEL popped on. The guy was nice enough to pull the plug before it could transfer anymore but the code that it came up with was a misfire in "cylinder 4". The next day the check engine light went off by itself and has not come on since but the issue is still there. Before I go out and spend a lot of money on new coils and plugs, some opinions would be appreciated. Thank you in advance!

[Bordom]

Swap the coils and plug to a different cylinder. If it follows, then you can then swap the coil with another cylinder. If it does not follow you need a new plug. If it does follow the coil, you need a coil

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[Timtheguru]

Clearly the FPR is failing

[vavJETTAw36]

Unfortunately misfires can be hard to diagnose because it is usually a side effect of some other issue. I would start by looking at ignition related items:

1) Check Coil: Move the coil to a different cylinder. If it follows to the new cylinder you have found the issue.
2) Plug and Plug gaps: Check the health of the plug. Plugs are pretty cheap (OEM NKG for ~$2 each) so maybe its a good time to change and gap the plugs.
3) ICM: Swap the ICMs. Located on the airbox, you should be able to simply swap the wiring without having to unbolt the ICMs.
4) Vacuum leak: This can easily cause misfires. No recommendation on troubleshooting. This will also cause misfires on other cylinders as well. Have you logged all 6? Its not until the misfire count reaches a certain number that it sends a CEL code.

[f4m0u5]

Clearly the FPR is failing

Lmao!

[cjt671]

When my lifter failed I had knocking and a misfire

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[treysgreen]

Have the heads ever been replaced?

[sidewayzgt]

Have the heads ever been replaced?

Yes, they are 2.8 heads but the knocking is very light.

[treysgreen]

Misfires could be indicative of a valve kissing the piston at some point. If a ridge is created in the piston it could misfire once the car heats up due to it creating a Hotspot and causing ignition.

[sidewayzgt]

The heads were done in 2008 and I have never heard it before. Would it take this long?

[treysgreen]

The heads were done in 2008 and I have never heard it before. Would it take this long?

I don't think so but it just something to consider if you've exhausted all other options.