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Old 07-15-2011, 10:43 AM   #1
BlksnshN
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Fuel Pump

Hi Everyone, I'm a new member here with a bit of a fuel pump dilema.

I'm working on my cousins 2006 G6 3.5L V6.

Car would crank but not start, couldn't hear the pump, Checked and no power at the pump. Replaced blown fuse and then had 12v on the Gray wire to the pump. Yet the pump would still not kick on.

Put in a used (not my idea) pump and still the pump does not turn on. I can jump both pumps directly to the battery with a couple of jumper wires and both of them turn on.

I still have 12v back to the pump along with a good ground. There is no visual damage to the plug or harness.

This one is really baffling me.
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Old 07-15-2011, 11:01 AM   #2
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the only thing that I would think of off hand is a possible issue with the wire from the fuses to the pump...since you've tested and know the pump works if you bypass and jump straight from the battery. but, I'm no expert
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Old 07-15-2011, 11:14 AM   #3
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Quote:
Originally Posted by BlksnshN View Post
Hi Everyone, I'm a new member here with a bit of a fuel pump dilema.

I'm working on my cousins 2006 G6 3.5L V6.

Car would crank but not start, couldn't hear the pump, Checked and no power at the pump. Replaced blown fuse and then had 12v on the Gray wire to the pump. Yet the pump would still not kick on.

Put in a used (not my idea) pump and still the pump does not turn on. I can jump both pumps directly to the battery with a couple of jumper wires and both of them turn on.

I still have 12v back to the pump along with a good ground. There is no visual damage to the plug or harness.

This one is really baffling me.
So the pump is not activated at all at KeyOn? Not even for a second or two? Have you swapped the pump relay out?
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Old 07-15-2011, 11:17 AM   #4
BlksnshN
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Nope, The voltage pops up with key on but the pump will not run. I've tried in the tank and out of the tank with no results.

Only way I've been able to get it to run is to take the pump and jump it to the battery with short jumper wires.
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Old 07-15-2011, 11:41 AM   #5
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Originally Posted by BlksnshN View Post
Nope, The voltage pops up with key on but the pump will not run. I've tried in the tank and out of the tank with no results.

Only way I've been able to get it to run is to take the pump and jump it to the battery with short jumper wires.
So you have a steady B+ out of the relay on the grey wire into the pump & the black ground checks out yet two pumps won't go hot?

Last edited by greenman; 07-15-2011 at 01:51 PM.
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Old 07-15-2011, 11:47 AM   #6
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So you have a steady B+ out of the relay on the grey wire into the pump & the black ground checks out yet two pumps won't go hot? I don't see how that's possible.
I don't either, That's why I'm quite confused.

Only thing that is bothering me is that the second pump is used from a less than reputable salvage yard. They had already purchased the pump and then asked me to install it.
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Old 07-15-2011, 11:54 AM   #7
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Originally Posted by BlksnshN View Post
I don't either, That's why I'm quite confused.

Only thing that is bothering me is that the second pump is used from a less than reputable salvage yard. They had already purchased the pump and then asked me to install it.
But you tested both pumps with B+ directly & they activate so I think you covered that. Since pump fuse 25 was blown at the onset, I have to suspect a harness issue. Yet you say that has checked out too. Is there fuel in the tank? Maybe the pump has an automatic cutoff (unsure). You have checked the ground for high resistance? You are using a multimeter & not a continuity checker.

Last edited by greenman; 07-15-2011 at 12:11 PM.
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Old 07-15-2011, 11:59 AM   #8
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12 volts doesn't mean much, will it light a high amp bulb. If not poor connection, no amperage.
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Old 07-15-2011, 12:00 PM   #9
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But you tested both pumps with B+ directly & they activate so I think you covered that.
Yeah, I just can't figure out what the difference is between me feeding it 12v directly off the battery and the PCM sending it the 12v through the harness.

I am using thick gauge house wire to jump from the battery, maybe that is allowing for more amperage to flow to the pumps? IDK, I'm reaching at straws now..
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Old 07-15-2011, 12:37 PM   #10
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slls has a very good point. Check the incoming power circuit for high resistance as well. And swap the relay out.
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Old 07-15-2011, 01:50 PM   #11
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12 volts doesn't mean much, will it light a high amp bulb. If not poor connection, no amperage.
I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.
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Old 07-15-2011, 02:27 PM   #12
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I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.
Continuity is not very helpful. You can have good continuity & very high resistance simultaneously.
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Old 07-15-2011, 02:33 PM   #13
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Continuity is not very helpful. You can have good continuity & very high resistance simultaneously.
I was checking resistance as well. It checked out at .03 Ohms.
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Old 07-17-2011, 11:59 AM   #14
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I have not worked on these circuits in a long time but GM used to switch all their computer controlled circuits except fuel pump by supplying constant ignition voltage and switching the ground side. The fuel pump at that time (early 90's) was switched 12v for safety. If you are able to light the lamp on the gray wire anytime the ignition is on then they switched to controlling the fuel pump by switching ground on and off. The up shot is a bad connection at the PCM or heaven forbid the blown fuse event took out the power transistor in the PCM, the power transistor is supposed to be protected but may not always work. YMMV as I have not looked at a wiring diagram for this vintage car yet, I just finally moved out of the 1990's by buying this 2009 G6.
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Old 07-17-2011, 12:08 PM   #15
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In the G6 there is a constant ground, when the ignition is turned on the PCM send power to the relay which then allows power to the pump for 2 - 3 seconds to prime it and then shuts off power if the computer does not detect ignition. So it's still about the same as the 90's.

Both of the vehicles I own are from the 90's too, much easier to work on. lol.
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