I have a P0304 code that reads as a Cylinder #4 misfire. First of all, how does the computer know which particular cylinder is misfiring? I can understand how it would know a misfire is occuring in a bank (using the O2 sensor), but other than having an injector short, how can a specific cylinder be identified?

For what it worth, Cylinder #4 has good spark, is getting fuel, and has 155 psi compression. I don't have a leak down tester, so I'm not sure about that value.

I'm wondering if the misfire could actually be another cylinder(s).

Thanks for any help.

 

100%, don't try to second guess it.
Injector issue for number for is a 204.
How do you know you have good spark, who's wires and plugs are you using?

 

Magnecor 8 mm and Bosch +4. I'm basing good spark assumption on seeing the plug spark when I pull it out of the head and run the engine.

 

Never assume when it comes to a Rover.
You can have a bad coil, carbon knock or a sticky valve causing that code.

 

Mike, any suggested trouble shooting approach based on the above?

 

And the ECU knows when it just sent a command that should have fired cylinder "X", and the timing involved, etc. It does the math for you. In the old days, some shops had big ignition analyzer scopes, and I could never figure out how to get baseball games on them....

 

If I crossed up two of the wires on the coil packs, would I get a second cylinder misfire code? Or is it possible that I could just get a single code for #4?