Misfire
Misfire
Steady Misfire
In the case of a steady misfire, isolating the misfiring cylinder is the first step in diagnosing the problem.
Items that can cause a misfire:
Spark Plugs
Coil Packs
Throttle Position Sensore
Lambda Sensor
Head Gasket Failure
A spark plug that shows heavy whitish to brown deposits may indicate a coolant leak either past the head gasket or through a crack in the combustion chamber. This type of problem will only get worse and may soon lead to even greater problems if the leak isn't fixed. Coolant makes a lousy lubricant and can cause ring, cylinder and bearing damage if it gets into a cylinder or the crankcase.
Inlet Manifold Gasket Failure
The Inlet manifold gasket can fail and allow air leaks and coolant/anti-freeze to leak into the cylinder ahead of the injectors. Tell tale signs can include rusty spark plugs on cylinder 1 and 4, sometimes even all four, lumpy idle or misfiring, high emissions, jerky acceleration and deceleration when coming off the accelerator, anti-freeze around the inlet manifold.
The gasket sits inside a recess in the face of the inlet manifold where it joins to the engine. There are tabs on either end on the lower side to pull it out, it may be blackened from use. Early gaskets are black, an improved one was manufactured and is known as the green gasket (it's green) which can be sourced from between a pound to six pounds (2008).
It can be changed without fully removing the inlet manifold by simply fully unscrewing the nuts on the manifold studs, you may find some studs will come out rather than the nut if rusted. The nuts under the inlet manifold are the hardest to access, especially on the later S1 Elise where the boot divider is a permanent fixture. Have ready both a short and long socket extension, preferably the type that allow angled movement on the socket, and long and short sockets. Removing the drivers side rear wheel arch liner will help greatly.