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Testing fuel pump relay
My car, a 1983 380SL, has all the symptoms of a bad fuel pump relay. The relay connector has 12v at #8 terminal, 12v at #9 with the key on, 12v between terminals 8 & 11 w/key on, 31 degrees of dwell (while cranking) at terminal #10, and 12v between terminals 11 & 12 while cranking. Bridging terminals 7 & 8 makes the pump run. My question: is it ok and feasible to start the car with the relay removed and terminals 7 & 8 bridged? Looking at the schematic, it seems it would be, but I'll rely on other's experience. I would like to know that the car would run with the pump energized, and at the same time start another thread to help members diagnose the relay (yes, yet another thread ). I've already ordered a relay, by the way.
Thanks in advance, whoever ventures....
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1983 380SL 1995 C280 1995 S500 coupe 1990 Mazda Miata 2004 Suzuki Hayabusa |
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A little more info...the car is a bit of a garage queen during snowy winters here in Missouri, and I generally don't take her out until a good rain washes the salt off of the roads, so she's been sitting for about 4 months. This was the second time out, a long drive of about 25 miles, and the car ran perfectly. I parked, and then returned about 20 minutes later to a no start condition. A little sniffing around revealed no fuel, so the diagnosing began. I add this to show that a car can run fine and with just another key cycle can lose the relay, in case it ever helps anybody diagnose. Happy Easter, everyone .
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1983 380SL 1995 C280 1995 S500 coupe 1990 Mazda Miata 2004 Suzuki Hayabusa |
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I consider the fuel pump relay a "safety" feature. That is, the relay is there to turn off the fuel under certain unsafe conditions. Primarily, if the engine isn't running for some abnormal reason...like if you've been in a crash or rollover. You don't want fuel under presure spraying around. So, in your situation, I wouldn't hesitate to jump the relay to start the car and get it home. This relay carriers a lot of current and it's not unusual for the points to burn away over time. I reccomend everyone keep a spare fuel pump relay in their emergency road kits in the car.
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Resistance is Futile. |
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Thank you for the reply. As anal as I am about the car, I already had her towed home yesterday. The relay should be in tomorrow so all should be well. That's good advice on carrying an extra relay, if the problem is so common. I might jump the terminals tonight and start the engine just to make sure all else is well. Thanks again
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1983 380SL 1995 C280 1995 S500 coupe 1990 Mazda Miata 2004 Suzuki Hayabusa |
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Just to close out this thread, I put the new relay in last night and she started right up and purred. Hopefully someday this will help someone
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1983 380SL 1995 C280 1995 S500 coupe 1990 Mazda Miata 2004 Suzuki Hayabusa |
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