603 priming on every start?
 

Last year ,when cold, my SDL would usually stumble on the first start-up requiring a quick stab at the accelerator to balance it out. It was more of an annoyance then a problem so I didn't think much of it.

I didn't really drive it most of this winter so it sat mostly unused for the past few brutally cold months. Now however the engine seems to be loosing it's prime every time I park it for more then an hour. The glow plugs work as they should and the starter cranks well but it doesn't fire for a good 30-50 seconds. (Usually it takes me 2 goes to get it running) I ran into a similar situation a few months ago when my new main fuel filter wasn't tight enough and air was getting into the system but I could see fuel seeping out so I fixed that very fast.

In this case I can't find any fuel leaks anywhere. Today I did a good cleaning around the IP to see if I can spot any leaks but I couldn't find any. (I will check again in the morning) Overall i'm stumped as to where the source of the leak could be.

Any thoughts?

Metal lines under the car might be rusted in the holders. Outboard engine primer bulb could be added under the hood for easier start up and testing for air.

I have seen it before. Fuels leak back into the tank due to a minute leak around hose clamp. You can prove it by leaving the car standing over night and then remove the spin on filter. It should be full or near full. If you find it half full then it explains your program. The other thing you can try is to hang a fuel bottle HIGHER than the spin on filter and see whether it helps.

I found the minute leak near the fuel heater which is not easy to access or easy to tighten the clamps. I by-passed it. Problem solved.

If the system is tight it will hold fuel. It has to have a point of air enterance otherwise. The check valves in the lift pump should also reduce bleed back if in excellent shape. Most have to be somewhat tired by now.

I don't know if your year and model uses O-rings to seal the Fuel Hoses or not. I also don't know if it has the Fuel Heater. The O-rings on both of those have been know to cause Air leaks.

The Valves inside of the Fuel Supply/Lift Pump could be not sealing well. When it was PeachParts they used to sell a Rebuild kit for the Fuel Supply/Lift Pump.
I think this is the thread on that:
Newer Model Lift/Fuel Supply Pump Rebuild
Anyone ever replace the valves in the fuel lift pump? - PeachParts Mercedes ShopForum

Could be. I have underbody panels which thus far have kept everything clean underneath the car. I'll have to wait for warmer weather to check these though.


I'm pretty sure my fuel hoses only clamp on. And yes I have a fuel heater (Ironically I never really noticed the little bugger until today while searching for the source of this leak :o )

I've thought about rebuilding the lift pump on both my SDL and the Gwagen. Again its something that i'm waiting for warmer weather to work on.

My car was doing this because of leaking delivery valve seals...

-J

[QUOTE=Fulcrum525;3306530]Could be. I have underbody panels which thus far have kept everything clean underneath the car. I'll have to wait for warmer weather to check these though.




I'm pretty sure my fuel hoses only clamp on. And yes I have a fuel heater (Ironically I never really noticed the little bugger until today while searching for the source of this leak :o )

I've thought about rebuilding the lift pump on both my SDL and the Gwagen. Again its something that i'm waiting for warmer weather to work on.[/QUOTE

I was not sure.
If your Hose uses a Calmp simply change the Hose. On mine it sucked a slight bit of Air only when the under the Hood temp was hot. I found that the Hose was so hard and inelastic that even though the Clampwas tight apparently when it was hot under the Hood it sort of was bending the Plastic on the the nipples of the Plastic Primary Fuel Filter and allowing Air in.
For about $3 for a foot of Generic Fuel Hose I solved the problem.

The 603 uses mostly standard fuel hose except for these 3 hoses, these have banjo fittings at each end (except for the end at the lift pump output).

(Note the 606 uses the "plug in" hoses with the notorious o-rings in the fittings)

- Lift pump "out" to main filter "in"
- Main filter "out" to IP "in"
- IP "return" to main filter "return"
These 3 hoses are rebuildable but it's much easier to just buy new ones. Don't forget the crush washers. Also be sure to blow out the banjo bolts with brake cleaner while it's apart.

The fuel preheater valve is rebuildable with a rebuild kit. This can be bypassed for the summer months but you will want it next winter.

The remainder of the fuel system is standard 5/8 hose with traditional clamps.

I think you have an air incursion in the fuel system somewhere up front. I would start by rebuilding all these items and see if that doesn't fix it.

Remember that the fuel system operates at a pressure lower than atmospheric on the supply side so if there is a bad seal it sucks in air rather than leak fuel.

I have used it on my OM606 engine, Now priming (if needed) does not kill the battery.

These are the o-rings on top of the IP correct? If so I do have a set.



Sounds like a good place to start and good preventative maintenance (particurally that heater)

Interestingly my G-Class also sprung a fuel leak the other day but it hasn't developed a hard start problem.

clubgwagen.com • View topic - Has anyone ever replaced fuel hard lines?

Annoyingly I can't quite figure out which hose to order :(
1980 Mercedes-Benz 300D Base Sedan - Fuel System - Page 1

One other thing to remember if you do this:

Do only one of the hoses at a time. The banjo bolts are not interchangeable. There is one odd bolt on the return line coming off the body of the IP that looks like it has a bb in it. That bolt must only be used in that location.

Well as it turns out I wasn't getting any air into my system. Turns out I had a couple of bad glow plugs. A classic indicator of "Just because the light turns on doesn't mean that it works...." On the bright side I did swap out the original 300D fuel pre-heater for my newer (Cleaner) 350SDL one.

For the first time in my life I own my own multimeter. I'll be putting it to future good use :cool: