2003 4 door 4x4 Blazer
#13
Last edited by Zgiovanni; 01-13-2022 at 02:57 PM.
#14
12.0 V at the battery is only 45% charged so that needs to be straightened out or you are going to have a bunch of problems. A fully charged battery is 12.6v.
Where are you testing voltage? At the fuel pump connector, fuse box priming tab, …? Where are you putting the leads? Is this during the initial 2 second prime at key on or after that? Is the fuel pump connected during this test or is the connector off of the pump?
George
Where are you testing voltage? At the fuel pump connector, fuse box priming tab, …? Where are you putting the leads? Is this during the initial 2 second prime at key on or after that? Is the fuel pump connected during this test or is the connector off of the pump?
George
#15
12.0 V at the battery is only 45% charged so that needs to be straightened out or you are going to have a bunch of problems. A fully charged battery is 12.6v.
Where are you testing voltage? At the fuel pump connector, fuse box priming tab, …? Where are you putting the leads? Is this during the initial 2 second prime at key on or after that? Is the fuel pump connected during this test or is the connector off of the pump?
George
Where are you testing voltage? At the fuel pump connector, fuse box priming tab, …? Where are you putting the leads? Is this during the initial 2 second prime at key on or after that? Is the fuel pump connected during this test or is the connector off of the pump?
George
#16
If you have a priming tab next to the relay see what the voltage is at key on for the two second priming cycle and tell me if the fuel pump is connected or not. If not, pull the relay and make sure you have power from the fuse to the relay contact 87 or 30. It’s hot at all times. Positive lead in the relay socket and Negative lead to battery ground. If yes then check the ground side of the relay coil, either 85 or 86 and then check the signal voltage to which ever relay coil contact was not ground between 85 and 86.
George
George
#17
If you have a priming tab next to the relay see what the voltage is at key on for the two second priming cycle and tell me if the fuel pump is connected or not. If not, pull the relay and make sure you have power from the fuse to the relay contact 87 or 30. It’s hot at all times. Positive lead in the relay socket and Negative lead to battery ground. If yes then check the ground side of the relay coil, either 85 or 86 and then check the signal voltage to which ever relay coil contact was not ground between 85 and 86.
George
George
Last edited by Zgiovanni; 01-13-2022 at 04:58 PM.
#18
Couple things.
Twice now you have tried to measure resistance on a powered circuit and that wont work. '
Ultimately what matters is that the net voltage to the fuel pump, measured right at the pump is adequate. If the battery voltage is low then of course the positive voltage at the pump connector will be low. If there is excess resistance in the circuit anywhere between the battery and the positive connector then you will have lower voltage at the pump. That same power flows through the fuel pump and then through the ground wire to the frame and then back to the battery negative terminal. Any excess resistance in the ground circuit has the effect of lifting the pump ground from the same voltage drop effect that can happen on the positive side. So lets say corrosion between the relay and pump causes the positive side to drop 4 volts and the ground circuit to lift 3 volts. The pump would only see 5 volts and either not work or burn up. One way to check these circuits is to disconnect them from power and measure resistance between both ends. That can tell you something but may not give the whole picture. The true test is measuring that net voltage under full pump load. Positive and negative meter leads right at the pump connector. If net voltage is low then we find out if its the positive or ground side. You back probe the connector or strip a little insulation off both wires and reseal then when you are done.
George
Twice now you have tried to measure resistance on a powered circuit and that wont work. '
Ultimately what matters is that the net voltage to the fuel pump, measured right at the pump is adequate. If the battery voltage is low then of course the positive voltage at the pump connector will be low. If there is excess resistance in the circuit anywhere between the battery and the positive connector then you will have lower voltage at the pump. That same power flows through the fuel pump and then through the ground wire to the frame and then back to the battery negative terminal. Any excess resistance in the ground circuit has the effect of lifting the pump ground from the same voltage drop effect that can happen on the positive side. So lets say corrosion between the relay and pump causes the positive side to drop 4 volts and the ground circuit to lift 3 volts. The pump would only see 5 volts and either not work or burn up. One way to check these circuits is to disconnect them from power and measure resistance between both ends. That can tell you something but may not give the whole picture. The true test is measuring that net voltage under full pump load. Positive and negative meter leads right at the pump connector. If net voltage is low then we find out if its the positive or ground side. You back probe the connector or strip a little insulation off both wires and reseal then when you are done.
George
#19
Couple things.
Twice now you have tried to measure resistance on a powered circuit and that wont work. '
Ultimately what matters is that the net voltage to the fuel pump, measured right at the pump is adequate. If the battery voltage is low then of course the positive voltage at the pump connector will be low. If there is excess resistance in the circuit anywhere between the battery and the positive connector then you will have lower voltage at the pump. That same power flows through the fuel pump and then through the ground wire to the frame and then back to the battery negative terminal. Any excess resistance in the ground circuit has the effect of lifting the pump ground from the same voltage drop effect that can happen on the positive side. So lets say corrosion between the relay and pump causes the positive side to drop 4 volts and the ground circuit to lift 3 volts. The pump would only see 5 volts and either not work or burn up. One way to check these circuits is to disconnect them from power and measure resistance between both ends. That can tell you something but may not give the whole picture. The true test is measuring that net voltage under full pump load. Positive and negative meter leads right at the pump connector. If net voltage is low then we find out if its the positive or ground side. You back probe the connector or strip a little insulation off both wires and reseal then when you are done.
George
Twice now you have tried to measure resistance on a powered circuit and that wont work. '
Ultimately what matters is that the net voltage to the fuel pump, measured right at the pump is adequate. If the battery voltage is low then of course the positive voltage at the pump connector will be low. If there is excess resistance in the circuit anywhere between the battery and the positive connector then you will have lower voltage at the pump. That same power flows through the fuel pump and then through the ground wire to the frame and then back to the battery negative terminal. Any excess resistance in the ground circuit has the effect of lifting the pump ground from the same voltage drop effect that can happen on the positive side. So lets say corrosion between the relay and pump causes the positive side to drop 4 volts and the ground circuit to lift 3 volts. The pump would only see 5 volts and either not work or burn up. One way to check these circuits is to disconnect them from power and measure resistance between both ends. That can tell you something but may not give the whole picture. The true test is measuring that net voltage under full pump load. Positive and negative meter leads right at the pump connector. If net voltage is low then we find out if its the positive or ground side. You back probe the connector or strip a little insulation off both wires and reseal then when you are done.
George
positive test was performed by back probing grey wire with positive lead and large black wire with black lead. Cycled key and observed during priming.
Results:11.99vdc during 2 second period.
ground test was performed with key out of ignition.
Back probed large black wire with positive lead and held black lead to clean frame piece.
Results:5.6ohms
So even though its a brand new fuel pump and the reading are within limits its still not priming. Likely new pump is bad?