Is my fuel selection valve *****?

[libsys]

Hi All,

I'm trying to track down an air intrusion problem, and I think I have it narrowed down to pre-lift pump. The truck starts right up, but then stumbles for maybe 20-30 seconds before it smooths out. I have a section of clear hose installed on the inlet of the lift pump. When I first start up after the truck has been sitting for awhile, I get air bubbles through the hose which clear up eventually. I'm also getting bubbles whenever I switch between tanks. Both tanks are full, so I don't think it's pulling air from the tanks. Is my selection valve shot? I don't see any signs of fuel leakage on the valve or the connections to it. What else should I be checking? Thanks!

 

[Big Bart]

Libsys,

Great question, I have never tried to watch the fuel line heading to the lift pump. Also does this happen regardless of which tank you leave on? (If yes then it is not likely the lines between the tank switch valve and the tank. But could be the tank switch valve.)

I would expect some air when switching tanks, the standby tank line is likely to drain back to the tank till called upon again.

However if you get air in the lines and a stumble after starting when you did not switch. Then likely you have an air leak and the fuel system is sucking in air and letting the fuel drain back towards the tank. Then when you start it the lift pump pulls the air followed by the fuel and pumps it to the fuel filter.

1) Check your fuel filter and bottom to make sure it is tight and not leaking.
2) Check the the line up from the lift pump to the filter to make sure both fittings are tight.
3) Look around at the fuel return system. Do you see any wet injectors at the base or diesel leaks? Mabye if you have not done in a while get the return line kit and put it on.
4) As you suggest it could be your fuel tank switch valve. They are not know for their long term reliability. Maybe bypass to see if the problem goes away. If it does replace the fuel tank switch.

These can be a PITA so let us know what you find.

 

[libsys]

It does happen on both tanks. It seems like it's a little worse on the front tank, but it's hard to say for sure. I think everything downstream of the lift pump is pretty tight. No signs of leakage anywhere, new return lines, new olives in the hard lines, put clear lines off the filter header and IP and got no bubbles. When it sits overnight, I'm not getting any air in the clear line on the lift pump until I start it up, which leads me to believe it's not siphoning down from the filter. Also, I should have mentioned before, I tried running it straight from a can of diesel and then let it sit overnight, and the startup the next day was much smoother.

 

[Big Bart]

Libsys,

They are cheap $30-40, easy to replace, and can leave you stranded when they quit working. So perhaps you should just slap one in this weekend.

Also get a new piece of rubber hose and new clamps for between the fuel line and the pump.

You may want to pick up some Brake Cleaner and scraper while you are at the autoparts store. (So can clean off any left over gasket off the block.

I would also get some Gascacinch or Permatex high tack gasket sealer. Glue the gasket onto the pump, put some on the block and you should be leak free.

Lesson learned when I did mine. I did not pull the top bolt out of the way (Left it partially in the pump.) The bolt fell out when I almost had the pump out. When you lift the pump out, there is a big hole into the crankcase. If that bolt had bounced in (I could not find it for 15 minutes so thought it did.), I would have been in a world of hurt to fish it out. So just realize you do not want anyting to fall into your crankcase while your pump is out of the way.

Share a couple of pics and let us know how it goes.

 

[TNBrett]

It sounds like you do have it narrowed down to some where between the tanks and the lift pump. I think my next step would be a very thorough visual inspection of the fuel lines. Maybe even find a small inspection mirror to check the harder to see areas. A small pin hole from rust on one of the steel lines could very well be your culprit. Or perhaps a crack in one of the plastic sections. Also, the quick connect fittings use an o-ring, so that’s another possible source. As you know, it only takes a small leak to let some air in and cause your problem. The challenge is that when the truck is running that section of the fuel system is under suction so you may never see a leak dripping fuel.


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[libsys]

I've never dealt with those quick connect fittings before. Can the o-rings be replaced?

 

[IDIBRONCO]

Yes they can. I've seen others say that it's not the easiest thing to do. Four letter words may be involved.

 

[79jasper]

I've done it. It's a pain.

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[Slicknik]

@libsys

if you have the ability to create vacuum or , pull fuel (truck off) from the fuel line pre/post lift pump you’ll be able to hear it by the tanks or selector valve .

All it takes is a auxiliary electric fuel pump to a gas can and run it off the battery for power. Then just stick your head under the truck and follow the fuel line back to the tanks.

Mine was the 0-ring in the fuel line at the rear tank connection wasn’t sealing.