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94 Buick Century Fuel Pump Relay

edited February 2012 in Repair and Maintenance
1994 Buick Century 3.1

Fuel pump relay is not powering the fuel pump. I was able at one point to jump the orange wire to the gray wire but it will not even do that now. I know the fuel pump works because I can jump from the battery to the gray wire and it will turn on.

I used a multimeter and tested the volts from the orange wire on the relay to the neg post on the battery and it is only reading about 1.3 volts. Is this normal?

Checked the fuel pump 15a fuse and it is ok.

I am getting spark. Could it be the crank sensor? How can I test that? (It is above the start I believe)

Could it be the ignition control module? How to test? Location?

What else can I test with the multimeter and post back with the results to help further diagnose?
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Comments

  • Have you tried replacing the fuel pump relay?
  • Yes I tried switching it with another relay but no luck.
  • I don't know if any advice I offer will be any good at all because I took a look at a Chiltons schematic. Anything from Chiltons is always suspect as to accuracy. However, proceeding on.... :-)

    The voltage reading at the orange wire should be battery voltage; 12 volts. Test this with the relay out of the socket.
    The gray wire is to the pump of course.
    If there is a dark green/white wire at the relay socket there should be voltage there for 2 seconds whenever the key is turned to the RUN position without energizing the starter motor. Without cranking the engine over that voltage will disappear after 2 seconds but if the engine is then cranked over the voltage will remain and keep the relay energized.
    If there is a black/white wire that should be a ground for the trigger part of the fuel pump relay.

    In other words, the dark green/white and black/white complete the circuit for the trigger part of the relay.
    If power is not provided through that dark green/white wire in the situation as described above this could point to a problem with the electronic ignition (no pulse to the ECM) or a fault with the ECM.
    An ignition pulse must be present to keep the relay energized and yes, a crank sensor could also be the cause.
    Automotive fuel systems are set up like this to conform to Federal laws which require the fuel pump to shut off on a non-runnng engine in certain situations; say an accident.

    Hope some of that helps anyway.
  • The security system (VATS, Passlock) should be ruled out first. Is the security light on while cranking? The ECM will inhibit the fuel pump and injector signals if not getting ok from security module.
  • I checked the ICM and PCM fuses inside the car and they are fine.

    Checked voltage at orange wire on relay and it is at 1.18 to 1.2 volts.

    I checked green/white wire when key was turned on to check for 2 seconds of power, and it only went up to about 3v max before it went down.

    There is no voltage to the green/white wire while turning the car over.

    There is no security light on while cranking the car.
  • edited February 2012
    When I was having stalling problems with my Riviera, one thing I did was freshen up all of the ground and positive connections to make sure they were good. Never did solve my problem but if you don't have battery voltage at the relay and do have 12+ volts on the battery, that says you are losing a connection someplace in the harness. Normally, you would just follow the schematic from point to point from the battery to the relay or visa versa to see where your voltage drops off. Assuming you've got your meter on the correct scale anyway.
  • I assume the orange wire that OK4450 refered to in his post was the power side of the relay connection. If that is correct then you have found the path that the trouble is on. There should be 12 volts there and so you need to find out where the other end ties to power at. You say the fuse is ok so there is either a bad wire connection after the fuse or something else between the two points has a problem.
  • I'm in agreement with Cougar about checking that orange wire circuit although there is some concern about the lack of voltage at the dark green/white lead while cranking the engine over.
    Don't worry about the 3 volts at that dark green/white lead as that could be normal. I do not know what the voltage is supposed to be on this model but odds are the 3 is correct as that is only the trigger circuit. A 12 volt automobile relay can be triggered with a 1.5 volt flashlight battery so there's no sense in overkill.

    You might consider the possibility of a poor connection at the junction terminal. All elec. power goes through that terminal except for the starter motor windings and odd things can and do happen when that connection corrodes or develops a scale. Follow the heavy lead from the battery positive terminal to a small cover located near the battery. Unscrew the retaining nut underneath, remove the wires, and clean all of the ends. Maybe you will get lucky and this simple thing is the cause of the problem.
    The manual does show that orange lead is powered directly from the battery, not through the ignition switch, and you should be showing about 12 volts at all times.

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