Andy:
Here's my take on your question. I have never had a fuel pump
give problems. However I have made sure that the fuel is clean,
the tank is clean, the filters are cleaned regularly, and the
pump points are serviced as per the manual. I also let the pumps
stand a few seconds after switching on to check to see if they
cycle too often. This tells me if the valves or diaphram is
leaking.
>I've just gotten a rebuildable SU fuel pump through EBay and plan to
> use it as a backup for my TD. I have read earlier threads on the
> subject, and think I have four options.
>
> 1) Club wisdom (FWIW) is to carry an extra fuel pump in the toolbox.
> Obvious drawback of trying to mount and plumb it on the road.
This would ensure the pump isn't subject to the elements, but I
would take it out of the car once in a while and check to see if
it still runs. I don't know if most problems are that the pump
quits "clicking", or the valves get so bad that it won't deliver
enough fuel. From what I read, they it appears that they just
quit "clicking".
> 2) Since others have found that fuel will freely pass through a
> non-energized SU, I could mount it in-line under the car in front of
> the fuel tank with a switch to turn on when needed.
When you need it, what's to say that it has gotten damaged,
corroded, or otherwise messed up from being UNDER the car. My
feeling is that this is the poorest location for the pump and it
needs to operated once in a while to make sure it works! Not
only that, but is the pump a high pressure or low pressure one?
>
> 3) It could be mounted on the bulkhead and outboard of the original
> fuel pump a la TD mark II. It could be plumbed in line with the
> principal fuel pump and energised with an A-B switch.
Again, it needs to be operated once in while to make sure it
hasn't packed up due to inactivity.
> 4) It could be mounted and plumbed exactly as in a Mark II, with both
> pumps running all the time, and the assumption that one could take
> over if the other failed.
I think this is the best way if you want it readily available. I
have a standard TD which has a stage III engine and other
modifications. To insure fuel delivery, I bored the drain plug
on the tank, put in a right elbow, and added a second fuel line.
To mount the pump, I used a piece of 1/4" flat iron mounted
between the original pump and the original mounting plate. This
piece sticks towards the outside of the car, and the extra pump
is mounted on it. It has been that way for 40,000 miles and 28
years with no problems. It is wired in and plumbed the same as a
MKII. When I turn on the key, I can verify that both pumps are
operating!
The only down side may be you might run into vapor lock problems
because the fuel flow in each delivery pipe is reduced to half of
what it was. Since I have alot more heat due to the modified
engine, I have wrapped the fuel lines with insulation from the
chassis rails almost up to the pumps.
> I have transistorized my main fuel pump, and wasn't planning on doing
> same to the backup pump.
>
All the reason more to run the pump once in a while. But it
still might go bonkers from not being used. The manual says to
service the pump periodically by cleaning the points and that's
the best prevention.
For most people, I think option one is the best. If you want it
installed on the car and ready to use, go to option four.
FWIW
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