FACTORY FUEL PUMP VOLTAGE ONLY 9V, NEVER GOES HIGHER, well that's what the FSM says.
03-18-07, 03:28 AM
#1
FACTORY FUEL PUMP VOLTAGE ONLY 9V, NEVER GOES HIGHER, well that's what the FSM says.
I am in the middle of my fuel pump rewire because I have read that at night and/or when all accessories are being used (A/C, stereo,ect) that the voltage through the stock wiring to the fuel pump has dropped to as low as 10V.
OK here is the kicker... that low voltage would be BAD if the pump did in fact see 12V under load and factory operating specs. BUT after reading the wiring schematic for the Fuel Pump Control System (4B-72 FSM 86-88) and reading the Inspection Signal testing procedures, the pump will see 12 volts for exactly 50 seconds after that the fuel pump resistor relay will only supply 9volts.
I know "supposedly" the pump will see 9v at idle and slight cruising (what I read from 1300cc.coms pump rewire instructions) but after looking at the schematic it doesn't tell me that it changes from 9v to anything higher. The resistor relay is the only path that allows the pump to recieve 12v. That is only for 50 seconds at start up (maybe for cold start reasons). After the relay opens voltage is back to 9 across the board.
My roomate actually pointed this out and I argued for a while just because of the numerous incidents where the rewire DID help voltage. BUt after reading and thinking about it, he is proving a valid point.
If this in fact the case then is there something in the ECU that increases the voltage to the pump when a load is applied? AFM? Just really confused?????
OK here is the kicker... that low voltage would be BAD if the pump did in fact see 12V under load and factory operating specs. BUT after reading the wiring schematic for the Fuel Pump Control System (4B-72 FSM 86-88) and reading the Inspection Signal testing procedures, the pump will see 12 volts for exactly 50 seconds after that the fuel pump resistor relay will only supply 9volts.
I know "supposedly" the pump will see 9v at idle and slight cruising (what I read from 1300cc.coms pump rewire instructions) but after looking at the schematic it doesn't tell me that it changes from 9v to anything higher. The resistor relay is the only path that allows the pump to recieve 12v. That is only for 50 seconds at start up (maybe for cold start reasons). After the relay opens voltage is back to 9 across the board.
My roomate actually pointed this out and I argued for a while just because of the numerous incidents where the rewire DID help voltage. BUt after reading and thinking about it, he is proving a valid point.
If this in fact the case then is there something in the ECU that increases the voltage to the pump when a load is applied? AFM? Just really confused?????
03-18-07, 03:50 AM
#2
I'm a boost creep...
Join Date: Jan 2002
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You getting all worried about nothing. The ECU switches the relay off (i.e. bypasses the resistor and provides full battery voltage to the pump) at high loads based on the airflow reading from the AFM. If you put a voltmeter on the fuel pump you can watch the voltage jump up at 2-3psi boost.
03-18-07, 10:48 AM
#3
HAILERS
Join Date: May 2001
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Your stuck in a rut.
The ECU Removes a ground signal from pin 3D when the engine is under a load. Pin 3D is a green/red wire and goes to the relay in question. The relay relaxes and 12 plus vdc goes to the pump.
About the 3.5K checkout. That 3.5K represents a HOT engine, not a cold engine.
And the relay puts out 12vdc during the Start procedure and goes away as soon as the engine starts.............unless it's HOT and then wait fifty seconds for the 12vdc.
The ECU Removes a ground signal from pin 3D when the engine is under a load. Pin 3D is a green/red wire and goes to the relay in question. The relay relaxes and 12 plus vdc goes to the pump.
About the 3.5K checkout. That 3.5K represents a HOT engine, not a cold engine.
And the relay puts out 12vdc during the Start procedure and goes away as soon as the engine starts.............unless it's HOT and then wait fifty seconds for the 12vdc.
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