If it says system too rich, bank one, it's a vacuum elbow with a hole in it. Usually on the left side of the intake manifold. If the engine cooling fan is also doing strange things, the culprit is the ECT sensor, which often starts as a rich code before it tells on itself. Generally an 02 sensor tells on itself very quickly, as do most other sensors. Vague codes are usually vacuum lines. Have only replaced two fuel pressure regulators on 850's, ever.

Hope this helps,
Chris