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OM606- Sanity check fuel line air leaks
jav Offline
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#1
OM606- Sanity check fuel line air leaks
I'm wrapping up my 606 conversion and I've been having an issue with air in the fuel lines.  So yesterday, I replaced all 6 plastic fuel lines in the filter/injection pump area.  Brand new OEM mercedes parts.  At the same time, I also replaced the SOV seal, the pre filter , and the pre filter seal.  Everything went on snugly and snapped in positively.  I lubricated every o ring with diesel prior to insertion.  I Primed the system and got the engine running.

I noticed a steady stream of air at the very first line going from the heat exchanger to the pre filter.  It appeared the air was coming in with the fuel coming from the tank.  So I went back and inspected and tightened every connection.  That seemed to correct the visible air bubbles going into the first clear line and all the lines then appeared to be solidly filled with fuel... that is until I shut off the engine.

Once the engine shuts off, an air bubble appears to exit from the pre filter and it appears the fuel is very slowly draining backwards towards the tank and the bubble grows.  I have no fuel pump other than the lift pump on the IP.  SO- i was planning on adding a back flow preventer (check valve) on the rubber hose before the heat exchanger.

The problem is... this morning the clear line at the bottom of the pre filter that goes to the SOV, is also empty of fuel and I see no leak??  Am I correct that even if the fuel were getting sucked back to the tank, it should NOT suck fuel backwards and against gravity at the base of the pre filter?

Am I missing something?  Is it normal to have to install a check valve on the fuel feed line on these conversions?  I' rather not add an electric pump but I'd also like to not fight air problems?  Suggestions?
(This post was last modified: 12-02-2018, 07:54 PM by jav.)
12-02-2018, 07:47 PM
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AlanMcR Offline
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#2
RE: OM606- Sanity check fuel line air leaks
I have two OM606's, factory installed.  I had to eliminate the pre-filter on both due to leaks that could not be fixed.  Even with new parts the air would leak in.  Either the bore diameter is oversized or the casting is porous.  Don't care, gave up trying.  The problem was worse on the Gwagen, probably due to the bigger drop down to the fuel tank.
Use the hose ends at the the fuel heater and SOV, and make your own hose that connects them directly.  Problem solved, permanently.  The pre-filter is way too small anyway.  Better to install your own that is bigger and closer to the tank.
If you still have your old parts they are perfect for this.
(This post was last modified: 12-02-2018, 10:50 PM by AlanMcR.)
12-02-2018, 10:48 PM
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jav1 Online
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#3
RE: OM606- Sanity check fuel line air leaks
(12-02-2018, 10:48 PM)AlanMcR Wrote: I have two OM606's, factory installed.  I had to eliminate the pre-filter on both due to leaks that could not be fixed.  Even with new parts the air would leak in.  Either the bore diameter is oversized or the casting is porous.  Don't care, gave up trying.  The problem was worse on the Gwagen, probably due to the bigger drop down to the fuel tank.
Use the hose ends at the the fuel heater and SOV, and make your own hose that connects them directly.  Problem solved, permanently.  The pre-filter is way too small anyway.  Better to install your own that is bigger and closer to the tank.
If you still have your old parts they are perfect for this.


Thanks Alan-

any opinion on a check valve?
12-03-2018, 07:54 AM
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AlanMcR Offline
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#4
RE: OM606- Sanity check fuel line air leaks
Make the system airtight and the problems all go away. A check valve adds a little bit of resistance to a system that already has too many impediments to free flow.
12-04-2018, 12:10 AM
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jav1 Online
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#5
RE: OM606- Sanity check fuel line air leaks
Alan-

so did you use clear tubing to fashion the new line bypassing the pre-filter or non clear fuel line?  Did you clamp it on to the old fittings or just force it on?
(This post was last modified: 12-04-2018, 08:06 AM by jav1.)
12-04-2018, 08:05 AM
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baldur Offline
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#6
RE: OM606- Sanity check fuel line air leaks
Fit an electric lift pump and you never have to worry about air causing slow starts again.
Baldur Gislason

12-04-2018, 10:09 AM
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AlanMcR Offline
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#7
RE: OM606- Sanity check fuel line air leaks
jav1: I used some clear reinforced flex line. Press fit with a spring clamp. Can't find the part numbers for either at the moment.

baldur: This is a fix for a design error specific to the coarse filter. For the remaining lines, not long after the air leaks in, diesel starts to leak out, especially under overpressure from an external pump. The OM606 fuel system design was terrible. Ideally one would eliminate the SOV and tap all the remaining parts for banjo bolts.
12-04-2018, 01:22 PM
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jav1 Online
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#8
RE: OM606- Sanity check fuel line air leaks
Baldur- the thought has crossed my mind Wink

Alan- I just realized you are the author to a post I've referred to many times regarding the Mercedes fuel system design issues... good read! I have to find away past this issue as it's been a thorn in my side to the progress of tuning my DSL-1. I get the engine starting and idling well and the next day I'm back to fighting air in the lines all over again.


You know I should have known something was up when I couldn't get the fuel supply line on the e300 to stop flowing when I removed the engine. It was the weirdest thing! I cut the line back at the firewall, well above the tank level and used a cup to catch the fuel in the line... except the fuel just kept flowing and I remember thinking... how the heck is this possible? The line is above the tank and it won't stop flowing?? I eventually just tied the feed and return lines together to contain the constant drip. German black magic?


The car never exhibited this problem that seems to be plaquing my conversion despite all new lines, seals, filter, pre-filter.
12-04-2018, 03:07 PM
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barrote Offline
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#9
RE: OM606- Sanity check fuel line air leaks
Haha yes indeed is german magic...
Is due to the tank beeing pressurized?
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12-04-2018, 03:26 PM
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jav1 Online
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#10
RE: OM606- Sanity check fuel line air leaks
Not sure how tank could be pressurized when return line was open???  No air pressure escaping return line- but fuel flowing... uphill- out of supply line.  Black magic I tell you!
(This post was last modified: 12-04-2018, 04:47 PM by jav1.)
12-04-2018, 04:46 PM
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baldur Offline
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#11
RE: OM606- Sanity check fuel line air leaks
(12-04-2018, 01:22 PM)AlanMcR Wrote: jav1: I used some clear reinforced flex line.  Press fit with a spring clamp.  Can't find the part numbers for either at the moment.

baldur:  This is a fix for a design error specific to the coarse filter.  For the remaining lines, not long after the air leaks in, diesel starts to leak out, especially under overpressure from an external pump.  The OM606 fuel system design was terrible.  Ideally one would eliminate the SOV and tap all the remaining parts for banjo bolts.

Yeah, but diesel leaking out is much, much easier to find and fix than air leaking in.
Baldur Gislason

12-05-2018, 07:51 AM
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jav1 Online
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#12
RE: OM606- Sanity check fuel line air leaks
Well-

bypassing pre-filter has not remedied the problem.  I suspect the SOV seal, or the SOV itself is a contributing source to the air leak?  Can anyone describe the port operation on the SOV and on the return fitting at the filter housing?

On the SOV,- there are 4 ports:

A: Hidden Nipple behind SOV that is sealed into the IP
B: Top forward Port - to output of Main fuel filter
C: Top rearward Port -  to output of Pre-Filter
D: Bottom port to suction side of lift pump


I presume when the SOV is DE-ENERGIZED, ports B & C are connected and Ports A & D are connected.  When Energized, Ports A & B are connected and ports C & D are connected?


Also-  why is there a return line fitting connected into the filter housing?  This is where the injection pump return line, the injector return line and the tank return line meet.  I get those 3 connections but why is there a sealed port into the filter housing?  Does the return passage somehow connect/interact to the pre-filter or main filter passage(s)?
(This post was last modified: 12-05-2018, 08:35 AM by jav1.)
12-05-2018, 08:33 AM
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Benzer Offline
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#13
Photo  RE: OM606- Sanity check fuel line air leaks
(12-02-2018, 10:48 PM)AlanMcR Wrote: I have two OM606's, factory installed.  I had to eliminate the pre-filter on both due to leaks that could not be fixed.  Even with new parts the air would leak in.  Either the bore diameter is oversized or the casting is porous.  Don't care, gave up trying.  The problem was worse on the Gwagen, probably due to the bigger drop down to the fuel tank.
Use the hose ends at the the fuel heater and SOV, and make your own hose that connects them directly.  Problem solved, permanently.  The pre-filter is way too small anyway.  Better to install your own that is bigger and closer to the tank.
If you still have your old parts they are perfect for this.

Hey alan, have you put the hose directly on the connection and secured with a hose clamp? I wanted to try that too. may I ask how long the conversion already works for you? I wanted to fix the hose with a bracket so that not so much movement comes in, not that the O-ring is leaking because of the vibrations from the engine. maybe you have a picture of your conversion? would be very nice!

greets Patrick


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12-05-2018, 09:34 PM
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Alec300SD Offline
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#14
RE: OM606- Sanity check fuel line air leaks
(12-05-2018, 08:33 AM)jav1 Wrote: Also-  why is there a return line fitting connected into the filter housing?  This is where the injection pump return line, the injector return line and the tank return line meet.  I get those 3 connections but why is there a sealed port into the filter housing?  Does the return passage somehow connect/interact to the pre-filter or main filter passage(s)?
On the OM617 fuel filter head, a banjo bolt secures the return line T-fitting to the filter head.
The port that receives this banjo bolt is not sealed.
It has a small orifice in the center of the well to provide the main (secondary) spin-on fuel filter with an air bleed off point.

The fuel flow returning to the tank purges the air out of the main fuel filter when the motor is running.
I believe your filter head is similarly designed.
12-05-2018, 10:21 PM
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jav1 Online
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#15
RE: OM606- Sanity check fuel line air leaks
Thanks Alec-

I think you might be right but then I guess I don't understand how it can function without some type of one way valve?  In my mind, the main spin on filter, well...the entire supply side of the system really,  is on the "suction" side of the pump.  If there is a passage from the spin on filter (fuel supply- suction- side) to the return line (which does have air in it), than under suction it would be more likely to suck in air from the return line than expel air to it... being that the supply side is at a lower pressure than the return side... no?

In one of my many attempts to purge the system of air after a no start,  I disconnected the rubber return line from the plastic tee where it ties into the filter housing.  I put about 5 PSI of pressure in the return line (and as a result into the tank) to force fuel through the supply side of the system in the hopes that it would purge all the air and fill the filter and all the plastic lines. I disconnected the last supply line that feeds the injection pump.  It didn't work.  I was getting fuel under pressure out of the return line TEE where the rubber hose normally goes so I suspect your correct that there is a connection between the supply and return  sides of the fuel system at the filter housing. the filters and lines never filled with fuel. I'm pretty sure you can't force fuel through the lift pump and/or SOV this way so the filters won't accept the pressurized fuel due to the back pressure from either the lift pump or the SOV.  I tried both with the SOV energized and de-energized so I suspect it's the lift pump that resists flow.

Also-  I bypassed the pre filter completely.  I read on another site the line that goes from the pre-filter base to SOV CAN be removed from the pre-filter base and connected directly to the fuel heat exchanger if you just rotate the fitting about 20 degrees.  That did work and it looked like a good seal.  The next day, that line was full of air.  I'm not sure if I had retightened the return line at the TEE and think perhaps the air came in through there??  

My next attempt is I'm adding a fuel check valve in the supply line near the tank.  I hope this works as I really don't want to add an electric lift pump.
(This post was last modified: 12-06-2018, 08:26 AM by jav1.)
12-06-2018, 08:14 AM
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Alec300SD Offline
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#16
RE: OM606- Sanity check fuel line air leaks
On an OM617 the primary fuel filter (clear plastic pre-filter) is on the suction side of the lift pump.

The secondary fuel filter on the fuel filter head (metal canister filter) is on the pressure side of the lift pump.
The T-fitting banjo is at the highest point in the fuel supply line.
Trapped air will collect at the high point and be returned to the tank as the engine runs (or by using the primer pump on an OM617 when the engine is not running).

On the OM617, the lift pump has two disc valves, one of which is a check valve to prevent fuel draining back to the tank (from the low pressure IP supply circuit) when you shut the engine off.
There is also a check valve on the engine side of the clear IP return line to keep fuel in the high pressure IP/fuel injector circuit.


A tight fuel system will have no air in the fuel lines.
Any fuel union is a potential point for air ingress.
The two basic principles above should apply.

On my OM617, if the IP gets air bound in the high pressure circuit (causing a no start situation), then I crack open the injector hard lines and crank the engine to more quickly purge the air out of the injector hard lines.
Once fuel dribbles out of all the injector hard lines, the IP high pressure circuit is re-primed.

Hope this helps.
12-06-2018, 02:59 PM
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jav1 Online
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#17
RE: OM606- Sanity check fuel line air leaks
I suppose that's also true on the 606 system while the SOV is energized (suction vs pressure side) HOWEVER... I think once the SOV is de-energized, the pre and primary filters connect (through the SOV - see my post above about which SOV ports flow- energized vs de-energized).  When the SOV de-energizes, almost all the clear lines including the pump outlet (pressure) line, are on an obstructed circuit with the return line IF that passage exists in the filter housing.  It is then that the air creeps into my system. The only clear line that appears isolated with the SOV off is the pumps suction line which I presume is tied to the IP pressure galley through the SOV.


I've cracked the injector lines on many a diesel... I'm, very familiar with the bleeding process.  My issue is that once the supply line from the tank empties, even after filling the primary filter full of fuel, the lift pump will suck the line air back into the filter and then introduce more air into the IP.  I've been trying to fill the filter and all the lines prior to bleeding to avoid that.
(This post was last modified: 12-06-2018, 03:49 PM by jav1.)
12-06-2018, 03:42 PM
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jav Offline
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#18
RE: OM606- Sanity check fuel line air leaks
Update: Installed check valve and got the truck running. I'll se in the morning if it starts. On the down side- I cleaned the area REALLY well and... it looks like my delivery valves need to be resealed.
12-06-2018, 09:53 PM
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Alec300SD Offline
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#19
RE: OM606- Sanity check fuel line air leaks
Did a little studying to get more familiar with the 606 fuel system.

The attached link shows the fuel flow on the 606.
http://www.peachparts.com/shopforum/3679786-post78.html
Air leaks on the sucton side occur before the lift pump (ie lines 1, 2 or 3 marked in red).
The fuel thermostat (item 155 in the diagram below) itself is a very likely culprit.

Additionally, air can leak into the metal fuel filter from failed o-rings (items 11 and 14) on the large hollow bolt (item 20) securing the metal fuel canister to the fuel filter head.

Have these o-rings been replaced recently?
Again, hope this is helpful.  Smile


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(This post was last modified: 12-07-2018, 02:10 AM by Alec300SD.)
12-07-2018, 02:02 AM
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barrote Offline
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#20
RE: OM606- Sanity check fuel line air leaks
Hy,
It seems u can't figure out why that bleeds off during overnight.
Question is, this fuel supply system is complicated but got no magic in it.
1st: the conection O ring rarely are cause of leaks, after 20 years they may need replacement.
Nevertheless there are 2 week spots that usually exibit air leaks or bleed. This is the O ring in the scren filter, nr 29 in the picture above(MB sels both screen filter and Oring as one part). Other is the check valve on pump return nr 125. The banjo bolt has a check valve prone to failure.
The lift pump also has check valves, but this last one lifetime and do not play any role in the overnight bleed issue.
If u replace this 2 units i can guarantee your problems will dissapear.
Good luck
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12-07-2018, 04:35 AM
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jav1 Online
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#21
RE: OM606- Sanity check fuel line air leaks
Alec and barrote,

The check valve in the supply line seems to have fixed the problem. 

All the o-rings, crush washers and lines are new.

I had a thought last nite and I think this may be the problem.  This is a conversion.  I put the om606 engine in my truck which didn’t have a return line.  I added one but I just added a fitting to the fuel tank pickup flange.. I didn’t extend the return line into the tank so the line is not submerged in fuel.  I suspect the air was traveling thru the return line into the filter housing when the SOV is de energized and allowing the supply line to drain back into the tank.  The check  Valve prevents this and the truck started perfectly after sitting over night.
(This post was last modified: 12-07-2018, 01:52 PM by jav1.)
12-07-2018, 08:42 AM
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AlanMcR Offline
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#22
RE: OM606- Sanity check fuel line air leaks
Sorry to hear you are still having problems with this system.  It really is terribly designed.  

There are o-rings around the delivery valves.  They usually get enough pressure that they leak visibly once they are a problem.  Also the fuel heater itself has a seal between the plastic and metal parts.

If the problem is on the suction side.  Get the engine started, then partially restrict the inlet hose (vice grips).  Shine a bright flashlight through the clear lines.  Often you can see where the bubbles start.
12-07-2018, 10:36 PM
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