Testing the fuel pump

 Fuel Pump, Fuel System  Comments Off on Testing the fuel pump
Jul 092013

It has been a long time since the fuel pump had been rebuilt, converting it from mechanical to electronic actuation in the process. Burlen Fuels offer an electronic conversion kit to overcome the known issues with point corrosion with the mechanical set up. While it would have been cheaper to buy a new pump, by reconditioning/converting it, I would gain a much better understanding of how it worked which might prove useful if there are issues in the future.

The electronic set-up had already been tuned to its maximum pumping speed, by rotating a Hall Effect fork. I just needed to check the flow rate was close to the designed 2.4 pints per minute by bench testing it with some paraffin before putting it on the car.

The pump raced when it wasn’t under load. So far, so good! However when the inlet pipe was placed in the bucket of paraffin it didn’t quite go as planned. It stopped immediately! I tried retuning the electric circuitry by repositioning the Hall Effect fork through its full arc of travel but it still refused to pump. It was a bit gutting having spent all that time and effort.

The technical department at Burlen Fuels thought it might be due to reverse pressure which would naturally slow the pump down. Although I wasn’t convinced as the outlet was simply pumping back into the supply bucket. I was running out of options and was starting to regret not buying a new pump!

I refitted the magnet attached to the end of the diaphragm spindle in the hope that this might be limiting its travel and therefore the strength of the pump. Eureka – the pump continued under load but at a much reduced rate, which would be expected.

The proof would be in the achieved flow rate which, over three tests, averaged out at 1.6 litres or 2.8 pints. Phew!

I was now happy that the pump was in working order and could be refitted to the car.

Feb 032012

The pump body and most of the other alloy parts were taken to Carb Clean to be ultrasonically cleaned. I thought this would be better than blasting with a lightly abrasive medium and was pleased with how the parts came out.

It became apparent that one of the common problems with this SU pump was the tendency for the points to stick, especially on cars stored over winter. After hearing stories of drivers having to use a hammer to whack the pump back into life, I decided it was probably a good idea to upgrade from points to electronic actuation with a kit supplied by Burlen Fuels.

A fuel pump repair kit was also ordered which contains all the various gaskets, non-return valves, diaphragms etc for a full rebuild. Whilst this was not exactly a cost effective choice, with the cost of the parts close to that of a new pump, it was done more out of interest to understand the inner workings of the pump. Most of the parts for the rebuild kit are shown in the picture along with the cleaned pump body and non-return valve clamping plate.

The rebuild of the pump body section was simply the reverse of the steps taken to strip the pump down. The only issue was the orientation of the domed diaphragm in the delivery chamber. I’d taken plenty of photos when dismantling the pump but none of them showed clearly whether the dome should face into the delivery chamber or the cover. The service manual suggested that it should face into the delivery chamber but the diagram also had additional springs and diaphragm plates which were not present on my pump. A quick call to the technical department at Burlen Fuels confirmed that this was the case.

Delivery Chamber Inlet Chamber Pumping Chamber

Stating the obvious but the only issue with the installation of the non-return values is to ensure their correct orientation. This can be checked by blowing backward and forwards through the value to determine from which side flow is possible. The only other difference between the two valve assemblies is the presence of a gauze filter on the inlet side.

The new armature guides supplied in the repair kit were 5 plastic figures of 8, as shown in the first photo above. The original guide was a single piece and the new guides seemed to be a backwards step rather than an improvement. So the original part was refitted and avoided having to hold five guides in place when refitting the armature/diaphragm into the coil housing.

Next the return spring is placed with the smaller circumference towards the armature. The pump body, armature/diaphragm and coil housing can then be reassembled and secured by 6 screws.

Converting the pump to electronic actuation requires a magnet carrier to be attached to the upper end of the armature spindle. First a plastic guide tube is pushed over the spindle down into the coil housing. This centralises the spindle movement within the coil housing. The magnet carrier is fully screwed onto the spindle before being backed off until it is aligned to be perpendicular to the line passing through the pedestal mounting holes. It is then secured in this position on the spindle by tightening an allen screw.

The bakelite pedestal is replace by a PCB which is mounted on spacers to raise it away from the coil housing. On one of the spacer mountings contains a ‘Hall Effect’ fork. The fork enables the electronic circuit to detect the travel of the magnet carrier and thereby control the energising of the coil.

The fuel pump operation can be ‘tuned’ by the rotational positioning of the Hall Effect fork. This is achieved by loosening the screw above the fork and slowly rotating the fork until the pump speed reaches its maximum. The fine tuning would wait until the final testing of the pump when flow rates would be checked.

Jan 312012

The hardest part of the process was actually the removal the fuel pump! It’s located in the boot space above the offside wheel arch. The pump is attached to the body via three rubber mountings to an L-shaped bracket bolted to the pump body and a circular bracket clamped around the pump’s coil housing.

Each rubber mounting is comprised of two threaded studs joined by a rubber section, which reduces the transmission of vibrations to the chassis when the pump is running. The problem was that, even with a period of soaking with penetrating oil, any rotation of a nut would simply be taken up by the rubber section deforming and not undoing the nut from the stud. Finally, after much cursing, I gave up and resorted to a bolt splitter.

Once removed from the car, the dismantling of the pump is a fairly straight forward process. I started by removing the six screws around the base of the coil housing which allowed the pump body and coil housing to be separated, revealing the diaphragm and pumping chamber.

The inlet and outlet value assemblies are retained under a clamping plate secured by two screws, as shown in the photo. Once the clamping plate was withdrawn, the valve assemblies, inlet gauze filter and gaskets could be removed. The valves had to be prized out which resulted in their destruction however they were to be replaced as a matter of course.

The dismantling of the pump body section was completed by removing the inlet and delivery chamber covers. The inlet cover is simply a cork gasket and cover retained by a central bolt and washer. As far as I can tell the inlet chamber smooths the flow of fuel by having an air pocket which can expand or contract according to the pressure in the chamber. Four screws retain the delivery chamber cover under which is an ‘O’ ring, diaphragm and plastic gasket, see photo. Again the chamber provides smoothing of the flow of fuel due to the flexing of the diaphragm.

The disassembly of the coil housing section was also a simple process. The black plastic end cover was withdrawn once the terminal nut had been undone and the tape sealing the end cover/coil housing join removed. Underneath the cover is the contact point assembly, which consists of a Bakelite pedestal holding the sprung upper contact points and a rocker mechanism holding the lower contact points. A small capacitor is connected between the upper and lower contacts to suppress arching across the points gap as arching causes premature deterioration of the contact points.

After the two screws had been removed the pedestal could be rotated away from the rocker mechanism. Both the upper and lower contact points were badly corroded. Finally the rocker mechanism and armature & spindle were removed. This can be achieved by disconnecting the leads to the rocker mechanism and then rotating it until free from the spindle. Alternatively the armature/diaphragm can be rotated anticlockwise until the spindle is free of the rocker mechanism.

When the pump was first removed what appears to be a capacitor (see the photo on the left) was connected across the positive terminal and earth. This part doesn’t appear on the Jaguar parts list so I assume this must have been added at a later stage. As previously mentioned capacitors were used to suppress electrical arching but I’m not sure whether this capacitor was added for this reason or possibly to suppress electrical interference produced when the pump is in operation.

 Posted by at 7:06 pm
Dec 252011

With the body shell and engine sent away for restoration, attention turned to the refurbishment of the electrical components. The first was the fuel pump which was looking slightly worse for wear and somewhat corroded after 40 plus years.

The SU AUF 300 fuel pump used in the Series 2 E-Types is a fairly simple, displacement type pump, developing up to 2.7psi and a flow rate of 2.4 pints per minute. At its core is a pumping chamber sealed at one end by a flexible diaphragm. Movement of the diaphragm enables the volume of the chamber to be increased and decreased.

SU AUF300 Fuel Pump

When the diaphragm is drawn away from the pumping chamber, the volume of a chamber increases causing a decrease in pressure and fuel is drawn into the chamber. Conversely, when the diaphragm then returns to its original position, the chamber volume is decreased resulting in an increase in pressure, which expels fuel from the chamber.

The pump body actually comprises of three chambers: an inlet chamber, the pumping chamber and the delivery chamber. The inlet and delivery chambers are connected to the pumping chamber by non-return, inlet and outlet valve assemblies. Therefore the passage of fuel is restricted to flowing into the pumping chamber from the inlet chamber only and from the pumping chamber into the deliver chamber. A one-way street!

The inlet and delivery chambers also provide a secondary function of smoothing the flow of fuel.

The AUF300 pump uses a coil housing and sprung armature & spindle assembly to control the movement of the diaphragm. The coil housing is attached to the main pump body and, as the name suggests, contains a wire coil that can be energised when power is supplied.

In an energised state the coil produces a magnetic field which acts on the armature, pulling it and the attached diaphragm toward the coil housing, increasing the pumping chamber volume. Thus petrol is drawn from the fuel tank, via in inlet valve assembly into the pumping chamber.

However when the power is removed, the armature spring pushes the diaphragm back towards the pump body. This forces fuel from the pumping chamber, via the outlet valve assembly, into the delivery chamber and on to the engine bay.

It is worth noting that the pump pressure is dependent on the force applied to return the diaphragm to its original position. Therefore fuel pressure generated by the fuel pump is largely determined by the strength of the diaphragm return spring.

The armature spindle passes through the centre of the coil housing to a contact point assembly. It is the movement of the spindle and the connected contact points that controls the power supply to the coil. When the diaphragm is in its original position, the contact points are closed allowing current to flow to energise the coil. The armature is drawn into the coil housing until the attached spindle pushes the contact point rocker assembly to ‘throw over’, opening the points and removing the electrical current to the coil. As the coil is no longer energized, the magnetic field acting on the armature is lost and the armature spring returns the diaphragm to its original position. The cycle then repeats. The throwing over of the points gives the pump its characteristic ‘tick tick’ sound.

 Posted by at 12:19 am