# JD 6420 fuel tank vent issues



## Trotwood2955 (Sep 4, 2012)

So another question in addition to the 7200 a/c issue below 

JD 6420. Have had the tractor about a year. It has always had a little bit of fuel seep/wetness around the top of the tank right underneath the cab but nothing serious. Probably just the hoses from the tank going bad. But over the last few weeks it has been leaking some around the tank cap, and now when you go to loosen the cap the tank feels pressurized. I figured the cap just wasnt venting correctly so bought a new cap to put on it. Didn't help, and if anything it is worse now. Now not only when you loosen the cap the tank feels pressurized but it also will squirt out some fuel around the top when you loosen it.

Also, a few weeks ago I went to start the tractor after it had been sitting for a week or two. It started fine, ran for two seconds then died. I cut the switch off and back on to let the fuel pump run a few seconds, and it started right back up and ran fine. It only did this once, and like I said the tractor had been sitting for awhile.

Other than that one time starting issue the tractor runs just fine. Could my problem just be the old fuel hoses from the tank going bad and getting some air in the system? Or is it the actual fuel pump down in the tank that could be on the way out? Thanks.


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## Tx Jim (Jun 30, 2014)

Trotwood2955 said:


> Also, a few weeks ago I went to start the tractor after it had been sitting for a week or two. It started fine, ran for two seconds then died. I cut the switch off and back on to let the fuel pump run a few seconds, and it started right back up and ran fine. It only did this once, and like I said the tractor had been sitting for awhile.Thanks.


This problem sounds as if fuel drained back into tank while sitting. Maybe the fuel line check valve is faulty or fuel line has a small hole/crack. I looked at the parts diagram and saw no tank vent so cap must have a vent built in it. Try running it with a shop towel covering fuel neck.


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## Trotwood2955 (Sep 4, 2012)

What/where is the fuel line check valve? I have never seen that on a parts diagram or know what it is if I have seen it on the tractor.

Wanted to say too, if it matters, this is an early 6420, tier 1, and does not have the common rail system of the later ones.


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## Colby (Mar 5, 2012)

We are in the exact same situation with our 6420. Replaced cap and all. Still chasing down the problems. Tractor has 47xx hrs


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## Trotwood2955 (Sep 4, 2012)

Yeah, other than that one time where it started and died immediately, tractor has no issues other than the pressurized tank and leaking fuel around the tank. But, I'd like to get it figured out before it decides to turn into something more serious and leaves me hanging on a busy day.


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## Orchard6 (Apr 30, 2014)

Ours leaks under the cab too! I've tried to figure it out but haven't had a lot of time to look it over. The starting up and dying thing is pretty common too. The fuel lines are prone to deteriorating internally and will develop pin hole leaks that allow air in the system. The fuel pump should be on the inside of the frame rail just below the oil fill on the left side. There was an update that involved pulling the sending unit and replacing the return line so that it dumped fuel further away from the pick-up so as to avoid sucking up air bubbles from the returning fuel turbulence.


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## Trotwood2955 (Sep 4, 2012)

Sounds like a pretty common problem. I have some extra hose in the shop, probably just going to replace those lines and see what it does. By the way, mine is an early model and pretty sure it has the fuel pump down in the tank, not on the frame rail like yours does.


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## Colby (Mar 5, 2012)

The frame pump fails on ours at least once a year.


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## Orchard6 (Apr 30, 2014)

Trotwood2955 said:


> Sounds like a pretty common problem. I have some extra hose in the shop, probably just going to replace those lines and see what it does. By the way, mine is an early model and pretty sure it has the fuel pump down in the tank, not on the frame rail like yours does.


Might want to check there anyways. Ours is a 2003 model year and it's on the frame. It also has the mechanical injection pump not common rail.


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## Bazooka (Sep 17, 2013)

This is a DTAC solution I found, Maybe worth a try:

*Solution Number: 81867*

*Solution Summary: Fuel tank building pressure causing tank to bulge or expand, low on power*

*Publication Date: Sep 27 2008*

**Paper copies of solutions may not be the most current solutions**

Complaint or Symptom :

Fuel tank swells or has pressure trapped inside the tank when removing the fuel cap. Maybe low on horsepower or has misfire under load.

Problem or Situation :



Fuel tank may be building pressure if the fuel cap is plugged or not breathing correctly.




Fuel pressure is getting into the fuel tank through the return line under load.

 Solution :



Check fuel cap vent for proper operation. Tank pressure may be a result of plugged fuel cap vent. Replace cap.



Remove the return fuel line from the engine and place in a bucket to determine if air bubbles are present in the fuel. If bubbles are present, air maybe entering the return fuel circuit from under the injection nozzle.

Check sealing washers under injection nozzle for damage. Sealing washer maybe damaged, missing. Injection nozzle down clamp screw not tight, or debris under sealing washer allowing cylinder pressure to enter the fuel return system.


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