Air in Diesel Fuel Lines - What else to change out?
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Newbie
Joined: Dec 2006
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From: North East, UK.
'99 E300 TD Wagon Avantgarde
Air in Diesel Fuel Lines - What else to change out?
I started having starting problems just before Christmas.
The problem is obviously air in the Fuel Lines - I can see it.
And the car runs fine/normal once started, just the fuel draining back out of the lines whilst it isn't running.
I have changed out all the see-through plastic fuel lines, pre-filter and filter c/w new o-ring seals but the problem persists.
I am going to strip the Intake Manifold out again and replace the metal fuel injection lines (showing some signs of corrosion), the braided leak-off line and replace the injector seals.
Can anyone suggest any other parts / seals that I can replace whilst I have the manifold off, that may be contributing to this problem ?
I am suspicious of the shut-off valve (from reading other threads) - do I replace the full valve or just its seals?
Thanks for any advice, Jon.
The problem is obviously air in the Fuel Lines - I can see it.
And the car runs fine/normal once started, just the fuel draining back out of the lines whilst it isn't running.
I have changed out all the see-through plastic fuel lines, pre-filter and filter c/w new o-ring seals but the problem persists.
I am going to strip the Intake Manifold out again and replace the metal fuel injection lines (showing some signs of corrosion), the braided leak-off line and replace the injector seals.
Can anyone suggest any other parts / seals that I can replace whilst I have the manifold off, that may be contributing to this problem ?
I am suspicious of the shut-off valve (from reading other threads) - do I replace the full valve or just its seals?
Thanks for any advice, Jon.
Super Member
Joined: Jun 2006
Posts: 525
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From: the Netherlands
'01 W210 E320 CDI
Does the car start like it runs on just a few cylinders?! If so it might be time to change out the glowplugs. Glowplugs do wear out and if one or two cylinders haven't been pre-heated properly the engine fires up weird but starts running ok after a few seconds. If you really have air in your fuel lines the engine will keep running *****ty and lose power or even almost stall when you're driving...
-edit-
btw I think you always see air or foam in a diesel fuel line, it's a high-pressure system and I believe the 'air' is filtered out only right before the injection pump. I dunno if my E220 Diesel has clear lines but I'll have a look under the hood when the engine is running later today and let you know!
-edit-
btw I think you always see air or foam in a diesel fuel line, it's a high-pressure system and I believe the 'air' is filtered out only right before the injection pump. I dunno if my E220 Diesel has clear lines but I'll have a look under the hood when the engine is running later today and let you know!
Last edited by Lancelot; Jan 14, 2007 at 02:42 AM.
Thread Starter
Newbie
Joined: Dec 2006
Posts: 4
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From: North East, UK.
'99 E300 TD Wagon Avantgarde
The car seems to start perfect in the morning (1st start of the day) and then just turn over without firing on the second start of the day.
It does not seem to be time or temperature related as I have tried both short runs and longer runs (to get the temperature up) - but always the second start was the same.
Car turns over, but does not fire - then eventually, but slowly, starts to fire - like it is just getting fuel drip fed through. As soon as it sounds like all (or most) cylinders are firing - it runs without problem and with no apparent loss in performance.
Subsequent starts for the day seem to go fine, firing up as soon as the key is turned
It can't hurt to change the plugs while I am there - at least I will know they are all good then.
As for the air maybe being present in the lines most the time - I thought I had seen the lines with no air when running, but now I have doubts.
Going to try and run the car one last time, before taking the intake manifold off, just to confirm.
Thanks, Jon.
It does not seem to be time or temperature related as I have tried both short runs and longer runs (to get the temperature up) - but always the second start was the same.
Car turns over, but does not fire - then eventually, but slowly, starts to fire - like it is just getting fuel drip fed through. As soon as it sounds like all (or most) cylinders are firing - it runs without problem and with no apparent loss in performance.
Subsequent starts for the day seem to go fine, firing up as soon as the key is turned
It can't hurt to change the plugs while I am there - at least I will know they are all good then.
As for the air maybe being present in the lines most the time - I thought I had seen the lines with no air when running, but now I have doubts.
Going to try and run the car one last time, before taking the intake manifold off, just to confirm.
Thanks, Jon.
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Newbie
Joined: Dec 2006
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From: North East, UK.
'99 E300 TD Wagon Avantgarde
What I have been lead to believe, is that when the engine is off - and hence the system not being pressurized - the fuel is draining back out of the lines.
And when I try to start, I am having to beat an airlock in the system.
I was also told that I should see a leak once the system is under pressure at the point where the air is entering. Makes sense but I have not observed a leak up to now.
The Specialist garage I spoke to said they had seen this problem a lot, but also added that diagnosis is difficult due to the number of seals/contributing factors. They did however suggest that one of the most likely culprits is the injector seals as diesel tends to rot them.
I could not get the car started, so am just awaiting parts to be delivered (and a bit of daylight) to do the job. Hopefully all will be well afterwards.
Jon.
And when I try to start, I am having to beat an airlock in the system.
I was also told that I should see a leak once the system is under pressure at the point where the air is entering. Makes sense but I have not observed a leak up to now.
The Specialist garage I spoke to said they had seen this problem a lot, but also added that diagnosis is difficult due to the number of seals/contributing factors. They did however suggest that one of the most likely culprits is the injector seals as diesel tends to rot them.
I could not get the car started, so am just awaiting parts to be delivered (and a bit of daylight) to do the job. Hopefully all will be well afterwards.
Jon.
Super Member
Joined: Jun 2006
Posts: 525
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From: the Netherlands
'01 W210 E320 CDI
I wish you luck. (no clear lines in sight on my E 220D) And hopefully it aren't the injector seals! In a worse case cenario their threads are baked solid to the cylinderhead with carbon residue. A problem common with the first CDI engines...
Newbie
Joined: Apr 2009
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1999 300 Turbo Diesel
Jon,
Am experiencing similar air in fule lines, in my 99 E300 D. Changed out every possible seal and all fuel lines, rubber hoses, filters, solenoid... to no avail.
Starting is good, but rough idle once warmed up, and can see the air bubbles flow from the line at the bottom of prefilter going to the fuel solenoid...
I just don't get it, seriously, should I go back and change out all new parts, once more, and pray for a better result????
Can any of your experts (Ohlord?) maybe please enlighten this humbled mechanical engineer???
Am experiencing similar air in fule lines, in my 99 E300 D. Changed out every possible seal and all fuel lines, rubber hoses, filters, solenoid... to no avail.
Starting is good, but rough idle once warmed up, and can see the air bubbles flow from the line at the bottom of prefilter going to the fuel solenoid...
I just don't get it, seriously, should I go back and change out all new parts, once more, and pray for a better result????
Can any of your experts (Ohlord?) maybe please enlighten this humbled mechanical engineer???
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Super Member
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W210 W140
I would check the Shut off Valve. That will cause air in your lines too. Its not uncommon for them to go bad.
While you're at it, check the metal fuel lines coming from your pump. This is the pressure side, but the seals attaching the metal lines to the pump tend to go bad too. This will cause you to have fuel seeping out into your engine bay.
While you're at it, check the metal fuel lines coming from your pump. This is the pressure side, but the seals attaching the metal lines to the pump tend to go bad too. This will cause you to have fuel seeping out into your engine bay.
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1999 300 Turbo Diesel
Ed,
Appreciate the suggestion. Good news, no fuel leakage whatsoever, that is good. All metal lines are tight, and clamped down per standard, no high pressure leaks.
Yet air seems to enter upstream from that fuel shutoff solenoid, seems in the pre-filter, and bubbles can be seen flowing thru the plastic hose #2 in the diagram.
No air in plastic line #1, however, that is good.
Everything is new installed, all OEM parts from dealer...
Have not even 100,000 miles...
Seems that air finds it way in some were between line #1 entering, and line #2 leaving the pre-filter... all newly installed hoses and seals...
Now what would you do? How diagnose where air gets in?
Appreciate the suggestion. Good news, no fuel leakage whatsoever, that is good. All metal lines are tight, and clamped down per standard, no high pressure leaks.
Yet air seems to enter upstream from that fuel shutoff solenoid, seems in the pre-filter, and bubbles can be seen flowing thru the plastic hose #2 in the diagram.
No air in plastic line #1, however, that is good.
Everything is new installed, all OEM parts from dealer...
Have not even 100,000 miles...
Seems that air finds it way in some were between line #1 entering, and line #2 leaving the pre-filter... all newly installed hoses and seals...
Now what would you do? How diagnose where air gets in?
Last edited by jelleeij; Sep 2, 2009 at 05:04 PM. Reason: typos
Super Member
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W210 W140
So you're saying that the line coming from the shut-off valve doesn't have any air in it. But, after the pre-filter you are seeing bubbles in line 2.
I would say double check all of your seals around that area:
-The lines and seals are very delicate and if you aren't careful you can damage the seals and contact during installation.
-Check to see if the seals on your pre-filter are o.k and seated properly.
-Also that your pre-filter is tightened down enough for a proper seal.
I would say double check all of your seals around that area:
-The lines and seals are very delicate and if you aren't careful you can damage the seals and contact during installation.
-Check to see if the seals on your pre-filter are o.k and seated properly.
-Also that your pre-filter is tightened down enough for a proper seal.
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1999 300 Turbo Diesel
That is correct, no air can be seen anywhere, but in line #2. The Fuel Return Line brings very fine bubbles (beer foam like) in the fuel return line. Noticed that when hooked up with temporary fuel lines, simply to isolate any other influence (see attached).
Renewed pre-fuel filter this week, with new seals, cleaned and fine polished the seating for that big o-ring, to ensure porper seating. Installed new o-ring in line coming from pre-filter.
Agree, need to be extremely cautious with thouse fragile lines. Guess it helps that my training ground was restoring Japanese motorbikes, where everything seems tiny and fragile... surely not designed with my big hands in mind.
My next cause of action is to order a new Fuel Filter Housing, because this just makes no sense anymore to me.
Sure hoping to maybe find a hairline crack in the back, once the old one comes off. Anyone has the torque spec of those two torx screws that mount the filter housing to the head?
They did not design these diesel engines overnight, so this problem must be overcome.... all in due time.
Renewed pre-fuel filter this week, with new seals, cleaned and fine polished the seating for that big o-ring, to ensure porper seating. Installed new o-ring in line coming from pre-filter.
Agree, need to be extremely cautious with thouse fragile lines. Guess it helps that my training ground was restoring Japanese motorbikes, where everything seems tiny and fragile... surely not designed with my big hands in mind.
My next cause of action is to order a new Fuel Filter Housing, because this just makes no sense anymore to me.
Sure hoping to maybe find a hairline crack in the back, once the old one comes off. Anyone has the torque spec of those two torx screws that mount the filter housing to the head?
They did not design these diesel engines overnight, so this problem must be overcome.... all in due time.
Last edited by jelleeij; Sep 4, 2009 at 03:29 PM. Reason: typos
Super Member
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W210 W140
Good luck. I'm at a loss on any more advice. Also check out www.peachparts.com. There are a ton of diesel Mercedes guys on there that may be able to help you.
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Joined: Apr 2009
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1999 300 Turbo Diesel
New filter bracked solved... poor initial quality
Okay, only $120 later, turns out that the pre-filter had too much clearance in the original OEM filter bracket and the seal did not, creating a vacuum leak into the diesel fuel.
When removing the (newly installed) pre-filter from the old housing, it just fell out by keeping the bracket upside down.
Now what a difference the new housing, it took me three c'mons, and lots of force, to finally force the prifilter into the housing... what a tight fit, like a glove!
Needles to say, no more air is seen in those clear diesel fuel lines since...
Root cause turns out to be poor manufacturing quality, or maybe I should say random manufacturing, by Mercedes or it's OEMs.
In conclusion, this car must have been running sub-standard since day one, and every owner must have tried to fix that "Gremlin".
Until finally I happen to stumble into this adsurd problem, and resort to replacing the most unlikely part.
Guess you gota be a bit crazy in the first place, to choose to drive a diesel... at least now for the first time, my car seems quieter than my 1 ton Bluetec Cummins pickup truck
Over, and out.
When removing the (newly installed) pre-filter from the old housing, it just fell out by keeping the bracket upside down.
Now what a difference the new housing, it took me three c'mons, and lots of force, to finally force the prifilter into the housing... what a tight fit, like a glove!
Needles to say, no more air is seen in those clear diesel fuel lines since...
Root cause turns out to be poor manufacturing quality, or maybe I should say random manufacturing, by Mercedes or it's OEMs.
In conclusion, this car must have been running sub-standard since day one, and every owner must have tried to fix that "Gremlin".
Until finally I happen to stumble into this adsurd problem, and resort to replacing the most unlikely part.
Guess you gota be a bit crazy in the first place, to choose to drive a diesel... at least now for the first time, my car seems quieter than my 1 ton Bluetec Cummins pickup truck
Over, and out.
Super Member
Joined: Jul 2005
Posts: 731
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W210 W140
Good to hear the problem got solved. Thanks for reporting back. Its good to have this information at hand if someone else is experiencing the symptoms you did. All in all, that was a pretty cheap fix.
Super Member
Joined: Jun 2008
Posts: 835
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From: Bay Area, CA
09' E320
I missed this one earlier....do you have a oring installed between the prefilter and fuel filter housing it is inserted into? Doesnt sound like it given the trouble you had sealing that connection.
You wouldn't be the first person to have inadvertently thrown that oring away when changing the prefilter (filter and oring are ordered separately).
You wouldn't be the first person to have inadvertently thrown that oring away when changing the prefilter (filter and oring are ordered separately).
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Joined: Apr 2009
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1999 300 Turbo Diesel
O-ring in pre-filter installed, and yes bought them as separate items at the dealer. Just could not believe how tight the fit is now.
Prefilter used to "slide" into the old bracket, whereas now it requires "brute force" to shoehorn in, tells me now the o-ring must seal vacuum.
Symptoms resolved include, gutless power, low torque, rough idle, and lots of turbo lag. Seems like driving a totally different car alltogether.
Dealer acknowledged for varying OEM parts quality... "quality all depends who made the part, Benz don't manufacture parts". So if you drive a 99 vintage E300 Turbodiesel, and experience vague performance, problems, do not overlook the tightness of the prefilter fit. Inexpensive and easy replacement, all in all.
Prefilter used to "slide" into the old bracket, whereas now it requires "brute force" to shoehorn in, tells me now the o-ring must seal vacuum.
Symptoms resolved include, gutless power, low torque, rough idle, and lots of turbo lag. Seems like driving a totally different car alltogether.
Dealer acknowledged for varying OEM parts quality... "quality all depends who made the part, Benz don't manufacture parts". So if you drive a 99 vintage E300 Turbodiesel, and experience vague performance, problems, do not overlook the tightness of the prefilter fit. Inexpensive and easy replacement, all in all.
Last edited by jelleeij; Sep 11, 2009 at 06:01 PM. Reason: typo
Super Member
Joined: Jun 2008
Posts: 835
Likes: 2
From: Bay Area, CA
09' E320
All fuel line, SOV, DV's and prefilter orings develop an oblong shape very soon after being installed.
The prefilter oring should be replaced every time a new prefilter is installed.
If you want a tighter seal, go to viton rings rather than buna nitrile that MB continues to use. Viton is a harder compound in addition to being more fuel resistant.
I've got the sizes and counts documented if you need them.
The prefilter oring should be replaced every time a new prefilter is installed.
If you want a tighter seal, go to viton rings rather than buna nitrile that MB continues to use. Viton is a harder compound in addition to being more fuel resistant.
I've got the sizes and counts documented if you need them.
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ZX10R
Air in Diesel Fuel Lines - What else to change out?
When dealing with air in diesel fuel lines, it's crucial to address potential issues comprehensively. Beyond purging air from the lines, inspect and replace fuel filters, as air can introduce contaminants. Check for loose connections, damaged hoses, or faulty seals that may allow air ingress. Evaluate the fuel lift pump, as it plays a pivotal role in maintaining proper fuel pressure. Regularly monitor the fuel system for any signs of leaks or compromised components. A thorough inspection and timely replacement of any worn parts will help ensure optimal diesel engine performance and prevent future air infiltration issues.
