Air leak. - PeachParts Mercedes-Benz Forum

Hatterasguy · #1 06-08-2004, 07:07 PM

I have an air leak, it is in the clear line that goes from the fuel pump to the spin on filter, the inlet line. At idle there are bubbles in the line and when I rev. the engine up to 2k-3k the fuel going in turns almost milky! I'm glad I changed those lines there nice and clear now I woudn't have be able to see the air leak with the old ones. The car runs fine, the only problem is it skips really badly in the morning. I'm thinking the IP needs to be rebuilt, but was planing on testing the injectors first. Could this air leak be related to the skipping? Could the fuel pump cause this? It is a 1987, 603, 300SDL.

WANT '71 280SEL · #2 06-09-2004, 01:41 AM

I would have a hard time believing that your IP needs rebuilt after only 235k miles. I would bet it's your injectors, but didn't you replace them? You are still suppose to have new ones pressure tested.
Thanks
David

TonyFromWestOz · #3 06-09-2004, 07:41 AM

Quote:

Originally posted by Hatterasguy
I have an air leak, it is in the clear line that goes from the fuel pump to the spin on filter, the inlet line. At idle there are bubbles in the line and when I rev. the engine up to 2k-3k the fuel going in turns almost milky!
SNIP

I am not familiar with your vehicle, if it has the 617 engine with a lift pump on the side of the IP, where you can prime the fuel system:
If this is the fuel line from the fuel lift pump to the Fuel filter or from the fuel filter to the Injector Pump, then the problem is upstream from the hose where you see the bubbles. Check the hoses at the tank and at the fuel line in the engine bay.
If it is the clear fuel line returning from the Injector Pump, it could be the same problem, or air leaking in at the filter or one of the fuel line banjo connections.

It is highly unlikely to be an injector or the Injector Pump.
If this is not the case, check these pipes anyway, as they are primary suspects. Also check the tank strainer, as any restriction here will create a slight vacuum, allowing air to be sucked into the fuel system. Then check your fuel filters for clogging, for the same reason.

P.E.Haiges · #4 06-09-2004, 08:43 AM

Hatterasguy,

I would concentrate on fixing the air bubble problem before touching the IP or injectors. Most of the air will go out the fuel filter bleed hole and back to the tank, but you may have more air entering the fuel system than the bleed hole can handle.

Some place there must be a hole in your fuel line. Try pressurizing the fuel tank slightly (No more than 1 PSI should be applied to the tank or it might expand) and look for leaking fuel along the entire length of the fuel line. Remember there is an expansion outlet in the fuel tank and it must be blocked to pressurize the tank. Also look for leaking fuel around the fuel pump. Eventually you should find fuel dripping on the floor in the location of the leak.

P E H

whunter · #5 06-09-2004, 09:18 AM

Sounds like a bad O ring on one of the lines attached to fuel filter housing.
Totally strip the fuel filter housing, and replace every O ring, even the ones on your new tubes.

Hatterasguy · #6 06-09-2004, 11:25 AM

The injectors are all new Want. I'm going to have them tested to try to track down a skipping problem. But for $50 each the better be fine out of the box.

whunter, the lines I replaced have crush washers on them, they are all pressure lines so I don't think air could get in threw them. Today I'm going to run a clear line from the tank inlet to the fuel pump. I'm going to bypass the fuel heater. This way if I see bubbles in the clear hose I'll know there comeing from the tank. I replaced most of the hard fuel lines under the car this winter it is possible one of the new joints could be leaking. I also removed and cleaned the fuel strainer while I was under their. I'll get back to you guys later after I do this test.

Thanks!

sixto · #7 06-09-2004, 05:10 PM

The skipping might be caused by a lazy glow plug or low compression in one cylinder.

Sixto
95 S420
87 300SDL

Alan Hamm · #8 06-09-2004, 05:30 PM

Which is more likely? Mine misses and skips like crazy when it is cool or cold out. Even when cycling my glow plugs a few times. When it is warm, no problem. I replaced the glow plugs early in the winter with no significant change.

Hatterasguy · #9 06-09-2004, 05:58 PM

The reason I think the skip is IP related is temp doesn't matter. It skips about the same weather I glow it or don't glow it. Time seems to matter more, I think the engine is loseing its prime somehow. Thats why I'm getting all the injectors tested, it sounds like maybe one is leaking down overnight.

whunter · #10 06-09-2004, 07:44 PM

Quote:

Originally posted by Hatterasguy
I have an air leak, it is in the clear line that goes from the fuel pump to the spin on filter, the inlet line. At idle there are bubbles in the line and when I rev. the engine up to 2k-3k the fuel going in turns almost milky! I'm glad I changed those lines there nice and clear now I woudn't have be able to see the air leak with the old ones. The car runs fine, the only problem is it skips really badly in the morning. I'm thinking the IP needs to be rebuilt, but was planing on testing the injectors first. Could this air leak be related to the skipping? Could the fuel pump cause this? It is a 1987, 603, 300SDL.

The bubbles entering the injection pump are causing the engine skip.
Air can only enter the fuel system from the gravity feed = fuel suction side.
The visible bubbles are showing that air is being sucked in.
If you need to prove that the skip is due to air bubbles entering the injection pump, follow the attached graphic.
The red is a temporary new fuel feed line, blue is an in line fuel filter.
Oops, corrected the colors, thanks.

sixto · #11 06-09-2004, 09:24 PM

Either I'm colorblind or you have red and blue reversed

Sixto
95 S420
87 300SDL

TonyFromWestOz · #12 06-10-2004, 08:37 AM

Here is another thought.
Using a clean fuel container, add a fuel line fron it via an in-line fuel filter to the lift pump. Check for air. If none, the problem lies in the lines to the tank. If they are present, then you have a problem with the lift pump and/or the filter/lines after it.
Relocate the fuel supply from the lift pump to the filter inlet (block the lift pump outlet to avoid spraying fuel everywhere)
If you have no problems, you have proven the problem is before the filter ie, the lift pump.
If you still have air problems, then the problem is the filter of connections to the IP.

Hatterasguy · #13 06-10-2004, 11:51 AM

Well I fixed it! It was a bad pre-filter. I spliced a clear fuel line in from the hard line that comes from the tank direct to the fuel pump and no bubbles. The old pre-filter always had a lot of foam inside it and part of the element was collapsed. So I put a new one in and no bubbles! I'm guessing the old one had an air leak in it.

whunter that is exactly what the bosch shop told me to do. I'm going to have to try it because it still skips. I think there is a fuel or air leak in the IP. I just want to make sure it's the problem before I pay $1k to get it rebuilt.

whunter · #14 06-10-2004, 01:18 PM

I would ask here on the forum about a good used injection pump.
With any luck; someone will have one on a parts car.
The savings will make you smile.

Hatterasguy · #15 06-10-2004, 08:20 PM

Just got an Adsitco catalog, they want $795 for an rebuilt one and $495 for a used one. I really don't want a used part, usually you just get someone else's problem. Also 300SDL or D parts cars seem hard to come by.