99 Yukon 5.7l V8 Fuel Filter Replacement

[McDermut]

I'm looking to replace my fuel filter, which is likely long overdue. I wanted to know if there's a specific process I should follow to depressurize the fuel line and avoid air in the line as much as possible. I've heard having the engine running and pulling the fuse is one way, but I want to make sure there's not a better or less potentially damaging way.

Any advice is greatly appreciated!

 

[96-2D-Hoe]

There's a schrader fitting under a cap on the fuel line that you can press to remove any pressure. Use a rag as gas will come out when you press it. It's on a hard line to the rear right/driver side of the throttle body. TBH it won't make much difference as plenty of gas is going to leak out anyway.

Otherwise run the gas down as much as possible, have a fire extinguisher on hand if you can, and put plenty of penetrating oil on the fittings long before you start.

 

[OR VietVet]

What @96-2D-Hoe said plus make sure to use the line/flare wrenches when you break the threaded fitting loose at each end. Make sure you use an open end wrench to hold the 6 point attached to the filter. Rethread back on by hand and make sure the fittings on the lines turn easily by hand. When you bottom out and tighten, make sure to use the wrenches again and snug tight but don't over tighten. When you restart, look for leaks at the fittings. If you live in the rust belt I would recommend using a penetrating fluid on the threads before removal and soak for at least an hour. When you restart, before checking the threads for leaks, turn the key to KOEO position and let the pump prime the line and tap that schrader fitting to help with air but I have never done that and still had no problems.

 

[96-2D-Hoe]

IMO A flare wrench is great if you have them. If not you could just be very careful not to twist or bend the pipe when you crack the fittings open and nipping them back up. Like I did

And by great I mean it's the correct tool for this type of fitting.

 

[OR VietVet]

That is called good luck. The line threaded fittings are a softer metal than a bolt. The flare wrenches are used because of the extra contact on the 6 points of that threaded fitting. With just an open end wrench, yes you can get lucky, you stand a greater chance of rounding the 6 points ad having more trouble re-tensioning when reassemble. In a pinch I have used a vise grip to tighten on the two sides of the 6 point and made sure it was tight but not so tight that it would squeeze too much and misshape the 6 point and then when I went to break loose, I did it with a snap real quick to break it loose and then switched to an open end wrench. I have also used an open end in a pinch and have good and bad results. The penetrant helps with that seize effect from a long time period or rust in the threads.

 

[96-2D-Hoe]

I'm very careful, and maybe just lucky. In my younger days in the UK I was an AC service engineer so I'm used to flare fittings. Back then I had a set of flare wrenches but rarely used them. But that was all copper.

I normally crack the fitting with the wrenches about an inch apart and then use my hands to remove the nut as soon as it's loose enough.

 

[McDermut]

There's a schrader fitting under a cap on the fuel line that you can press to remove any pressure. Use a rag as gas will come out when you press it. It's on a hard line to the rear right/driver side of the throttle body. TBH it won't make much difference as plenty of gas is going to leak out anyway.

Otherwise run the gas down as much as possible, have a fire extinguisher on hand if you can, and put plenty of penetrating oil on the fittings long before you start.

What @96-2D-Hoe said plus make sure to use the line/flare wrenches when you break the threaded fitting loose at each end. Make sure you use an open end wrench to hold the 6 point attached to the filter. Rethread back on by hand and make sure the fittings on the lines turn easily by hand. When you bottom out and tighten, make sure to use the wrenches again and snug tight but don't over tighten. When you restart, look for leaks at the fittings. If you live in the rust belt I would recommend using a penetrating fluid on the threads before removal and soak for at least an hour. When you restart, before checking the threads for leaks, turn the key to KOEO position and let the pump prime the line and tap that schrader fitting to help with air but I have never done that and still had no problems.

Thank you both very much! I wasn't aware the fittings were softer and required a flare wrench, looks like I'll be headed to the hardware store. Would y'all happen to remember what size flare wrench and open-end wrench were used on the filter? It's not so much for me as for anyone referencing this thread in the future. I can post the sizes that I used once I find out also.

 

[96-2D-Hoe]

I don't sorry. Just get under there.
One thing to remember when you close it back up is you only nip the fittings up. Don't overtighten.

 

[OR VietVet]

Can't remember the size but if I guessed it would be a 5/8". The 6 point on the filter, if I guessed would be 11?16" or maybe even 5/8". Again, just a guess.

The reason it is softer, the line fitting, is that hen you tighten the fitting on the line into the filter there is a flare there and the metal needs to be soft enough to mold to the flare shape in the filter. Just like on brake lines.

 

[exp500]

I think that one is 20 mm.