Dorman 692-044

[possum70]

I'm using this sending unit with my 5.3 swap. Do I need a charcoal canister or not? There is a small tube that doesn't go to supply or return line and someone told me they go to a charcoal canister.
Also, my original sending unit (1978) had a big tube than ran to the filler neck area. How do I incorporate these two pieces together? Do I need a new filler neck? Or do I cut and weld a hole into my new tank somewhere? Has anyone else run into this and if so how did you deal with it?

thanks,
possum

 

[possum70]

this is a picture of both sending units. Old one in the foreground, new one in the background. On the new one, I need to know what to do with the middle line. One the old one I need the big tube. My filler tune has a hose that goes to the big tube but there isn't one on the new tank or sending unit. Unless it's that tiny one in the middle. I'm trying to get an answer so I can get the tank put in my truck. Cross one more thing off this long list.

possum

 

[possum70]

Well, shoot. It's all the same photo and editing won't clear them.

 

[K85 Octane]

largest to smallest

Vent to filler
Supply
Return
Charcoal canister

Canister not needed but vent to filler, yes. And you are going to want a vented gas cap if you run without the canister

 

[possum70]

Do they have vented gas caps for a 78? It's the last year for an external cap.
And any idea on how to vent to the filler if the new sending unit doesn't have a tube for it?

possum

 

[K85 Octane]

what is the application for this sending unit?
you can use the 87-91 blazer units and just swap the pumps, then it will provide enough pressure
you will want the large vent nipple, smaller ones will cause burping while fueling

 

[possum70]

It's a 2003 5.3 into a 1978 blazer. 91 tank, 97 sending unit, EP381 pump.

possum

 

[K85 Octane]

You really should try the 91 blazer sending unit. It should match the tank depth better too.

Make sure you use the proper rubber hose to connect the pump and sending unit. Make sure it's E85 SUBMERGED compliant.

 

[dyeager535]

Take your cap of and take a look at it. A little playing around and you should be able to make it "vented". Note that all of them are vented, however the later ones with charcoal canister are vented at quite a bit higher pressure. I want to think I've seen 16PSI for later ones, and 3PSI for early.

However, my experience has been that doing this means you will lose fuel depending on vehicle angle and how full the tank is. Running proper venting (charcoal canister) IMO is better if you have that option.

I didn't play around with the cap enough to figure out if it is possible to reduce the pressure at which the cap "breathes", but I'm guessing it's a matter of spring pressure and possible with some more time spent on one.

There most definitely were gas caps of this style that were vented from the factory, but looking at the Stant catalog, you'll see that all of them are non-vented, whether they say so or not...they ignore emissions differences on the trucks, and list the same cap for all applications. Or did last I looked into this.