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Date: Sun, 11 May 2003 08:06:06 GMT
From: "someguy" <>
Subject: Re: wiring problem on a 85 900

"dave silva" <> wrote in > Greetings, > > I'm looking at a 1985 Saab 900 4d, fair condition all the way around. > Wife loves it. The good 'ole boy who owns it says it has a wiring > problem to the fuel pump. One day it stopped running. HE had someone > look at it, that person connected something to the fuel pump leads in > the trunk and the car started right up. I've never owned a Saab but > I'm guessing there is a relay and/or a fuse that controls power to the > pump. > > DOes the fuel pump run constantly like some chevy's or is it on demand > via a pressure sensor? > > I'm an aircraft electrician so these things don't intimidate me much, > (unlike mechanical problems) But I need a general direction or a > list of things to look for before I buy this car on spec. > > If the fuel pump is constantly on then i can just bypass the relays > and power it up (ok, not entirely safe) but if it runs on demand then > the system has to be right. > > His opening price was $700 as is, Does that seem high? It has 140,000 > miles, interior is decent, manual sunroof, 5-speed, etc, (car was not > for sale, i approached him about it) > > THanx > > Dave Silva The fuel pump runs constantly as long as the ignition is on and the engine is running (there is a fuel return system which feeds the unused fuel back to the tank). The pump is powered from the battery via a fuse and a relay. You can bypass the relay if you for instance want to empty the tank or want to check out the pump when it is still in the rear, have done that a few times using a switch soldered to two long wires that are crimped to the standard flat pin connections that plug into the relay box when the relay is removed. Some people used to go in and install a hidden switch in series with the fuel pump, making a very simple car theft system (the 900 classic is a great car but easy to steal, at least for the Swedish thieves that have learned the trick). However none of those methods are recommended since they impair the function of the car, for instance having the pump running when the engine has stopped could be very dangerous if you end up in an accident! Having the pump turned off due to a bad contact when driving could also make you end up in undesired situations. Thus my advice is to check the relay/fuse and the contacts in the relay/fuse box for any bad contact force or oxide and not do anything "special". Normally the cables running through the car should be fine and the problem should be either in the relay or fuse connections (maybe there is one more cable junction, I don't have the circuit diagrams any longer but you can find them in good repair manual). -- someguy

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