Engine Missfiring info LOOK HERE!!!

This was stolen directly from evom.net. I am not the original thread poster on there either. Thank you comatose721
http://forums.evolutionm.net/lancer-engine-tech/175200-engine-miss-2.html

"get a drink; this a long read. did you happen to pull the code from the CEL? that would really help diagnosing the problem although it went away. lots of times new problems spring off of the original one.

...but here's how it works in a nut shell. your engine works on compression. air and fuel mix and a spark ignites the two causing the piston to be forced back downwards, thus the crankshaft to spin. there are several other factors involved but that is the general concept you need to grasp.

alrighty now here is how misfire works. somewhere in that cycle there is a mishap. insufficent spark, poor fuel mixture, an inaccurate o2 reading, crappy air quality, poor vacuum, etc. are all things that can cause these little mishaps. this break in the cycle causes things to get a little funky. since one thing or another isn't working properly you will not be getting proper combustion....hence the loss of power during the misfire...

okay now we have an idea of how the motor works and one type of misfire

here are some things that you should check. start cheap and start simple.

- spark plugs: remove your plugs and make sure they are not burnt out, fouled, etc. if you do not know how to read a spark plug let me know. i have a nice site for you to check out then. look at all 4 plugs next to each other to identify which cylinder is misfiring. if needed, change and/or regap them.

- coil packs/plug wires: while the plugs are out check the coil packs and plug wires. inspect the insulation boot on the bottom of the shaft. look for signs of arcing. when your spark arcs it grounds itself to the cylinder wall (no good). signs of arcing usually include, but not limited too, a faint white or brown trail on the boot or pack. look closely for these. they dont just jump out at you. if you are unsure about arcing-->mail me pics of everything and ill give my two cents. the plug itself will be burnt around the base in more severe cases. if the insulator boot is 'bad' the pack may still be good. in most cases just the boot can be removed and replaced, held on by rtv silicone.

- PCV valve: ...positive pressure crankcase ventilation valve...its a long one and it sounds complicated...its simple. this is that silly gold,silver,or black threaded peice on top of your vavle cover (where that 3/8 vacuum line attached to the ONLY opening on top of the valve cover). go to your parts store and get a new one if it hasn't been replaced. they are between $3-6. it will improve fuel economy and help the motor function with less effort.

- air filter: it's simple. make sure it is clean and that it is free of debris. keep good, quality air in your engine.

- vacuum leaks: look under the hood for leaks in ANY of the vacuum lines. most vacuum lines branch from the intake manifold, throttle body, intake, and fuel rail. make sure that none of these lines are punctures, dry rotted, etc. lack of vacuum will cause misfire.

- EGR system: i believe it stands for 'exhaust gas recirculating system'...check it. make sure your EGR valve is not sticking open, or failing to open. while you check this, clean out any carbon build up on the butterfly within the throttle body. these are all problems usually associated with throttle lag and rpm hang but can contribute to misfire.

- oxygen sensor (o2): you already replaced yours so you shouldnt worry about this one. a bad o2 sensor will give inaccurate readings to your ECU. the ECU then tells the injectors to dump the wrong amount of fuel...misfire.

- fuel system: this is one of the more complicated sides of a misfire. check your fuel pump, fuel filter, and fuel lines. a bad pump, clogged filter or clogged line will starve the engine of fuel. if all of these are ok move onto the fuel lines under the hood (both feed and return lines). it is common to get a bad o-ring where the line bolts to the fuel rail causing a fuel leak (fuel pressure drops...yeah thats bad). it is likely that your fuel rail is fine so it's not a big deal if you don't pull that off. MOST IMPORTANTLY-->fuel injectors!!! a clogged, leaky, or defective injector will cause a problem. this is common. before you go replacing your injectors throw a can of injector cleaner in your tank of gas and see if that cleans the fuel system out. poke your head around for leaks and such. if there are no leaks you should be in good shape...but like i said, injector cleaner works miracles.

- timing: this is to complicated to explain...thus usually to hard to fix yourself. it is unlikely for the timing to just get "set off" in an 02 lancer unless you tampered with it in any way.

alrighty. that was a nice little read now wasn't it

...leave it as this-->if you are unsure of what you are doing when it comes to the fuel system...DO NOT DO IT. i dont want to find out you sprung a fuel leak and the car exploded on the freeway.

so to sum things up: start simple --> plugs, packs, air filter, PCV valve, and some injector cleaner. that is where the problem is 80% of the time. if it isnt in those things, then dive in deeper with the other things i mentioned. of course there is more to it than what i wrote but i am just trying to steer you in the right direction. let me know how things work out with the car. if you have any questions do not hesitate to ask me. i'm around here a lot. good luck. i hope to hear back from you soon.


Mark"