S210 E300 TDT 1998 - air in diesel (will not start)

[Preben]

Ok, so I have start issues. It somehow sucks air into the diesel fuel lines, and I am starting to loose hope...

I have replaced all o-rings myself, except the one behind the stop valve. I had to take the car to a repair shop to remove that, because the two screws were too hard to get out with simple tools.

Then I had the car running for 2 days, but noticed it used a little longer time to start than before. Had the car on a trip to a cabin, and when I started it after 1 night - it started and run for short time. Then it stopped. Couldn't start it again. I then checked some of the fuel lines, put them back again. Then force filled the whole fuel lines and the pre-filter and filter with diesel. After then cranking if for almost a minute it started.

Couldn't take it home (was alone and had two cars there), so I went back 2 days later. Then the fuel lines (before I started) showed no air, still it took some tries before it started. Run it home. Then I ordered new fuel lines for #1 and #2 (see the image with the red arrows). Also ordered new pre-filter and o-rings for that. Replaced this. Filled it up with diesel.

Still not starting. Still no fuel sucked to the pre-filter from the tank.

IF I disconnect #4 from the diesel filter and suck it (yes, I have had quite some amount of diesel in my mouth), I suck air. Even though it is diesel in #2. So I guess there is an air leak somewhere in #3 or in the new o-ring in the Stop Valve???

Please help me think through this. I have had problems for 2 months, and still I can not see the end of it.

PS: I have bought o-rings for diesel, but they seams to swell up. The first time I mount them they slide in as they should. But when beeing in the car for some days they get harder and harder to fit. Seams like the swell... Is that normal?


Explaination: Diesel is sucked from the tank, through the diesel heater, through line #1, through the pre-filter, through line #2, through the stop valve, through line #3 to the pump. From there there is no sucking, but pumping. So the air leak must come from line #1, #2, #3 or pre-filter or stop valve - if I am not wrong...

[biopete]

Check to make sure your crankshaft position sensor is plugged in. It is on lower part of engine near firewall below #6 glow plug. It comes off the main wire harness like a glow plug wire. I don't have car here to take a pic. It will cause the prefilter not to fill up with fuel. It could be going bad. I don't know how to test it. That would be good to know. I can't remember if you have to take intake off to see it. You can start the car without the intake on for a minute to test.

[TMAllison]

The CPS is on the transmission bell housing. Can be seen from the drivers side of the engine bay. I don't know how it not being plugged in or working would tell the mechanical lift pump not to pump? Maybe if it faults it prevents the SOV from opening?

Sounds like a leak, if that's the issue, is on the suction side of the lift pump. Lines 1-3 + the SOV oring. Have a friend crank and watch for where air first appears. The leak will precede that point.

The white horseshoe clips should be pulled back (loose and floppy) after the lines are installed. They are spreaders and are only pushed close during removal of the fuel lines.

Might want to crimp the hold down washer at the pre-filter. Sometimes they flatten out and don't provide enough downward pressure to create a seal.

[Preben]

I have tried to find the crankshaft position sensor, but haven't suceeded. Anyone who knows where this is? However I don't understand neither how this can affect a leak in the lines.

I have now tried to suck in the filter-end of the #4 line. I then get only air.

I then deconnected line #3 from the stop valve, and plugged the line with my finger and sucked again the same place. Then it's sealed: no air.

So it seams like the leak must be around or in the stop valve. The problem is that I haven't succeeded now to remove the screw that holds the stop valve. It is mis shapen, so I can tigthen it, but not loosen it. I had the car to the repair shop to fix that and exchange the SOV o-ring, and they say they have put the new o-ring there - but I see they have not put in a new screw... Argh...

My thought is that they might have put the o-ring on the wrong edge. Then it will leak...

PS: If I try to blow into the #4 line while #3 is connected to the stop valve, I can not. So how come I can suck air, but not blow it back?

[Preben]

Update:

Just to test, I disconnected #2 on the SOV end, and tried to suck there. I then sucked diesel all the way from the tank, thtough the pre-filter and into line #2.

So it seams like the SOV o-ring is the error.

If so: so much for paying a repair shop to fix my car...

[TMAllison]

The SOV bolts are Torx head. Can't remember the size.

[Preben]

Size 30 I believe. I have those. I also have size 35. I bought those to have something to try open up the rounded old torx head.

I am able to open the torx on the right side of the SOV, but not the other. :-(

I might remove the intake manifold (I am bot sure how to do that) and then try to do some "hard hitting tries" to unscrew the old torx.

[jay_bob]

It is possible to have a leaky hose such that the fuel does not leak out but air gets in.

I would replace all 6 hoses as well as the prefilter (it. 26) and o-ring beneath the pre-filter (it. 29). I would not replace just the o-rings but the entire hose assemblies.

They are available from M-B for about $100 total. Also be sure to pick up the 3 washers needed for the fuel return to IP body line (it. 126-qty 1, and it. 128-qty 2).

I did this on my W210 and it made a major difference in the performance of the engine.

You will have to remove the IM to do this. So be sure to order a new IM gasket and O-ring between the IM and intercooler pipe.

This is not difficult if you have ability to safely lift the front of the car. Ramps will be sufficient.

If you are using ramps drive up on the ramps first.

Loosen and remove the 12 Torx T40 bolts holding the IM to the head.

Follow the IM down into the depths on the left side, there is a 10 mm bolt holding the EGR exhaust sucking pipe onto the EGR valve. (The EGR valve is attached to the bottom of the IM and will be removed as a unit with the IM.) Take this pipe loose, it is corrugated and can be slightly moved aside.

Now the fun part. Get under the car and remove the lower underbelly shield.
Gather up about a foot of socket extensions and put a 10 mm standard hex socket on the end. Look up under the car just inboard of the left front tire and you will see the intercooler pipe coming from behind the radiator, sweeping up to meet the IM. There is a pipe clamp that holds the intercooler pipe to the IM, you will need the 10 mm socket to loosen this bolt.

Also look up, there are 2 rubber hoses. One goes to the EGR valve and the other is the boost pressure sensing from the IM port. Disconnect them.

Now from above, gently but firmly pull straight up to loosen the IM from the intercooler pipe.

Notice the gaping open holes on your cylinder head. Do not let anything fall in these holes. Place clean cloths or paper towels in these openings.

Your IM will be filthy from EGR gunk, search for threads on how to clean it out. Then find more threads on how to bypass the EGR on an OM606.962 to keep it from happening again.

Ok now back to your hoses. The white clip is a little counterintuitive, the white piece is supposed to be loose on the fitting, if it is snug, it is providing pressure on the release mechanism.

Once you get all 6 hoses swapped and the manifold back on, you will have a big air bubble in your fuel system. If you used ramps, this will be exacerbated since your engine is now elevated higher than the fuel tank.

The W210 has a self-crank system, however it will time out before the air gets a chance to be purged. You will need to turn the key and hold, no more than 30 seconds at a time, until the engine catches and fires.

[Quahog]

you will be glad you did. They may not be responsible for your no-start condition, but they aren't helping either. They are a pain to get to, so it makes sense to do the job completely. In my case, I never experienced hard starts, but ran much stronger after replacement.

[Tubularfab]

I'm not sure your "suck test" has any validity on this fuel system. The way this shut off valve works is rather odd - and the supply goes through that valve before the lift pump.

Also, when you turn the ignition on it powers the shut off valve very briefly, then shuts it off unless the engine is rolling over on the starter. So, it's difficult to run an ignition on test of the shut-off valve.

I had a miserable time getting air out of the injection pump on my '97. I literally put an hour of cranking use on the starter getting it going - and it had no leaks. It just didn't want to purge and run...

[KarTek]

It's possible that the shop did not put the o-ring in the right place on the SOV. I have made the mistake, it's easy. The ring goes on the lower part of the part that goes into the pump. I have a picture somewhere that I will attach here when I find it.

Found it...

[Preben]

It's possible that the shop did not put the o-ring in the right place on the SOV.

That is what I believe. But since they put the old bad screw back in, I can't check. (Can not open it). They said they will open it again to see. I also said I expect them to put in a new screw, so I easily can unscrew it later myself with ordinary tools.

I HAVE replaced the fuel lines on the suction side of the diesel pump. So there are new lines from the diesel heater to the suction pump. There are also new o-rings and new pre-filter with o-ring. On the other side there are no suction, but pressure. So if the other lines leaked, they should be wet with diesel - not getting air in. Right?

I'm not sure your "suck test" has any validity on this fuel system. The way this shut off valve works is rather odd - and the supply goes through that valve before the lift pump.

I am not sure neither. However it seams strange that if I suck, but disconnect the outgoing line from the SOV and seal the line with my finger, I get no air. When I plug it back into the SOV, and plug the ingoing holes in the SOV with my fingers, I get air.

I don't know hos the SOV is supposed to work. I don't even understand why there is an o-ring on it's side, since it looks like the diesel is just running though it from top to bottom.

May be you can share your insight on this?

I am just quite frustrated that it does not start. It doesn't suck diesel very well, so there is nearly no diesel coming into the main diesel filter. So the main diesel filter is also emptied when I crank the engine.

[ROLLGUY]

I have never tried this, but in theory it should work. Use your Mityvac with the brake bleeding components connected to the return hose attached to the hard line going back to the tank. Pump it enough to suck the fuel through the supply and filters, and out the return and into the collection container. That should prime the system enough to start the car. Again, in theory it should work. I am sure something like this is used in the factory when the cars were built. I can't imagine them cranking the starter for minutes at a time to prime the system.

[Preben]

It probably works. But not on my car, because somewhere between the pre-filter and the filter it leaks air. I don't have a mityvac, but I have a vac I use in my garage. It sucks pretty well (that was an awkward comment :-) ). Can try that tomorrow :-)

Great idea.

[ROLLGUY]

You own a Mercedes Benz Diesel and not a Mityvac (or Chinese equivalent)?
Using a "shop vac" may work as well, but you may get fuel in the vac hose. With enough vacuum, you should be able to see where the air is coming in if your hoses are clear enough.