Fuel Pump Polarity

Post by **PSL184** » Tue Nov 25, 2008 5:52 pm

I would have thought that the SU electric pump would run either positive or negative earth.... but, I have seen them advertised for sale by our usual suppliers and they list both types and the positive earth versions are more expensive - anyone know why ??

Post by **alanworland** » Tue Nov 25, 2008 6:18 pm

I changed from positive earth to negative earth a while ago and all seems fine!
I think that the 'pip and crator' that gets burnt on the contacts will now occur the other way round - so in 40 year time my contacts will be returned to new!

Post by **PSL184** » Tue Nov 25, 2008 6:23 pm

Thats the same as I thought Alan - just doesn't make sense as to why I need to specify pos or neg earth and the pos earth type cost more !!!

Post by **Leo** » Tue Nov 25, 2008 6:58 pm

The electronic SU Pumps are supplied either as Negative or Positive earth and they look identical to the traditional points type apart from a small alloy tag with electonic embossed on it.
In my experience they are not as reliable as the points type and prone to sudden failure.

Leo 69 Travellewr

Post by **PSL184** » Tue Nov 25, 2008 7:19 pm

Aha - that might explain it then.... I guess what it doesn't explain though is the difference in price? Cheers Leo.

Post by **bigginger** » Tue Nov 25, 2008 8:09 pm

'cos not many people are going to buy a positive earth one, I imagine

Post by **polo2k** » Tue Nov 25, 2008 8:28 pm

I was thinking of the extra insulation but thats a good point!

Post by **bmcecosse** » Tue Nov 25, 2008 8:49 pm

Yep -it's only the electronic versions that are earth sensitive. But if you do change polarity - you should at least stone the points - or fit a new set. Same applies to ignition points !!

Post by **bigginger** » Tue Nov 25, 2008 9:26 pm

polo2k wrote:I was thinking of the extra insulation but thats a good point!

Extra insulation? Eh?

Post by **Onne** » Tue Nov 25, 2008 11:19 pm

to insulate it from the body of the car, if one were to run a positive earth pump on a negative earth vehicle.

Which is impossible anyway as there is the matter of the fuel line.

Post by **alanworland** » Wed Nov 26, 2008 9:10 am

Rubber section in it?
Doesn't sound a very good idea though.

Post by **bmcecosse** » Wed Nov 26, 2008 11:29 am

Seems a long way for a short-cut!

Post by **bigginger** » Wed Nov 26, 2008 9:12 pm

Onne wrote:to insulate it from the body of the car, if one were to run a positive earth pump on a negative earth vehicle.

Which is impossible anyway as there is the matter of the fuel line.

Now why didn't I think of that? Must take more stupid pills tomorrow...