Air in fuel

CATCRD · **Posted:** Wed Aug 08, 2007 5:16 pm

CATCRD wrote:

I already tossed the stock fuel filter when I converted to the Cat one. Short of buying a new filter, does anyone know the measurements of the seal in question between the heater puck and the mounting head? I bet I could find something if I knew a rough size to look for, thickness, etc.

Would the seal off a 1R0750 work? It's probably 1/4" thick though.

Bump. Anyone remember how thick that seal they pulled off of the old mopar filter was?

mikec1203 · **Joined:** Tue Nov 28, 2006 10:16 pm **Posts:** 9

Just for one more data point, here is my experience: I had the oem filter and head for 18k miles. For the last 10k of that I had pretty severe bucking when letting off of the accelerator after getting up to speed in 5th (60mph) or after a “floor-it” pass, worse when engine was cold. I had the TC replaced under the recall because the shop thought that was the problem with the bucking. They did not replace the trans pump.

At 18k I put on the CAT filter conversion. The bucking disappeared completely and the Jeep ran great. However, I started having problems with the engine cutting out right after a start. I could get 10 to 12 pumps on the primer then crack the bleed valve and get lots of air. It would start and run fine after I did this. Next day I would need to do it again or it would cut out right after starting. Note that it would never cut out if it was running already, just on start up (within 5 seconds of starting). Also not that I could never see any seeping or leakage in the fittings or at the puck/head seal. I did replace the puck/head seal with a filter seal when I put the CAT filter conversion in.

Not seeing a way to remedy the air problem easily, I bought the complete head/filter assembly on-line for about $125 and installed that. Starting problem seems to be gone, there is still no bucking when letting off of the throttle in 5th (I think the original filter had just gotten plugged up to some point). However, I still get about six pumps on the primer at any time. I can also pump it up and bleed, leave the vehicle without starting, come back a few hours later and get five more pumps. Still don’t see any seepage anywhere. Also, once while pumping I could hear gurgling that sounded like it was in the tank??

Anyhoo, I took the Jeep to a new dealer because I’m still seeing oil at the engine/trans interface (rear main seal was replaced six months ago) and I’m having some noise from the transmission at take off as well as a vibration under acceleration. Also told them about the cutting off problem and being able to bleed air from the filter any time I try. They said that there is a flash for the PCM that addresses the air in the filter!!?? They have done this on my Jeep. Wondering if it is true or just them not really knowing what’s going on. They are also going to put in the upgraded trans pump and cooler, saying they always do that on the converter recalls. I wish the first dealer had done that.

Sorry for the long post, just wanted to relay my experience to add data.
Regards,
Mike

Cowcatcher · **Posted:** Thu Aug 09, 2007 1:17 pm

I don't know how one could possibly eliminate air in the fuel system with a flash. Just seems impossible.

bugnout · **Posted:** Thu Aug 09, 2007 1:50 pm

mikec1203 wrote:

Not seeing a way to remedy the air problem easily, I bought the complete head/filter assembly on-line for about $125 and installed that. Starting problem seems to be gone, there is still no bucking when letting off of the throttle in 5th (I think the original filter had just gotten plugged up to some point). However, I still get about six pumps on the primer at any time. I can also pump it up and bleed, leave the vehicle without starting, come back a few hours later and get five more pumps. Still don’t see any seepage anywhere. Also, once while pumping I could hear gurgling that sounded like it was in the tank??

Did you reinstall the CAT filter on the new head or are you stock?

I've had similiar experience. No leaks or sepage, can bleed air anytime. CRD starts great when cold takes a couple extra cranks when warm. I never bleed the air before I added the bleed valve and CAT filter, but thats not to say that it wasn't there, I just never did it. I also don't remember if it took a couple of extra cranks when warm on the stock filter or not. Just didn't pay attention.

The more I read about the injection pump and the fact that its sucking fuel through the filter, the more I think that the air is being forced out of solution in the filter, and the fact that the head is the highest point on the fuel system means its the collection point.

I don't have a lot of experience but it seems to me what is needed is an air scrubber that can release any air that collects in the filter head. if we can just replace the bleeder valve with something like that then Bob's your Uncle.

BVCRD · **Posted:** Thu Aug 09, 2007 2:53 pm

Cowcatcher wrote:

I don't know how one could possibly eliminate air in the fuel system with a flash. Just seems impossible.

It is. The computer isn't the issue. Even IF you replace the fuel head gasket, that won't solve the air problem IF the air is microscopically suspended in the fuel. No way out of this situation with the current configuration, in my mind. What we need is a newly designed filter head, and/or one of those burper things that they used when home brewing beer that lets the CO2 gas out.

UFO · **Posted:** Thu Aug 09, 2007 7:31 pm

BVCRD wrote:

Cowcatcher wrote:

I don't know how one could possibly eliminate air in the fuel system with a flash. Just seems impossible.

It is. The computer isn't the issue. Even IF you replace the fuel head gasket, that won't solve the air problem IF the air is microscopically suspended in the fuel. No way out of this situation with the current configuration, in my mind. What we need is a newly designed filter head, and/or one of those burper things that they used when home brewing beer that lets the CO2 gas out.

But you would need pressure to push it out, and the line and filter are under suction. What ultimately is needed is a fuel tank return at the top of the filter head, like a Mercedes diesel. Or a low pressure pump to push air and fuel through the filter head, if the lift pump will tolerate it. If the lift pump truly is a gear type (displacement) pump, that may not be possible unless it has a pressure bypass.

retmil46 · **Posted:** Sat Aug 11, 2007 1:38 pm

Racor's take on entrained air in fuel.

http://www.parker.com/racor/productCatalog/2007/7480G%20CD%20(04-16-2007)%208.pdf

retmil46 · **Posted:** Sat Aug 11, 2007 1:57 pm

Part 2 from Racor on air in diesel fuel.

http://www.parker.com/racor/productCatalog/2007/7480G%20CD%20(04-16-2007)%209.pdf

techTim · **Posted:** Sat Aug 11, 2007 2:26 pm

Some visible bubbles can be the result of fuel
going into a vapor. Depending on the fuel
temperature, at about 12 inches of mercury,
diesel fuel will begin to vaporize and a stream of
bubbles may be seen emanating from the point of
the lowest negative pressure. Fuel vapor bubbles
disappear as soon as the negative pressure is
removed or after the fuel is pressurized on the
pressure side of the transfer pump. The proof
that air bubbles are air and not vapor is that they
appear when there is very little negative pressure
involved. They also do not disappear after being
pressurized by a lift pump, unless of course the
pressure is high enough to compress them beyond
the point of visibility (about 50 microns or less).

(quote above from RACOR PDF)

so, the vacuum system is allowing entrained air to become visible, i.e. problematic? and a lift pump will not help? or will a lift pump negate the vacuum altogether.
seems to me that the common rail pressures would be enough to compress the air bubbles.
A "burp" valve, or in this case, a T with an orifice and return to tank, as mentioned in the RACOR PDF, should prevent air from getting into the CP3 and common rail system to begin with. right?

(quote)
Racor has two filter assemblies available that will
solve the problem. The 600 Series has an outlet
directly on top that, when connected with an
orifice fitting, will send any air directly to the return
system. An air vent must be fitted with an orifice
between 0.020 to 0.040 inches (0.5 to 1.0 mm).
This filter series is available in four sizes and can
handle flow rates up to 120 GPH (454 LPH).
Models 325 and 330 provide a location for an
air vent fitting that is designed to do the same
thing. The air vent must be fitted with an orifice as
mentioned above. These models will handle flow
rates up to 75 GPH (284 LPH).
If it is not convenient to change to a different filter
head, another solution is to provide a tee fitting
in the outlet or outlet line with one of the tee’s
ports aiming straight up and connected to a line
leading to the return system. This air venting port
of the tee fitting must be fitted with an orifice as
mentioned above.

what do you guys think about this idea?

MACKJ · **Posted:** Sun Aug 12, 2007 7:37 am

techTim wrote:

Racor has two filter assemblies available that will
solve the problem. The 600 Series has an outlet
directly on top that, when connected with an
orifice fitting, will send any air directly to the return
system. An air vent must be fitted with an orifice
between 0.020 to 0.040 inches (0.5 to 1.0 mm).
This filter series is available in four sizes and can
handle flow rates up to 120 GPH (454 LPH).
Models 325 and 330 provide a location for an
air vent fitting that is designed to do the same
thing. The air vent must be fitted with an orifice as
mentioned above. These models will handle flow
rates up to 75 GPH (284 LPH).
If it is not convenient to change to a different filter
head, another solution is to provide a tee fitting
in the outlet or outlet line with one of the tee’s
ports aiming straight up and connected to a line
leading to the return system. This air venting port
of the tee fitting must be fitted with an orifice as
mentioned above.

what do you guys think about this idea?

Already on it, half finished my fix.
PM me if interested.

retmil46 · **Posted:** Sun Aug 12, 2007 11:18 am

techTim wrote:

Some visible bubbles can be the result of fuel
going into a vapor. Depending on the fuel
temperature, at about 12 inches of mercury,
diesel fuel will begin to vaporize and a stream of
bubbles may be seen emanating from the point of
the lowest negative pressure. Fuel vapor bubbles
disappear as soon as the negative pressure is
removed or after the fuel is pressurized on the
pressure side of the transfer pump. The proof
that air bubbles are air and not vapor is that they
appear when there is very little negative pressure
involved. They also do not disappear after being
pressurized by a lift pump, unless of course the
pressure is high enough to compress them beyond
the point of visibility (about 50 microns or less).

(quote above from RACOR PDF)

so, the vacuum system is allowing entrained air to become visible, i.e. problematic? and a lift pump will not help? or will a lift pump negate the vacuum altogether.
seems to me that the common rail pressures would be enough to compress the air bubbles.
A "burp" valve, or in this case, a T with an orifice and return to tank, as mentioned in the RACOR PDF, should prevent air from getting into the CP3 and common rail system to begin with. right?

That's the whole idea of a lift pump, or as they also call it in the Racor pdf, a transfer pump. Instead of a vacuum in the filter and supply to the CP3, you have a positive pressure. If you check on other diesel forums - TDI, Duramax, Powerstroke, etc - just by keeping the supply side at a positive pressure it has minimized and/or eliminated the effects of fuel vapor and entrained air.

Note what it says about diesel vapor. The vapor bubbles disappear once the negative pressure is removed, or the fuel is pressurized by a lift pump. The lift pump by itself will eliminate this part of the problem.

It also says that depending on temperature, diesel vapor bubbles will form around 12" Hg vacuum. The higher the fuel temp, the lower the vacuum required for these vapor bubbles to form, and also that much easier for entrained air to come out of solution and form visible bubbles of a size and amount that can affect the suction of the CP3. Besides keeping the fuel temps at a level that will ensure good lubrication of the CP3 and prevent the ECM from reducing engine output once these temps reach a certain point, that's the other reason I added a fuel cooler in the return line.

Ranger1 has actually observed the formation of diesel vapor and air bubbles in the plastic prefilter he has installed prior to his Racor filter. He noted that with the lift pump running, the prefilter stayed full of fuel at idle and also when he revved the engine several times. For comparison, he turned off the lift pump, so that he was running as a vacuum system, and let the engine run for several minutes to ensure it was at stock vacuum levels. He then revved the engine again, and saw vapor/air bubbles literally boiling out of solution on the downstream side of the prefilter. Once he turned the lift pump back on, the bubbles went away.

With a vacuum on the fuel system, the difference in pressure across even a coarse prefilter was enough to cause the formation of visible vapor/air bubbles. Now imagine what is going on with a CAT 2 micron filter.

To make use of the orifice vent on the outlet of the filter and recirc any air back thru the return line to the tank, it's going to be much easier if you have positive pressure on the outlet of the filter instead of a vacuum - ie, a lift pump.

Note that they said visible air bubbles appear with very little negative pressure (vacuum). That implies that if you keep the supply side at a positive pressure with a lift pump, you can minimize the formation of large visible air bubbles that would adversely affect the CP3.

Going by the Racor pdf, a lift pump by itself should eliminate diesel vapor bubbles altogether, and minimize the formation of air bubbles of a size that could affect the suction and operation of the CP3 injection pump. An orifice vent on the outlet of the filter, coupled with a lift pump, would help get rid of any large visible air bubbles that do form.

The problem we're seeing with isn't on the high pressure rail side. 25,000 psi should easily compress any air bubbles that are present at this point. The problem is on the supply side, having air mixed in with the fuel to the point that it causes the low pressure side of the CP3 to lose suction, such that it is unable to supply the high pressure side of the pump with sufficient fuel to maintain adequate rail pressure to the injectors, and also tha lack of lubrication caused by too much air which can damage the pump itself.

If you read the first half of Racor's pdf, their premise is that entrained air in diesel fuel is a fact of life - you can't eliminate it, but you can deal with it.

MACKJ · **Posted:** Sun Aug 12, 2007 5:19 pm

[quote="retmil46
That's the whole idea of a lift pump, or as they also call it in the Racor pdf, a transfer pump. Instead of a vacuum in the filter and supply to the CP3, you have a positive pressure. If you check on other diesel forums - TDI, Duramax, Powerstroke, etc - just by keeping the supply side at a positive pressure it has minimized and/or eliminated the effects of fuel vapor and entrained air...
Besides keeping the fuel temps at a level that will ensure good lubrication of the CP3 and prevent the ECM from reducing engine output once these temps reach a certain point, that's the other reason I added a fuel cooler in the return line...
With a vacuum on the fuel system, the difference in pressure across even a coarse prefilter was enough to cause the formation of visible vapor/air bubbles. Now imagine what is going on with a CAT 2 micron filter.
To make use of the orifice vent on the outlet of the filter and recirc any air back thru the return line to the tank, it's going to be much easier if you have positive pressure on the outlet of the filter instead of a vacuum - ie, a lift pump... An orifice vent on the outlet of the filter, coupled with a lift pump, would help get rid of any large visible air bubbles that do form...
If you read the first half of Racor's pdf, their premise is that entrained air in diesel fuel is a fact of life - you can't eliminate it, but you can deal with it.[/quote]

What he said, summarised above.
Beautifully put Mitchell.

techTim · **Posted:** Mon Aug 13, 2007 11:41 am

so who has a lift pump that will work, I remember that someone (?) has installed a centrifugal pump so that if the pump should ever fail there is no restriction, that makes sense to me. What do we hear from MrMopar about the pressures affecting metering in the Dyno room, is that a concern?
I think my CAT filter will stay on the shelf till it is coupled with a lift pump, Drharv's problems spook me at this point.

Cowcatcher · **Posted:** Mon Aug 13, 2007 12:29 pm

techTim wrote:

so who has a lift pump that will work, I remember that someone (?) has installed a centrifugal pump so that if the pump should ever fail there is no restriction, that makes sense to me. What do we hear from MrMopar about the pressures affecting metering in the Dyno room, is that a concern?
I think my CAT filter will stay on the shelf till it is coupled with a lift pump, Drharv's problems spook me at this point.

That's where I'm at too although the CAT may never go on if the FEDS make Jeep change the filter head back to a RACOR with a recall.

BiodieselJeep.com · **Posted:** Mon Aug 13, 2007 12:41 pm

concerning the T'd in return line to take out air:

Correct me if I am wrong, but connecting a return line to the filter head would only work it you had possitive pressure on the main line (aka transfer/lift pump). Otherwise, with a suction system like ours, all you do is pull in the air and return fuel through...not force the air back into the return line.

retmil46 · **Posted:** Mon Aug 13, 2007 1:39 pm

BiodieselJeep.com wrote:

concerning the T'd in return line to take out air:

Correct me if I am wrong, but connecting a return line to the filter head would only work it you had possitive pressure on the main line (aka transfer/lift pump). Otherwise, with a suction system like ours, all you do is pull in the air and return fuel through...not force the air back into the return line.

Exactly.

retmil46 · **Posted:** Mon Aug 13, 2007 1:42 pm

techTim wrote:

so who has a lift pump that will work, I remember that someone (?) has installed a centrifugal pump so that if the pump should ever fail there is no restriction, that makes sense to me. What do we hear from MrMopar about the pressures affecting metering in the Dyno room, is that a concern?
I think my CAT filter will stay on the shelf till it is coupled with a lift pump, Drharv's problems spook me at this point.

That would be me, and a couple others by now. From Kennedy Diesel, www.kennedydiesel.com . Look under the categories he has on the website for Duramax engines.

techTim · **Posted:** Mon Aug 13, 2007 10:55 pm

thanks retmil,

MODs, what do you guys think about a sticky for the best lift pump, fuel cooler system, et all, etc.....?

oh, and mrMopar64, you out there?
what was the problem with running the lift pump? can the preventative thinking behind a lift pump coupled with a 2-3 micron filter protecting the CP3 and other high dollar (injectors, etc) parts lead us to other bad things?

Cowcatcher, any reason you think the feds in their infinite "wisdom" will step in here? I have a gut feeling they will, but that could be gas.

apologies for the ramble, been catching up today.

:wink:

Cowcatcher · **Posted:** Tue Aug 14, 2007 12:58 am

tech Tim,

While there have been no accidents that anyone is aware of or lost vehicles as a result of the leaking fuel head it is an accident waiting to happen when you have fuel, heat and electricity mixing. There have likely been close to a dozen complaints filed here alone with the Feds about this issue and they are monitoring this site and likely others plus they are being proactive on the issue in requesting us to supply them with more complaints. Assuming that they do act they already have as much or more in the way of identifying the problem as they may have had on the blower motor and other failures at other manufactures so it seems to me that they will lean on DC to correct the problem.

DC will have a couple of choices. First of all they can go back to Bosch and say fix it. If Bosch has not already started down that road it will take months to do, or DC can go back to the filter they used before the Bosch, Racor, and send Bosch the bill for 11,000 filter heads. When you are buying that many heads you are probably looking at a cost of $50K and I am not sure Bosch can fix theirs for so little money on a limited run product. I think it would be cheaper for both Bosch and DC to bit the bullet and replace the head with the Racor because I think the only other solution is to remold or redesign the puck and make it out of different material then replace the whole pump as there would be more shop labor in replaceing the puck rather than the whole head.

At least that's my story and I am sticking to it. :wink:

Joe Romas · **Posted:** Tue Aug 14, 2007 6:58 am

Cowcatcher wrote:

tech Tim,

I think the only other solution is to remold or redesign the puck and make it out of different material then replace the whole pump as there would be more shop labor in replaceing the puck rather than the whole head.
:wink:

Dave.
Did you mean PUMP or PUCK :?:

I'm thinking there is already a lot of wear going on in our pumps. MrMopar once wrote there is a coating in our pumps for wear but it seems to me when it wears it would fall off and cause great problems :roll:

(drvhard

)

Thanks
Joe

Air in fuel

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