Weird Starting Issue, Twice Now
 

On two occasions, I parked facing up on a friends hill (one month apart) and when I went to start the car (98 E300D) cranked but wouldn't start. I took off the fuel filter and it was half full so I filled it with diesel and the car started after cranking a bit.

I figure that the fuel drained back out of the filter, but there are no fuel leaks anywhere. This never happens when I park in my own driveway which is flat.

Is there a check valve or some other thing I should check. I know I can avoid the problem by parking front down hill, but would like to solve it correctly. I searched but couldn't find any clues.

Hope someone out there can help.

You must have an air leak somewhere allowing the fuel to drain back to the tank when pointed uphill. Until the air leak becomes a fuel leak, I'm not sure how to find it.

That is what I thought, an air leak "up stream" of the fuel filter, but I thought if air leaked in, surely diesel would be leaking out????

Any chance that your fuel tank was low? and all the fuel just went towards the back of the tank

No, the tank was at least 3/4 full. It has only happened two times in my life, and both times on my friends uphill driveway. I am sure it is siphoning the fuel back out of the filter, and if that is happening, then air must be coming in somewhere. I just can't figure out where.

Did you ever figure out the cause. I have the same problem. Will not start after sitting if pointed uphill. Roll it to a flat or downhill spot and it starts.
Thanks
Wendell

It is an air leak in one of the clear diesel lines. I ordered all the parts and have them ready to install. The only downside is that you have to remove the intake manifold to get to all of them. I ordered from Duval Motor in Gainseville, FL (FYI they are a real Mercedes dealer but have an online website with discounted parts and they are very helpful if you call them, too.)

Apparently there isn't any pressure in the lines so the fuel doesn't leak out, but when stopped the air can get in and allow the fuel to siphon back to the tank.

You can R & R the fuel lines by removing the windsheild washer bottle and flipping it up and out of the way. Thsi will allow you some access to work.

The white clips are pushed tightly closed to spread the shoulders of the fuel lines for removal. When installing there should be a definate "click" as they seat. Takes about 15 minutes.

Dont forget the pre-filter o-ring.

If the lines are in good shape the o-rings only can be replaced. If yellowed you should probably replace everything.

Compliments of Ncof300D
Snap-on Hose seals
O-ring
13mm OD
8mm ID
2.5mm thick

Shut-off Valve seal
O-ring
17mm OD
12mm ID
2.5mm thick

If you have all the parts....start with replacing the O ring behind the shut off valve and the fuel lines that run from the primary fuel filter and the one or two others that are accessible without rmoving the manifold. Then test it on the hill. If that works then you can do the others when you have a little more time to remove the manifold.
Good Luck,

That is great information regarding the stats on the o-rings. I wish I knew that so I could have bought them elsewhere. I replaced the one behind the shutoff valve and had to drive all the way to our dealership and pay $3.50 (still cheap compared to having the service department do it) for the o-ring.