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No power to fuel pumps until ignition is in the start position 200 1977

uid 27's pic
posted by  Art Benstein on  Sun Mar 15 15:43 CST 2009
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last visit: Fri Oct 17 20:10 CST 2014
[RELATED]

The 77 has a fuel pump relay. It is a pretty ordinary thing, and does not know about ignition pulses. No car should sustain the fuel pumps with key on engine off; that would present a fire hazard in a crash.

You can see here, there's a switch on the airflow meter controlling the fuel pump relay in the 76 which was again implemented in 77. In 78 volvo did away with that and used a special electronic relay to sense pulsing at the coil primary, a good indicator the motor is turning.





I was wrong about vacuum being needed during cranking. The fuel pump relay is held closed by the starter solenoid voltage, and once running, vacuum is needed to keep it held closed.

--
Art Benstein near Baltimore

"Everybody's got to believe in something. I believe I'll have another beer." (W. C. Fields)






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