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From digest.v7.n605 Mon Nov 17 12:48:52 1997
From: (Dan, Marilyn, Phil Patzer)
Date: Mon, 17 Nov 1997 03:30:08 -0800
Subject: 535i bucking, smoking problem

The standing fuel pressure for the injection system is controlled by how much fuel is returned to the gas tank in this recurculating type system. When fuel pressure regulator fails to open fully, the pressure at the injectors will rise and the engine will be forced onto a very rich diet. Running at full speed will clear up all the symptoms. Slow running, or Idling will result in snorting, smoking, stalling. Continued driving will result in failure of the oxygen sensor, the catylist and potentially a catylist fire. I've seen the interior carpets scorched by the heat of after-burning catylists.
The pressure regulator is at the front of the fuel delivery rail on a '87' 535i, and is quite easy to remove and replace. Use extreme caution in removing the regulator as there can be considerable pressure behind it. Some would advise removal of the fuel pump relay with engine idling as this would allow the pressure to bleed down considerably prior to removal of the regulator.
Doing this on an otherwise cold engine would be recommended. Wrapping the regulator/fuel rail junction with lots of paper towel will reduce the "explosive" spray of escaping gas. All common sense warnings come into play here.
Lubricate the pre-installed O-ring well with something like vasoline, and the O-ring will draw into place as the regulator is bolted in evenly turning each bolt just a couple of turns at a time.

Dan Patzer

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