Potential Petrol Pump Problems

Octagon Newsletter March 1991

By Stephen Golde

The SU electric petrol pumps are, unfortunately, one of those, 'take it for granted' things. It works so leave it alone, it works maybe, but is it working properly, reliably and for how long? Are they a potential safety hazard? Please read on and the information compiled here hopefully will help someone prevent a possible serious problem, maybe even a fire!

The clicking that is heard when the ignition is turned on is that of the petrol pump. To check the operation of the pump proceed as follows: Turn ignition off, disconnect 12 volt supply and be sure the wire does not touch the chassis as it will be live when the ignition is turned on. Turn on the ignition and momentarily touch the wire on the pump terminal. It should operate (a clicking sound will be heard). If it does not operate, don't panic, allow a few minutes for the pressure to drop in the petrol line and try again. If the pump is not working the problem may be caused by dirty contact points or a hardened diaphragm that will not deflect. An important check to be made here is that the vent hole in the magnet housing points down. This vent hole must be kept clear of dirt. A straight, blunt piece of wire can be used, being careful not to push so hard through the vent hole as to bend the wire. It should get no further than the armature. If it deflects past this it is possible to rupture the diaphragm. (I must point out that I have come across some pumps that do not have a vent hole.)

Now for the most important part. The vent hole is also a drain. If the diaphragm leaks petrol through into the pump magnet housing and the vent/drain hole is blocked up a very serious problem could occur. (Especially if the end cap is cracked or broken.) The petrol could be ignited by the contact points sparking and a fire could result. This actually happened to a friend's car but fortunately was caught before the problem got out of hand. With the vent/drain hole unobstructed and the diaphragms leaking, the petrol will not travel to the end of the pump magnet housing, but will simply drain away. (This is your indication that a new diaphragm is required.)

Other things to note here are that the early type pumps have exactly eleven brass spacers to centre the armature in the solenoid. This is important. Also if the end cap is cracked or broken it must be replaced. The cap serves several purposes. It must keep dirt and moisture out but also prevents the contact points pivot pin from dropping out. After checking my own car I found the cap broken, leaving the contact point pin exposed. When undoing the end cap securing nut be careful not to put too much strain on the long brass terminal stud protruding through the end cap. This stud is secured only by the Bakelite mounting block or pedestal and will break away easily. One reason for this is if a steel washer is used on the terminal post, this will corrode and damage the threads.

Sealing up the end cap with either a rubber boot or insulating tape around the end cap to pump body joint will make a fairly water tight seal. Remember, if using the SU type rubber boot it also has a drain hole in it and should face down. If nothing else, please check to see if your vents are clear for the sake of preserving our treasured cars. This may avert a slight inconvenience or, who knows, even a total disaster.

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