Is there a common cause for code P0308? I’ve searched and found mostly issues with V6 and non supercharged S-Types.

I replaced the coils and plugs a couple months ago. The only other recent change is a Banshee Screamer intake. I can’t imagine the intake is the cause. Maybe I damaged a vacuum line in the process of installing it? I’m going to swap coils with another cylinder to start.

Is there something super common that I should look towards first?

 

Swapping the suspect coil with a known-good unit from another cylinder is a good first step in troubleshooting.

What brand coil did you install? Some no-name specials and discount chain house brands have been known to cause trouble right out of the box.

 

I replaced the coil and I’m still getting the misfire. It’s a definite low RPM, light throttle “miss” or skip.

 

Still getting P0308 for #8 cylinder? Or did the code follow the suspect coil?

 

If replaced with a new one, swap with another in case new is bad.

 

As above, did the code follow the faulty coil?

Mellow

 

"Is there a common cause for code P0308? I’ve searched and found mostly issues with V6 and non supercharged S-Types." Cylinder eight misfire on a V-6, now that is a really tricky one to diagnose...

 

Yes the most common cause is a faulty coil pack!
Mellow

 

Ok...ok...wise guy...lol. Most of the misfire threads I've found are for the V6. I replaced the #8 coil with a new one. It still gave a P0308 code, but it took days for it to show up. I cleared the code and it hasn't come back yet, but I can feel feel an intermittent "skip" or "miss" at low speed, light throttle cruising. It makes me think that it's either the fuel injector or a vacuum leak. It doesn't seem effected at heavy throttle.

I've been planning on rebuilding the supercharger and putting a 6% pulley on it, so I guess I'll replace all the vacuum lines and having the injectors reconditioned while the blower is out.

 

A vacuum leak is likely to impact more than a single cylinder, no? That suggests an injector as the next possible culprit. Good, plan...

 

Could be an injector, but inlet manifold gasket leak is possible too. Try to see if there are any vacuum pipes coming from that branch of the manifold. If there are any, check them for leaks but also check their destination. Example: on some cars the vacuum pipe for the brake servo comes from one end of the manifold. If the brake servo leaks it induces a lean mixture on one cylinder (this is only general advice. I don't know if the V8 has this or not).

 

Check fuel trims. Any leak will show there.