hum from gas tank area - not fuel pump

hi again, just had my fuel delivery issue solved - it was not the pump, it was some sort of needle valve However, now that I've got it back together, there is some sort of a hum coming from the fuel tank area, and it appears not to be from the pump, as it only appears when the engine is running, as opposed to just turned on. As I would like to take this apart as few times as possible, I am curious as to what it could possibly be.. or is there something tricky like saab fuel pumps only come on when the car is actually running? thanks, -trip

Reply to
trip
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It still may be the fuel pump. I think the pump only runs for a very short time when the key is first turned on unless (until) the engine is running. Probably a safety thing...

-Fred W

Reply to
Malt_Hound

Yes I think the fuel pump relay or something associated with it (might vary depending whether the car has much in the way of emission control add-on's or not) needs to see 12 volts on a certain wire to tell it the engine is running to keep the fuel pump going otherwise it will cut out. My 1985 900i is set up like this. Turn the key to 'run', then the fuel pump starts for a few seconds before it stops again if I haven't moved the key to 'start'.

The fuel pump in my 1983 900S doesn't seem to do that though - whenever the key is in 'run' the fuel pumps continues going even if the engine hasn't been started. That would well be a wiring fault or simply an artefact of the build year. The 1982/83 C900's seem to have been caught in the middle of some big transitions in ingition system design, etc.

As an example, my car, despite being a '1983 build' (Sep 1982 contstruction at Trollhattan, early 1983 fitted with Australian compliance plate), has points ignition. Only the C900's sent to the USA received hall-effect ignitions from the 1982 build year up according to the senior tech at Saab Serve where my car is currently having some work done on it so it can pass rego. C900's imported to Australia didn't get hall-effect until the 1984 build year.

Also, only the C900's sent to the USA with 8V engines have all the fancy emission control electronics that the Bentley manual talks about as living under the rear seat. None of the 8V C900's imported to Australia seem to have that. Don't know what the story is with 16V C900's though since they were a totally different design in terms of emissions and emission control.

Regards,

Craig.

Reply to
Craig's Saab C900 Site

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