'B' vs 'non-B' pump
My experience from 2012 is that my original ('B' suffix) pump started being noisy all the time, although the car still ran fine. (2002 VW Golf Tdi 1.9 PD engine)
I tried and failed to locate a 'B' suffix pump, so got a used 'non-B' pump for about £40, which has been working fine ever since.
I was initially concerned that the new design of pump would result in an undriveable car when the lift pump failed, but in fact I have found it is not quite that simple - at least with my car. The car will indeed not run with the new pump UNLESS the tank is more than about 1/3 full. If the fuel is above the required level then the fuel seems to be pulled through just fine. I'm not sure why this should be, but it does suggest that if the new pump fails and the fuel level drops to a point where fuel cannot be drawn up by the tandem pump(?) then adding a couple of gallons of fuel to the tank should get it going again.
Since replacing that pump I have become interested in maximising fuel efficiency, and I notice that the pump uses a full 3.7A of electrical power, which of course has to be generated by the alternator using diesel. The electrical power needed to run the car with engine running but no lights, wipers, blower motor, etc, is just 7.4A, so half of that electrical base load is down to the lift pump.
In fact I've modded the car so I don't use the alternator, but charge the battery off the mains every night, and that does save about 8% on fuel overall, so my issue is not directly to do with fuel consumption, but more to do with extending my alternator-free driving range. Switching off the lift pump would double my day-time fine-weather driving range. I'd quite like to fit a switch that I can press if needed to prime the fuel lines for starting (although I'm not sure that is even necessary) and then leave in the OFF position for normal driving.
For those ordinary mortals who use alternators, doing without a lift pump should save some fuel, although for me it's about putting less strain on my battery.
For my car the mpg hit if using an alternator is about 0.25mpg per Amp of electrical load, so the lift pump would decrease mpg by about 1mpg. However, a previous poster reported improved mpg when his/her lift pump was not working of around 3mpg, and that, from my experience, is way above the saving one could expect as a result of lower electrical load. I wonder if the improved mpg was down to a higher fuel temperature as a result of the fuel not being circulated back to the tank. If that is the case then even with my alternator-free arrangement I might see improved mpg.
It looks like if I fit such a lift-pump-kill-switch I'll also need to mod the fuel pump to allow pull-through at any fuel level in the tank. Apologies if this has already been linked to here, but can anyone point me in the direction of some instructions on how to perform the mod for the 'non-B' pumps?