Spark Plugs

[mooshie]

My car has been turbo now for about 2 years and done about 7000km in that time (love the work car!) I recently noticed a slight hesitation when cruising along at very light throttle and decided to start with the electrical side of things to try to find the cause. Cap and rotor on the distributor looked fine, leads looked fine but when I checked the plugs they looked like this-

http://img844.imageshack.us/img844/9695/dsc01945a.jpg

I also discovered that the idiots have put in NGK BCPR7E plugs which are 1 stage colder than the standard plugs for the B18A found in a DA9 and not the BKR7E-11 plugs (1 stage colder) for the B18C which I have.

as you can see the plugs have a bit of carbon fouling on the tips and I am wondering if I even need to go for the 1 stage colder plug? I have a set of BKR6E-11s at home for the 6 but does anyone think i should try these in the DA9? I am pretty certain that the fouling, which is even across all cylinders, is causing the hesitation but not sure if it is being caused by the heat range or a rich mixture, AFR from the last time it was tuned-

http://img255.imageshack.us/img255/6971/afr.png

oh, gap is set to 0.85mm instead of the normal 1.1mm too

[TODA AU]

Is the engine std compression?
How much boost are you running?
Have you done a number of short trips recently?

The plugs do look partially fouled so the cause of the hesitation is likely the plugs.
7000km in 2 years is not a lot but it could be a simple as old plugs, so try a new set at the std heat range & see how you go.
BKR6E-11’s gapped to 0.85~0.9mm should do the job & being hotter they’ll resits fouling a bit longer.
Re WOT mixtures from tune, if anything these are a little on the lean side depending on how much boost you’re running.
I’m not saying your tune is out, but looking at your plugs, I’d say you’re mixtures off boost are a little on the rich side.*
This can be caused by issues other than the tune but not always. (Blocked air filter & slow speed short trips can also be the culprit)
Also, running colder plugs than std in a turbo car is not generally issue but in saying so using colder plugs means getting the cruise tuning right is critical.
My guess is it could probably afford to go quite a bit leaner on cruise, together with more timing.
Looking at your mixtures at WOT. Depending on how much boost you’re running, basing this on a guess that you’re running around 8psi,
It would likely make the same power more with more fuel & more timing with better response.
Richer mixtures under boost aren’t so much of a problem if the plug heat range is right & it’s able to clean itself
Too hot a plug & you’ll have detonation issues.



To read plugs @ WOT, you need to do a couple of dyno runs or complete a pass at the drags & shut down as you cross the line.
You need to pull the plus & read them without allowing the engine to return to idle otherwise you don’t get a true picture of what’s going on.


Hope that helps

[mooshie]

Yep standard comp
boost is set at 8PSI
and no, generally when I drive the car it is for a weekend cruise so at a minimum 20km without stopping

Right, so I might try the hotter plugs and see how they go. I am looking at getting a bigger turbo soon anyway so will get the tune sorted then.

Thanks for the comprehensive response!