7.4 TBI too rich

[titan101]

Hey guys, I have a 1992 7.4 TBI engine and its running too rich. My plugs are all black. I have changed the distributor, plug wires, spark plugs, MAP sensor, Coolant temperature sensor so far. I'm getting 15" vacuum off the PCV TB nipple and the MAP TB nipple. I have base timing set to 4 degrees. I get a constant 12 PSI of fuel pressure. My best guess is that I have a Vacuum leak some where. I reconnected the tan/blk wire after setting timing and watched the timing with the light and it seems to jump around but that might be because of the rough idle. Any other ideas?

[sturgillbd]

Is the engine stock? If so, 15" of vacuum is low and I would look for vacuum leaks.

[titan101]

Yes it is stock. It kinda pops a little when you hold the rpm steady is that from over fueling?

[sturgillbd]

If plugs are black, it is probably misfiring. Being low on vacuum, the ecm thinks the engine is under load and adds fuel.