Occasionally I get a hard start when the car is at operating temp. Happened tonite at pharmacy window. Turned the clanker off at the window, at restart in 3 mins, it cranked and cranked, then started to fire slowly and finally lit.(83 300SD)

New fuel filter, air filter, primary filter had a little stuff, not performance altering gook, just a little and still hard started couple times with new filter . Hard start is intermittent.

Thoughts? Glow light doesn't come on hot, most times fires immediately and cold, every time. New battery too.

Thoughts??

Vacuum is not bleeding off the shut off valve. Next time it happens, pull the brown vacuum line from the shut off valve and see if it fires right up.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

The Vacuum Issue Kerry mentioned seems to have happend to at least 3-4 Members of the 2 Forums I hang out at.

Hotter thinner Fuel can leak by poorly seated Valves in the Fuel Supply/Lift Pump and any worn parts. It would also leak past the Fuel Pressure Relief/Overflow Valve easier making it harder to hold pressure.

Was this ever a Car that used SVO or WVO? A few People have had their IPs worn prematurly by using that.

It can be other things but When I worked in a Fuel Injection Shop one of the tests was to rev-up the Calbration Stand and get the Fuel Injection Pump really hot and then bring it quickly down to the starting rpm. If the Fuel quanitity at the top end was correct and the starting rpm Fuel was below spec it was an indication of too much wear in the Elements or in the case of a Rotary Fuel Injection Pump the Head and Rotor.
However, from what I have been reading in the Forums it takes something unusual for that to happen to a Mercedes Car (although I have seen it on Bosch Inline IPs on Commercial Vehicles).

I had a small Air leak that only showed up when the Engine was really hot. It turned out that My Fuel Inlet Hoses were hard and inelastic and even though the Clamps were tight. Evidently when everthing was under the Hood was nice and hot this caused the Plastic Filter under the Hose to warp and let Air in. I had hard starting but not as bad as you have.

A couple of short lengths 5/16" ID Fuel Hose cured that.

Old Style Hand Primer with the Shiny Aluminum Body. If you have one that could be the source of an Air Leak.

Try Pumping a lot on the Hand Primer before starting Hot and see if that makes a difference.
Does it start easier on a Full Tank of Fuel than it does when it is nearly empty? If so that could indicate a Fuel Supply problem.

Try adjusting your Idle speed to the Higher spec that is on your Emission Sticker.

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84 300D, 82 Volvo 244Gl Diesel

I'm with Kerry.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

The car never used wvo, etc. I owned the car for 10 plus years and never an issue. I just got her back after friend owned her 3 years and he reported a hard hot start. I have noticed she doesn't shut down correctly, takes a while to die. I bet the vacuum issue is the culprit. What's the fix?

AND Your Due Diligence INVESTIGATION !

CLUE:
It's either:
The Vacuum shut off valve
A leaking Vacuum valve @ the Key/Switch.
OR
Bad Vacuum line(s).

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'84 300SD sold
124.128

Appreciate the clue, pal! You folks are a great source of information.