Air in fuel filter head - technical questions

turbobill · **Posted:** Sun Oct 02, 2011 6:27 pm

I have 2005 Limited CRD. Bought Nov 10, 2010 with 96,100 miles. Found this forum and did the ERM, ORM and read up on lift pump mod to fix the air in the fuel filter head problem. No problems at all for about 5 months, then my Jeep failed to shift into OD one day. Read that it may be caused by air in the fuel filter so I bled the filter head and the tranny worked fine. From May to recent times the period between having to bleed the filter head became shorter and shorter until is was about every 3 days. The Jeep always started fine and idled fine and would run just fine, only OD was not there. I have driven with the tranny not shifting into OD for many miles and the engine never faltered. I did have the tranny shift out of OD several times while I was driving the car and when I would check there was air in the filter head. Bleeding it always fixed the tranny shift problem. Verified I had the old style head so I replaced it. When I did the heater plug dripped Diesel so I think it was leaking.

Within 2 days of replacing the head the tranny stopped shifting in OD and there was air in the filter head. I did a very thorough job of bleeding and checked/tightened all connection on the filter head/filter/H2O sensor, thought it was residual air from the swap, but in a day the same problem occurred. The problem occurred several times.

I bought a Mr. Gasket (I know not the highest quality pump but relatively available and relatively cheap) diesel pump (4 to 7 PSI) and installed it next to the battery temporarily for a diagnostic check. Before I hooked up the pump outlet to my filter I hooked up a long section of hose, dropped in in a bucket and turned on the pump. Fuel was flowing almost immediately. I let it run until I was sure there was no residual air, then hooked up my filter and opened the bleed valve. I turned on the pump until I got a solid stream of diesel for a bit then closed the bleed valve.

The Jeep runs great. It has only been 24 hours but I checked the pump and it is hard as a rock, no air in the filter head (yet).

So my technical questions are:

Where did the air come from before installing the pump?
a. First look I thought it was the plastic connector to the metal fuel line at the tank, so I didn't think the pump would fix it as it should pull as much air in as the old design.
b. Can the air be feeding back from the engine's primary fuel pump via siphon since the filter is higher than the fuel tank?

I am concerned there is a latent problem that remains and that it will give me problems at some inopportune time. Is there any evidence that the lift pump will force air out of the filter head through the injectors? My hook up is not as robust as the original hook up with a pump and two more hose connectors.

I am going to run in this configuration for a couple of weeks and verify no problem then do a permanent install by the fuel tank. I am considering taking out the plastic to metal connector and installing the pump plastic in, metal out. I think I can find a spot for the install. Looks like at least one other person has put their lift pump in this spot, any advice would be greatly appreciated.

papaindigo · **Posted:** Mon Oct 03, 2011 8:00 am

Prior to swapping the fuel head you clearly had a source of air at the fuel heater plug. I'm somewhat speculating but after the fuel head swap you still could be getting air at the fuel head if the fuel filter or the WIF at the bottom of the filter are not on tight. This source would be masked by the lift pump. Grab a couple of dry paper towels and use them to carefully inspect around the fuel head to filter and filter to WIF interfaces any leak will show as a wet spot on the towel. Tighten as needed. FYI the fuel filter has a large outer and small inner gasket. When swapping filters the inner gasket on the old filter does not always come off; if it does not be sure to remove it as a double gasket (old + new) can cause the filter to not tighten up properly.

If no leak per above my guess would be the stock fuel pump probably "pulls/sucks" harder, in order to get fuel thru the filter than the lift pump. If so it's possible that the stock fuel pump alone is pulling air in thru one or more of the quick release fittings. The inline pump being lower PSI and upstream from the filter would be less likely to pull air into the system. Lots of folks run just fine with a lift pump (engine compartment or back by the fuel tank) so I'd be inclined to say just run with the lift pump and see how things do.

IMHO you do not have a siphon problem.

The only way to absolutely prevent air getting into the system would be to get rid of the quick disconnect fittings entirely. Then it really shouldn't matter whether you are running the stock fuel pump with or without an inline or intank pump. Vehicles ran just fine for decades with a "puller" pump driven by a cam off the engine but they all had solid fuel lines with only a bit of "rubber" connector (e.g. no quick disconnect - stupid worthless over engineered solution to a none problem). The only times I ever saw a problem with those old systems was if the "rubber" connector went soft it could collapse as fuel was pulled thru the lines.

turbobill · **Posted:** Thu Oct 06, 2011 10:09 am

Thanks, Papaindigo. I have gone over the system thoroughly looking for any signs of leaks and the system seems to be very tight.

After thinking through the system set up with a lift pump, I believe your second hypothesis is correct. I believe the lift pump provides a low pressure lift for the fuel AND prevents the lower pressure from the cam driven fuel pump from pulling air into the system BEHIND the pump. Since the only connectors behind the pump are the quick disconnects it appears that may have been the source of the leaks and now they don't leak air because the lift pump can't pull hard enough to move the air through the disconnects.

Should be a simple job to remove the fuel line supply disconnect and replace with a piece of fuel line rubber hose and clamps and see what happens. The plastic and metal lines seem to be the same OD so it should be simple enough.

I would prefer this solution as I can avoid installing an expensive lift pump, if I can get the same performance with an "air tight" system. 3 inches of rubber hose and two clamps are much less likely to fail that an inexpensive pump. I have searched the forum and have not found any documented "air in the fuel head" fix of removing the quick disconnects.

I will say that all of the benefits that have been listed by the forum after installing a lift pump are there on my CRD now. Less noise, smoother acceleration, easy starts, better fuel milage and NO AIR in the fuel head since the pump was installed.

Since my pump is mounted in the engine bay I can leave it, put the fuel system back "stock" with the quick disconnect removed and see what happens. If I get air back, I can go back to the pump and start saving my pennies for a Kennedy, or maybe an in tank lift.

If the system is tight and no air is brought into the system then I can see how long it holds. When I bought my truck it had 91,000 miles on it and still had the original style fuel head. It appears much of the service, if not all, was performed by the dealer, and I have to assume if there had been these type problems in the past the dealer would have at least swapped out the fuel head.

I am going to run the lift pump another couple of weeks to be absolutely sure the pump is a "fix" then remove the connector. I will report back to this thread later.

Thanks again Papaindigo.

papaindigo · **Posted:** Thu Oct 06, 2011 10:29 am

Apparently the CRD fuel lines are the same as for the KJ gasser which does have an in tank fuel pump. In the gasser system the fuel line is pressurized from the tank all the way to the engine and the quick disconnect fittings/O rings are designed to keep pressurized FUEL from leaking OUT. The CRD is the reverse in that the fuel system is not pressurized between the engine mounted fuel pump and the tank; in fact it's under something resembling a vacuum (not the right term but you get the idea) as fuel is pulled to the fuel pump. In this situation the quick disconnect fittings/O rings are are trying to keep AIR from leaking IN. In an ideal world the latter would be ok but if air is leaking in at one of these fittings it's unlikely that fuel will also leak out, diesel being less viscous than gas, which makes finding air leaks extremely difficult at the fittings, in contrast to right at the fuel head.

Your idea of replacing quick disconnects with hose is fine and others have done so. However, it is my understanding that there is a quick disconnect located on top of the fuel tank such that replacing it with hose involves dropping the tank. Not a terribly difficult job per other posts on the forum but if a lift pump solves the problem why bother IMHO.

turbobill · **Posted:** Thu Oct 06, 2011 1:43 pm

Papaindigo, the only reason to replace these quick disconnects with firm connections would be to obviate the need for the lift pump and save both the cost and any future reliability issues with the pump. I am using a "cheap" ($50) pump and would not feel comfortable doing long distance road trips with this pump having to operate continuously for 6 to 8 hours at a time. I would be looking at least at a Kennedy ($300) or an in tank lift pump ($400).

Thanks for the input on the quick disconnect on the top of the fuel tank. I will do some research before I cut the quick disconnects out of the system.

papaindigo · **Posted:** Thu Oct 06, 2011 2:09 pm

For what it's worth: 1) yes if I had the time I'd drop my fuel tank and get rid of all the quick disconnects; 2) I'd certainly do #1 before spending the $s to do an in tank pump if an in line lift pump did not fix the problem; 3) the Kennedy single pump is currently $220+shipping direct from Kennedy; 4) I have a Facet 40109 marine rated pump that's supposed to be able to run almost forever but have yet to install it as a 2n gen fuel head solved my air in fuel problem; 5) some such as BlackLibertyCRD wire their in line pump so it only runs at startup for like 30 seconds to push air thru the system (seems to work fine); and 6) BlackLibertyCRD even came up with an interesting way to automatically bleed the fuel head into the fuel return line (e.g. dump any air back into the fuel return).

If you have any interest in the latter 2 items email me an I can send you the writeup.

turbobill · **Posted:** Fri Oct 07, 2011 2:32 pm

Papaindigo, I cut out the quick disconnect between the metal line and the plastic line today and replaced with 3 inches of rubber fuel line. I have also disconnected my inline fuel pump. Interestingly, I have notices some episodes of rough idle and one hard start with the inline fuel pump before cutting out the quick disconnect. After my idle was VERY smooth, even better than when I first put in the in line pump. I think I was getting air from the quick disconnect. I have a road trip Saturday, about 370 miles round trip so I can get a good test on whether my fuel system is air tight now. Oh, after disconnecting the in line pump my idle remained Very smooth and acceleration and starting are pristine.

We will see. I have sent PM.

Thank you for all your help. I will post results after I finish my trip this weekend. It may not be fully conclusive as the other plastic to plastic connection on top of the tank could have a small leak that will take several hundreds of miles to show up, but right now I am convinced my major air contributor, after I put the new fuel head on, was that quick disconnect.

It is very easy to get to so I think taking that connector out of the supply line should be a standard action for air in the fuel head problems.

Joe Romas · **Posted:** Sun Oct 09, 2011 4:11 pm

Turbobill

Many here, myself included, think if the lift pump in a Cummins powered Ram is good enough for same it will certainly work well for a CRD :BINGO:

The second plastic fitting on the tank is for the return and should not cause air in the fuel problem.

turbobill · **Posted:** Sun Oct 09, 2011 5:46 pm

So we finally reach the end of this post. First, thanks to Joe Romas for responding. I agree with you completely, a lift pump will work just fine. In tank is preferable to in line as far as operating and maintaining the CRD is concerned, but there is a cost and hassle factor, for me, that I am taking into account.

I cut out the supply line quick disconnect and put my fuel feed back stock, hoping the quick disconnect was the source of my air. I drove 410 miles on Saturday and my CRD performed flawlessly. I drove the Jeep to church this morning and the tranny would not shift into OD - air in the fuel head again. So I have reconnected my pump and all is well again, the quick disconnect was not the source of my air or at least not the only source.

All my connections are tight, completely leak free as far as diesel is concerned. I am running a Mr. Gasket Diesel, only low pressure pump (4-7psi) and it is working great. My concern is the ultimate longevity of the pump. I know the Kennedy is very reliable and Papaindigo has suggest I look at the Facet marine pumps, which I am doing. I would like to have a centrifugal pump line the Kennedy since the system could draw fuel through the pump if it stopped rotating. I would like to avoid a diaphragm pump if possible since it would serve as a block if it failed, stranding the driver. I have seen lots of write ups on the forum on various pumps but, other than people defending what they own, or not minding it if they are stranded occasionally, most positive write-ups are on the Kennedy.

So I am officially joining the "danged if I know where the air is coming from, but a lift pump is an easy technical fix so I am now a pump man" crowd. The pump REALLY makes my CRD idle smooth, accelerate nicely and even runs quieter, especially since I cut out the quick disconnect.

turbobill · **Posted:** Mon Oct 10, 2011 4:36 pm

Just a final note. Inline pumps always say to install as close to the tank and lower than the tank. The manufacturers say that the pump should NEVER be used as a PUll pump, only as a push pump, but many of us have pumps installed under the hood and they work great. Thinking about this my conclusion is that since the pump is more of an assist pump since it is inline with a much more powerful pump, the lift pump never has to lift fuel, in fact the pump will pump against a pressurized fuel filter. I don't think that there are any appreciable differences in stress on the pump, where ever it is installed in the fuel delivery piping other than at start up or if you run the fuel tank dry.

Just my two cents.

Air in fuel filter head - technical questions

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