92 Townie with diesel... Has plenty of power when fuel tank is full but once it goes past 1/2 tank it has very little power and puts out lots of black smoke when under power.... Does the townie have an in-tank fuel pump? I haven't a clue why this is happening!

Rob

- (#9567) Rob, 24 Mar 04 19:54

No in-tank pump. Try replacing the filter, and if that doesn't help I'd guess the lift pump inside the injection pump is starting to go...

- (#9567) david miller, 25 Mar 04 01:09

NOt sure that the lift pump would know how much fuel is in the tank? Try checking out the tank breathing system as a blockage here could cause the tank to vacuum and cause fuel starvation. Next time it happens, stop and remove the filler cap to see if there is a vacuum in the tank. Also look at the tank to check that there is no visible damage. I have seen cars where the breather was blocked and the tank was literally sucked flat.

- (#9567) John Shaw, 25 Mar 04 13:33

Rob. Air tightness has to be maintained through the fuel line from the tank to the filter/priming pump and on to the injection pump. It's worth checking that the fuel line, from the tank, to the hand priming pump, (mounted on top of the filter assembly), is sound. If there are any air leaks here, fuel will drain back into the tank.
Unfortunately, the suction and discharge reed valves, in this priming pump, are within a sealed housing and cannot be checked for dirt or debris which might hold the check valve open and, therebye, allow the "head" of fuel, in the pipe, to fall. A full tank would help to overcome a small air leak but, as the tank level falls, the injection lift pump might struggle to maintain sufficient volume. The inlet and outlet pipes, on the hand priming pump, can be a source of trouble and replacing the tired spring clip hose clamps with a Jubilee type, might help.

- (#9567) John Davis (Leics), 25 Mar 04 16:06

I'd guess as there's no cold starting issues that there's no airleaks in the fuel supply system. But, as John D points out, the amount of work the lift pump must do depends on the height it's having to lift the fuel by. And as it's the same little vane pump that lifts the fuel AND pressurises the pump body for transfer and timing control it's easy to see why supply issues can so affect power output.

Get the filter changed!

- (#9567) davi, 26 Mar 04 00:36