Last week I took my Sapph out for the first drive of the year. At first it was indling a bit rough, but after driving it it seemed fine again. But on boost it developed a misfire, so I drove it home again. But just before I got home it really started to drive badly. I just round out it's running on 3 cylinders. Cylinder nr 3 isn't doing anything. I unplugged all injector plugs each at a time and at nr 3 I didn't notice a change in how it's running.

But how do I find out if it's fuel or spark related? I did take the plug out and that was almost completely dry. If the injector was working would the spark plug be soaked?

The car is running an MSD wasted spark setup, so if it was spark related it should be 2 cylinders having problems, right? That is assuming the spark plug itself and the lead are ok.

 

What injectors are you running?
You can get the injectors checked and cleaned, there are loads of companies doing it, like asnu.
Can you pull the plug and Earth the end and quickly look for the spark when cranking it's?...just to rule the spark out.

 

Just to make sure the plug and the plug lead weren't the problem I swapped them over from cylinder 2 and 3. And in fact the problem also moved from cylinder 3 to 2. In the end it turned out the spark plug was knackered.

The only thing i'm worried about is whether the unburned fuel from running on 3 cylinders has contaminated the oil. It has been running on 3 cylinders for a few minutes I guess, mostly idling.

 

Just change the oil to be sure, can't hurt

 

I know. It's just that I put for 80 euros of oil in it 50 miles ago.

 

Welcome to car ownership. Don't risk a €4000 rebuild for €80.

 

I am not going to risk a rebuild over it. I only wonder if it really is a risk, or that I am worrying for nothing.

 

Hi Marc,Let a tiny bit of oil out and check if it smells of petrol and if it still smells and looks fresh and clean I would be very suprised if the new oil has been compromised.