[Healeys] SU fuel pump polarity

Kees Oudesluijs coudesluijs at chello.nl
Tue Jun 26 02:41:43 MDT 2018

These pumps are both equipped with a diode and both are thus polarity 
sensitive. The difference is in the colour code of the wiring of the 
diode. Red in one diode is black in the other. If you have a negative 
earth pump you can use it on a positive earth car if you change over the 
two wires of the diode and visa versa. These are later SU-Burlen pumps, 
not original SU´s. They probably have the taped plastic stepped caps 
instead of the Bakelite cylindrical caps sealed by a rubber band and 
taped over by tape with the SU logo.

The older SU AUF301 pumps usually have a capacitor, a greyish/yellow 
cylindrical item with the the wires at both ends. These pumps are not 
polarity sensitive.

I usually replace the diodes and capacitors by a transil, in fact a 
2-way Zener diode which is bipolar and limits the voltage across the 
points to 18V, thus practically preventing sparking. These are also not 
polarity sensitive.

The transil will cost you though, $0,10-$5!!!, depending on quantity.

The AZX1307 is not the correct pump for the AH. The original on later 
cars was AUF300 series, mostly 301 but there are some variations. The 
replacement of the AUF301 is AZX1308 which delivers a higher pressure, 
if my memory is correct 3,8psi versus 2,7psi

Kees Oudesluijs

Op 23-6-2018 om 00:18 schreef hspethmann at t-online.de:
> My Healey:
> BJ8 MKIII 1964
> # L27347
> pos. earth
> Fuel pump for the last 20 years:
> SU AZX1307
> now with a slow, but steady clicking every 15 to 20 sec , when 
> ignition is on.
> I thought, the easiest solution is to change the pump with a spare 
> pump I have in my trunk for about the same time as the first one. Both 
> pumps look the same on the outside. Both pumps are wrapped in black 
> tape.  But the label on the box of the spare pump says: AZX1307 neg. 
> earth.
> In the archives I found a very instructive contribution by Steve 
> Russel from Aug 2009. And it ended with the words: "A picture would be 
> worth a lot of words right now."
> So I removed the cap on both pumps to see if there is any difference 
> in the wiring and took a picture, attached to this mail..  Both pumps 
> look the same inside. You see the old pump on the left, the new one on 
> the right.  Under the cap you see a piece that looks like a capacitor, 
> labeled as BZX1013. But following the explanation with terminal 1, 2 
> and 3 clockwise beginning with the power input stud and ending with 
> the internal ground terminal I suppose the "capacitor" is a diode. But 
> when there is no difference in wiring between the old and the new 
> pump, why could it be, that the old one looking like a neg. earth ran 
> 20 years in a car with pos. earth?
> I'm confused and hoping for your wisdom to shed some light on the problem.
> Best
> Achim
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