I think I asked this before but didn't get any suggestions so will try again.

My '85 300CD with 142k miles runs perfectly except that lately, when it sits overnight, the engine stumbles a couple of times when first started. Feels like it is getting air in the fuel system or something to that effect. Runs fine after missing a few beats. Won't do this unless it sits at least overnight.

This is new and something is causing it. I looked for fuel leaks but see none. Fuel filters are in good shape.

Any ideas on what might cause this?

Thanks,

Nic

If you don't see any physical signs of fuel leakage anywhere, check at the top of the main filter where the soft return lines come together. Either one of these lines leaking, even the slightest bit will allow air into the system but will not leak any fuel out. The way to check is after it sits overnight, pull the small line, the one that runs from number one injector, from its fitting atop the filter. If no fuel runs out, this is the problem, you have a leak somewhere at the top, probably one of the soft lines.

Good luck,

Thanks Larry.

That sounds right. I replaced those "soft" lines a couple of months ago and may not have a good seal. Will examine closely. Is there any substance I can put on the fitting to ensure a seal? The lines just push on and have no clamps.

Nic

I would not use any sealer, the key is to have new enough line that it is pliable, there is no significant pressure on these lines. If you got a new stick of the line and put it on, did you get one a little short? The main one to concentrate on is where it pushes on the fitting at the top of the main fuel filter.

Good luck,

Okay, after hearing what you have to say, let me just get off the fuel line thing for just a second. It could very well be a fuel line issue, however, I have the same car and I know my fuel system is in fine shape (knock on major wood here). I too have had the same problem and have attributed it to 1) Injection Pump Adjustments, and 2) Valve Adjustments. When was the last time your valves were done? Also, I've had this problem in the very humid climates. You may want to use a fuel additive for water dissipation. I hope this sheds some light on the issue without having to rip apart the fuel system.

Randall,

I had the valves done fairly recently by a good shop so unless they messed something up....

It is very humid here and I don't use additives (except Techron just before each oil change). What type of additive are you referring to regarding water dissipation?

But this is new trait of car and just feels like air is getting in. I'll redo the soft return lines (thats easy) this weekend and see if it goes away.

Will report back next week.

Nic

Sounds pretty typical really. I just started using Redline in my car, and I've used Lubro Moly Diesel High Test and "Silo Heavy Duty" additive. It helps start up, especially in the cold. Also, be sure you light your pre-chambers long enough. Let them burn past the light going out, about 5 seconds more, it makes all the difference at times. Also, moisture may be in the fuel due to the humidity.

I have the exact same problem and have yet to figure it out. I've adjusted the valves, replaced the soft return line, installed new glowplugs, replaced the valve seals and I use Power Service at every fillup (I also gave it a dose of Techron). Nothing has gotten rid of it, although the new valve seals helped a tiny bit, so I'm guessing my problem may lie in oil leaking past the valve guides and causing the car to "hiccup" in the morning until the oil is burned off. I'm just going to live with it since the issue doesn't seem to really have any serious side affects aside from the minor annoyance that my car doesn't run as perfectly as I would like.

The reason I think this is caused by oil leaking in the cylinder after sitting overnight is because some of the old glowplugs had oil on them when I changed them out. Most likely they should have nothing but black soot on them, and I bet that oil can cause this problem.

Greg
'84 300D

Nic:

Oil from bad valve guides and or leaking valve guide seals will make the motor run rough for a few seconds after sitting all night. An amazing amount of oil can seep down the vavle stems when they are hot.

Cheapest fix is new valve stem seals (provided you don't have and leaks in the fuel system).

Check all the suction lines if the fuel system for bad hoses, though, as leaks here will run the fuel back into the tank rather than on the ground, so no smell or visible leakage. Air gets sucked into the fuel pump, however, and can cause rough idle and hard starts.

Return lines make no difference in running, just leak fuel on the ground instead of returning it to the tank.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!