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 |
ClayPerrine |
May 17 2010, 11:15 AM
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#2
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Life's been good to me so far..... Group: Admin Posts: 15,503 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille |
No... it would not be in the fuel pump side.
Think of the fuel pump circuit this way... You have a battery in the car. From the positive side of the battery a wire runs to a fuse. From the other side of the fuse it runs to the relay. From the output of the relay a wire runs to the fuel pump. From the other side of the fuel pump a wire (in this case the vehicle chassis) runs to the negative side of the battery. Now in your mind, replace the relay with a switch, because the fuel pump relay is a switch that the computer can turn on and off. So now YOU can turn the switch on and off. We have eliminated the fuel pump, because it doesn't show voltage at the positive side when the problem is happening. So we move up to the switch (the relay). You say you can hear it clicking, so when the problem happens again, take the relay out and put in a jumper wire from pin 30 (pin 30 is the one farthest forward) to pin 87 (farthest rearward). That will bypass it and if everything else is OK, should make the pump run. If that doesn't fix it, then check the voltage at Pin 30 on the relay board. It should always have 12v on it. If it doesn't, the pump won't run. So if it doesn't, check the fuse in the relay board. The right hand contact should have 12v, and the left hand contact should connect to pin 30 on the fuel pump relay. If neither side has 12v, then you have a problem in the wiring harness between the relay board and the battery positive cable. So now disconnect the 14pin connector, and check pin 14 for 12v. If it is not there, then you have a problem in the wiring harness. I would suggest checking all of the red wires on the positive side of the battery. They get corroded from battery acid and fail at times. Another thing to check would be the white wire in the engine harness. It powers the aux air regulator on the D-jet system. If it is grounded anywhere, or the aux air regulator is bad, the fuel pump won't run. |
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