In a conventional diesel system, and this includes the 1-HDT / HDFT
engines, the injector pump has two functions.
The first is to act as a supply pump to the main injector pump.
The second is to pressurize that diesel and send it to the injectors.
The pumps in our engines, like most others, suck diesel out of the fuel
tank. You will note the "hiss" as you remove the fuel cap when you
refuel - a sign of partial vacuum.
With time the supply pump becomes less efficient. Some people on the
list comment that when their vehicle has a low tank and particularly if
it is facing uphill then the engine speed drops and/or runs badly.
In this example the pump is having to suck the fuel out of the tank and
pull it uphill to the pump, the vehicle being on a slope with the pump
quite a bit higher than the tank, compounds the problem, when facing
downhill there is less height difference hence the problem does not
The Walbro, in common with others like PIERBURG, is a low pressure
electric pump. It operates at approx 0.75 bar. It is fitted close to the
fuel tank and sucks fuel out then delivers it at low pressure through
the fuel filter housing to the injector pump.
Other than compensating for a worn supply pump there are several other
benefits to a low pressure delivery as opposed to a "vacuum" supply.
With any diesel system getting air in the diesel supply line gives
serious problems and can be very difficult to fault find. Where you have
a system that operates in a partial vacuum there is always the potential
for air to enter that system. Therefore by pressurising the system air
ingress is prevented, naturally any leak of diesel would be easy to see.
Conversely you can't "see" an air leak!!
Changing fuel filters is far easier, fit the new filter and switch the
ignition on, the air is expelled with no need to operate the plunger on
the filter housing.
Finally, and this the more technical bit, when injection pumps are
calibrated they are supplied with diesel at a low pressure. This
"biasses", for want of a better word, their settings. When on the
vehicle the pump is now having to pull the fuel hence it is not
operating at the optimum bench set calibrations. By fitting a walbro or
the like , we can mimic the bench calibrations and the injection pump
settings are optimised.
Have a look at this link for Walbro pumps. I have used this supplier a
couple of times, he is excellent. http://www.autoperformanceengineering.com/
80 series specific pump: Series 6000 - Model 6065
Rember flow rates are in US GALLONS which are not the same as good old
Confused - Hogsheads and Firkins - you are now!!!
Hope this helps.
First I'll install the turbo and after will think of something more....
''always look at the bright side of life-taram-taram taramtaramtaram...
On Aug 18, 2006, at 4:32 PM, Gareth Jones wrote: