Hi all, my first post here and thanks in advance for any advice that can be given.
Recently purchased a 1989 Volvo 740. I replaced the clutch, the timing belt, engine mounts, and spark plugs. The car always ran a little rough spitting and sputtering then after a little while it would run great. Every time I disconnected my battery to do work on the car, the car seemed to take longer to run well. I kept getting a reoccurring 221 code. Meaning too rich or too lean. So I replaced my maf sensor, my fuel pressure regulator. Still kept running like crap. I noticed that my rear fuel pump randomly stopped working so I pulled the connector and found there to be only six volts at the rear fuel pump?
Has anyone experienced this? Power comes on with the ignition in the run position. Any idea what it would be? Has anyone experienced this before?
1989 Volvo 740 gremlins
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jimmy57
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6V when the engine is running?
Go to the connector in engine bay for the oxygen sensor. It is in front of passenger, usually right by the silver A/C accumulator. There will be a green wire with single flat blade and a two wire connector. On the sensor side it is two white wires. On the wiring harness side there is a black and a green. The green wire is on the circuit with the fuel pumps. Use a bent paper clip or other piece of solid wire and jump 12v from batt + to that green wire. It is OK for oxygen sensor to be plugged in. Now check to see if fuel pump feed is still only 6V. It should feed fuel pumps 12V and make the engine run as it should. Don't get distracted by the test. The oxygen sensor has a heater and it should only be powered if engine runs. Since pumps run with engine running it was easy for the fuel pump relay to supply the fuses for the under car and in-tank pump fuses (5 and 11?? behind ashtray) and also splice the oxygen sensor electric heater feed to the same relay.
If the power supply jumped direct to the pumps fixes the issue then the circuit for pumps needs to be checked. Determine which fuses are for main and in-tank pump. I remember it being fuses 5 and 11 but I may have that wrong. Find the fuses and with engine running and jumper removed under hood from before, check the voltage between ground and the contacts you can touch on the fuses. Check voltage at both contacts and it should be 12+ with engine running.
Go to the connector in engine bay for the oxygen sensor. It is in front of passenger, usually right by the silver A/C accumulator. There will be a green wire with single flat blade and a two wire connector. On the sensor side it is two white wires. On the wiring harness side there is a black and a green. The green wire is on the circuit with the fuel pumps. Use a bent paper clip or other piece of solid wire and jump 12v from batt + to that green wire. It is OK for oxygen sensor to be plugged in. Now check to see if fuel pump feed is still only 6V. It should feed fuel pumps 12V and make the engine run as it should. Don't get distracted by the test. The oxygen sensor has a heater and it should only be powered if engine runs. Since pumps run with engine running it was easy for the fuel pump relay to supply the fuses for the under car and in-tank pump fuses (5 and 11?? behind ashtray) and also splice the oxygen sensor electric heater feed to the same relay.
If the power supply jumped direct to the pumps fixes the issue then the circuit for pumps needs to be checked. Determine which fuses are for main and in-tank pump. I remember it being fuses 5 and 11 but I may have that wrong. Find the fuses and with engine running and jumper removed under hood from before, check the voltage between ground and the contacts you can touch on the fuses. Check voltage at both contacts and it should be 12+ with engine running.
Okay so I double checked my measurements.
I am getting 6 volts for the sending unit and 0 volts for my pump, with my key in the run position. When I have someone turn the ignition to the run position I am not seeing the priming voltage I expected to see. The in tank pump would usually run for a second or two then shut off?..
With the car running I am seeing varying voltages for the sending unit and 14 volts for the pump.
With the connector plugged back together the fuel gauge has stopped working, and the pump still doesn work.
I am getting 6 volts for the sending unit and 0 volts for my pump, with my key in the run position. When I have someone turn the ignition to the run position I am not seeing the priming voltage I expected to see. The in tank pump would usually run for a second or two then shut off?..
With the car running I am seeing varying voltages for the sending unit and 14 volts for the pump.
With the connector plugged back together the fuel gauge has stopped working, and the pump still doesn work.
Update!!
I am getting 14 volts when the car is running to the fuel pump connector. Just to be safe I took jumper leads and applied direct power to the in tank fuel pump and it didn't turn on. So I'm assuming the pump is dead... What I don't understand is what controls the priming circuit for the fuel pump.
When the key is in the run position the in tank fuel pump would usually run for 2-3 seconds. Now it does not.
Does anyone know what controls the in tank fuel pump priming?!!
I am getting 14 volts when the car is running to the fuel pump connector. Just to be safe I took jumper leads and applied direct power to the in tank fuel pump and it didn't turn on. So I'm assuming the pump is dead... What I don't understand is what controls the priming circuit for the fuel pump.
When the key is in the run position the in tank fuel pump would usually run for 2-3 seconds. Now it does not.
Does anyone know what controls the in tank fuel pump priming?!!
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