Fuel System Problem

[soule64]

Looks like I goofed something up with the fuel system and I hope someone might help.

What I have - 87 model 16 gallon tank and sender with an ep381 pump. Steel braided hose to the corvette regulator and return to sender. More steel braided hose to the engine fuel rail. Used another hose from the vent port (next to the main filler port) on the top of the tank and ran it to the charcoal canister for tank ventilation. Filler neck and cap from an 85 connected to the tank fill port with a standard filler hose. Small port (vent?) on the sender is capped as well as the 5/8' port on the filler neck. I figured the large line to the canister would provide enough ventilation.

What happened - Driving home last night a lane opened up in front of me and I hammered it. Ran the engine up to around 5k and out of nowhere, the cab was filled with gas fumes - I mean it was overpowering. I limped home about a mile away and popped the hood. the right side of the engine bay was soaked with fuel. How it didn't catch fire I'll never know because it was everywhere. I pulled the canister and it was so full of fuel that I couldn't push any air through it. The line from the canister back to the pump was full of fuel.

So, I am trying to picture this in my head how so much fuel (or any for that matter) got to the canister. Shouldn't that line actually pull a small amount of vacuum as fuel is pushed to the engine? Since all of the other ports are sealed, how did the engine keep running without tank ventilation? The pump should have cavitated under the Vacuum, but instead the fuel is pushed out of the ventilation hose/canister? Why did this happen under engine load/high rpm and not all of the time (been driving it for 2 weeks) - with the throttle wide open you are burning more gas thus relieving line pressure, right? The in-tank is constant pressure and wouldn't be affected by engine load - it works at 100% as long as it gets 12vdc.

I am not sure what I did wrong with this thing. Any help or suggestions would be greatly appreciated.

[STOCKISH]

Not sure what you did but this is how mine is hooked up. The main filler and 5/8 port on the tank are hooked up to the stock 86 filler neck. Also, I have a small vent on the "vent" port on the sender like the one used on a rear axle. Hope you get it all figured out.

[Big Port Jimmy 6]

I would think run the vent port on the tank top to the neck. run the small line to the canister if you have the evap solenoid on the intake hooked up and working run the canister line to the evap solenoid. Run a vent line off of the tank and above the level of the tank with some type of one way vent if you don't have the solenoid. Check the gas cap it could be stuck and not venting also. Jay

[soule64]

Changed things around and it seems to be working ok. Connected the tank vent to the filler neck port. Also punched out the vent plug on the inside of the cap. Pulled the canister and line entirely and kept the vent port on the sending unit plugged. So far, so good.

Still pondering the "why" part of it. I talked with one of the engineers I work with and his theory was that it might be something like the 'bang' that you hear in your plumbing when you shut the water faucet off real quick. That because the throttle was wide open and a large volume of fuel under high pressure was suddenly stopped when I let up off the gas, the pressure sort of rebounded through the regulator and the only way out was through the vent line to the canister (my tank was full and I was going uphill)
I don't know if I buy his theory, but as long as it doesn't happen again I don't care. I now travel with a fire extinguisher, however...

[low_84_inchaska]

why are you using the charcoal canister?

[soule64]

I figured it would make for a cheap filtered vent for the tank. Plus, it would cover up a big ol' dent I put in the top of the inner fender

I do need to ask another question, however - should the fuel tank/system be completely ventilated or should it have some vacuum or does it even matter?

[low_84_inchaska]

ha! i was wondering cause i am not using it and wondered if i had plumbed it wrong lol

[glock35ipsc]

My sending units have three outlets; feed, return, and a third that I assume originally went to the canister. I have it plugged, and bought new vented caps and haven't had any problems with it in over 5000 miles so far. I have a couple of vents that I was going to put on the tanks, but haven't seen the need to yet, so I haven't.