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So,, WTF am I looking at..?

shady

shady

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I ordered a new spectra premium tank for a gmt400 suburban. (95)
And it has these 2 holes that I find no reason for... :dunno:
What could they go to stock...?
Should I just weld patches over them?
This issue is going to hold up my first start date I think. :doah:

IMG_20220420_153407069.jpg

IMG_20220420_153411573.jpg
 
And No, they aren't in my old tank lol.
It has a different type of holes lol
 
I'm not sure what to do about em.. :dunno:
 
Thanks guys.... Just rush ordered 2 of them.
I suppose they went to the evap canister or something.?
Not sure wtf I'm going to do with em.
Some how, capping them sounds like the wrong answer.
 
These a pressure vent, or vacuum vent..? I don't want to suck my tank in lol.
Don't have a charcoal canister. Or evap system at all.
I can run a line from both to a T and then all the way to the engine compartment if needed. But worried about what happens then.

If it's just letting air in I'll put a one way valve in it. If it's letting fumes/pressure out, I don't want it filling my engine compartment with gas fumes lol.
 
You need vents that flow both ways. One way or another you have to account for expansion and the removal of fuel as it is pulled out of the tank.

Just by looks those seem to be more complicated than just a way to put a fitting into the tank. Blowing or sucking on the fitting will tell you how they operate most likely.

Maybe they've got check balls to keep the vents from filling going up or down hill and a full tank? Seems overly complicated to me, but I'm sure there is a reason.
 
I'm sure that at least probably have rollover valves in them or something :dunno:

I found a routing diagram, and they go right into the evap can. But that has a vacuum on it most of the time I thought.... So how would the tank get air in?
Whatever happened to frickin vented gas caps lol.

I read a bunch of forum posts on Google search of guys sucking their tank in, and the truck not running right with the line to these plugged.
So I guess they let air in. But with the canister hooked to vacuum, it makes me wonder how.
I gotta figure it out by this weekend, because the tanks going in lol.
 
The evap system is a bit more complicated than just being a vacuum. Valves, charcoal, etc. If I recall correctly they are normally plumbed into the air cleaner, which really isn't vacuum. On later stuff perhaps they did use vacuum, you'd really have to know how the system works. Vacuum on the tank seems like a bad idea in general, you'd run the risk of collapsing the tank and vent line of course, not to mention an easy way to get fuel into a non-fuel line.

My solution for an unvented tank initially was to take the gas cap apart and make it vent, but the problem with that is the cap will dump fuel if the incline is steep enough and the fuel neck not high enough. Worked fine 99% of the time.
 
Tie them together and put a tee in the middle then run that line to an inline fuel filter to use as a vent filter. That is as long as they are just open vents and don't require vacuum on them to function properly.
 
I watched a few videos about evap systems and none said anything about letting the tank breathe. Only pulling vapor out. I'm not opposed to adding a canister, but my engine has no provision for an EVAP solenoid, or even the ability to control one lol. I may run it up front and tie into the air box. That wouldn't be too bad really.

I'll know more about how they function tomorrow I guess
 
On my last harley, a 99 Twin Cam, it kept dieing on me after about 25-30 miles. kept acting like it was out of gas.

Long story short, wound up drilling 3 3/64 (#40) holes in the underside of the cap. Worked fine ever after.

May screw with your OBD II system, idk. Just food for thought.

Edit: brain fart, are the newer style caps for these tanks vented?
 
I was already thinking about that. Since the diesel tank didn't have vents, it had to have used a vented cap to let air in and not suck in the tank.
I still have the diesel cap in it lol.,

For this weekend I'm going to T them together, and run a hose out to the frame. Then plug it. Then I can get to that hose and do whatever if I have issues, without dropping the tank again.
 
All it has to do this weekend is start, and run
 
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