All, a buddy of mine has an XJ-S that he rebuilt the engine on after the PO cooked it. Ever since putting it back together, it's ran really rich.

We're talking black smoke and gas washing into the oil.

I don't know much about these fuel injection systems as I'm mainly a Mercedes Benz guy, but if it was an MB of the era, I would suspect a stuck cold start injector.

Any ideas where to start?

We've already changed the plugs which were completely fouled.

Thanks

Al

That year doesn't have cold start injectors, so you can rule that off the list.
When I replaced the V12 in mine I had the same problem. After running just a few minutes the plugs were completely fouled and I found a ton of gas in the oil. I had already rebuilt the injector harness, so I started checking the wiring to the sensors and found multiple cracks in the insulation. Basically I just replaced all the sensor wires and ignition wires and the car started up and ran perfectly. Even though the wires weren't broken, the corrosion had created enough resistance to confuse the ECU, causing it to overfuel.

Thanks, that makes sense!

Excessive fuel pressure? Or raw fuel being ingested via ruptured fuel pressure regulator diaphragm?

Cheers
DD