StevenK

Hey guys running a thirdgen with the stock tank and upgraded Walbro pump. When you run your tank down and open the cap to refill your gas, does it suck in a *LARGE* amount of air (say 2 or 3 seconds worth of AIR with the cap off)? I'm thinking my return line is not working or something, I've never had a car suck in that much air, some yes, but now like the entire tank is a vacuum.

Another reason I'm thinking I have a problem is my new Fuel Pump is really noisy, and I'm wondering if it is because I'm forcing it to do extra work due to a bad return....

Any ideas?

ghettocruiser

iTrader: (17)

Ive never had it suck in air..??? Ive had alittle puff come out before. Or maybe it was a quick puff in... Im not sure but it was never more than .5 seconds long. ALmost like cracking open a bottle of beer...

Justin

StevenK

This is more like opening a gallon of coke that you just rolled down a long hill.

And now that I think about it, I dont know if it was puffing out or in, I didn't put my hand over it to check which direction the air was going, only that I knew a hell of a lot of air was going through the gas filler.

ghettocruiser

iTrader: (17)

Well gas builds pressure in a closed container. So ide guess and say it was probably exhaling. Maybe the vent/evap set up you have isnt purging or bleeding off the pressure.

Whats your set up as far as tank venting or evap??

Justin

StevenK

I've got the fbody motorsports FPR running into the rail, then I have the stock evap plastic thing with a rubber hose going to the return line.

I think... I'll take some pictures when I get home today.

On a good note, I got my A/C lines made yesterday, so I'll probably throw those on at the same time :-D

Randy_S

iTrader: (1)

Like the others said, it sounds like its not letting the pressure off like it should. My fuel pump is very noisy when I get below 1/4 tank in my '92. I dont know if its aftermarket or not, I never checked it. I just know you can here it from about 20' away when its idling.

Dave88z

I had a similar problem with my third gen after I got it running with my old motor. I had a holley 255 pump, and after driving for a short distance it would get real loud. After some diag. I noticed my fuel pressure would also rise and the car ran very rich. I finally found that the heat shield around the gas tank was removed when my exhaust was made. The heat from the exhaust was must have been heating the gas in the tank causing the extra pressure. I installed a custom heat
shield and applied heat reflective tape the gas tank....problem was gone!

StevenK

Good info, I'll look into that as well.

I have a FP gauge on my pillar, the pressure is staying a constant 57 lbs as always. The sound can be hear with a full tank or an empty tank. It can be heard from a cold start or a warm start.

My guess is I have my fuel return hooked up wrong, I'll take a look at some posts here and compare with what I have done and get back to ya'll

Thanks for the help guys, I'm really enjoying driving this beast around again, I just have to get rid of all these damn noises, if its not the fuel pump its the front end making noise, if its not the front its the pass door rattling. Ahh, the joys of owning a 16 year old car.

StevenK

Ok a little update.

I checked the gas cap, the air is being pushed out of the tank, so the tank is under positive pressure.

The incoming fuel line comes from the tank, through a filter to an AFPR. On the bottom of the AFPR the extra gas to go back to the tank. Then on the other side of the AFPR the 57lb fuel pressure is going to the fuel rail (2000). Then I have the "evap" line coming from the stock location on the driver's side frame rail up to the little plastic thing near the fuel rail going to the throttle body.

I was talking to another guy here that has done a LS1 swap and he has the plastic tank from a donor car, he said there is a pressure sensor in the tank, and the computer uses that and "special timing" to release extra pressure. He said I could probably get some kind of aftermarket pressure release box and hook that up, but he said since the ECM is controlling the release, if that box were to release at the wrong time I could notice a drop in power while that happens.

So now I'm pretty stuck, I have no clue how to fix this. Its seems like every day my brand new Walbro pump is getting louder and louder, and the cold start idle is starting to act weird too. Yesterday my friend noticed that the fuel pump noises would change during start up when the engine would bog down and hit stall saver, like when the stall saver asks for more gas to keep the engine running the fuel pump would get quieter. It also seems that when I get on the gas the fuel pump gets quieter as well, but I'm not 100% sure on that as the exhaust is overpowering the pump sound.

Any ideas on where I should go from here?

Ohh and if I let the car sit overnight and pull the gas cap off, it still has enough pressure for about 1 second of air release when I loosen the cap...enough where I can feel the air on my hand.

Dave88z

OK, lets think this thru. When the fuel pump removes fuel from the tank, air needs to enter the tank to displace the missing fuel. If this did not happen, the fuel tank would implode.
On a stock 3rd gen tank there is a small white plastic ball with vents on it. This is a one way valve that should only allow air into the tank. It is located near the fuel filter and runs into a hard line that goes into the sending unit.
We know that when fuel is heated it expands. Heat is caused by the fuel pump, return fuel heated by the hot fuel rails, or the exhaust pipe near the tank. On the stock 3rd gen cars, the excess pressure and resulting fuel vapors were sent into the charcoal canistor under the hood. From there the vapors were sent into the manifold and burned to reduce emmisions. The pressure valve on the tanks of the 4th gen cars release the vapors differently. I have seen people run into problems when trying to remove the charcoal canistor. You can not just plug the line or the pressure can build up in the tank causing the fuel pump to make wierd noises or driveability problems.
I hope this helps, good luck.
Dave

StevenK

Damn....I already threw away my coal canister....

So...if I get a new canister, I assume I need to hook up the sensor on it to the LS1 harness?

Or should I just bite the bullet and hunt down a 4th gen tank? I'd prefer not to since I've already got the new fuel pump.

tuske427

iTrader: (1)

couldn't you just install a GM fuel tank vent valve?

I don't have the part number offhand, but it will let air enter or excape as needed. It takes a little pressure to activate. 1psi or something like hta.t Stock gm part...

It was a reccomended part from an aftermarket electric fuel pump kit I bought for my Belvedere. It's to solve the problems mentioned above.

This would be simpler/ cheaper than reattaching another charcoal canister or swapping tanks.

PM me if you wantthe part number. I can look it up at home.

StevenK

I don't know, I've never heard of it...

I assume it just goes in place of the white part that allows air only one way?

Dave88z

Whats going on with the lines that used to run into the charcoal canistor? Are they open, or did you plug the ends?

StevenK

You know how the third line comes up the frame rail with the rest of the fuel lines but comes farther forward towards where the canister used to be? Well I took the rubber line coming from that hard line, removed it from the canister and hooked it up to the plastic evap switch/sensor part that goes near the fuel rails.

Dave88z

I am not familiar with this switch/sensor. Does it allow the gas fumes to enter the intake manifold? I would imagine you are using 4th gen computer/harness but maybe this part is not working properly.
I would disconnect that line and let the tank fumes vent out. See if that helps the problem and then you can further diagnos the situation.

C for Chevelle

didnt read many responses but the tank on my '94 toyota pickup v6 does the same thing.. everyting on the fuel setup and delivery is stock and has always done this. kinda weird. i havent blown up yet though so i run it

StevenK

Dave, I'll pull it off the plastic part that sits on top of the intake near the fuel rails and goes into the TB and let you know how it goes....

Dave88z

Be sure to plug the hole in the TB, otherwise you will have a vacuum leak.

StevenK

Ahh good point, I'll do that at the same time.

I saw a picture of someone's swap (nonthirdgen) and the dude just had a basic paper looking round filter (like a PCV filter or someting) on the tank's extra line....

Can you do that? Seems like gas would eat up / soak the filter and just make the car smell like gas all the time...