Fuel Pump Diagnostics |
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Fuel Pump Diagnostics |
solex |
Mar 21 2010, 12:40 PM
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#1
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Senior Member Group: Members Posts: 789 Joined: 12-January 05 From: Long Island, NY Member No.: 3,439 Region Association: North East States |
Hi All,
Need a little help to diagnose a fuel pump problem in a 75, I do not hear the pump when I turn the key to the run position. The car was running, I had a few occasions where it would not start, let it sit for a few days and it was start right up. The grounds: under the relay board, battery and transmission have all been cleaned. All fuses are good. The relay is working as I can hear it click into position. When the key is in the run position relay terminals 30 and 85 shows 12 volts. Terminal 86 show 0.03 volts and terminal 87 show zero volts. There is no voltage at either of the fuel pump terminals. The readings at the relay is counter to to what Haynes states (86 should read 12 and 85 should be ground). I not sure where to check next, really do not want to pull the tank. Any assistance would be appreciated. Thanks, Dan |
solex |
May 19 2010, 09:22 PM
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#2
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Senior Member Group: Members Posts: 789 Joined: 12-January 05 From: Long Island, NY Member No.: 3,439 Region Association: North East States |
Clay,
Thank you for spending the time to explain, it is much clearer. But unfortunately I cannot duplicate the problem in my garage. I guess I will let the car idle over the weekend for a bit and see if I can reproduce. Interesting thing about the aux air regulator, why would that cause a problem in the start up? Dan |
ClayPerrine |
May 20 2010, 06:35 AM
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#3
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Life's been good to me so far..... Group: Admin Posts: 15,523 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille |
Clay, Thank you for spending the time to explain, it is much clearer. But unfortunately I cannot duplicate the problem in my garage. I guess I will let the car idle over the weekend for a bit and see if I can reproduce. Interesting thing about the aux air regulator, why would that cause a problem in the start up? Dan The output side of the fuel pump relay feeds both the fuel pump and the aux air regulator. The insides of the aux air regulator have an electric heater in them to heat the bi-metallic element that closes the air bleed holes. So if the heater is bad, and drawing too much current, it can cause enough of a voltage drop to prevent the fuel pump from running. One way to confirm this would be to disconnect the aux air regulator and tape up the end of the wire. If you don't tape it, and it hits ground, it will blow the fuel pump fuse and cause the car to quit. |
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