350 leak

JPVortex · Apr 5, 2023

Canadian Rust Bucket said:
Definitely possible if the gasket is bad. I'd check your lines first though. There should be three - a pressure, a return, and a vapor line. If the o-rings are bad in the pressure or return lines they'll leak at the joint. Feel around on each line, looking for gas on either. If you have a short run of flexible hose there, it could have split where it's secured to the lines out of the tank as well.

Your TBI is fairly low pressure. You could try turning the key to the run position without turning the engine over, and crawl under to check the pump out while it runs. Maybe have an assistant turn the key for you so you spend less time futzing around trying to get eyes on the pump. Of course this is all predicated on the assumption that your truck only leaks when it's running. If it leaks just sitting there, I'd look for a hole in the tank.

it only leaks while running as far as I can tell. I just replaced the return line with rubber hose, and the vapor and feed line seemed to not leak at all, the rubber hose on the top of those by the pump seemed okay too.

Also talking to the previous owner, the fuel tank and pump are both newer units.

It also seemed to stop once I drove like 50 miles on a full tank, so it seems to really happens when the tank is full.

I'm suspecting either a problem with the pump seal or with the vent tube possibly. I'll probably lower the tank at some point though and see what's going on.

JPVortex · Apr 5, 2023

Also def not the lines because the fuel was down both sides of the tank

JPVortex · Apr 5, 2023

Also seems like the fuel gauge stopped working when I filled it up.

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Canadian Rust Bucket · Apr 5, 2023

JPVortex said:
Also def not the lines because the fuel was down both sides of the tank

Yeah if it's down both sides that definitely points to the pump gasket. The vent tube is offset to one side, but not as far as the lines, so that is still a possibility too. Watch out for your ground wires when you drop the tank, they can get hung up on the crossmember or frame.

JPVortex · Apr 5, 2023

Canadian Rust Bucket said:
Yeah if it's down both sides that definitely points to the pump gasket. The vent tube is offset to one side, but not as far as the lines, so that is still a possibility too. Watch out for your ground wires when you drop the tank, they can get hung up on the crossmember or frame.

Yeah I'm going to drop the tank, replace the pump seal and I'll look at everything else too and for a hole in the tank.

JPVortex · Apr 6, 2023

Another thing I noticed is my air filter appears to have a bit of oil on it. Would that be a sign at all of the intake gaskets or something else? Looking underneath again its def soaked from up high dripping down low, so I think between the intake gaskets, pressure sending unit and distributor gasket that'll fix the big leak.

JPVortex · Apr 6, 2023

Also, I put a pan beneath the engine/transmission to see how many drops would come off. When I went to go look I found no big drops of oil from the engine but a giant spot right by where the transfer case is. Looking at the transfer case it also looks all wet and it has been slinging oil onto the underbody of the truck.

Not sure if both are making puddles or if it's just one or the other. I feel like the leak is way too far forward to be an output shaft seal, what other seals could go bad in the tcase?

JPVortex · Apr 10, 2023

Got an update on the fuel tank situation. Tank is off the truck and it smelled like gas by the pump. The tank has no rust and no visible holes. I was told the pump was newer too, so Im not going to replace the pump but am replacing the snap ring and seal for it. I am also replacing the vent tubing with new 5/8 hose because the end by the tank has tiny cracks starting(maybe it was seeping from there too)

I did notice all the white around the pump, I bet fuel was soaking that and caused some sort of metal corrosion or something in that area.

Hopefully this will solve my leak!

Heres a pic of the fuel pump on top of the tank. Some debris but no major rust on it and the lines coming off of it seem decent to me.

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GoToGuy · Apr 11, 2023

Fuel does not cause corrosion. Where did you get that idea from? It would evaporated. Depending on what area of the country you live in it could be any of a hundred possibilities. Farm waste, salted roads, corrosive sea coast, high humidity climate....
Overfilling your tank is not a good idea.
You should clean and inspect those metal lines closely. If you did not find any hoses leaking probably one or more of those metal lines could be cracked.
You want to find a leak? Gravity. Everything runs downhill.
Next time try doing an engine or transmission wash. Get rid of all the old residue. With clean surfaces you can see exactly where the fluid is coming from and what is leaking fluid.

Hipster · Apr 11, 2023

JPVortex said:
Got an update on the fuel tank situation. Tank is off the truck and it smelled like gas by the pump. The tank has no rust and no visible holes. I was told the pump was newer too, so Im not going to replace the pump but am replacing the snap ring and seal for it. I am also replacing the vent tubing with new 5/8 hose because the end by the tank has tiny cracks starting(maybe it was seeping from there too)

I did notice all the white around the pump, I bet fuel was soaking that and caused some sort of metal corrosion or something in that area.

Hopefully this will solve my leak!

Heres a pic of the fuel pump on top of the tank. Some debris but no major rust on it and the lines coming off of it seem decent to me.

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That sending unit looks pretty crusty, not uncommon for the tubes to be rusted through or cracked and leaking as mentioned, you're already there to replace it.....

350 leak

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