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Fuel pump not getting power, iwanted to bypass relay and run it to battery. Last suggestion said the fuel pump would blow up the tank. How then does the fuel pump get power?
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Have you checked the fuel pump relay to see if it is sending power to the pump ? The computer grounds the relay when the computer "sees" oil pressure or engine RPM.
Fuel pump relays are designed to trigger the power from using the power system of the vehicle to a direct battery power connection. Relays save the sensitive power used accessories by not robbing the power from them and bypassing them to use the power right from the battery source.
For example, if a relay was not used for the pump, it would lower the idle on your car everytime it turned on. Having a relay allows the pump to run and not steal valuable voltage from the cars system. These fuel relays are also a safety device in case of a car accident. The car has shock sensors that react in a car accident and shut the fuel pumps off through the relays so the occupants do not burn in an accident. If these continued to run after an accident and fuel continued to be pumped at a high pressure rate, you can imagine what the consequences might be.
Relays make the route to the battery to run the item, more direct. Bypassing the cars needed power to run the vehicle.
Don't bypass the fuel pump relay . power to the relay comes from the ignition switch on start cycle .when the engine is running the oil pressure switch takes over the circuit .so if you crash and the engine .stops so does the pump . If the fuel line brakes a bypassed pump will keep pumping spraying fuel and you could burn.
The main fuel pump in a Volvo is really well built and rarely fails(Bosch simply makes great fuel pumps). A good survival trick if you think a main fuel pump might be bad... give it a quick tap with a wrench. For best results, if possible, tap the pump when cranking the engine (while power is going to the pump). If the pump is bad, often the tap will make it come to life and it may stay running until you shut it off. This trick can get you back on the road and get you home in an emergency. If it's a bad fuel pump relay, this will NOT work as there will be no power going to your pump. If this is the case, you might try the below relay bypass "jump" trick to get power going to the pump. TESTING YOUR FUEL PUMP How to "JUMP" the fuel pump circuit at your Volvo 240 fuse panel:The fastest method to make the main fuel pump run (bypassing the Fuel Pump Relay) is by jumping two circuits at the fuse panel (left side driver's kick panel).
You can make a jumper from a wire with stripped ends or even a straightened paperclip. Jump the circuits on the right side of the fuses for best results For a 1979-84 240, jump fuse circuit #5 to #7. For a 1985-93 240, jump fuse circuit #4 to #6.
If the main fuel pump doesn't begin running when jumped (you should definitely hear it humming), you either have a faulty fuel pump or faulty wiring to the pump (bad wiring is really common under an old 240, near the pump). This test of course assumes your battery is good. If one of the fuses blows during this test, the pump circuit wiring is shorting to ground somewhere between the fuse panel and the pump.
thx
The mechanic should have never bypassed the relay, this may be where you're smelling the burning of wire or a component overheating. Whatever he bypassed the relay to, it is probably pulling to many amps, causing the wires to overheat, which could be a big fire hazard. The mechanic spliced into other components wired for a specific amperage fuse. The fuel pump needs to be wired into the relay. The fuel pump usually has it's own fuse and relay. This is where your issues are coming from. Whatever he spliced into, is drawing to many amps and causing a major draw from the battery. I would get this reversed before the car is setting on the side of the road in flames. There is some major rigging done to get your car to run, but i would not trust this at all. So I"m assuming the relay was the real problem, since it runs and he bypassed it. The relay should be under the hood fuse box. The relay is only about $10-15 depending where you by it from.
how did you jump the fuel pump relay, by bypassing the relay or by applying power to contact that closes the relay? If you bypassed the relay completely you need to b ench test the relay you can do this easily by using any 12v dc power source. If you tested the fuel pump relay by applying power to the relay and the pump run and developed pressure. I suspect a wiring or ground issue. Good luck
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