Fuel tank replacement

[midnightrumbler]

I will be replacing the fuel tank in my 6.5 diesel and was curious after the removal and install, will I need to purge the lines? If a purge is in need, I am guessing now would be a good time to replace the fuel filter as well as I have no idea when it was last done since I just bought the truck.

[GMC Hauler]

I will be replacing the fuel tank in my 6.5 diesel and was curious after the removal and install, will I need to purge the lines? If a purge is in need, I am guessing now would be a good time to replace the fuel filter as well as I have no idea when it was last done since I just bought the truck.

just use the lift pump to purge the air through the top filter vent before you start. I never had a problem the two time I dropped my gas tank.

[midnightrumbler]

Could you please explain how I would do this? I have never owned a diesel before so this is all new to me. Thanks in advance. I know that the lift pump is under the drivers side on the frame rail I just do not know how to purge as of yet.

What sort of symptoms could a leaking fuel tank cause in a truck besides loss of fuel if anything?

[GMC Hauler]

open the filter bleed valve on top of the filter, in the valley of the engine, all the way up against the firewall. put a length of hose on it to a suitable container.

There is a red wire not connected to anything in the wiring harness, under the hood, drivers side, closest to the windshield. connect that to 12 volts. watch any air come out of the bleed valve you opened. When the line is clear of air, reverse this to restore the engine to ready condition.

LEaking fuel tank, i do not think it can cause much more than a loss of fuel.

[midnightrumbler]

I opened up the bleed valve ontop of the filter and put twelve volts to the only red wire I could find and nothing happened. I am hoping I have the right red wire as the only one I can see on the drivers side near the firewall closest to the window has a white cap on the end and comes out from the fuse box.

Is this the right wire?

[GMC Hauler]

Mine comes out of the harness, and is loose (not connected to anything).

Is the key off?

If this is the correct wire, and your key is off, you may have a lift pump problem. This wire provides direct power to the lift pump.

[midnightrumbler]

The key is off when I am performing this option and I can feel the lift pump operating when the truck is running. The lift pump feels like it is pulsating which I am not sure if this is normal or if I should feel a continuos flow.

The red wire has a 3" cap on it as if something should be connected into it which again leads into a fuse box under the hood. It appears as if this is the only loose red wire under the hood. This is a 3500 Dually so I am not sure if location of the wire would be different.

Is there another way to bleed the valve?

[GMC Hauler]

Try capping the lines with something when you disconnect them. Yu should not introduce enough air to worry about.

You should get something out of the valve in the top with the lift pump running. This may point to another problem. . .

[GMC Hauler]

So when you hook up that red wire to 12 volts, do you hear the lift pump run?

[midnightrumbler]

GMC HAULER,

I just read another forum that states the following

ON and OBD one truck(94-95) the lift pump prime connector is in a different location. look at your DLC connector for checking DTC codes. the following photo shows the pinout and where to apply 12 volts to run the lift pump for priming the fuel sytem.

Unfortunately the photo is not working and I have no idea where to apply 12 volts.

My truck is a 1995 Silverado 3500 Dually. Your truck may be an OBDII which is why you can locate the red connector under your hood

[GMC Hauler]

GMC HAULER,

I just read another forum that states the following

ON and OBD one truck(94-95) the lift pump prime connector is in a different location. look at your DLC connector for checking DTC codes. the following photo shows the pinout and where to apply 12 volts to run the lift pump for priming the fuel sytem.

Unfortunately the photo is not working and I have no idea where to apply 12 volts.

My truck is a 1995 Silverado 3500 Dually. Your truck may be an OBDII which is why you can locate the red connector under your hood

Ok. That could be the difference.

When you turn the key to on, before you turn it to start, do you hear the lift pump run?

[midnightrumbler]

When I turn the Key to on, I do not hear the Lift Pump kick in, it only comes on when the truck is at idle. Again, It seems to pulsate and not put out a continues flow. The truck hesitates on accelaeration and dies out or bogs down while driving.

Again, The OBDII is different from the OBDI in this aspect

I also found that the Lift Pump will not prime the Injection Pump during Wait-To-Start (WTS, or glow plug cycle) on '94-'95 OBDI vehicles. The Lift Pump will only run in Start (when cranking the engine.) GM changed this on '96-'02 OBDII's - the lift pump primes both during WTS and Start on the latter year engines.

I am trying to find more info on the location of the 12volt source for the lift pump for OBDI's

Thank you for the help thus for GMC Hauler, You have been a great help.....

[JohnC]

The red wire in the ALDL connector, upper leftmost, IIRC.

[6.5TDTahoe]

will be a worthyi tem to have in the truck all the time It covers 35 issues the truck can encounter! Worth the money!!