Fuel pump

Tiny
CINDY MARTIN GRIFFIN
  • MEMBER
  • 2003 MITSUBISHI GALANT
  • 130,000 MILES
I am not getting power to the fuel pump. We have replaced the pump and checked the relays.
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Monday, April 10th, 2017 AT 3:36 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
When are you checking? Have you checked for spark? Please list which engine you have.
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Monday, April 10th, 2017 AT 3:54 PM
Tiny
CINDY MARTIN GRIFFIN
  • MEMBER
2.4 engine. We are getting power leaving the relays.
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Monday, April 10th, 2017 AT 4:11 PM
Tiny
CINDY MARTIN GRIFFIN
  • MEMBER
Is there a kill switch?
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Monday, April 10th, 2017 AT 4:19 PM
Tiny
CARADIODOC
  • EXPERT
You need to be specific. Are you testing at the fuel pump relay? The automatic shutdown, (ASD) relay? If you are testing for voltage at the connector for the fuel pump, you had better not have twelve volts there unless the engine is rotating, (cranking or running). The exception is you should see twelve volts there for one second when you turn on the ignition switch. If you are able to hear the hum of the pump for that one second when you turn on the ignition switch, the pump circuit is working.

About ninety five percent of crank/no-starts that involve a dead fuel pump also include no spark. That is why I asked if you have spark. Too many people get hung up on the first thing they find missing, and overlook the rest of the symptoms. You could have a problem in just the fuel pump circuit, but those account for perhaps one or two percent of no-starts.

There is no kill switch. "Inertia" switches are a troublesome Ford thing. Some other manufacturers might use them, but I am not aware of them. Other than that initial one-second burst, the Engine Computer turns on the ASD relay when it sees signal pulses coming from the crankshaft position sensor and camshaft position sensor. The ASD relay sends current to the ignition coil(s), injectors, oxygen sensor heaters, and fuel pump, or a separate fuel pump relay. This way, if a fuel line is ruptured in a crash, there will be no fuel pressure in that line. With no pressure, the engine cannot run. There will be no signal pulses from the two sensors when the engine is stalled. The computer turns the ASD relay off when there is no sensor pulses. That stops the fuel pump from dumping raw fuel onto the ground where it would be a fire hazard.
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Monday, April 10th, 2017 AT 4:20 PM
Tiny
CINDY MARTIN GRIFFIN
  • MEMBER
What and where is the ASD located?
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Monday, April 10th, 2017 AT 4:24 PM
Tiny
CARADIODOC
  • EXPERT
Sorry for the confusion. Mitsubishi calls it the "multi-point fuel injection", (MFI) relay. The fastest way to test this circuit is to use a test light, and back-probe the red wire at any fuel injector, either of the two sensors, or at the mass air flow sensor. Digital voltmeters can work, but they respond too slowly to see the initial twelve volt pulse.

You should see the test light turn on for that first one second when you turn on the ignition switch. What is important is does it turn on again steady while you are cranking the engine.

The rest of the circuit is a little different than what I am used to seeing, so I am going to have to back up and study it. The ignition coils have their twelve volts switched on with the ignition switch, not any relay, so we cannot use them for any test procedure. There are two fuel pump relays. Fuel pump relay number one turns on any time the ignition switch is on. Fuel pump relay number two is the one that is turned on by the Engine Computer. They are in series, so both must turn on to have twelve volts to the pump. That will be on the white/black wire at the pump.
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Monday, April 10th, 2017 AT 4:57 PM

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