Air in fuel lines
Thread Starter
Junior Member
Joined: Sep 2010
Posts: 20
Likes: 0
From: SF Bay Area
1998 E300 TD
Air in fuel lines
Problem started when E300 hesitated when start, and progressively getting worst under certain conditions. All fuel lines changed including two o-rings in the fuel filter header. Did not help. A column of air ~2 inches gathered on top of the return line after engine off. When started cold, air is observed in two other lines, bubbles gradually decrease as car warmed up.
Is there any way to check for air leaks? The mechanic recommends replacing the shut off valve as the next logical step, but I rather find out where the leak is prior to throwing more $ to the car.
Thanks a lot.
Is there any way to check for air leaks? The mechanic recommends replacing the shut off valve as the next logical step, but I rather find out where the leak is prior to throwing more $ to the car.
Thanks a lot.
Super Member
Joined: Jun 2008
Posts: 835
Likes: 2
From: Bay Area, CA
09' E320
Its not rocket science. Follow the fuel path, note where you first see bubbles appear. Your leak always precedes that point in the fuel path. Fix that leak. Repeat the excersize to see if there was more than one leak.
http://bp3.blogger.com/_p71v9ofBM6w/...h/fuelflow.JPG
Line 8 is the "return" line. Its black rubber so you can see if it has fuel in it or not....just ignore 6-8. They are all return lines.
If you mean that line 1 is the line that drains back 2" at shutdown you need a different mechanic. All 606's do that. Completely normal. That line is the start of fuel delivery.
Waste a can of carb or brake cleaner on the fuel filter/pre-filter housing and the top and sides of the IP first. Is easier to see/feel for leaks if everything is clean first. Dont forget the SOV oring and the DV's (DV's don't usually show bubbles anywhere as they are at the end of the fuel path but can cause a slight stumble).
The SOV is ~$200. The oring is ~$2. A new SOV doen't come with an oring, just like the pre-filter doesnt.
http://bp3.blogger.com/_p71v9ofBM6w/...h/fuelflow.JPG
Line 8 is the "return" line. Its black rubber so you can see if it has fuel in it or not....just ignore 6-8. They are all return lines.
If you mean that line 1 is the line that drains back 2" at shutdown you need a different mechanic. All 606's do that. Completely normal. That line is the start of fuel delivery.
Waste a can of carb or brake cleaner on the fuel filter/pre-filter housing and the top and sides of the IP first. Is easier to see/feel for leaks if everything is clean first. Dont forget the SOV oring and the DV's (DV's don't usually show bubbles anywhere as they are at the end of the fuel path but can cause a slight stumble).
The SOV is ~$200. The oring is ~$2. A new SOV doen't come with an oring, just like the pre-filter doesnt.
Last edited by TMAllison; Sep 14, 2012 at 11:40 AM.
Thread Starter
Junior Member
Joined: Sep 2010
Posts: 20
Likes: 0
From: SF Bay Area
1998 E300 TD
Thank you very much TMAllison, the fuel flow chart is very useful.
Line 1 is indeed where the diesel drains back once the car shuts off, the air column starts building and is sucking in air from the end attached to the fuel filter housing.
What bother me most is while running cold, large quantity of air bubbles shows flowing in lines 2 and 4, decreasing as the engine warms up. I did have a couple of occasions where the car won't restart after driving short distances. That's when all the lines were replaced including the o-rings within the fuel filter housing.
I looked for visible evidence of fuel leak also. Everything that I can see looks dry. Wish I know how to pressurize the system and push for evidence. THis idea was rejected by the mechanic. I am ready to go somewhere else.
What is "DV" and where is it?
Thanks much.
Hey, we are kind of neighbors in the Bay area. Did you junk your E300?
Regards
Line 1 is indeed where the diesel drains back once the car shuts off, the air column starts building and is sucking in air from the end attached to the fuel filter housing.
What bother me most is while running cold, large quantity of air bubbles shows flowing in lines 2 and 4, decreasing as the engine warms up. I did have a couple of occasions where the car won't restart after driving short distances. That's when all the lines were replaced including the o-rings within the fuel filter housing.
I looked for visible evidence of fuel leak also. Everything that I can see looks dry. Wish I know how to pressurize the system and push for evidence. THis idea was rejected by the mechanic. I am ready to go somewhere else.
What is "DV" and where is it?
Thanks much.
Hey, we are kind of neighbors in the Bay area. Did you junk your E300?
Regards
Super Member
Joined: Jun 2008
Posts: 835
Likes: 2
From: Bay Area, CA
09' E320
Again, fuel running back toward the cyl head within line 1 when the engine is off is completely normal.
If you have air in line 2, it comes from where 2 connects to the bottom of the pre-filter housing, the prefilter oring, line 1 connectng to the top of the pre-filter, or where line 1 connects to the fuel thermostat mounted on the cyl head. The only other options are the hard lines from there back to the tank. Those leaks are not common.
pre-filters sometimes arent cast well or can crack, orings sometimes dont seal well. Your washer/bolt holdign the prefilter down might not be exerting enough pressure to seal everything.
The reason there is no fuel leaking is that the system is under suction through line 3. Air enters because of the vacuum the suction pump creates.
DV = Delivery valves. x6 on top of the IP. Each has a crush washer and oring. Don't mess with them if you don't know what you are doing.
My 99 E300 was totaled recently when a mech opened up a water passage in the head while trying remove GP #6. I had tried 3 times and it kept rounding over and I couldn't get it out. His lia ins company offered me a deal I couldnt refuse. They now own the car and it is in parts heaven.
If you have air in line 2, it comes from where 2 connects to the bottom of the pre-filter housing, the prefilter oring, line 1 connectng to the top of the pre-filter, or where line 1 connects to the fuel thermostat mounted on the cyl head. The only other options are the hard lines from there back to the tank. Those leaks are not common.
pre-filters sometimes arent cast well or can crack, orings sometimes dont seal well. Your washer/bolt holdign the prefilter down might not be exerting enough pressure to seal everything.
The reason there is no fuel leaking is that the system is under suction through line 3. Air enters because of the vacuum the suction pump creates.
DV = Delivery valves. x6 on top of the IP. Each has a crush washer and oring. Don't mess with them if you don't know what you are doing.
My 99 E300 was totaled recently when a mech opened up a water passage in the head while trying remove GP #6. I had tried 3 times and it kept rounding over and I couldn't get it out. His lia ins company offered me a deal I couldnt refuse. They now own the car and it is in parts heaven.
Newbie
Joined: Apr 2010
Posts: 10
Likes: 0
90 300GD diesel SWB
At the back right corner of the intake manifold on the side firewall are 2 black rubber lines attached to the steel fuel lines that come from the fuel tank. These lines are crimped on with special clamps. Check the rubber hoses to make sure they are tight and not degraded. The top line is the return the bottom line is the feed.
Mark
Mark
