FUEL SENDING UNIT QUESTIONS

[ROARING 455]

Sup fellas, my names Pete and I'm working on a 1974 gmc c15. I'm fixing to start cleaning up and blowing out my fuel and brake lines for reinstall. Question I've ran into tho is about the center line coming out of my sending unit. It's plug off at the other end so I'm guessing it had something to do with a canister that may have use to be there?. Does it really have to be there? Reason I ask is cause if not I want to do away with it and find different types of clamps for the lines that I will be using. Anyways I'm sure some of you experts here can give me help with this and I appreciate any info thats thrown my way.

[LTZ C20]

Welcome. There was a vent line that run to the front into an evaporative emissions canister. If you don't plan to use this factory setup you can replace the sending units with non venting models (or just cap the line right at the sending unit, eliminating the hose completely). You can then remove the steel lines on the frame and just use vented gas caps.

The purpose of the vent was to direct fumes from the fuel tank into the canister and then from the canister into the engine where they were introduced into the into the incoming air flow and burned with air/fuel mixture.

Using vented gas caps does the same thing only it just vents into the atmosphere instead of being burned in the engine. The evap system was made so it does not vent into the atmosphere.

Either way is personal preference unless the area or state your vehicle will be or is registered in requires factory smog equipment to be installed and functional. In which case you have to retain the system. If you happen to be in California then your ok to remove it if you so desire as the smog requirements are for 1976 and newer, anything 1975 and older is smog exempt. You said your truck is a 1974. I can't speak to the requirements of anything, outside California.

[ROARING 455]

K well I'm out of Texas and as long as I've been here I've never heard anything about the ventilation questions I had. So with that being said I'm going to go ahead and remove the line and use a vented gas cap then. I don't plan on using the canister which wasn't with my truck when I bought it so I'm not going to waste time and money trying to find one. Thanks for the info brutha!

[LTZ C20]

Well then you should be just fine. As I remember, Texas doesn't require a smog certificate or emissions inspection so long as you don't have any of that. You are free to remove the system and use vented caps.

[hatzie]

Some of the 1974 trucks outside of Cali had something similar to an axle breather on the end of the vent hose.  That's probably what you thought was a plug.
Easier to find than vented gas caps.  The charcoal can isn't that complicated and doesn't hurt performance at all.

[BBM3]

My '75 K10 had those vent caps presumably from the factory and the black cap was missing on both.
I wound up plugging the short vent hoses and gutting the spring operated check valve from the non vented gas caps.
It works however sometimes the vented fumes smell like a big fuel leak especially when the fuel expands in the summer.
Every trip the junk yard I look for a correct charcoal canister. If I ever find one I will plumb and install it.

[BBM3]

I just noticed in the second picture the fuel sender is facing the wrong way. The outlet, vent, and return lines should be facing the frame. It will work that way just take care that the lines don't kink. Even a little kink will lead to fuel starvation with symptoms of vapor lock.

[hatzie]

My '75 K10 had those vent caps presumably from the factory and the black cap was missing on both.
I wound up plugging the short vent hoses and gutting the spring operated check valve from the non vented gas caps.
It works however sometimes the vented fumes smell like a big fuel leak especially when the fuel expands in the summer.
Every trip the junk yard I look for a correct charcoal canister. If I ever find one I will plumb and install it.

Most of them had white caps that's just the picture I could find.  Real easy to find rear axle vents.  They're the same thing.

You can buy a new 3 hose charcoal can to fit most of the late 70's GM trucks thru 1979.  AC Delco 215-153.

I'm not a greenie... the garage smells better with a carbon can vs raw vents.

The bracket from all of this generation 73-91 will likely fit that can.
Tee the vapor purge line into the PCV hose with SAE J30R7 emissions hose and replace the PCV hose while you're at it.
The purge valve vacuum signal is usually ported vacuum above the throttle plates.
The third is your tank vent(s).  Use SAE J30R7 Hose on these lines too.

SAE J30R9 is the stuff to use for fuel supply and return hose.  It has a more aggressive barrier layer than J30R7 so it lasts longer when exposed to liquid fuel.  Use Constant Tension Spring Clamps on the fuel supply, vapor, and return hoses...  not worm clamps.  Worm clamps don't work well on hoses smaller than 5/8" OD and they don't compensate for thermal expansion and contraction.



My Droid from orbit

[BBM3]

Sorry for the thread jack ROARING 455
Hope this helps you too.

Thanks hatzie,
I'll need to make a mounting strap, no problem.
You are correct venting the tanks to the atmosphere works but really stinks up the garage and is a potentially explosive fire hazard.
This is what was originally on the vent side of my fuel senders.

[hatzie]

That's actually stock for 1975 HD emissions. In kinda rough shape too.  If that one took that much of a pounding what do the gearbox and axle vents look like?
I actually thought about venting my tanks to the Carb side of the air cleaner when I still ran gasoline in the 76.  The axles and gearboxes vent there even with the diesel airbox.
I still have the can but purge is a challenge on a diesel.
My Droid from orbit

[87fleetside]

Yes, even on my 87 tbi setup the center is a vent. By the way when you use cap's locks it's my understanding you are yelling. LOL!

[ROARING 455]

Definitely all good brutha I'm still learning off of everything that's being said. But I'm kinda in a bind now tho. I went ahead and ran just the supply and return line cause I was gonna go ahead and do away with the process of finding and canister. Here's a few pics of what I've done so far, I also started a build thread in the welcome forum since I couldn't find a build only forum. I still have tons of pics to post and taking more as I progress.
 

Sorry for the thread jack ROARING 455
Hope this helps you too.

Thanks hatzie,
I'll need to make a mounting strap, no problem.
You are correct venting the tanks to the atmosphere works but really stinks up the garage and is a potentially explosive fire hazard.
This is what was originally on the vent side of my fuel senders.

[BBM3]

The freshly painted frame, those new grade 8 fasteners, and fuel lines look great.
Consider starting your own build thread in the "Members Rides" section.
There are many members here that will follow, learn, and help with your project.

[Stewart G Griffin]

How did you clean the frame?

[ROARING 455]

The freshly painted frame, those new grade 8 fasteners, and fuel lines look great.
Consider starting your own build thread in the "Members Rides" section.
There are many members here that will follow, learn, and help with your project.

Members Rides, got cha brutha! I've started in the welcome section and still going strong. Would u know anything about being able to transfer what I've already posted in the welcome section to the member rides section? I'd hate to have to start all over again. Thanks for the support and help tho!