Bubbles not welcome -odd air in fuel system - Page 2 - PeachParts Mercedes-Benz Forum

Diseasel300 · #16 05-25-2018, 10:54 AM

Can you actually SEE the bubbles coming up the tube from the IP? On an OM616/7 there is a spring-loaded check valve in the banjo bolt on the return line from the IP. Assuming it isn't all corroded, it should prevent air from passing through. That would leave your only source of air as the crush washers back there OR elsewhere in the system. Keep in mind that air rises, any air trapped in the system will show up at the highest point, which is at that return line.

Shern · #17 05-25-2018, 11:36 AM

Quote:

Originally Posted by Diseasel300

Can you actually SEE the bubbles coming up the tube from the IP? On an OM616/7 there is a spring-loaded check valve in the banjo bolt on the return line from the IP. Assuming it isn't all corroded, it should prevent air from passing through. That would leave your only source of air as the crush washers back there OR elsewhere in the system. Keep in mind that air rises, any air trapped in the system will show up at the highest point, which is at that return line.

I’m familiar with this valve (Overflow relief), and yes I can see the bubbles rising -akin to stray soda carbonation, slow and arhythmic. I have previously removed the overflow valve to measure and stretch the spring. Possible air incursion from the series of crush washers? I remember there being an odd number

Diseasel300 · #18 05-25-2018, 12:21 PM

You should have a total of 3 crush washers. One on the bolt head of the banjo bolt where the spring and BB go. One on each side of the banjo fitting (one against the bolt face, one against the IP) to seal the banjo fitting against the IP and banjo bolt. If you're missing a crush washer, you've identified the problem.

barry12345 · #19 05-25-2018, 12:51 PM

Happy to see someone doing the primer pump test before a morning start. Should be done on all these cars fuel systems. Any noticeable change and there are issues. Unless their engines catch and run right. The same as they did before the test.

Anyways. I hear your pain. I might consider dividing the system up. By closing the line between the filter and the injection pump. Letting the engine sit overnight and checking for the presence of air. No air then close the system before the fuel filter and repeat the test.

I think I too have seen at least one member mention issues with the fuel filter holder itself.

What has been in the back of my mind for years. The fuel has to go somewhere to let the air actually enter. Perhaps as in your case the relief valve does not have a good seal. Because the air otherwise could not show up in the return line if it could not get past a tightly closed relief valve. Metal to metal sealing in many check valves is perfect.

The relief valve is a regulated check valve essentially. They are quite reliable until dirt gets on their seats. Then a form of flow erosion starts on the sealing surfaces. Or in the time frame over the years as the systems fuel pressure drops off. These valves may become overworked. Basically opening and closing all too frequently with the car in operation. This itself creates actual wear. Another potential penalty of not knowing what your operational fuel pressure is.

So perhaps in a real good fuel system check and restoration. The actual condition of the sealing of the relief valve should be taken into consideration. Yours for example has some leakage in all probability when closed. Is almost an absolute as air shows up in the return line after sitting overnight. This leakage is inconsequential if small when the valve is in actual operation. The cure could be just a real cleaning of the seat for the ball. Or if physical wear has occurred the installation of an in line check valve just after the relief valve.

Gravity with the filter tower being higher would let fuel escape through a poorly sealing one. . Close the output of that relief valve down and see what the start seems like next morning. Of course there will be no visual change in the return line.

You put new valves in the lift pump so there probably is no back draining through them. Some fuel escaping past the pistons in the injection pump should on average not be much of a factor. I am really not totally certain about that at the same time. Yet the earlier injection pumps did have a self contained oil sump. That would have become flooded with diesel fuel. If the elements cylinders where not pretty much totally sealing.

My point is still the same. Air will not enter to replace the fuel if the fuel has no place to go. The fuel will not leave either if air to replace the lost volume is not available from somewhere.

If I were to totally restore the fuel system on one of these cars. I would put a pressure gauge on the system. Run the engine and shut it down.. Watching how long the system holds residual pressure. If it drops fast there is either leakage through the lift pump valves or the relief valve.

You get the occasional example of these cars. Where even if they sit for a prolonged period. When starting it is almost instantly. Those cars are getting full fuel loads through their injectors right away.

I have a 240d with a total new engine and accessories. Installed by a Mercedes dealer just shortly before my acquisition. It acts like this and I do not think the high compression factor is what makes the total difference. It is more just a case of every component is working properly by design.

For example put an old slightly leaky relief valve in the system. The valve still performs its intended function but also has a slight leakage perhaps by just a dirty seat for the ball. The startup charactaristics of the engine might become different though.

My guess is that if you are getting air into the system after the lift pump. You probably have two issues. Fixing one will make it much better but the second issue might remain.

I really dislike it when my mind starts shifting gears in some other persons thread. At the same time do you just keep it all to yourself?

Last but not least. Does the fuel system in that 240d of mine actually hold the residual fuel pressure till the next startup? I have never checked yet to see if it is doing that. All I know is the starter is barely engaged and turning and the engine is running. This cannot occur unless the injectors are dumping a full load of fuel almost instantly into the engine. The simple test this poster used and I have as well. Plus recommended to other members before. Is to me at least quite useful.

I have also never given much thought as to how air can get in and fuel does not escape through the same place when the fuel is pressurized. I just assumed it was a case of molecular size difference between air and fuel. Or the attraction forces between them are differant. Any form of venturi effect is out of the question as the rate or speed of the fuel flow is very low.

Same effect as when you have a water pump leakage. Many times if you refill the cooling system with water the leak stops. The molecules In the anti freeze are either much smaller or slip easier past each other. I have used this before to buy some time to change water pumps out.

\ How this discovery was made at least to me. I changed my water for anti freeze mix in my 1950 mercury. The flathead v8s had two water pumps. both started leaking. Put water back in and the leakages stopped.

Try to excuse my hopefully infrequent posts of this nature. I was just sitting here this morning thinking. Beer will soon be cheaper than gas up here in eastern Canada. So drinking instead of driving may soon be a more economical option. Also it would help me to fit into the local Canadian stereotype better.

Shern · #20 05-25-2018, 01:51 PM

Quote:

Originally Posted by Diseasel300

You should have a total of 3 crush washers. One on the bolt head of the banjo bolt where the spring and BB go. One on each side of the banjo fitting (one against the bolt face, one against the IP) to seal the banjo fitting against the IP and banjo bolt. If you're missing a crush washer, you've identified the problem.

They're still there... Possible however they weren't adequately tightened.
Recently acquired a metric washer kit on amazon, think I'll replace them all to be sure.

Quote:

Originally Posted by barry12345

Happy to see someone doing the primer pump test before a morning start. Should be done on all these cars fuel systems. Any noticeable change and there are issues. Unless their engines catch and run right. The same as they did before the test.

Anyways. I hear your pain. I might consider dividing the system up. By closing the line between the filter and the injection pump. Letting the engine sit overnight and checking for the presence of air. No air then close the system before the fuel filter and repeat the test.

I think I too have seen at least one member mention issues with the fuel filter holder itself.

What has been in the back of my mind for years. The fuel has to go somewhere to let the air actually enter. Perhaps as in your case the relief valve does not have a good seal. Because the air otherwise could not show up in the return line if it could not get past a tightly closed relief valve. Metal to metal sealing in many check valves is perfect.

The relief valve is a regulated check valve essentially. They are quite reliable until dirt gets on their seats. Then a form of flow erosion starts on the sealing surfaces. Or in the time frame over the years as the systems fuel pressure drops off. These valves may become overworked. Basically opening and closing all too frequently with the car in operation. This itself creates actual wear. Another potential penalty of not knowing what your operational fuel pressure is.

So perhaps in a real good fuel system check and restoration. The actual condition of the sealing of the relief valve should be taken into consideration. Yours for example has some leakage in all probability when closed. Is almost an absolute as air shows up in the return line after sitting overnight. This leakage is inconsequential if small when the valve is in actual operation. The cure could be just a real cleaning of the seat for the ball. Or if physical wear has occurred the installation of an in line check valve just after the relief valve.

Gravity with the filter tower being higher would let fuel escape through a poorly sealing one. . Close the output of that relief valve down and see what the start seems like next morning. Of course there will be no visual change in the return line.

You put new valves in the lift pump so there probably is no back draining through them. Some fuel escaping past the pistons in the injection pump should on average not be much of a factor. I am really not totally certain about that at the same time. Yet the earlier injection pumps did have a self contained oil sump. That would have become flooded with diesel fuel. If the elements cylinders where not pretty much totally sealing.

My point is still the same. Air will not enter to replace the fuel if the fuel has no place to go. The fuel will not leave either if air to replace the lost volume is not available from somewhere.

If I were to totally restore the fuel system on one of these cars. I would put a pressure gauge on the system. Run the engine and shut it down.. Watching how long the system holds residual pressure. If it drops fast there is either leakage through the lift pump valves or the relief valve.

You get the occasional example of these cars. Where even if they sit for a prolonged period. When starting it is almost instantly. Those cars are getting full fuel loads through their injectors right away.

I have a 240d with a total new engine and accessories. Installed by a Mercedes dealer just shortly before my acquisition. It acts like this and I do not think the high compression factor is what makes the total difference. It is more just a case of every component is working properly by design.

For example put an old slightly leaky relief valve in the system. The valve still performs its intended function but also has a slight leakage perhaps by just a dirty seat for the ball. The startup charactaristics of the engine might become different though.

My guess is that if you are getting air into the system after the lift pump. You probably have two issues. Fixing one will make it much better but the second issue might remain.

I really dislike it when my mind starts shifting gears in some other persons thread. At the same time do you just keep it all to yourself?

Last but not least. Does the fuel system in that 240d of mine actually hold the residual fuel pressure till the next startup? I have never checked yet to see if it is doing that. All I know is the starter is barely engaged and turning and the engine is running. This cannot occur unless the injectors are dumping a full load of fuel almost instantly into the engine. The simple test this poster used and I have as well. Plus recommended to other members before. Is to me at least quite useful.

I have also never given much thought as to how air can get in and fuel does not escape through the same place when the fuel is pressurized. I just assumed it was a case of molecular size difference between air and fuel. Or the attraction forces between them are differant. Any form of venturi effect is out of the question as the rate or speed of the fuel flow is very low.

Same effect as when you have a water pump leakage. Many times if you refill the cooling system with water the leak stops. The molecules In the anti freeze are either much smaller or slip easier past each other. I have used this before to buy some time to change water pumps out.

\ How this discovery was made at least to me. I changed my water for anti freeze mix in my 1950 mercury. The flathead v8s had two water pumps. both started leaking. Put water back in and the leakages stopped.

Try to excuse my hopefully infrequent posts of this nature. I was just sitting here this morning thinking. Beer will soon be cheaper than gas up here in eastern Canada. So drinking instead of driving may soon be a more economical option. Also it would help me to fit into the local Canadian stereotype better.

It's a good call giving that thing a solid cleaning. An oddity I recall when removing the relief valve was the obscene amount of fuel I lost during the exchange. I was expecting a minor trickle, but the fuel just never ended. If I had to guess I'd go with half a gallon? There was obviously enough pressure to create something of a siphon. Might have had something to do with the way I was parked. I've been reluctant to pull it again.

funola · #21 05-25-2018, 04:29 PM

Quote:

Originally Posted by Shern

(......................)

An oddity I recall when removing the relief valve was the obscene amount of fuel I lost during the exchange. I was expecting a minor trickle, but the fuel just never ended. If I had to guess I'd go with half a gallon? There was obviously enough pressure to create something of a siphon. Might have had something to do with the way I was parked. I've been reluctant to pull it again.

Here's a couple of things you can do to prevent losing that much fuel.

1. Jack the front end so the IP is higher than the tank. Open the fuel filler cap to release any pressure in the tank which could still push fuel out any open lines in the engine bay.

2. Crimp the short rubber fuel hose between the small clear primary filter and lift pump. This should stop any siphon action.

Shern · #22 05-25-2018, 05:50 PM

Quote:

Originally Posted by funola

Here's a couple of things you can do to prevent losing that much fuel.

1. Jack the front end so the IP is higher than the tank. Open the fuel filler cap to release any pressure in the tank which could still push fuel out any open lines in the engine bay.

2. Crimp the short rubber fuel hose between the small clear primary filter and lift pump. This should stop any siphon action.

This worked perfectly, thank you.

So I pulled the valve and replaced all three crush washers. Now I can get the damn car started... This is the first time it's ever happened. Had hard lines off many times, changed injectors etc, always rolled over after the third attempt.
Up to six now with no joy.

I have to be air bound. I suppose the correct protocol is to crack an injector line to release air, but I've never had to do that before...

Shern · #23 05-25-2018, 06:59 PM

Wow was that a process...

Cracked injector line one -nothing after several cranks. Buttoned it back up.
Primed again and again, however the action wasn't sufficient to open the relief valve.
In the middle of a cranking cycle I began rapidly pumping the pedal which fired the engine momentarily, at which point I ceased pumping -engine died. Did it all again 60 seconds later, but this time turned the idle adjust knob to full once the engine caught. Ran long enough to recharge the battery then repositioned the car so nose pointed down the driveway (2/3% grade).

Everything's back to normal. Hypotheses welcome.

funola · #24 05-25-2018, 08:07 PM

When chasing air in fuel, the first thing to do is put a temporary clear return line in place of the cigar hose. There should be no air in there at any time, engine running or not. Do you have a clear line there?

Shern · #25 05-25-2018, 08:14 PM

Quote:

Originally Posted by funola

When chasing air in fuel, the first thing to do is put a temporary clear return line in place of the cigar hose. There should be no air in there at any time, engine running or not. Do you have a clear line there?

I’m happy you asked -I’ve had a photo of your setup on my desktop for a week now. I too would like a permanent diagnostic window. Here’s the question...
If the cigar hose is 5/16 ID,

A.) what dimensions are the clear line segment?
B.) how to did you attach it to the port on the fuel filter?

From the photo, I’ve no idea what’s going on under that hose clamp.

Edit: also, the top of the IP return line is what, the second highest point? That’s clear and has been consistently filled with a bubble for the past month upon first start of the day. Once I find that clear, I’ll be further along on the right track

funola · #26 05-25-2018, 08:34 PM

Quote:

Originally Posted by Shern

I’m happy you asked -I’ve had a photo of your setup on my desktop for a week now. I too would like a permanent diagnostic window. Here’s the question...
If the cigar hose is 5/16 ID,

A.) what dimensions are the clear line segment?
B.) how to did you attach it to the port on the fuel filter?

From the photo, I’ve no idea what’s going on under that hose clamp.

Edit: also, the top of the IP return line is what, the second highest point? That’s clear and has been consistently filled with a bubble for the past month upon first start of the day. Once I find that clear, I’ll be further along on the right track

Do not try to copy what I did there. That short segment is Nylon and it will not be easy to find all the parts needed to duplicate it.

Go to Home Depot or Lowes and get a short length of 1/4" i.d. 3/8" o.d. clear pvc tubing. Dip the end in boiling water to soften, widen/ stretch it (use needle nose pliers) so that it fit over the 5/16 barbs for the cigar hose. It'll be hard to find small hose clamps that fit the small diameter PVC tubing. Clamps are probably not needed since the tubing is a very tight shrink fit but to be safe, take some heavy duty rubber band, multi wrap the tubing over the barb, tie a knot as temporary hose clamp.

Shern · #27 05-25-2018, 08:43 PM

Quote:

Originally Posted by funola

Do not try to copy what I did there. That short segment is Nylon and it will not be easy to find all the parts needed to duplicate it.

Go to Home Depot or Lowes and get a short length of 1/4" i.d. 3/8" o.d. clear pvc tubing. Dip the end in boiling water to soften, widen/ stretch it (use needle nose pliers) so that it fit over the 5/16 barbs for the cigar hose. It'll be hard to find small hose clamps that fit the small diameter PVC tubing. Clamps are probably not needed since the tubing is a very tight shrink fit but to be safe, take some heavy duty rubber band, multi wrap the tubing over the barb, tie a knot as temporary hose clamp.

I will do just this.

Meanwhile, I’m not getting any bubbles while running. I’m finding a two or 3 inch long bubble in the IP return line every morning. If I’m losing prime (seems I am), it’s a very slow process. I’m looking for something subtle.

funola · #28 05-25-2018, 09:13 PM

Quote:

Originally Posted by Shern

I will do just this.

Meanwhile, I’m not getting any bubbles while running. I’m finding a two or 3 inch long bubble in the IP return line every morning. If I’m losing prime (seems I am), it’s a very slow process. I’m looking for something subtle.

When you install the temp clear cigar hose, I expect you will see bubbles there when running. Are all parts of your fuel system dry? They should be. Fix any parts that are wet/ smell of diesel till dry with no more diesel odor.

funola · #29 05-25-2018, 09:34 PM

Finding air bubbles in fuel is not easy. I have a 1.6 idi turbo VW that has a 3 tank veg system so there's a lot more plumbing than a straight diesel. I have a lot of clear lines all over in strategic spots so I can see at an instant if there are problems. I have been chasing a small bubble at the outlet of the diesel fuel filter (highest point) after sitting overnight for a long time. It started to get worse with small bubbles in the diesel return to tank line when running and requires longer crank times (2 seconds or so) instead of firing instantly. I decided to replace all questionable hoses that look dried up and took apart the two 3 port valves, cleaned and tested them with the Mityvac to be sure they are working and leak free. Put everything back together and I was still getting small bubbles in the diesel return to tank line when running. My fuel system is totally dry or so I thought. I poked around more and noted some slight wetness on the daisy chain injector return line at the barb of injector #2. It was not dripping wet so I could not smell it, it was hidden behind some wires so was hard to spot. I pulled the line off, cut it back to expose a good section, put it back on the barb and no more bubbles. The engine fires immediately upon cranking again.

Shern · #30 05-26-2018, 12:54 PM

Thanks for this fun, much appreciated. Yes, all parts of my fuel system are dry. Interesting re: daisy-chain inspection. It's really getting to that point. Replaced all of the hose clamps last night that weren't the flat geared type. Swapped out crush washers on the Overflow valve, still found a 3 inch long bubble in the return line this morning.

I noticed while priming, I was getting a few bubbles with each pump of the primer from the clear line between the lift pump and the secondary fuel filter. Odd...
If the primer pump (new style) was letting air in, I'd likely find a bubble in the clear line to the secondary filter, each morning no?

When the engine is running, no bubbles in any of the clear lines. I'll install the temp clear line at the cigar hose this afternoon, but I have to admit, I'm not following the logic of this:

"When you install the temp clear cigar hose, I expect you will see bubbles there when running. "

If I'm not seeing bubbles in the clear line (or any of the clear lines) at the point right before the cigar hose -how would that work?