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Registered
Join Date: Oct 2005
Location: Capistrano Beach, Ca.
Posts: 7,235
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One bit of clarification (and Tony, please correct me if I'm wrong here.) Terminal 85 is the ground connection for the coil of the relay, but it will lose the ground continuity once the engine begins to draw vacuum and open the air flow sensor. What this means for you is, you should not run a permanent ground to 85, here's why:
Grounding 85 sends the current path in the relay to terminal 87--the starter--when the ignition is in the "on" position. The fuel pump will not run until the starter is engaged. When the starter is engaged, the fuel pump starts and once vacuum exists in the intake, the air flow sensor opens and you lose ground contact at terminal 85. The loss of ground "opens" the relay and alters the current path to terminal 87a so the fuel pump continues to run in the ignition "on" position. With this arrangement, if the engine should somehow stall, the fuel pump will shut down because vacuum is lost, the air flow switch closes grounding terminal 85, the relay now closes and diverts the current path to terminal 87 (starter) and you're back to the beginning--no running fuel pump in the "on" position.
Running a permanent ground to 85 will result in the current path (within the relay) to always be to the starter and once the engine starts, the current path will remain from the starter and the fuel pump will shut down as soon as you release the key from the start position.
If you did the check Tony posted, and all terminals were correct as described and the pump did not turn on when terminal 87 was hot (start position), then you may have a problem with the air flow sensor switch. You posted you had no ground at 85 during your tests which would indicate a fault with the air flow sensor or the adjustment of the sensor plate. However, double check and be sure you tested each terminal exactly as Tony posted, especially the test to see if 87 is powered when the key is in "start" only, and the continuity to ground of 85. BTW, are you certain the air flow sensor is plugged in? You'll likely need a mirror and flashlight to check the connection on the intake, and look for a brown/black wire connector near the 14-pin connector in the engine compartment. The brown/black wire should be coming out of the wiring harness. It would be near the small, three terminal fuse block on the electrical panel at the back left corner of the engine compartment.
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L.J.
Recovering Porsche-holic
Gave up trying to stay clean
Stabilized on a Pelican I.V. drip
Last edited by ossiblue; 01-18-2011 at 05:49 PM..
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