To find cylinder #8, you need to:
1. Identify the engine: Determine the exact engine type (e.g., 4.6L V8, 5.4L V8, 6.8L V10). This information is usually on a sticker under the hood or in your vehicle's documentation.
2. Consult a repair manual: A repair manual specific to your year and engine will have a diagram showing the firing order and cylinder numbering. This is the most reliable way to locate cylinder #8.
3. Look for casting numbers: Sometimes, the cylinder numbers are cast directly onto the engine block itself, though this isn't always the case and might be hard to see.
Without knowing the specific engine in your E-250, it's impossible to give you a precise location.