Fuel flowing during filter change

[My99Yukon]

After my MPFI Conversion, I decided it would be good to also change the fuel filter. I have done this before with minimal mess and spillage. This time, however, I had a very different result, despite the fact that I had bled the pressure from the system during the MPFI install.

I went through the usual procedures, cracked the front fuel line nut but it seemed like extra fuel was spilling out...too much for a depressurized system. I then cracked the rear nut and after the usual spillage, it just kept flowing. The worst part is that I had bought a K&N fuel filter and I could not get the rear nut to seat and the entire time I am getting doused with fuel.

I reinstalled the old filter and took it to a quick oil change shop the next day. They had the same issue.

Some background:

12 months ago, the Yukon would not start in the middle of a trip. After a tow to the dealer (I do my best to avoid dealer's ever), my faithful fuel pump had died. They dropped the tank and replaced the fuel pump. A more expensive job than I had wanted to do on my trip. I have not replaced the fuel filter since after my dual battery install.

The quick oil change tech said it seemed like the fuel pump was still active even with the key off.

Any thoughts on:
1. electrical issues that might cause this either as the result of my dual battery work or the dealer's replacement of the fuel pump.
2. diagnosing any electrical faults/shorts that I could start with before I bring it back to the dealer who swapped the failed fuel pump?

Thanks for the help!

 

[Tonyrodz]

After my MPFI Conversion, I decided it would be good to also change the fuel filter. I have done this before with minimal mess and spillage. This time, however, I had a very different result, despite the fact that I had bled the pressure from the system during the MPFI install.

I went through the usual procedures, cracked the front fuel line nut but it seemed like extra fuel was spilling out...too much for a depressurized system. I then cracked the rear nut and after the usual spillage, it just kept flowing. The worst part is that I had bought a K&N fuel filter and I could not get the rear nut to seat and the entire time I am getting doused with fuel.

I reinstalled the old filter and took it to a quick oil change shop the next day. They had the same issue.

Some background:

12 months ago, the Yukon would not start in the middle of a trip. After a tow to the dealer (I do my best to avoid dealer's ever), my faithful fuel pump had died. They dropped the tank and replaced the fuel pump. A more expensive job than I had wanted to do on my trip. I have not replaced the fuel filter since after my dual battery install.

The quick oil change tech said it seemed like the fuel pump was still active even with the key off.

Any thoughts on:
1. electrical issues that might cause this either as the result of my dual battery work or the dealer's replacement of the fuel pump.
2. diagnosing any electrical faults/shorts that I could start with before I bring it back to the dealer who swapped the failed fuel pump?

Thanks for the help!

How's it run since the dealer did the pump? Normal? Did you try removing the fuel pump fuse to see if the flow slowed down?

 

[My99Yukon]

How's it run since the dealer did the pump? Normal? Did you try removing the fuel pump fuse to see if the flow slowed down?

The yukon was strong and ran as well as ever...maybe better but I didnt notice anything in particular. For the last 12 months, since the fuel pump install, I hae had no isisues. I did not try pulling the fuse. I was under the truck, soaked with gas and didnt think about that. I was just trying to get the compression nuts seated.

Without pulling the filter again, which I don't plan to do, it seems like some type of electrical diagnosis is the next logical step. Thoughts?

 

[Tonyrodz]

The yukon was strong and ran as well as ever...maybe better but I didnt notice anything in particular. For the last 12 months, since the fuel pump install, I hae had no isisues. I did not try pulling the fuse. I was under the truck, soaked with gas and didnt think about that. I was just trying to get the compression nuts seated.

Without pulling the filter again, which I don't plan to do, it seems like some type of electrical diagnosis is the next logical step. Thoughts?

If it's still pushing or pulling fuel while the key is off I def do think so.

 

[My99Yukon]

The problem is that without taking the filter off again, I can't determine that. Perhaps the dealer, while they are trouble shooting the fuel pump with do this to see the issue. I feel my pocket book draining as I type...unless I can run some electrical diagnostics on the fuel pump so the dealer can just fix their wiring issue or I can find another solution. Dropping a vehicle at the dealer and saying "please help" or " can you figure this out" is always painful

 

[My99Yukon]

One other troubleshooting note:

The tech pointed out that the gauges still seemed to have power and still registering data from the sensors, ie fuel, oil pressure, temp but not the battery. I don't remember a time when the gauges were all at zero with the key off.



1. Should they all register zero?
2. Any thoughts on where to begin troubleshooting the wiring if they should be zero?
3. Do you think these issues are related?

 

[Tonyrodz]

One other troubleshooting note:

The tech pointed out that the gauges still seemed to have power and still registering data from the sensors, ie fuel, oil pressure, temp but not the battery. I don't remember a time when the gauges were all at zero with the key off.

View attachment 202701

1. Should they all register zero?
2. Any thoughts on where to begin troubleshooting the wiring if they should be zero?
3. Do you think these issues are related?

That's weird. They should be at zero. I suk at electrical, so I couldn't even point you in the right direction, sorry. Hopefully someone more knowledgeable will chime in.

 

[My99Yukon]

Perhaps @SunlitComet will stop by and share his ridiculous wealth of electrical knowledge and analysis!

 

[east302]

I have two 98s, the only gauges that zero out when off are the voltage, tach and speedometer.

Maybe the relay is sticking? But I would think that if the pump is running with ignition off then your battery would be toast.

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[My99Yukon]

on my 99 yukon then we share the same three gauges that zero out so perhaps that is normal. I agree that the batteries would be toast if the pump was continually running, if even a little. I am not sure if a little current would cause the pump to turn slowly or if the pump is either on/off binary style. thanks for the schematic. I will finally have to learn how to read those as part of my trouble shooting. electrical has never been a focus but better late than never.

Thanks for the info and brain power.

 

[east302]

According to the diagram, it grounds at G404 and nothing else shares it. This is the only thing I found showing the ground, but it has to have a lead from the pump.

Disconnect the ground from the frame, put a multimeter probe on the disconnected wire and put the other probe to the frame. If you have 12V with ignition off, then the pump is constantly energized.


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[My99Yukon]

Thank you East302. Great feedback. I will check that out as soon as I can get my hands on a multimeter...hopefully tomorrow. Input like this from members like you is what makes this forum so special. It is also why I contribute what I know, have learned the hard way and don't know.

Much appreciated.

 

[HiHoeSilver]

I'm curious about this simply from an electrical standpoint. I so wish I had a shot of my OBS dash, but I think I remember exactly what you're describing. I remember thinking it was weird that my NBS all zeroed out with key on, engine off. Going by my not so great memory, I'd say your experience is normal.