In Reply to: How to tell if your fuel pressure regulator is bad posted by Richard V on April 02, 2000 at 13:14:05:
: Does anyone know how to tell if the fuel regulator is bad? I realize the fuel economy has to be 1st sign, but I have a hesitation conditions on my '92 535I 5 speed, more noticeable when cold, but also noticeable (not as much) when warmed up, and I am suspecting the fuel pressure regulator. I can disconnect the 02 sensor, and the problem goes away. I have surmised, that I may have a rich fuel mixture and the 02 sensor is telling the system to "lean out" consequently, the hesitation.
As far as I understand, the O2 sensor, when unplugged caused the DME to enter an open loop state, which slightly enriches the mixture.
Just as an experiment, try plugging the hose from the carbon canister to the inlet manifold. I have long been suspicious that this may be contributing to a similar hesistation condition on my '91 535i 5spd.
I experimented with this recently, and am convinced that drivability improved. I have now installed a "restrictor" orifice in the hose, which allows the canister to be purged, but in a limited way.
I have an electric purge valve, but don't know what is correct operation for it. I do know that it operates, in a pulsed manner, all the time. I'd have thought that it should be not operating at high manifold vacuum ie. idle and part throttle.
Anyway, food for thought.