I've been experiencing an odd issue with my 603 over the last week. It seems to be a lottery game as to when it will fire during cranking. Typically, the first and second tries cranking I get no combustion. There is NO apparent connection to engine temperature, because I can generate the problem dead cold or immediately after shutdown (< 30 secs), so I'm convinced it's unrelated to the glow plug circuit. Starter has no trouble turning the motor very well, and battery is brand new, so it's not a cranking speed issue. When the motor does fire, it's usually the instant the starter begins to turn it over. When it doesn't fire, you crank crank for several seconds with no indication of combustion whatsoever. My first impression is that it's a function of the IP/injector system somehow shutting off fuel entirely. I've also noticed that the manual shutdown lever rests in the shutdown position when the engine is off - is this normal? There is actually spring resistance to pushing it back to the run position. When the engine is running, it is in the proper position where you can push down to cut fuel flow. I don't know if this is normal or a clue of the nature of the problem.

Any ideas? Thanks in advance. I searched, but didn't come up with anything yet.

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1987 Mercedes 300D

I'm not.

The 603 doesn't like to start without glow plugs.......hot or cold.

Before you do anything serious, put a voltmeter on one of the plugs and turn the key to the #2 position. See if you get 12V at the plugs.

If the plugs are OK, then you've got to search for an air leak in the fuel lines.........close to the engine.

Interesting - I failed to mention that the glowplug circuit is definitely NOT working properly. That's on my list of things to investigate next week. It, however, had not ocurred to me that the glowplug system was remotely necessary on an immediate restart when the engine was fully warmed up, so I'd jumped to the conclusion that this was a separate/additional problem. Given your advice, I'll hold off until I can resolve the glow issue and see if it resolves this at the same time.

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1987 Mercedes 300D

there was another member who I think had a similar problem awhile back on here with the shutdown lever but I dont remember the exact details, maybe someone else remembers what it was exactly? I believe his name was want71280SEL or something like that

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

The shut-off lever will stay in the horizontal position after shut-off until vacuum bleeds (so to speak) from the system. Could be hours. If you turn the key to ON/RUN, the lever should pop back to vertical.

When you have a starting problem, check the position of the shut-off lever. If it's stuck down while you're cranking, pull the hose off the shut-off vacuum actuator. If the lever jumps up, the problem is in the key switch. If the lever stays down, the problem is inside the IP.

Sixto
93 300SD

If I reversed the vacuum lines when replacing the key switch, could that have this effect? Replacing the switch/steering lock/tumbler was one of the repairs I made to get the car back up and running.

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1987 Mercedes 300D

Yes, When the ign switch is on, it will release the vacuum to the shut off system. When the switch is off, it connects vacuum to the shut off system. If swaped, it will hold vacuum to the shut off system but cause a vacuum leak to the vacuum system.

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84 500 SEL (307,xxx miles)

I switched them just now when reinstalling the cruise amp. I only tried it once, but so far/so good. Thanks for the advice!

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1987 Mercedes 300D

For what it's worth, switching the vacuum lines back did permanently resolve this issue. Hopefully this helps somebody down the road...

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1987 Mercedes 300D