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molurch, GMC Mechanic
Category: GM
Satisfied Customers: 20901
Experience:  GM, Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics.
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where is the fuel pump relay on 91 gmc sonoma

Resolved Question:

where is the fuel pump relay on 91 gmc sonoma
Submitted: 5 years ago.
Category: GM
Expert:  molurch replied 5 years ago.



should be located Driver side Firewall under hood





When the key is first turned ON, without the engine running, the ECM will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure to normal operating pressure. If the engine is not started within two seconds, the ECM will shut the fuel pump OFF and wait until ignition reference pulses are present. As soon as the engine is cranked, the ECM turns the relay ON, which powers the fuel pump. The ECM continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi).



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