Is there a check valve in the Fuel Suction Line?

Wobbly · **Posted:** Mon May 19, 2008 7:56 pm

Is there a check valve in the Liberty CRD's fuel suction line, perhaps like the "drainback check valve" shown here: http://www.glacierdieselpower.com/image ... xposed.pdf

BlackLibertyCRD · **Posted:** Mon May 19, 2008 8:15 pm

It would be at the fuel head inlet. That causes the fuel head to hold vacuum and release air bubbles from the fuel. The air accumulate at the top near the check valve unable to escape until bleed off. Some diesel fuel don't have much air in it so no problem. When I'm on the west coast I never have a problem, here on the east coast I have problems so I added a lift pump to prevent the fuel head from going under vacuum. Without the check valve the fuel in the lines will drain back to the tank causing starting problems.

Wobbly · **Posted:** Mon May 19, 2008 10:30 pm

BlackLibertyCRD wrote:

It would be at the fuel head inlet. That causes the fuel head to hold vacuum and release air bubbles from the fuel. The air accumulate at the top near the check valve unable to escape until bleed off. Some diesel fuel don't have much air in it so no problem. When I'm on the west coast I never have a problem, here on the east coast I have problems so I added a lift pump to prevent the fuel head from going under vacuum. Without the check valve the fuel in the lines will drain back to the tank causing starting problems.

Could some of the complaints of non-starting which are attributed to air in the fuel filter be caused by this check valve leaking? If it leaks, would not fuel move forward through the IP as well as back via the suction piping? Non-starting must be caused by lack of fuel at the IP. Air at the fuel filter would not prevent starting per se.

PS: Nice write up on your pump and bleeder job. Wish I had reviewed them yesterday before posting.

Wobbly

Joe Romas · **Posted:** Tue May 20, 2008 7:29 am

Wobbly.

On another thread it was determined the CP3 pumps have "feature" where they bleed the air themselves before starting. It was in a thread by DRHRV as I recall who's injector pump died after he updated to a CAT filter. It has been found with the 05 and 06 KJ CRD's they relocated the fuel filter head higher then previous models and that seems to be when air trapped in the filter heads became a problem. Air problems have been traced to every part of the fuel system from the push on connections on the tank to a loose hose on the fuel line at the CP3 :wink:

The hand prime pump has a valve in it. Before adding a pump I just put a plastic tube on the bleed screw and pumped till no air bubbles came out without closing the bleed screw each stroke. I've had a lift pump for about 9 months and have not had a drivability problem since. Air problems showed up the first day I bought it less then a mile from the dealership. Early VW's had a check valve in the tank and it caused cold weather problems and the cure was to remove them.

Joe

dgeist · **Posted:** Tue May 20, 2008 9:44 am

Wobbly wrote:

Is there a check valve in the Liberty CRD's fuel suction line, perhaps like the "drainback check valve" shown here: http://www.glacierdieselpower.com/image ... xposed.pdf

Wow. Interesting read. That really does motivate me not to let the levels run low in the tank.. of course they designed it so it would sacrifice overall performance to save the skins of those who run it a little too close to empty. Speaking of which, with the bypass limited at 8psi, what's the input pressure needed byt the VM2.8?

Wobbly · **Posted:** Tue May 20, 2008 2:29 pm

Joe Romas wrote:

Wobbly.

On another thread it was determined the CP3 pumps have "feature" where they bleed the air themselves before starting. It was in a thread by DRHRV as I recall who's injector pump died after he updated to a CAT filter. It has been found with the 05 and 06 KJ CRD's they relocated the fuel filter head higher then previous models and that seems to be when air trapped in the filter heads became a problem. Air problems have been traced to every part of the fuel system from the push on connections on the tank to a loose hose on the fuel line at the CP3 :wink:

The hand prime pump has a valve in it. Before adding a pump I just put a plastic tube on the bleed screw and pumped till no air bubbles came out without closing the bleed screw each stroke. I've had a lift pump for about 9 months and have not had a drivability problem since. Air problems showed up the first day I bought it less then a mile from the dealership. Early VW's had a check valve in the tank and it caused cold weather problems and the cure was to remove them.

Joe

The cascade overflow valve http://www.lostjeeps.com/forum/phpBB3/vie ... hp?t=25047 allows air to flow to the tank when starting. So if the check valve in the filter head leaks wouldn't fuel empty from the line from the filter to the IP and exit the pump through this valve? Air from the tank would flow back to the filter.
Bosch's literature on the common rail system shows an intank pump.

Wobbly

Joe Romas · **Posted:** Tue May 20, 2008 3:53 pm

Wobbly wrote:

So if the check valve in the filter head leaks wouldn't fuel empty from the line from the filter to the IP and exit the pump through this valve? Air from the tank would flow back to the filter.

Wobbly

As I see it there would have to be a air leak somewhere above the check valve to allow a leaky check valve to let the fuel run back into the tank.

But there does not have to be a air leak at all. Just air seperating from hot fuel then collecting in the hightest place in the fuel system, the filter head. It's been talked about before that with the high pressure of the common rail system he temperature of the fuel returning to the tank is hot and the air seperates. Also the fuel returned to the tank is dumped back into the basket in the tank where the pickup is. It's also been determined that at a certain fuel temperatue the engine power is cut back. It's a vicious circle :lol:

Wobbly · **Posted:** Tue May 20, 2008 7:11 pm

Joe Romas wrote:

Wobbly wrote:

So if the check valve in the filter head leaks wouldn't fuel empty from the line from the filter to the IP and exit the pump through this valve? Air from the tank would flow back to the filter.

Wobbly

As I see it there would have to be a air leak somewhere above the check valve to allow a leaky check valve to let the fuel run back into the tank.

But there does not have to be a air leak at all. Just air seperating from hot fuel then collecting in the hightest place in the fuel system, the filter head. It's been talked about before that with the high pressure of the common rail system he temperature of the fuel returning to the tank is hot and the air seperates. Also the fuel returned to the tank is dumped back into the basket in the tank where the pickup is. It's also been determined that at a certain fuel temperatue the engine power is cut back. It's a vicious circle :lol:

I see the problem thusly:

1. The engine won't start because no fuel is being injected.
2. No fuel is injected because rail pressure is too low.
3. Rail pressure is too low because there's no fuel in the high pressure pump.
4. No fuel is in the high pressure pump because no fuel is in the low pressure pump.
5. No fuel is in the low pressure pump because no fuel is in the piping from the fuel filter to the low pressure pump.
6. The fuel that was in the piping from the filter to the low pressure pump travelled back to the tank because of gravity.
7. Air travelled from the tank to replace the volume of fuel that travelled to the tank. Some of this air ends up in the fuel filter.
8. With enough battery capacity, and assuming that the starter didn't burn up, the low pressure pump would eventually pull fuel from the tank and the engine would start. It's a positive displacement pump and as such requires no priming.
9. Air in the fuel filter is a symptom, not a cause of non-starting.
10. Besides the proven mehods of using in-tank or inline pumps to get fuel to the low pressure pump, it might be possible eliminate the extra pump by looping the return line to the tank so that it has a high point above the fuel filter elevation. This would prevent fuel from draining from the line from the fuel filter to the low pressure pump and back into the tank when the engine is stopped.

The loop won't fix the performance issues though. As you note, an extra pump solves those problems.

Wobbly

Joe Romas · **Posted:** Wed May 21, 2008 7:30 am

Wobbly wrote:

I see the problem thusly:

1. The engine won't start because no fuel is being injected.
2. No fuel is injected because rail pressure is too low.
3. Rail pressure is too low because there's no fuel is in the high pressure pump.
4. No fuel is in the high pressure pump because no fuel is in the low pressure pump.
5. No fuel is in the low pressure pump because no fuel is in the piping from the fuel filter to the low pressure pump.
6. The fuel that was in the piping from the filter to the low pressure pump travelled back to the tank because of gravity.
7. Air travelled from the tank to replace the volume of fuel that travelled to the tank. Some of this air ends up in the fuel filter.
8. With enough battery capacity, and assuming that the starter didn't burn up, the low pressure pump would eventually pull fuel from the tank and the engine would start. It's a positive displacement pump and as such requires no priming.
9. Air in the fuel filter is a symptom, not a cause of non-starting.
10. Besides the proven mehods of using in-tank or inline pumps to get fuel to the low pressure pump, it might be possible eliminate the extra pump by looping the return line to the tank so that it has a high point above the fuel filter elevation. This would prevent fuel from draining from the line from the fuel filter to the low pressure pump and back into the tank when the engine is stopped.

The loop won't fix the performance issues though. As you note, an extra pump solves those problems.

Wobbly

Before the patient dies completly there are surley symptoms telling of the impending death :lol:

If ignored it will eventually not start or stop while running. If the driver ignores the symptoms yes it will eventually result in a no start :wink:

Granted some owners are not aware of what's going on. One constantly blasted me here for griping about the problem almost two years ago. Untill his wife called him one day :roll:

Is there a check valve in the Fuel Suction Line?

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