S4 juddering between 3 - 4.5 rpm

[Piggyturbo]

S4 feels like misfire between 3 - 4.5 rpm in 2nd upwards
If I half put foot down it boosts OK through it
No codes???

 

[aragorn]

probably is a missfire, that RPM range is peak torque, so hardest to ignite the fuel/air mix.

Could be a bad coil or worn spark plugs. Plugs are cheap so do those first!

 

[Piggyturbo]

But surely that would bring a code up?? Checked the netsany possible things

 

[aragorn]

Nope, most S4's dont do missfire detection.

 

[Piggyturbo]

OK last onetgen wouldn't coil make this do all the time??

 

[aragorn]

The spark voltage depends on cylinder load. The insulation inside the coil can break down at high voltages but work fine at lower voltages, which results in the engine running fine, but only missfiring at peak load, when the spark voltages are highest.

 

[Piggyturbo]

Would these be OK thanks

 

[aragorn]

yes thats a good way to go!

Requires soldering and crimping up some connections etc though...

 

[Piggyturbo]

Will it cause any damage driving the car normal

 

[aragorn]

as long as its not missfiring all the time there shouldnt be an issue.