A customer recently came in needing an engine rebuild.  He also wanted
me to replace almost everything else in the fuel injection system and
ignition system.  He had actually accumulated the parts already so I
just installed what he had.  New AFM, distributor, cap, rotor, plug
wires, plugs, filters, ground strap, and temp sensors.  However after
the new engine was installed the van would exhibit a Jekyl and Hyde
personality.  It would run great for a few days.  Then it would run
really badly (rich) making a put-put-put sound.  Then for no apparent
reason, it would run great again.  I swapped in my digitool ECU and it
ran the same.  I couldn't see any readings on the digitool that were
really out of line with normal.  When it was running great or running
bad the readings were the same.  Finally after pulling my hair out for a
few weeks, I decided to replace the entire engine wiring harness.  But
first a voice told me to check the fuel pressure.  I checked it and it
was 7 psi higher than it should be.  Also the pressure was bleeding down
rather quickly after the engine was shut off.  I tested per Bentley and
found that the Fuel Pressure Regulator was the bad.  Installed a good
used one and now the van is great!  No more J and H!  I think what was
happening was that the fuel pressure was just high enough to be right at
the limit of where the fuel injection could compensate for the richer
running and allow the van to run decent most of the time.  But then
sometimes the pressure went just a little higher and the fuel injection
would go haywire trying to compensate (thus the rich
running/put-put-put).  Just my theory.

Just wanted to pass this on to the list.  If you have been testing your
sensors and they are all reading good, check your fuel pressure before
banging you head against the wall.

Ken Wilford
John 3:16
www.vanagain.com