How to remove air from the fuel system and/or find an air/fuel leak on a 6.2L - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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Old 06-27-2006, 09:14 PM   #1 (permalink)
High Sierra 2500
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How to remove air from the fuel system and/or find an air/fuel leak on a 6.2L

This thread covers bleeding the air out of the fuel system on these engines, which is necessary after running out of fuel, after the vehicle has been sitting for a long time, or after replacing any part of the fuel system.

It also includes a method for finding an air leak (or a fuel leak) in the fuel system. Symptoms of an air leak include surging, hard starting, no start, rough running, rough idle, and stalling.

These methods should not be used on trucks with very rusty fuel tanks, as it is possible to blow a hole in the tank.

Last edited by High Sierra 2500; 02-16-2008 at 03:07 AM.
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Old 06-27-2006, 09:16 PM   #2 (permalink)
High Sierra 2500
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To bleed air (or old fuel) out of the system on early models (1982-1984):

Hook an air compressor hose into the return line at the injection pump (IP). The line you want is the rubber one that goes into the front of the IP. Alternatively, you can stick the air hose into the filler neck, but that is not as effective. You can also modify a fuel cap with a valve stem off of a tubeless tire and use an air chuck to supply the air, which works good. Whatever way you choose, the next step is to loosen the fitting on the outlet side of the fuel filter. Loosen it enough that fuel will come out readily, but donít take it all the way off as you will need to be able to tighten it fairly easily. Put a pop bottle with a funnel stuck in the neck under the fitting to collect the fuel. With the fuel cap on tight, turn on the air to about 4 psi. Give it some time to fill the fuel tank. Fuel will start to run out of the fitting and into the pop bottle. When the pop bottle is about full, tighten the fitting. Then turn off the air. Disconnect the air line, wait for any remaining pressure to bleed out of the tank, and then reconnect the return line to the IP. If you used the modified fuel cap or the hose in the filler neck, you can ignore these last few steps.

Once you have bled the air out of the system to that point, you may need to crank for a while to get it to start. It is not necessary to loosen injector lines to bleed the system to the injectors on the 6.2. Simply crank until it starts. You will need to do this in several cranking sessions of about 15-25 seconds in length so that you do not burn out the starter.
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Old 06-27-2006, 09:17 PM   #3 (permalink)
High Sierra 2500
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To bleed air (or old fuel) out of the system on 1984 and later models:

These trucks were equipped with a combination fuel filter/water separator/fuel heater ("square" filter). If your truck is equipped with a "round" filter, see the procedure for early model trucks.

Hook an air compressor hose into the return line at the injection pump (IP). The line you want is the rubber one that goes into the front of the IP. Alternatively, you can stick the air hose into the filler neck, but that is not as effective. You can also modify a fuel cap with a valve stem off of a tubeless tire and use an air chuck to supply the air, which works good. Whatever way you choose, the next step is to open the air bleed valve. It is located on the top of the fuel filter mounting block. There is a hose fitting right next to it. Hook a hose onto that, and run the hose into a pop bottle (this will collect whatever fuel you bleed out). With the fuel cap on tight, turn on the air to about 4 psi. Give it some time to fill the fuel tank. Fuel will start to flow out of the bleed valve and into the pop bottle. When the pop bottle is about full, close the bleed valve. Then turn off the air. Disconnect the air line, wait for any remaining pressure to bleed out of the tank, and then reconnect the return line to the IP. If you used the modified fuel cap or the hose in the filler neck, you can ignore these last few steps.

Once you have bled the air out of the system to that point, you may need to crank for a while to get it to start. It is not necessary to loosen injector lines to bleed the system to the injectors on the 6.2. Simply crank until it starts. You will need to do this in several cranking sessions of about 15-25 seconds in length so that you do not burn out the starter.

Last edited by High Sierra 2500; 06-27-2006 at 09:23 PM.
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Old 06-27-2006, 09:17 PM   #4 (permalink)
High Sierra 2500
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To find an air/fuel leak:

Utilize air pressure to test your fuel supply system for leaks. The procedure for connecting the air is the same as the one used to bleed the system, however you donít loosen the fitting at the fuel filter (on 1982-1984 models) or open the bleed valve (on newer models). Once you have the system under pressure, crawl under the truck and look for fuel leaks (it might be a good idea to wear safety goggles when you do this). Work slowly from the fuel tank to the injection pump. You need to look very closely, because any leaks are likely to be very slow leaks. Check every connection, every hose, the fuel pump, the fuel filter(s), and the tank switch (if the truck has dual tanks). In short, check everything. When you think youíve checked everything, go back to the fuel tank and start over. A good thorough inspection should take about fifteen or twenty minutes. Anything that is just barely seeping fuel needs to be repaired. Fix any leaks, test it again, and when you get to the point where it no longer leaks, bleed the air out of the system. Replace the rubber hose on the return line with a clear hose before you start the engine. Start the engine and let it run for a while. If it runs good, take it out on the road for a short distance. Then look at the clear hose and look for any bubbles. If there arenít any, you are probably in good shape.

If everything looks good, but the engine wonít start the next morning, you probably need to replace the fuel pump. Replace the pump, bleed the air out of the system, and you should be in good shape.

Last edited by High Sierra 2500; 06-27-2006 at 09:24 PM.
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Old 08-01-2006, 10:00 AM   #5 (permalink)
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Well Done

Hey High Sierra,

This skinny is very well written, easy to follow, and very helpful. I'm still working but will let you know how it comes out. Many thanks!!

Warm regards,

G
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Old 08-17-2006, 01:23 AM   #6 (permalink)
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Did all that and finaly found the leak I Have been looking for for a year under the Fuel filter mount where the hose connects to the Outlet. Slight leka but enough to drain the system Probably got some sort of vibration fracture in it as it appears to be leaking where the tube attaches to the Seperator/Fuel filter mount.
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Old 08-19-2006, 04:11 PM   #7 (permalink)
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i found my leak in the intake to the IP
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Old 10-19-2006, 01:44 AM   #8 (permalink)
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You do not have to loosen injectors to bleed the air out on 6.2?..I disagree,when I had my leak all the cranking in the world wouldn't bleed the system.I also needed a battery charger and removed the glowplugs to make it easier on the starter with all that cranking.It was my understanding that this system isn't self bleeding,so one has to crack the injectors until fuel seeps out to remove air in lines...
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Old 10-19-2006, 09:56 AM   #9 (permalink)
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You don't need to loosen the lines. It will indeed bleed the injector lines out with ease with all the fittings tight.

You are right, the system is not self bleeding. That is why you use air pressure to push the air out of the lines before the injection pump. Beyond the injection pump, the only way to get the air out of the injector lines is by cranking the engine. The lines from the injection pump are fairly short and it doesn't take that much cranking to remove the air from them. You do not need to loosen the lines to bleed the air. Even if you do, there will still be some air left at the end of the injector lines and how do you get that out? By cranking, of course...

Most of the time when people do loosen the injector lines, it is to see if they are done bleeding the system. They know that once there is fuel at the injectors, they have completed the bleed procedure.

When the bleed procedure is performed correctly, you will find that you can simply crank the engine a couple times and it will start.

If you are doing things correctly using the air pressure method to bleed the lines, there is usually no need for a battery charger since it takes very little cranking to get the fuel through the injection pump and to the injectors. If you messed up somewhere along the way (it happens to all of us) then you have to crank long enough to draw the fuel a long way and that will kill the batteries and starter. Usually it only takes one or two 15 second cranking sessions before the engine starts if you have done things properly.
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Old 11-16-2006, 01:14 PM   #10 (permalink)
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Does this inspection also cover the symptom of having to use throttle at half open to crank when cold or less than hot? Menaing engine temp regardless of ambient air temp... even 90 degrees?
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