Occasional cough, very occasional stall. Help!

todski

New member
Hi,

2005 2.2l 4 cylinder 311CDI Uk.

I get an occasional cough when driving like I'm getting the odd bad firing in a cylinder. This happens most often when I'm sitting at a steady speed and then need to put my foot down a bit to go up a hill or overtake. Sometimes it stalls it. When it happens the temp guage jumps up a bunch and goes down just as fast.

The van had a bad case of the black death so I've resealed all the injectors, had one new (fluffed the extraction of one and broke it). Did all the filters, oil, air, cabin air, and fuel at the same time. Happy to say all the injectors seem well sealed and dry after 2000 miles. The problem started about 1000 miles ago.

I thought "this must be an injector" so I did a leak-off test (see the picture). I had only short lengths of tube (about 5 inches) so I only ran the engine for under 10 seconds for the three old (probably really old) injectors to fill their tubes. The new one (refurbed, on the left in the picture) had dramatically less fill. I did it a couple of times to check I hadn't done anything stupid like make a bad connection with the tube..



While I did the leakoff test I noticed some air bubbles in the fuel pipe going to the fuel rail. Theres also a big bubble sitting at the top of fuel filter. See pic:



So my questions are:
-How do I bleed these bubbles out of the fuel system?
-What do you think of the results of the leakoff test?

Thanks a bunch!!!
 
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MillionMileSprinter

Millionmilesprinter.com
There was no photo attached, but based on your description, you've got two things going on:
1. The tubes should be no more full than about an inch or 2.5cm. Any more than that, you should look at replacing them. Full tubes? without a doubt, replace them.
2. Bubbles in the fuel line speak to a leak in the fuel system somewhere. Usually its at the filter.
Both of these conditions will lower the fuel pressure and (at least in the US Sprinters) will cause the ECU to shut the van down or it will just be starved for fuel and shut down on its own.
 

autostaretx

Erratic Member
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todski

New member
There was no photo attached,
Ooops, wrong button. Been a long time since I used a forum! I'll try n get the hang of it.

but based on your description, you've got two things going on:
1. The tubes should be no more full than about an inch or 2.5cm. Any more than that, you should look at replacing them. Full tubes? without a doubt, replace them.
Ok, damn, thats gonna cost!

It should be noted that I did the leakoff test with the engine running and the sensor plugged in, not just turning over without the sensor.

Also, the refurbed injector isn't the exact same part number I've realised. Its A 613 070 08 87 and the other older injectors are A 611 070 06 87. The parts place said it'd fine. Anyone care to tell me if that's true?

...cause the ECU to shut the van down...
That has happened a couple of times.. However, it started before I changed the fuel filter - it was the last filter I did, and I was't going to do it (because it looked hastle to get the clips off) until the coughing started..

I've searched this forum for "air in fuel pipes" and there are a LOT of similar questions, so sorry for asking another:

Is it possible that air would get in through the fuel rail to injector fuel pipes? That's the only place I fiddled with the fuel supply massively before I changed the fuel filter. I didn't get them to fit back hugely satisfactorily. Possibly one or more got bent hacking out black death? Any tips for bending them back to shape or should I fork out for a couple of new ones?

I found on this forum that I should shake the connection at the center hole of the fuel filter to see if air goes in. It did not. I also found that I should ensure the connections look like AlteredSprinter's diagram. Check.

Thanks for your help anyway, appreciated.
 
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MillionMileSprinter

Millionmilesprinter.com
in a word, NO. The fuel at the filter is under NEGATIVE pressure because it is being SUCKED up from the tank, through the filter and into the low pressure fuel pump on the front of the engine block. So any "leak" before the pump will suck air IN. On the other side of the fuel pump it's under POSITIVE pressure, which means that if there's a "leak" as we usually think of it: a puddle of fuel will appear.
The engine would cut out before you changed the fuel filter because of the worn out injectors (as evidenced by the leak off test).
Its probably still the same reason after you changed the fuel filter, but the bubbles in the fuel line are most DEFINITELY from a leaky seal at the fuel filter.
The bubbles only make the fuel pressure even lower (air compresses more than diesel fuel) so you are probably stalling out even more now...
 
B

billintomahawk

Guest
The diverter valve is a mystery to me.

What is it's role. What does it do?
I imagined several roles for it.

What happens if it leaks?
Or breaks?
bill in tomahawk
 

Nautamaran

2004 140” HRC 2500 (Crewed)
The bypass valve is a thermistat that uses warm fuel returning from the engine to preheat the fuel heading back towards the engine. This has advantages during combustion, and it helps thin the fuel in colder conditions making it easier for the low pressure pump to lift fuel through the filter element.

But since the return line is now connected to the supply line, any air in the system has a second chance to be sucked through the engine... I imagine the engineers thought of that and designed the valve to discourage bubbles from being diverted, but it’s still possible, so a malfunctioning valve failing open would make it harder to purge air from the system by recirculating it, and failing closed would leave the fuel cold, with an increased viscosity that would result in a higher vacuum and more air being pulled through any leaks (which is likely why MB went to a lift pump in the tank?).

-dave
 
B

billintomahawk

Guest
The bypass valve is a thermistat that uses warm fuel returning from the engine to preheat the fuel heading back towards the engine. This has advantages during combustion, and it helps thin the fuel in colder conditions making it easier for the low pressure pump to lift fuel through the filter element.

But since the return line is now connected to the supply line, any air in the system has a second chance to be sucked through the engine... I imagine the engineers thought of that and designed the valve to discourage bubbles from being diverted, but it’s still possible, so a malfunctioning valve failing open would make it harder to purge air from the system by recirculating it, and failing closed would leave the fuel cold, with an increased viscosity that would result in a higher vacuum and more air being pulled through any leaks (which is likely why MB went to a lift pump in the tank?).

-dave
So just to be clear, fuel is sucked from the tank into the fuel filter by the low pressure pump. This same vacuum pulls that fuel out of the fuel filter up to the high pressure pump which(after compressing it) sends it on to the injectors. The fuel that is not injected is returned to the fuel filter or the tank depending in part on the temperature of the fuel in the filter. This decision is made by a thermo valve in the diverter valve that shunts fuel to the filter rather than allowing it to return to the tank directly.

And for the reasons you listed the diverter valve an contribute to starting and restarting problems.

Geez Dave, it looks so innocent. An innocent killer.

Guess I need spare.


bill in tomahawk
 
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todski

New member
I've got new injectors to replace the bad ones, I'll have Saturday free to do it.

Thinking about the air in the line - is it possible that not priming the fuel filter has left air trapped in the system? Or does it automatically purge air, and it's coming in?

I've got a new Vass connector and line from low pressure pump to filter ordered. The white legs clip at the top of the fuel filter Vass connector is broken so, if air is going in, I think it's there.

Finger crossed the Vass connector and low pressure pump/filter line will rid it of air, but I'm worried I've got air trapped in there and it's not purging.
 

todski

New member
I installed the new injectors today. Also renewed the line to the low pressure pump. It started up after not too much cranking.

The renewed line is very clear so I could see a lot of air going round straight after the changes, but it soon cleared down to only the odd big bubble going through the line. Took it for a test drive. Could feel the difference with the new injectors! Engine cut out going up hill with the EDC light coming on but started again straight away. Did it again on another steep hill at home.

Opened the hood and there's sort of the same size air pocket that was at the filter before.. Wasn't that joint/o ring which I changed!

So I started her up again and put one end of a big screw driver on each the three connectors. The one which has two hoses with a T junction that goes onto the filter (I'm assuming this is the bypass valve??) was making a suspicious slurping sound. However, this is the old T junction and the new MANN filter came with a new o ring.. My question is

How does this T junction work? You've got two lines on it, one looks like it connects to fuel return pipes, where does the other come from or go? Is it powered by low pressure or is it fed by pressure from fuel return?

What about the third connection - the one that fits on the L shaped metal tube, that fuel from the tank?

Just trying to get my head around how this fuel filter is working and the connections. I've looked through the parts manuals and they have the same type fuel filter in 04 and before.. but the parts manual doesn't include this T junction valve even though the filter in the manual has the same port on it! Grrrr.

I tried the method by hkpierce on using a Vass connector and a pump on the top connector of the low pressure pump - this to see if I had somehow trapped air in the fuel filter. I got clear fuel coming through but lots of bubbles - loads when I really jacked the pressure up.. When I do this, what is the vacuum I'm creating actually sucking? Only the tank? Or does it pull through this T junction valve too?

Thanks for any thoughts, I'm trying to plan what to do should I still have problems after I change the valve and the valve o ring.
 

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