Is there a easy way to get air out of fuel system.

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Neal

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Joined
May 13, 2009
Posts
539
Location
East Texas
We changed our fuel filters and must have let air get in. Will not start now.
2008 Winnebago Journey
Freightliner XC-S chassis
Cummins 6.7 diesel S# 46778114
2 filters, side by side at frame rail
I was under the impression, by cycling the ignition, it would self prime.
Is there an easy way, or am I going to have to open up the system to let air out.
If so, where is the best place to open, or will it have to be more than one place?
In the past we have not had this problem.
 
Did you replace both filters at the same time?? Usually I will stagger replacement times to avoid that problem, My engine has the MANUAL PUMP that needs to be pumped by hand to "bleed" the system. By staggering the replacement timing I avoid the need to reprime.>>>Dan
( Your 08 will self prime with the electric lift pump when using the ignition key, just keep at it.>>>)
 
Yes, we did replace both filters at the same time. We did fill the filters with fuel, before installing, but ran out of fuel on the second one, maybe 3/4 full.

We have probably cycled the ignition 20 times. Decided maybe would have to open something up to let the air escape.
 
When you turn on the key the Lift Pump runs for a short time.  Do not just turn the key on and off.  Leave it on for about a minute before trying to start it or turn it off and repeat the waiting cycle.
 
  Some engines will run with a bad lift pump, the injector pump will pull fuel from the fuel tank. However, once you open the suction side of the fuel system, like changing filters, it won?t recover the prime. One way to check is to loosen the fuel filter and cycle the lift pump. Fuel should come out once any air is bled out. For mechanical lift pumps you have to crank the engine. If no fuel comes out, your lift pump is most likely bad. With electronic fuel injectors you normally don?t have to ?bleed? air from the system.
 
On my ISC engine, same as Bill W said.  Turn the key on for 30 seconds, then off and back on for 30 seconds again.  Usually 6 sequences works for me. I also replace 1 filter, start the engine and let it run for 3 or 4 minutes and the replace the 2nd filter.  All ways cary spares.

Bill Dane
99
Country  Coach
 
Yes, your Cummins 6.7L will cycle its lift pump with every key cycle (as HueyPilot described).  Air in the lift pump & primary filter is usually quickly expelled with several key-cycles, but air in the secondary filter (at the fuel injection pump) can be hard to get rid of.  Follow the procedure and don't despair if it takes 20 cycles - it will eventually start. Probably stall a few times too, but will get going.  Once in a rare while it may be necessary to loosen the fuel line at the engine end (between filter and injector pump) and cycle the key until only fuel jets out.

The best technique is to change the primary filter and then re-start the engine, clearing away any air that resulted from that. Then do the secondary filter.

Unless you have encountered some unusually bad fuel, you might be able skip changing the secondary (engine mounted) filter every other change time. Nearly all the routine junk gets trapped in the primary - the secondary is there to catch whatever gets by the primary. If you are changing filters simply because it is time, with no apparent fuel problems, odds are the secondary is fine.  I offer this possibility solely because in some (many?) rigs the secondary filter is a pain to get at and change. If it's easy enough, changing both is always the safest approach.
 
Both of our filters are beside the transmission and appear to be plumbed with hoses to what I think is the injector pump, to the rear of the flywheel. One hose from the water separator filter to the pump and 2 hoses from the second filter to the pump. It does not feed straight from one filter to the other. The filters are easy to get to and we have changed both, each time. Before we changed the filters, we looked at the glass water separator bowl with a flash light and tried to convince myself, they didn't need changing. It looked like pure diesel. We have never seen any water in this bowl or drained any water from our lanyards.

After your suggestions, we loosened a filter & cycled the ignition, no fuel. Then Removed both filters & cycled the ignition, no fuel.
We called Freightliner and asked them if we had a lift pump in our fuel tank. He did not think so, but was not sure. We did find where a owner changed his lift pump on an older Winnebago.

I suppose the loops in the fuel hoses between the filters & injector pump would be a likely place for air to get trapped and if it has no pump or it is not working would add to my problems.

Last 6 of our vin is Z08210.

I think we will call Winnebago next week & ask if it has a fuel pump in the tank and if so, where is the fuse.

Thanks to everybody for all the help.
 
https://youtu.be/QeSNJhzdS1A

I hope I did this link right so you can see it.  This guy does a much better job of describing the fuel system than me. He refers to a fuel transfer pump, which I was calling a lift pump. One some models, just turning the key on only bumps the pump. Some systems you actually have to crank the engine for a second to actually activate this pump, then it runs for 25 seconds or so. There is a magnetic sensor on the crankshaft pulley that has to see ?X? revolutions before waking up many of the vehicle electronics. The pump will be external to your fuel tank. Good luck and hope you don?t have to take it somewhere.

 
Remember the filters are on the suction side of the pumps. If you loosen them and then try to pump, your doing nothing but sucking more air.
 
  Filters are on suction side of the injector pumps, not lift pumps, or transfer pump, whatever you wanna call it. Fuel comes from the tank to a pump, then through filters, then to injector pump basically. At least on my two New Holland diesel tractors, my Cat dozer, my Duramax. Maybe there are some that have filters between the fuel tank and the first pump, but I have never seen one. But I only post what I have seen and experienced and I definitely make no claims to knowing it all. Just trying to help a fellow RVer troubleshoot before heading to a dealer.
 
OK, Thanks to all you guys keeping me going.
We got underneath, trying to see across the top of fuel tank, to see if we saw any indication of a pump. (The one that someone posted a picture of looked very similar to ones we have changed on chev pickups.) Could not tell if it had a pump, but did see what looked like a slobber tube hanging over the top edge of the tank. Figured it must be pressure relief to keep tank from burping back on you while filling up.
We put the water separator filter & bowl back on, opened the bowl drain and put air into the slobber tube. When fuel started running, we closed the bowl drain valve, put the second filter on and left it loose. Put air back in the slobber tube until it started leaking. Tightened up the filter and cranked.
It started on 3rd or 4th crank.  :) :D ;D

I will still call winnebago & try to find out if there is a lift pump at the tank.

 
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