About a year ago was doing a trip from NSW to WA (Australia) when our 
1991 D/Cab developed a mis-fire(2.1l).The strange thing about it was that 
it only occured when fuel level was under half or when going down hill?
(The down hill bit was no real problem since the whole trip is basically 
flat and straight). Pulled off to side of road and found fuel pump was 
making some pretty strange noises- shit just what we need no replacement 
and 2000Km from nowhere. Luckly had plenty of fuel aboard - kept going 
refuelling when required. Made it to Esperance WA (great place - white 
beaches - great surf - plenty of fish and no people) ordered new fuel 
pump - arrived a week later 10 mins to replace it all ready to head back 
to the surf started motor and fuel pump making the same noise!!!! 
What are the chances of a new fuel pump being u/s? As you might have 
quessed it wasn't and to cut a long story short after hours of thought 
and lots of looking - inside the fuel tank there is a filter(it appears 
as a pressed cicle in the middle of the tank when viewed from below) that 
 requires no maintenance as it is keep clean by the return flow of fuel 
from the fuel rails. From this filter runs a moulded plastic line to the 
tank outlet - I could find no clamps and could only assume that it is 
held in place due to the fact that it is installed under tension in the 
factory - this plastic line had come adrift - when you have a good look 
at the tank the outlet is no where near the lowest point in the tank - 
when tank is under half full, fuel moved around and lets a mixture of fuel 
and air in to fuel pump (noise explained - pumps starts to cavitate).When 
going down hill fuel moves foward air/fuel etc.etc.
Also inside the tank and incorperated with the fuel filter is a low fuel 
cut off - this seems to operate as a safety device that DOES NOT ALLOW A 
MIXTURE OF FUEL AND AIR TO ENTER THE FUEL PUMP !!!!!!!!!!!!!!!!!!!!!!!!!
I remember reading once in a Bosch handbook that they can saftely run 
fuel through the middle of the pump as there is never an explosive 
mixture present inside the pump - all fuel and no air.
How Lucky was I.

-----------------------------------
Brett Delaney       
'91 D/Cab
'91 TRISTAR
Ph  (049) 287222
Fax (049) 651690
brettdel@nswbeta.nsw.BoM.GOV.AU
-----------------------------------