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Load test Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 11 Jun 2003 10:18:51 In Reply to: saab 9000 fuel pump 1990 turbo, Yoni, Wed, 11 Jun 2003 07:32:39 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When you checked for voltage at the fuel pump, did you check with the pump still in the circuit? Typically many folks pull the connector off the pump, stick a meter in, see 12 volts, and assume the pump is bad.
Before you replace the pump, hook up 12 volts to it and hear if it runs.
The pump gets power from the fuel pump relay. The contacts on the relay can get dirty and pitted over time. Dirty contacts have high resistance. This resistance may be so high that the pump doesn't get enough current to start. But a voltmeter has very high input impedance - it takes almost no current to work. You won't see the contact resistance if the pump isn't connected and presenting a load.
You might very well have a bad pump. But before you do that, make sure it isn't the fuel pump relay. If it is the relay, you can replace it, or you could pop it open and clean the relay contacts with a little fine sandpaper or Scotchbrite.
Because many electrical systems in cars have switch contacts that can get dirty, it's always best to measure voltages with the load (motor, light, etc) IN the circuit. Otherwise you can end up replacing perfectly good parts.
Good luck!
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