So I got my car back today after having a check engine light on. The code meant that I had a misfire in cylinder #4. But my mechanic tested it and it didnt seem to be misfiring. He checked the spark plugs and its all fine now. This is wierd. Any ideas/thoughts? But what causes misfires? Driving hard, bad mods, etc.?

 

Driving hard does not cause misfires. Abusive driving may, should you mechanically over rev and bend a valve, could do it.

Misfiring is caused by incomplete or non-combustion.

Low compression (rings/cyls/valves)
Weak/dropping spark
Ignition timing
poor fuel quality
Lean mixture (fuel pressure, air leak, clogged injector, low demanded fuel from a skewed sensor input)
Rich mixture (spark issue, too much fuel, not enough air)

There is no direct path to finding the cause of a misfire. It takes patience, and experience.

The first place to start:

CEL, and the freeze data stored with the misfire code. Particularly the fuel trim, which will show if it's lean or rich. Even so, fuel trim is not an exact science. Two cars can have the same trim readings, and one can have a misfire. It needs to be calculated with the other parameters such as engine load. I have learned I can not convey how to do this on the internet, but I do it on a weekly basis.

Second place is engine basics. Compression, ignition timing, and valve adjustment (99% of s2k's come with slightly loose valves from the factory...this will NOT cause a misfire.) however, if a valve is barely bent, or a poor VA has been done, the valves may be suspect. Tight valves are a surefire way to cause a misfire.

AFTER those have been sorted, then move on to the usual suspects like plugs, coilpacks, injectors, wiring, ECU.

 

Me too. Can I interest you in a job?


And with Billman.

 

Samething happen to me man, I took it into honda an they ask me a few probing questions to figure that it was my gas...Right after i put "BP" gas into my car it started to sputter...When i took it to honda everything was find, an all they did was reset the ecu to get the light off..

So mine was caused by bad gas..

 

You'll find most dealers get lost quite easily with misfires.

Unless you can find slows2k's

Hey my car loves BP never ran so good

 

ok thanks ya'll!

 

PLugs, plug wires, coil packs, oil fouling, compression under 100psi, bad gas, carbon fouling, knock sensor issue, MAF issue.

 

S2k has no plug wires, and no MAF.

These listed are the farthest stretch to cause a misfire on an S2000. I can guarantee it is none of the listed.

 

How do you tell if a coil pack is bad? I can't find any specs on the coilpacks