The car runs absolutely perfect 99% of the time, no problems with acceleration and drives like a dream, other than when it's parked on a slight downhill grade (front-end facing down) and has sat for a little while (as little as an hour). The symptoms are that of a pump that's lost it's prime for some reason.

Does this sound like the Fuel pump check valve is going out? Do these tend to get weak before they fail completely ?

The car has a new fuel filter (problem was there before the filter change as well).

I sold the car to my friend which is located approx. 60 miles from me, and the car is with him so, I can't check the fuel pressure etc... I'm hoping someone has experienced this and can provide a quick fix.

The fuel pumps are pretty pricey for these things, so I want to figure out what it is before I tell him to start throwing parts at it. LOL

Thanks for any help/insight you can provide.

TJ

 

maybe not fuel problem.

there is a low spot on the tank where the fuel pump sits.
better read for any fault codes.

 

Hi Sleepwalker,

Thanks for the quick reply.

Before handing the car over to him which was Saturday Morning, I ran the codes just to make sure there wasn't anything going on with the car. Specially cause I was selling it to a friend. Then on Sunday evening he called me with this problem.

Everything is clear - no codes at all

When you say maybe not fuel problem, what do you think it might be ?

The car runs fine 99% of the time. When it's parked on a downhill grade, sometimes it won't start. Just cranks like it's out of gas. Then if you push the car so that it's at least level or the front-end higher than the rear-end it starts right up.

I'm thinking that it's the fuel pump check valve, and when the car is parked at that angle the check valve (depending upon the cars exact position) has a slight leak that lets the fuel drain out of the input side of the pump and thus the pump has a hard time sucking the fuel "uphill" when it's dry. kind of like it lost it's prime.
Does that makes sense ?

 

hmmnnnn....

the pump is just a simple rotary design with no check valve anymore.

you got two fuel level sensor and on the other side without the pump, a jet suction which is powered by the return line transfer the fuel to the other tank which got the pump.

if this jet suction is faulty, you may find the other half almost empty and the other side with more fuel.

this problem doesn't happen on full tank? try it.

maybe the transfer pipe inside is kinked.

???? i really got no idea.

 

Check this fellow member's site. you'll see a bit of what i mean.

 

This one.

 

How weird. So your software doesn't show a Fuel Pressure Check Valve anywhere ?

I went to http://www.europartsdirect.com/?source=mbforum and plugged in 1996 Mercedes C280 and under the Fuel Pumps menu, you'll see a Fuel Pump and Filter link, once you select that, there amongst the Filters and Pumps is a Fuel Pump Check Valve for $10.86 Bosche Part Number BSH015542

Also, my Alldata software shows a labor time of .7 hrs for replacing it.

Actually my Mitchell OnDemand mentions a Fuel Delivery Check Valve as well.

Yikes ... now I'm really confused, as I trust your software way more than mine. LOL

Thanks again for your help,
TJ

 

the only check valve i know comes with the fuel pump on 104 engine.

i have no idea which version you got.

such is designed to prevent formation of air bubbles inside the fuel line with engine off and can only hold for about half an hour.

yes, i am weird so pardon my innocence. i have more than 300 mercedes-benz engine type combination inside my head and must have confused yours with a different one.

have a nice day.

 

No worries mate !

You're not weird at all.

And it's a blessing that you have all that info inside of your head as it helps MANY MANY people in here daily.

In my software, when I try to find where the check valve is located, all that is listed is a TSB about "Engine is difficult to start when warm" TSB#DDAF07_30-U-6402A Apr 97

I think I'll just bite-the-bullet and order the fuel pump and that check valve that they list for $10 then just replace them both (that is if I can find where that check valve goes LOL).

Take Care and again MANY THANKS for your help!

TJ