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Lone Star State
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Discussion Starter #1
I’m not getting power to the fuel pump. I have power to the fuel sending unit, but I understand that’s on a different circuit. Pump is good as I've tested the pump while in the tank with a separate 12v power supply.

The fuel pump relay appears to be function properly (I tried two) and the Fuel pump fuse in the trunk is good. But I don’t have any power to the fuel pump in any state; “initial key on” or “cranking.”

I even tried using a “fuel pump relay” switches that has an "on/off switch" which will energize the fuel pump when switched “on.” In the past I’ve been able to use this switch to empty my tank, so I know it works.

With key "on or off" I have continuous 12v going to “pin 87” on the relay switch which I believe is the power feed. Then w/key on I get continuous 12v going to “pin 85.” None of the pins are showing a momentary (2-3 secs) 12v with initial “key on.” With initial "key on" I believe there is supposed to be one pin that provides a 2-3 seconds 12v to momentarily energize the fuel pump for prime. I have no pins that are functioning this way.

Any ideas where to explore next?

 

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Fuel level gauge is indeed a circuit unto itself from the EMC. If your indicator reads a given fuel level, you know its OK. If you want to T/S the power loss to the pump, you can start at the 5 pin connector at the pump an sensor module assembly. Using a meter set up to read voltage, look for power at pin 5 to a good alternate ground source, or the normal ground path which uses pin 4. If the normal pump relay circuit is intact, it would give you that voltage reading for those 2 sec. at ignition turn on. If no joy, we can then back track to see where that power problem is located at (if you want to that is)..
 

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Lone Star State
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245 Posts
Discussion Starter #3
Checked my 4 pin connector at the pump.
Pins 3 & 4 are the "fuel level sensor." Getting 5v on pin 4 with "initial key on."
Pins 1 & 2 are the "fuel pump." No voltage reading on either pin with "initial key on" or "crank."

This is my connector:
 

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When mine lost fuel level signal, I eventually found a broken wire by the harness connector at the front right corner of the rear subframe.
 

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That would be the next place to check, as pointed out by "J Wikoff" Its a 14 pin plug, an the pump power makes a pass thru that connector using pin A, an the wire is gray in color.
 

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Lone Star State
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245 Posts
Discussion Starter #6
That would be the next place to check, as pointed out by "J Wikoff" Its a 14 pin plug, an the pump power makes a pass thru that connector using pin A, an the wire is gray in color.
Is that located from underneath the car, or in the engine bay? I'll start looking.
 

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Under the car, just a little forward of the right rear tire.
 

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Lone Star State
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Discussion Starter #8
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Was the G8 in storage for any duration of time?
 

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Lone Star State
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Discussion Starter #10
Was the G8 in storage for any duration of time?
No, my issued occurred all of the sudden while on the road. I don't think any varmints have been chewing on the wires.
 

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You could verify and or eliminate the entire wire run from the fuel pump relay to the pump. Remove the fuel pump relay located on the I/P fuse block. Pin 87 of that relay base has 12 volts applied to it at all times. If verifying that you have that 12 volts on the 87 socket, install a jump wire from 87 to the 30 on that base. That will force the pump to run all the time until the jump wire is removed. If no action, that wire has become open somewhere between that relay an the pump.

Also, how did you intercept that pump wire when you added that pump override circuit ? For example, if the wire was cut in that left kick panel area to add your override circuit, maybe it came apart.
 

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Lone Star State
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Discussion Starter #12
The "bypass relay" shown below does what you've explained; it jumps pins 87 & 30. I tried it and it won't activate the pump. I supposed my issue is somewhere between the relay and pump. This "on/off relay switch" was tested and the on/off switch does function as expected. Any chance I have a computer communication problem?

 

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Did you verify 12v to pin 87?
 

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Since you say in your first post, that you have 12 volts full time on pin 87, then OK. You could easily have that 12 volt reading with a multi meter, but loose that 12 volt reading when a load is applied to it. If you know for sure that when you add a load (like a light bulb) from pin 87 to ground, that it illuminates, then you must have a damaged wire downstream from that relay location. Since its been proven that a problem can happen at that 14 pin connector back at the fuel tank, you should at least verify that it "is not" the source of the problem. That would allow you to narrow down the faulty location.
 

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Lone Star State
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245 Posts
Discussion Starter #15

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Lone Star State
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Discussion Starter #16
Since you say in your first post, that you have 12 volts full time on pin 87, then OK. You could easily have that 12 volt reading with a multi meter, but loose that 12 volt reading when a load is applied to it. If you know for sure that when you add a load (like a light bulb) from pin 87 to ground, that it illuminates, then you must have a damaged wire downstream from that relay location. Since its been proven that a problem can happen at that 14 pin connector back at the fuel tank, you should at least verify that it "is not" the source of the problem. That would allow you to narrow down the faulty location.
Tackling the connector next. Also, I'm following the Boots-a-Pump wiring too just in case it's in the BAP.
 

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I see you have now thrown a curve ball into this fuel pump problem. Think you better show/talk exactly how "that" new wrinkle fits into the big picture here. Such as, if you wired it up into the oem fuel pump wiring when installing that BAP. For sure (at least for me) you need to get that explaned as well as verifying "its" condition.
 

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Lone Star State
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Discussion Starter #18
I see you have now thrown a curve ball into this fuel pump problem. Think you better show/talk exactly how "that" new wrinkle fits into the big picture here. Such as, if you wired it up into the oem fuel pump wiring when installing that BAP. For sure (at least for me) you need to get that explaned as well as verifying "its" condition.
I'm not sure how the shop wired it up, but I do know the fuel pump is not stock, it's a dual pump setup. I'm digging through the trunk next to do a further inspection of the BAP.
 

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Which brand boost-a-pump (bap)? Has it been installed long? Dual pump setup as in one runs all the time and the other comes on with boost? Definitely check the wiring associated with the bap. Have you tired contacting the shop that did the installation?
 

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Lone Star State
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245 Posts
Discussion Starter #20
Which brand boost-a-pump (bap)? Has it been installed long? Dual pump setup as in one runs all the time and the other comes on with boost? Definitely check the wiring associated with the bap. Have you tired contacting the shop that did the installation?
Well I feel like a dufus. Originally I did look several times all around my Kenne Bell BAP controller dial
and didn't see a fuse holder anywhere. But after watching a few YouTube videos about installing a BAP, I learned there is indeed a dedicated inline fuse holder for the Kenne Bell BAP. My controller dial is above the battery, but the BAP brain is located across the trunk on the passenger side rear wheel tub behind the trunk liner panel. There I found the blown 30 amp fuse and after replacing the fuse the fuel pump is working again.
I promptly went to roof of house and jump off hoping it would end my misery, but I landed safely in the snow down here in frigid Texas. I dusted off my hurt pride and went into the house and had some Kibbles 'N Bits 'cause I can't get to the grocery store.
Thanks everyone for helping me during this painful experience. The encouragement and input really kept me going to the end. I appreciated all of the help and the G8 board community very much. :)
 
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