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How to test for air in your fuel

5K views 3 replies 3 participants last post by  9297oldram 
#1 · (Edited)
There are many ways for checking for air in your fuel:

  1. This first one is the easiest but also the least accurate. Pump the primer and and see how many pumps it takes till you hear the OFV buzz. Here's a VIDEO to show how. Note, if the test says you have air in the fuel then you might have a bad Overflow Valve or a bad lift pump/primer, but if it tests good then you don't have air in your fuel.

  2. This is the most common way,

    Loosen up the 10mm bleed bolt on top of the banjo bolt pointed at in the picture (It's looks different in the picture because I have a fuel pressure gauge), and pump the primer and see if any air comes out. When you tighten the bleed bolt back up be careful not to strip the threads, you don't have to do it to tight, give it some feeling.

  3. Disconnect the return line and put the end in a bucket of diesel and see if there are any bubbles coming out.

  4. run a clear piece of pipe anywhere in the line after the fuel heater but if you put it after the lift pump that would be better, that way if the seals on the input of the lift pump are also being tested. And then all you do is look for bubbles going through the line.

  5. The best way is to get a fuel pressure gauge, that way you can test the the for low fuel pressure also (if you have low fuel pressure then you might have air in your fuel so do one of the above tests).

To find the air leak you can pressurize the fuel tank with a compressor from the fill cap to 10psi MAX, that way instead of having suction pulling air in, you would be pushing fuel out so you can see it drip. Some people have took a fuel cap and and drilled a hole and put a fitting in it so they can watch for drips, but you can wrap a rag around the air nozzle and stick it in, and have someone else watch for drips or you can park on a driveway so you can see drips on the concrete.

Thanks for reading, this is my first how-to so please let me know what you think.
Recommendations are very welcome
 
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#2 ·
I have spare fuel tank cap with an air fitting tapped in so I can pressurize the low pressure fuel system to 10 psi max with compressed air.
Very easy to find any air leaks but I guess if you don't have a compressor your method would work.
 
#3 ·
Thank you sir!
I added that info to my original post.
If anybody has anything they would like me to add let me know.

Thank you,
Brad
 
#4 ·
No 2 I find is the easiest, just be sure to let the truck set for a few hours to give the air bubbles a chance to rise to the top.
 
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