Landsharkoz - Home of the Porsche 928 In Australia - Tech Tips

Immobiliser Installations

A general alert for immobiliser installations: check that the installer has not routed the wire carrying to full current for the fuel pump through the immobiliser control module. The current is too high for the module, so it will fail sooner or later (about 18 months for mine). The fix is to re-splice the power wire for the relay (need to remove the relay board in the footwell to get access), so it is not something which you can do quickly on the side of the road.

Terminals 30 and 87 for the fuel pump relay are those which have to be bridged to run the fuel pump without the relay (for testing or emergency use only; the fuel pump will not be cut off automatically when the engine stops. eg; in the event of a crash). The wires attached to these terminals are of a heavy gauge (doh! they have to carry up to 16 amps).

Dim-witted installers splice the module into one of these wires (whichever is positive, I guess; terminal 30 from memory), using the light gauge wires attached to the immobiliser module (doh: they are not designed to carry heavy current). The irrationality of splicing a tiny wire into a heavy gauge wire seems to escape most installers.

The fuel pump isolation should be via the terminal for the relay pins which CONTROLS the operation of the relay (Pin 15?? - only from memory and electrics is not my field). The wire to this carries only a relatively low current.

Bruce Buchanan's experience: around 80 per cent of 928 "fails to start" are caused by burglar alarms and immobilisers.

Glenn Evans, '80 928 Petrolblaumetallic 'S' look. 5 speed.

Please note: these comments are the writer's personal opinions. I take no responsibility nor give any kind of warranty as to the accuracy of the statements included on these pages. The information in Tech Tips is based on the extensive experience of Porsche specialists and owners who drive, service and even race their 928. Although this information is generally considered 'best practice' niether 928 Australia, Landsharkoz or the Webmaster will accept any liability for such information, or, for any use to which it is put. If you have doubts about a specific point, or if you have any questions, you should consult your Porsche specialist or post a question on the Landshark mailing list. - Leonard Zech, Webmaster.