2nd Gen Non-Engine/Transmission Fuel Tank

[snake]

1995 diesel, what would cause air pressure to build up in fuel tank? Been seeing this for about two weeks how. When I take the fuel cap off get a blast air that comes out.



Thanks, David

 

[EricBu12]

try a replacement cap and see if that does it

 

[surfbeetle]

Same year, same problem. Only I thought that it was a rush of air going in, not out as if I leave the truck parked overnight, I have to manually prime it to get it started. I went to a dealer and bought a diesel locking gas cap for my truck. No change.



I had taken it to a mechanic and he said that my vent must be clogged. He said that if it is hot in the day, the fuel expands then when it gets cold in the evening, the fuel contracts and sucks the fuel back into the tank from the engine. Where is the vent? I only see the hose that goes from the tank to the top of the filler tube.

 

[duckcarvr]

check and see if your tank has a vent tube on it, that could be blocked-crimpes. ive had this before but it was always air rushing in. robert

 

[snake]

Same year, same problem. Only I thought that it was a rush of air going in, not out as if I leave the truck parked overnight, I have to manually prime it to get it started. I went to a dealer and bought a diesel locking gas cap for my truck. No change.



I had taken it to a mechanic and he said that my vent must be clogged. He said that if it is hot in the day, the fuel expands then when it gets cold in the evening, the fuel contracts and sucks the fuel back into the tank from the engine. Where is the vent? I only see the hose that goes from the tank to the top of the filler tube.

Did you find the problem?

 

[snake]

try a replacement cap and see if that does it

Tried that no change.

 

[HCannon]

Have the same thing happening. Have to bump the starter and let the elect pump pump for a spell and then it will start. Cooler it get at night, the longer it takes. Someone tell us the best thing to do.

 

[Joe G.]

There is a small pressure relief valve on top of the fuel tank module. It may be clogged. Try leaving the cap off or loose at night and see what happens.

 

[PC12Driver]

For normal ops, if a fuel tank vent is plugged the tank will have a negative pressure. Temperature expansion may cause a slight positive pressure, but odds are it wouldn't be there every time you remove the fuel cap. If there is a positive pressure, air has to be getting forced into the tank from somewhere.



Now, I don't speak 12v, so maybe someone who can translate 24v into 12v can help out. But a while back there was a fellow with a 24 valve truck who was getting a pressurized fuel tank and traced the problem to the copper injector sealing washers. On the 24v heads there is a galley around the injectors that leads to a return fuel line on the back of the head (so any fuel leaks just go right back to the tank). Either a copper washer went bad or an injector hold-down lost torque, and he ended up with engine compession entering this galley, thus pressurizing the tank via the return line. He changed out the washers and the problem was solved.



Like I said, this was for a 24v so hopefully someone can translate. But there really isn't another source of pressurized air next to the fuel system, so maybe it's worth a shot?

 

[surfbeetle]

Snake,

No, I have not found the problem. I hope to get time this weekend to see. I too didn't have luck with a new fuel cap. I truly believe the issue is a lack of proper venting from the tank. I just have to figure out where its clogged.

 

[GAmes]

surfbeetle,

Have you read this thread? Skip page 1 if you want.





https://www.turbodieselregister.com...ssion-1994-1998/204958-lift-pump-failure.html

 

[snake]

There is a small pressure relief valve on top of the fuel tank module. It may be clogged. Try leaving the cap off or loose at night and see what happens.

Joe, I as thing about that on the cap, leaving it loose over night. Let's see what happens in a few days.

On the clogged pressure rollover valve. How would it get clogged ? That means I have to drop the tank,

or left the bed it's up. The questions is how the valve got clogged ?

 

[Joe G.]

I don't know how it could get clogged. The only reason that I know that there is a pressure relief valve on the fuel tank module is that mine will leak a little bit if I forget to shut of the aux tank fuel transfer and the main tank fills up into the filler neck.

 

[snake]

I don't know how it could get clogged. The only reason that I know that there is a pressure relief valve on the fuel tank module is that mine will leak a little bit if I forget to shut of the aux tank fuel transfer and the main tank fills up into the filler neck.

Joe, Until I get time to work on the pressure relief rollover valve, by drop the tank or the bed. Just leave the fuel cap loose a little bit. I don't thing that it will cause any problems in the fuel system ? Thinks for your help. On that pressure relief rollover valve is that screw in the fuel tank module? or what tools did I need ?



Thanks, David

 

[Joe G.]

First of all it's not a roll over valve. That's a different gadget. This thing is just a little spring loaded valve in the top of the fuel tank module to relieve excess pressure. You can see it from the side without lifting the tank. Some trucks were sold with the red shipping cap still over the roll over valve. That caused this symptom. I don't think that is the problem with a truck as old as a '95. The roll over valve should vent the tank. I mentioned the pressure relief valve because mine does leak when there is pressure in the tank and the tank is full. I have no idea if it is your problem or not. It is certainly something you should check when you are trying to fix this.

 

[surfbeetle]

surfbeetle,

Have you read this thread? Skip page 1 if you want.





https://www.turbodieselregister.com...ssion-1994-1998/204958-lift-pump-failure.html

Yes, I saw it but that was before you had gotten it buttoned back up... It does makes sense because the last time I manually primed the pump, I had diesel on my hands from somewhere around the pump. I will look better in that area to see. Since the parts are cheap enough, I will just call Cummins Cal Pacific to see if they have it. I know that the pump itself is good, when I originally took it into a mechanic, he tested the pressure to see if it was okay.

 

[Joe G.]

Surfbeetle,

You can fix the push button leak with a 50 cent O-ring from NAPA without taking the lift pump off.

 

[surfbeetle]

Surfbeetle,



You can fix the push button leak with a 50 cent O-ring from NAPA without taking the lift pump off.

Is this the push button cover itself or something else? Do you have a size or part number? Thanks

 

[Joe G.]

The push button cover is just to keep the button clean. The O-ring When mine leaked I took the old O-ring to NAPA and get the closest match from their O-ring box. Read page 7 of the writeup I sent you. It shows where the O-rings are and where the push button cover is.

 

[surfbeetle]

Thanks, I will do that. I just now got around to checking my email this morning.