Air in the fuel and fuel range, Ultimate Solution

Ripple · **Posted:** Sun Dec 31, 2006 10:33 pm

I'm just day dreaming here but I think it would be great if to both extend the fuel range, and fix the annoying bucking problems associated with an air leak in the fuel line, to fit a 30 Gallon stainless steel tank and a FASS pump with a filter and deaerator.

as far as the tank, it looks like custom made stainless steel tanks (I live in Ohio rust is a real threat) runs around $550. Also, if it was extended to 30 gallons it would push the range from ~420 up to 630miles. I would like extended range so I can go a week and the weekend on on fill instead of 1.5 fills. also a custom tank could get the much needed drain plug welded in too, in case of a bad tank of fuel.

the FASS pump runs around $600 and will prefilter (10 micron), deaerate and pump the diesel up to the front, rather than rely on the high pressure pump to vacuum it up to the front. from what I have been reading, having to vacuum fuel up the high pressure pump is the main reason some of us are getting air in the fuel.

please post comments and ideas.

Goglio704 · **Posted:** Sun Dec 31, 2006 11:06 pm

A lift pump to provide mildly pressurized fuel flow is on my wish list along with a primary fuel filter plumbed ahead of the existing filter. Several have mentioned it before. Mr. Mopar says the lift pump idea won't work, but didn't really elaborate as to why. The Duramax diesels are probably the most similar to our CRD in terms of fuel delivery, and a lift pump is a popular mod for them. I seem to remember reading something about having to engage the lift pump after starting on the Duramax to prevent hard starting. I know from the service manual that the output of the suction portion of the CRD injection pump is pressure regulated. I have a solenoid type lift pump that I may experiment with. If I get serious about this, I'll probably buy a centrifugal lift pump from Kennedy diesel.

http://www.kennedydiesel.com/

MrMopar64 · **Posted:** Sun Dec 31, 2006 11:52 pm

A lift pump is very bad for these engines. It will severly throw off the calibration for the fuel and is not good for the CP3 high pressure pump as it already features a gear-driven low-side suction pump internally. Black smoke, severe misfiring, and horrid fuel use leading to the washing of the cylinder walls and dilution of the oil will result from its use. DO NOT use a lift pump on the VM engine in the KJ CRD. Just a warning as I've been through this trial-and-error before with them.

Goglio704 · **Posted:** Mon Jan 01, 2007 12:42 am

Mr. Mopar,

First off, I'm not trying to argue. That would be pointless if you've tried a lift pump, but I do have some questions. What was the output pressure of the pump you used? It would take a while to find it back, but I know the service manual talks about the suction pump in the injection pump having a regulated output. Seems like that would prevent the overfueling you describe. I thought the Duramax also used the same pump with the built in suction pump. If so, I wonder how they make it work? Speaking as someone with a leaking fuel filter base, I can tell you that sucking fuel all the way from the tank is piss poor in terms of reliability and troubleshooting.

RFCRD · **Posted:** Mon Jan 01, 2007 1:06 am

Goglio704 wrote:

Mr. Mopar,

First off, I'm not trying to argue. That would be pointless if you've tried a lift pump, but I do have some questions. What was the output pressure of the pump you used? It would take a while to find it back, but I know the service manual talks about the suction pump in the CP3 having a regulated output. Seems like that would prevent the overfueling you describe. I thought the Duramax also used the CP3 pump with the built in suction pump. If so, I wonder how they make it work? Speaking as someone with a leaking fuel filter base, I can tell you that sucking fuel all the way from the tank is piss poor in terms of reliability and troubleshooting.

Try sucking fuel from 35 feet away from the fuel tank. Oh I forgot, commercial buses use real fuel lines and flaired fittings. One possible solution is to use a weak lift pump and a pressure regulator just ahead of the filter assembly. Mr. Mopar is correct, you have to be very carefull how much pressure you feed to the pump and return loop (which should have a special restriction fitting to regulate back-pressure). If this is like other unit-injector style systems, you also can't restrict the fuel return line or it will smoke like a freight train.

Goglio704 · **Posted:** Mon Jan 01, 2007 1:18 am

So the issue is overwhelming the return lines and creating backpressure? That would make some sense to me since the built in pump would dump its excess to the return system. If a lift pump caused there to be more return flow than the system can handle, I could see that being trouble. A regulator would fix that problem, but it might be hard to find one with the correct range.

greiswig · **Posted:** Mon Jan 01, 2007 1:53 am

MrMopar64 wrote:

A lift pump is very bad for these engines. It will severly throw off the calibration for the fuel and is not good for the CP3 high pressure pump as it already features a gear-driven low-side suction pump internally. Black smoke, severe misfiring, and horrid fuel use leading to the washing of the cylinder walls and dilution of the oil will result from its use. DO NOT use a lift pump on the VM engine in the KJ CRD. Just a warning as I've been through this trial-and-error before with them.

I'm with others, MrMopar...I'd like to hear more about this. First off, you say you've been through "this trial and error" before. What does that mean? Have you tried fitting a lift pump to this engine before and seen what you describe?

If so, what was the output pressure from the lift pump? Surely something like a 1-2PSI lift close to the fuel tank would alleviate the suction/air leak problems without overwhelming the stock pump. I wouldn't expect that to be a problem. But most lift pumps are more like 4PSI, I think. Are you saying that's the issue?

Ripple · **Posted:** Mon Jan 01, 2007 9:52 am

one reason for mentioning with the lift pump is that you can only vacuum up to a certain point, about -15 psig or 30 inches of mercury column. no matter how hard you suck, you only get -15psig vacuum.

so if the fuel filter is 1/2 plugged , and your running bio that is partially waxed in on a cold morning, plus normal line and filter restriction you can burn though that 15 PSI really quick. fortunately for us diesel and bio-diesel have very low vapor pressures. even then, I can still see a point were the vacuum gets down low enough to vaporize the fuel and create 'air' pockets.

I had another idea on the tank. if it's custom made, the bottom could be made of thicker steel to act a a built in skid plate. on the down side, the main area to take up space for the extra capacity would be toward the axle, wrapping around the pumpkin. making gear oil changes really hard to do.

Bgame · **Posted:** Mon Jan 01, 2007 10:15 am

MrMopar64 wrote:

A lift pump is very bad for these engines. It will severly throw off the calibration for the fuel and is not good for the CP3 high pressure pump as it already features a gear-driven low-side suction pump internally. Black smoke, severe misfiring, and horrid fuel use leading to the washing of the cylinder walls and dilution of the oil will result from its use. DO NOT use a lift pump on the VM engine in the KJ CRD. Just a warning as I've been through this trial-and-error before with them.

Looks like some people do not know what a FASS is and have never used one....

no-blue-screen · **Posted:** Mon Jan 01, 2007 10:16 am

Ripple wrote:

one reason for mentioning with the lift pump is that you can only vacuum up to a certain point, about -15 psig or 30 inches of mercury column. no matter how hard you suck, you only get -15psig vacuum.

so if the fuel filter is 1/2 plugged , and your running bio that is partially waxed in on a cold morning, plus normal line and filter restriction you can burn though that 15 PSI really quick. fortunately for us diesel and bio-diesel have very low vapor pressures. even then, I can still see a point were the vacuum gets down low enough to vaporize the fuel and create 'air' pockets.

I had another idea on the tank. if it's custom made, the bottom could be made of thicker steel to act a a built in skid plate. on the down side, the main area to take up space for the extra capacity would be toward the axle, wrapping around the pumpkin. making gear oil changes really hard to do.

This makes sense to me. I recently bled the air from my system by priming my pump and then opening the bleed valve several times until I got a steady stream of diesel coming from the bleed valve. The CRD ran much much better after that.

What you say makes senese to me because I was getting violet bucking after hard accelleration that would last for about 60 seconds or so. What I am guessing happened is that the engine was requesting more fuel than could be pulled from the tank which created air pockets and caused the bucking.

Again this is only a guess, but it seems to make sense. The problem I see with a lift pump is that you are adding pressure to the fuel system and and if the stock pump tries to regulate that pressure it can't which can cause bad things to happen. I don't know all the technicals, but it just seems like common sense that if a lift pump were adding say 2psi, and the stock pump tries to regulate pressure that the excess fuel has to go somewhere.

DarbyWalters · **Posted:** Mon Jan 01, 2007 11:03 am

There is a company in Austalia that makes an enlarged fuel tank. It is made of thick steel and acts as a skid also. I forgot how much bigger it was.

TJM ( the ones who made the bumper for OZ ) make custom tanks also in Australia:

http://www.tjmgeebung.com.au/explorer_fuel_tanks.htm

RFCRD · **Posted:** Mon Jan 01, 2007 11:11 am

Goglio704 wrote:

So the issue is overwhelming the return lines and creating backpressure? That would make some sense to me since the built in pump would dump its excess to the return system. If a lift pump caused there to be more return flow than the system can handle, I could see that being trouble. A regulator would fix that problem, but it might be hard to find one with the correct range.

My understanding is overwhelming the return lines and creating backpressure is the main reason this won't work. However, I probably mistated my point earlier. The issue is not the suction system design, it's the quality of the plumbing. Most lift pumps on diesels are used for system priming purposes only. Once a prime is obtained and the engine is running, the pump is turned off. As long as you have a primer mechanism (manual hand pump in this case) an aux pump unnecessary.

Virtually all commercial buses have Detroit Diesel engines using a suction system pulling fuel from a tank 35 feet away through 3/8 inch ID lines and double filters. The fuel pump is a constant-flow style pump which is gear driven off of the engine. It has only been @ 10 years since electric lift primer pumps have been available, then only as a special order option. Most experienced diesel mechanics consider an electric primer pump as a convenience item. Suction type systems are very reliable, as long as the plumbing is tight.

The problem with the CRD system is the quality of the hardware used. I can tell you that when (not if) my lines start to leak, they will get replaced with steel-braded lines and flaired compression fittings. Also, look carefully at the fuel filter head, it's a two-piece design. The heater unit is a separate, add-on spacer between the head and the filter. My theory is that thermal expansion & contraction from the heater is causing leaks to develop where the heater mates to the head. It is also possible that the force applied when changing the fuel filter causes the heater/spacer to loosten slightly and leak.

DarbyWalters · **Posted:** Mon Jan 01, 2007 11:18 am

Long Range Fuel Tank for KJ at :

http://www.longrangeautomotive.com.au

115L means 30.3 gallons

Goglio704 · **Posted:** Mon Jan 01, 2007 11:42 am

RFCRD wrote:

Goglio704 wrote:

So the issue is overwhelming the return lines and creating backpressure? That would make some sense to me since the built in pump would dump its excess to the return system. If a lift pump caused there to be more return flow than the system can handle, I could see that being trouble. A regulator would fix that problem, but it might be hard to find one with the correct range.

My understanding is overwhelming the return lines and creating backpressure is the main reason this won't work. However, I probably mistated my point earlier. The issue is not the suction system design, it's the quality of the plumbing. Most lift pumps on diesels are used for system priming purposes only. Once a prime is obtained and the engine is running, the pump is turned off. As long as you have a primer mechanism (manual hand pump in this case) an aux pump unnecessary.

Virtually all commercial buses have Detroit Diesel engines using a suction system pulling fuel from a tank 35 feet away through 3/8 inch ID lines and double filters. The fuel pump is a constant-flow style pump which is gear driven off of the engine. It has only been @ 10 years since electric lift primer pumps have been available, then only as a special order option. Most experienced diesel mechanics consider an electric primer pump as a convenience item. Suction type systems are very reliable, as long as the plumbing is tight.

The problem with the CRD system is the quality of the hardware used. I can tell you that when (not if) my lines start to leak, they will get replaced with steel-braded lines and flaired compression fittings. Also, look carefully at the fuel filter head, it's a two-piece design. The heater unit is a separate, add-on spacer between the head and the filter. My theory is that thermal expansion & contraction from the heater is causing leaks to develop where the heater mates to the head. It is also possible that the force applied when changing the fuel filter causes the heater/spacer to loosten slightly and leak.

I think the scenario you describe is possible for developing a leak, especially long term, but mine is actually leaking from inside the driver's side electrical connection. Pull the plug and operate the primer and you get a nice slow drip from inside the socket. The connections back at the tank are where I would expect trouble eventually. Once it transitions to metal tubing, I think it is one piece until it gets to the tank. I wonder if the suction pump in the CRD can pull through an additional filter without problems? I don't like the single filter setup, because I don't like messing with the last line of defense everytime I change a filter. Anytime you open that up to change the filter you put the pump at risk. My replacement filter wasn't even sealed up. Just a filter in a box. A little cardboard crumb fed to the pump would not be good. I removed the hose to the pump and pumped a quart through with the hand primer just to make me feel better. A primary filter ahead of the factory filter would let me leave the factory filter in place for 50k or more.

RFCRD · **Posted:** Mon Jan 01, 2007 12:06 pm

Goglio704 wrote:

I think the scenario you describe is possible for developing a leak, especially long term, but mine is actually leaking from inside the driver's side electrical connection. Pull the plug and operate the primer and you get a nice slow drip from inside the socket. The connections back at the tank are where I would expect trouble eventually. Once it transitions to metal tubing, I think it is one piece until it gets to the tank. I wonder if the suction pump in the CRD can pull through an additional filter without problems? I don't like the single filter setup, because I don't like messing with the last line of defense everytime I change a filter. Anytime you open that up to change the filter you put the pump at risk. My replacement filter wasn't even sealed up. Just a filter in a box. A little cardboard crumb fed to the pump would not be good. I removed the hose to the pump and pumped a quart through with the hand primer just to make me feel better. A primary filter ahead of the factory filter would let me leave the factory filter in place for 50k or more.

Looking at the same fuel leak on mine (atleast DC is consistant). My heater plug was wet when it came back from the dealer after they changed the fuel filter. I cleaned the socket and plug with some ether/solvent and haven't noticed any wetness since but haven't tried to use the primer pump.

I also don't like single filter systems. Looking at making an "L" bracket to suspend a course primary filter in front of the factory filter (use the mount position for the factory filter. There should be enough room to install a standard Detroit Diesel primary head & filter. One simple thing that I believe would help is installing a check-valve just ahead of the fuel filter to prevent back-flow to the tank. If you can eliminate back-flow, it is less likely a suction leak will cause an air pocket and/or loosing prime when the engine is off.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

I installed a clear, inline plastic filter in the inlet line to the CRD filter. Not having the time recently to fabricate anything else on this Jeep, I still wanted a way to see if any air bubbles or debris were in the fuel itself. My reason for this was some rough stumbling recently when starting - but that issue was solved by the air boost sensor cleaning. I'm interested in your check valve idea, especially if one that fits inline with the rubber inlet hose is available. If anyone has a link to an inline check valve suitable for our CRD diesel fuel, I'd be interested.

Just looking at the tremendous amount of knowledge shared on this forum over the last 18 months, it appears that these items need some kind of remedial modification if one wishes to keep their CRD past warranty:

1. Fuel line replacement (high quality) for fuel tank to body fuel line and body fuel line to fuel filter
2. Auxillary CCV or EHM to remove excessive oil mist from engine blow-by, at least on some CRD's, determined by CAC inspection.
3. Airbox modification to eliminate excessive dirt, debris and water into the air filter and MAF sensor
4. Transmission torque converter replacement, with correct stall speed and construction suitable for the VM Motori diesel engine
5. EGR modification to reduce soot level in the engine air intake plenum

Items 1 through 3 have been solved, with 5 still not widely available. 5 may be solvable with the ECM software from InMotion. Item 4 may become available in the future.

Until item 5 is solved, the items 1 - 3 in the following list maintenance is required to keep the CRD running correctly - item 4 recommended regardless.

1. Boost sensor inspection and cleaning at 5K intervals, inspection only at 3K mile intervals in case of premature soot blockage
2. CAC hose and intake cleanings, in case of oil leakage from the turbocharger seals - not required on all CRD's, but inspection at 10K intervals worthwhile
3. EGR flow control valve inspection and cleaning with safe, intake (non-oil based) spray cleaner, especially on the butterfly valve at 10K intervals
4. Inspection and tightening as required of all fuel line and CAC clamps at 5K mile intervals
5. Annual inspection of glow plugs with ohmmeter test

MrMopar64 · **Posted:** Mon Jan 01, 2007 3:02 pm

My experience with the lift pumps was with the engine on a dyno. I tried using pressures from 1psig up to 7-8psig and all had the same effects. What happens is that the internal gear pump on the CP3 delivers a certain pressure internally to the HP side of the CP3. By using a lift pump, you thus increase this pressure even more. The end result is that by having more pressure on the low-side, you throw off the calibration of the control of the HP metering unit (electric solenoid on the CP3). Additionally, force feeding the gear-driven suction is in no way approved by Bosch as per their documentation on the pumps.

How the Duramax owners solve this problem I am not sure as their CP3 pumps and EDC software are quite different. Based on what I saw, they only use it at certain times (i.e. WOT) where you want the extra fuel anyways if you're shooting for black-smoke performance.

In any case, not trying to stir people up, just trying to pass along my experiences and save you all the headaches on your daily driver.

Goglio704 · **Posted:** Mon Jan 01, 2007 3:56 pm

Mr. Mopar,

Thanks for the info. I am always ready to listen to the voice of experience. Apparently, if this was going to work, a person would have to regulate the input to the injection pump to stay in the negative range. Not really sure where a person would find a diesel ready regulator to do that. Time and money would probably be better spent improving the fuel lines if leaks develop. One other question: does the system monitor suction restriction? I would like to add a primary fuel filter , but don't want to do more harm than good by restricting the flow to the pump.

Ripple · **Posted:** Mon Jan 01, 2007 6:35 pm

Wow, sounds like there is alot more to the fuel system then I thought. I'm learning alot from this thread!!

Based on what I can see here, it sounds like best way to correct the fuel issue is to use better hardware to make the feed line and leave the overall design alone. so better hardware (AN style), a modest prefilter and a check valve close to the front is the recipe.

Also I emailed those aussie gas tank people. it's great they have this product already and is commercially available.

retmil46 · **Posted:** Tue Jan 02, 2007 12:53 am

On the lift pumps you used on the dyno - were they positive displacement or centrifugal?

After reading thru all the sections on the fuel pump, fuel delivery, and high pressure injection in the FSM, I have to say that I'm baffled as to how a lift pump could cause the severe problems you described. Was there perhaps some key difference between your dyno setup and what we actually have in the vehicles? Or perhaps using a positive displacement pump that was truly trying to force-feed everything, vice a centrifugal pump?

Not doubting what you're saying, just trying to understand why as little as 1 psi on the suction of the low pressure gear pump could cause such problems on the high pressure side. There could conceivably be situations in which you could inadvertently have positive pressure on the suction of the pump (ie, fuel tank vent becomes clogged and builds up pressure in hot weather or from hot return fuel). If nothing else, it might help from a future troubleshooting standpoint to understand how sensitive this is.

Perhaps the FSM doesn't go into enough detail describing what's going on, but as I said, from reading thru it, I still can't understand how 1 psi on the suction of the gear pump could cause severe misfiring and oversupply of fuel in the high pressure rail with electronically controlled injectors.

By the FSM, the output pressure of the gear pump is regulated to 78 psi max by the cascade overflow valve, which maintains pressure by recircing fuel to the suction side of the pump, not the fuel tank. From the way it was described, this is basically a spring loaded relief valve.

The electric solenoid valve controls the suction to the high pressure pump. From what I understand, the ECM controls this valve using pulse width modulation (PWM), cycling it to regulate the output of the high pressure pump and maintain pressure in the high pressure rail (along with the fuel rail solenoid valve), by comparing actual pressure in the high pressure rail against it's programed value for XX conditions.

On top of this, the go/no go test for replacing the primer pump on the filter head is that it should be able to pressurize the fuel filter to at least 10 psi when repriming the system. If it can't achieve 10 psi, it has to be replaced. In other words, the suction of the low pressure pump could be up to 10 psi and higher on startup after repriming the fuel system.

Air in the fuel and fuel range, Ultimate Solution

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