Hi all, ive had a missfire for a while now, so thought i ought to get to the bottom of it!

I replaced the plugs that were 10k overdue, then replaced the injector plugs, as i knew they were crap anyway. The missfire still persists though, could it be a coil? (most rear n/s plug was noticeably lighter in colour too) Also the revs used to go higher on its initial startup, but now it just goes straight to normal idle speed in a slightly lumpy fashion!

Dont mention compression please! :nono:

 

Cheers Steve

Compression? Damaged valve will cause missfire when cold and also low compression ;)

 

Checked the temp sensor?

Ive not checked compression, hoping its nothing that severe! you dont think it could be a coil then?

Cheers Steve

Doubt its coils, they usually get worse as they warm up not better. Check the temp sender first, ecu assumes worst possible case for the sensors if it doesn't get an acceptable value from them. In the case of temp, its max, so the ecu is fuelling for a warm engine. Have you done a power balance test? With the missfire, disconnect each coilpack in turn until you find the one that doesn't make any difference (ie no drop in revs). This is your problem cylinder. Helps narrow it down a bit. Just a thought, you cleaned the PTU connections?

Not cleaned PTU or checked temp sensor. Looked to be running rich to me with all the plugs bar one black and sooty, the other was just dark grey (n/s/r cylinder) Has just been driven in and out the garage for a week though. I will try the coil test tmoz, hopefully point me in the right direction? You can always find something wrong with a 300!

Cheers Steve

nsr cylinder always runs hotter since its the last in the chain to get the coolant. Plug runs slightly hotter and therefore appears slightly cleaner than the rest....

Oh right! Still havent had chance to disconnect the coils and find the faulty cylinder yet. Ended up going to trax instead, hopefully get chance one night after work, i'll let you know what i find??

Thanks Steve

Clean up all these connectors, they control your idle in various ways.

Another interesting little job, hope it is something straight forward, always fear the worst with my 300!

Thanks Steve