Fuel Pump Relay Prime
JIMS59VETTE
12-07-2007, 08:34 AM
I have a 96' 5.7L and am trouble-shooting a no start situation. I see +12v on the fuel pump relay n.o. contacts which should be there all the time. I don't see +12 coming from the n.c. contact side. Where does this prime voltage originate and when should it be present? Also, should the +12v for the relay coil be present from the instant the ignition key is turned to the on position? I'd appreciate any assistance......Jim:runaround:
envoyxuv
12-08-2007, 05:20 AM
The fuel pump relay should have 5 terminals, marked on the relay:
Terminal 85 is the pcm (powertrain control module) control. This energizes the relay coil-- you should have battery voltage on this terminal when the engine is cranking/running, and momentarily for about 5 seconds when the key is turned on but the engine isn't cranked over.
Terminal 86 is ground for the relay coil.
Terminal 87 is fused power from the under hood fuse block, ECM B fuse, 20 amp.
Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal. By applying battery positive (+) voltage to the jumper wire with the relay plugged into the fuseblock, you can verify whether the fuel pump runs or not. The terminal is a red wire, usually with a female spade connector on the end of it near the fusible links under the hood.
Terminal 30 is the fuel pump supply voltage circuit.
By jumping terminals 87 and 30 together on the fuse block, you can also verify whether or not the fuel pump operates if you can't find the prime wire. Also note; the ECM B fuse is hot at all times.
Terminal 85 is the pcm (powertrain control module) control. This energizes the relay coil-- you should have battery voltage on this terminal when the engine is cranking/running, and momentarily for about 5 seconds when the key is turned on but the engine isn't cranked over.
Terminal 86 is ground for the relay coil.
Terminal 87 is fused power from the under hood fuse block, ECM B fuse, 20 amp.
Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal. By applying battery positive (+) voltage to the jumper wire with the relay plugged into the fuseblock, you can verify whether the fuel pump runs or not. The terminal is a red wire, usually with a female spade connector on the end of it near the fusible links under the hood.
Terminal 30 is the fuel pump supply voltage circuit.
By jumping terminals 87 and 30 together on the fuse block, you can also verify whether or not the fuel pump operates if you can't find the prime wire. Also note; the ECM B fuse is hot at all times.
JIMS59VETTE
12-08-2007, 10:13 AM
Who was that masked man? You couldn't have answered my question any more precise. I did see the red wire with the spade plug. Your knowledge and assistance are sincerely appreciated.
JIMS59VETTE
12-10-2007, 04:08 PM
update; just got finished metering out the fuel pump wiring . It was perfect to the connector. Looking towards the pump I read some where in the three meg ohm range, which is proof enough for me that I have a bad fuel pump. I'm getting prepared to create an access panel as in my previous posting and ordering an AC-Delco fuel pump ( which seems to be the pump of choice by those who have changed many a fuel pump) right after the Holidays. Wish me luck.
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