Saab 900 Turbo Fuel Pump relay

[bernardgreen]

Today I helped a friend out. The relay for the fuel pump appears to be not operating relaibly. Fortunately he had a spare ( old ) that appears to work OK

The relay has a revolutions per minute rating printed on the case and on opening it there is a small electronics board. ( I have yet to reverse engineer this to discover its function ).

The circuit diagram of the vehicle shows a simple relay controlled by ( I assume ) the ignition switch. Two terminals for the coil and two for the normally open contact.

What relevance if any does the revs per minute have ?.

 

[Burnerman]

I would think - and strictly guessing here - that the relay gets so many input pulses that it has a time delay on its contacts so its not buzzing open and closed all the time.
This, of course, may be complete cobblers
John

 

[Belle427]

I believe its a dual function relay that acts as a rev limiter, it cuts the fuel somehow at higher rpm's.

 

[bernardgreen]

I believe its a dual function relay that acts as a rev limiter, it cuts the fuel somehow at higher rpm's.

I think that is close to the answer. Use the same type of relay for several purposes. In the fuel pump supply it is in a socket connected so as to NOT use the electronic speed sensor but in another position such as control of the turbo the socket is wired such that the coil is controlled by the speed sensor.
More investigation is needed......