Oh no, I have air in fuel lines... PICTURES!
 

I love this site and I'm thankful for all the help I have gotten. I would have to say, my only complaint is not enough pictures.

Anyway, here is the situation. 1987 190D with a OM602.
The car will not start warm or cold without the aid of the glow plugs. Even when the engine is at operating temperature it will not immediately restart.

For the moment, lets assume the compression is good. The engine seems to run fine and there is barely any detectable blow-by.

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The fuel tank return line was temporally replaced with some clear vinyl 5/16 hose so I could inspect the lines for air. As seen in the photo above there is zero air bubbles in the return line when the engine is idling and when the engine is revved. Everything seems fine.


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On the other hand, the tiny pre-filter has a crap load of air in it. This filter has always had air in it and I figured it was normal. From what I gather, apparently this is not normal and needs to be dealt with... correct?

Anyway, if I shake the pre- filter around a bit while the engine is running I start getting air bubbles in the return line and the engine will start making a high pitch sound.

The fix....??

I'm assuming there is an air leak on the supply side of the fuel line. This car is very solid and relatively rust free so chances are the hard lines are probably ok. Could the air leak be coming from the connection to the fuel tank?

Update...

So I crawled under the car and had a look at the fuel tank supply line....

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The hose going into the tank appears dry.


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This is where the tank hose connects to the hard line. the hard line looks a bit crusty but is also appears dry.

Although the hard line looks solid, I suspect the corrosion may be more significant than the pictures shows.... but not enough to cause a fuel leak.

Any thoughts?

The prefilter tends to have air in it. Because of how the fuel system works, it's just about impossible to burp the bubble out.

Be aware that the worm-style hose clamps you have on your car have been known to cause air ingress issues on more than one occasion. I fought with them on my own car. Fuel-injection style clamps are much superior and create a better seal.

Leave the clear line on overnight and check it the next morning. It should still have a solid column of fuel in it.

Some day try replacing the plastic filter with one that has a 90 degree on one end install the 90 degree end closest to the Lift Pump and point the body of the filter down and see if that does not get rid of your plastic filter air bubble.

I saw a picture one time of test equipment. You put the Injector in the machine and then pressureized air was applied to the Nozzle end of the Injector. If the innards of the Nozzle were not still seated good air get inside of the Injector and would pass out of the top of the Injector including the return.

It that happens it would account for Air Bubbles in the return line because air is being compressed in the Cylinder till the Fuel starts to be injected. And during that compression time air could be getting pushed past the nozzles.

I don't know if it possible on a Mercedes but if you pump faster then the fluid can move you can get a vacuum bubble; but that would be on the suction side.
I am not sure if a vacuum bubble looks the same as an air bubble.

You might try runing the engine with out the Fuel Tank Cap on. If the bubbles go away then you may have a tank vent restriction/issue.

One way to find out on the suction side is to bypass the inlet hose coming from the fuel tank and add a section of hose and draw from a seperate container.

Thanks for the quick feedback!

I have a 90 degree pre-filter on its way. I'll pick up some FI clamps tomorrow.

Unfortunately I had to remove the clear hose and put the fuel system back to normal so I could drive the car tomorrow.

I'll probably do the overnight clear fuel line experiment on thursday or friday.

Stay tuned!

Check the in-tank filter, its under that rubber boot leading into tank.

This sight is not uncommon

http://www.team-bhp.com/forum/iipcache/150683.jpg

If blocked will draw air no matter how good pipes are.

Totally agree too on hose clamps, they don't draw up round more of an oval shape

You could pull the supply line off the bottom of the tank and see how fast it drains. You could also swap the suppply and return and see if you are still drawing past a restriction or not.

Interesting... How much fuel should be in the tank if I flip the lines?

This gets too complicated for me. I'd start at the tank by draining it and pulling that tank screen unless it's been done on your car. Diesel is nasty.

You're correct, the primary filter always has a bubble unless you bleed it off by parking the car front end down on a hill and open the fuel exit end of the filter. It's not worth the trouble, imo.

If the car is parked level and the tank has a significant amount of fuel in it the head pressure of that fuel should push it through the filter. That's one of the reasons the left side engine mounts go before the mounts on the right. Fuel runs through clean lines without assistance other than gravity.

I'd replace all the rubber hoses between the tank screen and the secondary filter while I had the lines empty. Hoses and clamps are fairly cheap and cleaning the screen is a matter of soap, water and something to dry the water off of it.

Should I go ahead and order a new in tank filter in case the old one is crap and the o ring is FUBAR? Probably not a bad idea?

Meanwhile, if I eliminate all or most of the air in the pre-filter and the air pocket returns then is this semi normal or a clue.

Right now the car has about 3/4 tank of fuel. It will take a few days to burn most of it off.

I'd try to clean it first. I've only cleaned a couple of the tank screens but neither needed to be replaced. I bought a new one before I removed the first but didn't use it. The rubber o-ring was fine.

I guess it's ok to buy the o-ring just in case but evidence indicates the screen is good. If it had a hole in it or was torn you'd see the results in the primary filter real quick.

Changing the screen will be fine if you select a good quality. I don't prefer putting junk in if the original is still usable. If you can wait to soak that old screen overnight you can probably spray it out with a garden hose and get it clean.

I went ahead and ordered a new screen plus o-ring and the hose just in case. Chances are the screen hasn't been touched in 30 years. Anyway, the parts should be here before the weekend.

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Depending on what your tank filter looks like you may need to consider cleaning the tank It's not uncommon for tank liner coatings to give way over time re-blocking filters, this tends to happen mostly with bio or veg fuels.

Diesel Fuel Fun
 

What he's talking about is properly called the 'siphon' ~ in general, if you disconnect the rubber fuel hose under the hood from the metal pipe leading from the tank forward, as long as there's 1/2 tank of fuel or so, fuel should begin to pour of of the open stell pipe in a hood diameter stream, not just dribble straight down .

Dirty in tank fuel screens are much more common than many realize, to the point that I check every one that comes through my hands ~ even those that run O.K. because a marginally cruddy in tank screen will allow good running in town but starve the engine for fuel on the open highway .

It's normally a very simple if greasy anf filthy job to clean the Mercedes in tank screens with a toothbrush and whatever cleaner you choose .

Be certain to let it dry fully before re installing ! .

: Originally Posted by Clemson88 View Post

If the car is parked level and the tank has a significant amount of fuel in it the head pressure of that fuel should push it through the filter. That's one of the reasons the left side engine mounts go before the mounts on the right. Fuel runs through clean lines without assistance other than gravity.


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__________________
David"

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Cheers nate, it was this bit that confused me -

"That's one of the reasons the left side engine mounts go before the mounts on the right"

Engine rotates to this side giving mount a harder time, that was my understanding.

Doc, you will need a large wrench to undo filter, can't remember size off hand - maybe 22 - 24mm?

That is so. That mount also is often exposed to fuel leaks from changing filters and leaking lines which pass over it. Diesel is responsible for the loss of many young LH engine and engine shock mounts.

Don't overlook the IP leaking oil down on it either. Between IP oil leaks and diesel fuel leaks, my 2 year old LH engine mount is toast. RH side under the turbo is still just fine.

I didn't notice my IP leaking but the cam cover had both sides of the engine covered including both engine shocks, shock mounts and engine mounts.

I haven't started my engine in two years. I probably have an IP leak and didn't know it. Oh boy, I've been looking forward to dealing with the injection pump on his car. It will be my first.

Diesel Oil And Rubber / Plastic Bits
 

@ David ;

Oops ~ I wasn't sure .

Oil leaks more on the left side of the engine most of the time and Diesel contaminated oil attacks and destroys rubber (motor mounts) and plastic like you can't believe .

This is why it's so important to keep after the weeps & seeps plus wash the engine every so often ~ failure to do so creates a cascade effect wherein something is always breaking because the oil leaked onto it degraded it .

Sorry missed the interpretation, read across - agree, diesel works it way into all sorts especially rubber.

Update.



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New right angle pre-filter with correct clamps


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Air bubble in filter is nearly impossible to get rid of



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Picture of engine bay right before a cold start. The car had been sitting +12 hours. Zero air bubbles were seen during cold start and idle.


Video of start up...https://youtu.be/TKEK23SUgd4

It looks fine to me, some of my Diesels have these bubbles, others do not .

As long as there are no bubbles in the fuel coming from the tank when the car is running you're good to go .

One thing I noticed in your video is the stop lever bobbing up and down. That means it's not properly attached to the stop mechanism and is resting on the linkage inside. Believe it or not, that could be your problem. When the engine is running, that lever should be fully up and feel like it's spring-loaded.

Back to the fuel issue - lack of bubbles is a good sign, that means your fuel system is tight. The bubble in the prefilter is normal, don't lose sleep trying to get rid of it.

Check glow plug resistances. If you find one high, it needs to be replaced (probably the whole set in that case). That startup is pretty rough.

Interesting observation on the stop lever. I honestly have no idea what it is connected to inside the IP. I do know the lever will shut off the engine when pushed.

Is the lever somehow connected to the vacuum shut down device ?

The lever should be connected to the vacuum pod, the spring inside is what keeps it pulled up. With it resting on the stop linkage internally, the bobbing up and down can cause the engine to pulse or hunt, similar to how it would behave if you were feathering the stop lever by hand.

I had the same thing happen the first time I changed the O-ring on the stop lever shaft. I wasn't careful and it fell off inside. The bobbing definitely caused a lot of loping and weird behavior at idle, I can only imagine it would do the same thing when hitting chugholes and dips in the road.

It took a while, but I was finely able to investigate the odd behavior of the shut off valve Diseasel300 mentioned. I'm not really sure how the valve was connected, however when I removed the valve and put it back in, it operated normally. I suspect the valve was not engaged correctly. Anyway that issue is solved, so a big thanks to Diseasel300 for the heads up.

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This shut off valve was difficult to get to because of all the stuff that had to be removed. Perhaps whomever replaced it before took a few short cuts and installed it improperly.

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While in the neighborhood I went ahead and replaced the glow plugs. I also reamed the cavities prior to putting in the new plugs.


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Also while in the neighborhood I checked the compression.
cylinder#1 350 psi
cylinder#2 340 psi
cylinder#3 330 psi
cylinder#4 310 psi
cylinder#5 350 psi

Is it running any better though? That's the important question!

The car seems to run the same, I'll have to wait a few hours and see what is does on a cold start.

While looking for fuel leaks after servicing the engine, I discovered the fuel warmer gizmo was starting to drip fuel. I went ahead and removed the warmer and attached the fuel feed line directly to the lift pump.

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Looks like this thing was previously mended with spit and chewing gum.

Anyway how important is the fuel warmer? will it effect fuel economy or is a cold weather thing? The car is not fitted with a block heater so it will pretty much not be used in the winter.

I guess the PO didn't know about the O-ring on that plastic fitting? If it was dripping fuel, that's your air leak guaranteed. Extremely common location for air ingress, especially since it's on the suction side of the pump.

Deleting the fuel heater won't affect anything. It's most important to heat the fuel when the weather is cold, but because of how the system works it isn't going to heat the fuel until the engine warms up. I've run with and without the fuel heater on my SDL and notice no difference in fuel economy. Given the amount of problems that fuel heater thermostat causes, it isn't worth keeping on the car anyway.

Ok, sounds good. I'll toss the fuel heater in the box of other parts that have been deemed unnecessary.