MadDogWRX

Hi, I changed my spark plugs today. On removing the old ones that were NGK pfr7b`s that had covered about 20Km I noticed that all of them were very dark in colour (near enough black) especially the two from the drivers side of the engine ( 3 & 4 iirc ). Gapped to 0.7mm

Is this someting I should start to worry about?

Car details - MY95 WRX - K&N Induction + Full Decat + ScoobyECU + Vta D/V + run on Optimax or Tesco 99 + Sti Fuel Pump + Motul full syn 10w40.

Thanks
Paul

lightwave693

i think a dark plug means its running rich, dark as in covered in fluffy carbonish type stuff.not black with oil which means kanckered valves seals,pistonrings etc..


plug should be a nice tan type colour when running proper.

might be wrong, just talking from experience with other engines. im yet to pull out my plugs in the scoob and have a look.

Rich

MadDogWRX

fluffy carbonish type stuff.

Thats the stuff, its not oiley at all.

So does that mean I`m running rich on no 3 & 4 cylinders more than 1 & 2 then, if so is this better than running lean or just as bad.

lightwave693

what was the plugs on 1&2 like? running rich isnt as bad as lean, lean leads to very high temps on a turbo car, and can melt pistons, u prob know that tho. running rich is not as bad but should be sorted.

if u was rich on all 4 cyls then id suggest that ur map is off and could cope with a bit more boost to use up that extra fuel....

just 2 might suggest an injector service or replacement..

can anyone back me up?

Rich

Houghton

iTrader: (1)

The state of the plugs can depend to a certain extent on how the car was last used. If you started up from cold to move it or drove a short distance without full operating temps, then the plugs could give a false rich appearance as excess fuel would have been injected, especially in the current cold conditions.

Some maps can also richen No.3 as that's the 'hot' one.

MadDogWRX

All the plugs were a dark brown/black colour, but 3 & 4 were defo. the darker pair.

Running a ScoobyECU map on a Z4 boosting to around 1.1bar.

Would I see a benefit from fitted a MBC (dawes device)

Houghton - I did drive a couple of miles to pick up the plugs and I changed them as soon as got back, so would this have given the plugs a richer colour.

Houghton

iTrader: (1)

I'd have thought that after only a couple of miles the engine isn't at operating temp so still getting a rich mixture. IMO I wouldn't take the plug condition as representative.

Don't know much about your ecu but on some, cylinders can be individually set for mixture.