1979-1993 & 94 Conv [Subscribe to Daily Digest] |
Saabnutt:
I'm not sure you're checking things correctly. You say it has 12 volts when key is on - - it should. The skinny lilac colored wire from ECU to relay is the one that carries the "run" command - - it goes to ground when a proper functioning ECU senses that the car is either, A. Cranking, or B. Running.
A clever little check on whether the ECU is actually failing to signal the relay to run is, buy a tap-clip crimp-on connector at hardware store or auto parts place, crimp it onto that lilac wire, then run a jumper from it to ground.
With that jumper in place, with good relays and a good pump, the fuel pump will run all the time the key is on. If your ECU isn't telling the fuel pump to run, that jumper will give you a functional running car if other facets of ECU are otherwise all right and if ECU is getting a signal from the Hall sensor.
I have actually read recently on this site that the ECUs sometimes fail to provide that signal, and the post referred to a circuit to patch in to replace the failed signal. Do some searches.
The ground-tap wire trick is only to be used in a pinch temporarily, or for diagnosis, as the fuel pump signal the ECU should send is actually a safety feature - - in a crash, if a fuel line ruptures, a constantly running fuel pump with ignition on could feed the inferno that takes your life, if say you're knocked out or trapped in the car. A fuel pump running only when engine is running would shut off as soon as the engine lost fuel pressure from the ruptured line.
Note, an ECU without a good signal from a Hall sensor will NOT run the fuel pump.
posted by 71.173.9...
, Wed, 1 Aug 2012 14:29:43, Thu, 2 Aug 2012 10:00:10
, Thu, 2 Aug 2012 11:12:24, Thu, 2 Aug 2012 16:30:42
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