My 1991 350SD is experiencing hard start, rough idle after starting, and white smoke until warm. Once the engine runs for a couple of minutes everything is great and she performs like a champ. Restarting the engine when warm is no problem. A little back ground info: recently had the intake manifold off to replace a leaking gasket (Cleaned out years of crud from the intake manifold) and to replace the shut down valve. When reassembling everything I accidently shorted out one of the glow plugs with a wiring harness bracket (glow plug light would not come on). Once the wiring harness was properly attached the glow plug light comes on but now this problem when starting up. Not sure how to check my glow plug system or if this is the problem. Any help would be appriciated.

Sounds like you burned out a glow plug. The best way to test them it to pull them and give them 12v and see if the glow bright orange. If it doesn't glow bright orange then the plug is bad. You can test them in place testing the resistance, but I've never had good luck with that.

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+1

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

A quicker though not as telling test is to check continuity at the glow relay connector. The acceptable value is in the archives, something like 1.2 ohms. It takes some doing to remove 603 glow plugs so you might as well replace them if you're going to remove them.

Sixto
87 300D

I tested the glow plugs and had my local mechanic retest them. The glow plugs are all good. He thinks I might have a fuel delivery problem and wants to pull the injectors and send them to a local shop to check spray pattern. Could I have done something wrong by cleaning the manifold or when replacing the shutdown valve - I had the Alda off? Before spending big bucks I would like some confidence this is the right direction.

Maybe there's something else wrong in the glow system. Did the mechanic confirm that they are actually working or just that they are good?

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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

Did you short something in the glow-plug relay switch??? You may have to replace that relay, if so. Check to make sure that the relay switch is working for all five glow plugs.

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002

I wouldn't rule out the glow plugs jsut yet. The GP relay could be bad, or the strip fuse bad as well.

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No doubt the glow plugs survived the short but it might have fried the glow relay. Is there someone near you with a known good 603 relay, even a non afterglow relay, you can swap in to test? If you have the equipment, check the glow plug wires to confirm each is flowing about 10 amps during the glow cycle.

Sixto
87 300D

I'll try tonight swaping a relay from my 1987 300D and let you know. Hope it fits.

I'm trying to swap out the relays as suggested. Problem is the small connector on my 87 300D has 4 prongs with a plastic "L" to guide it into position. This "L" shaped guide interfears when trying to plug in the 5 prong connector from my 91 relay. I guess I could break it off but not sure. Please advise. Will the 87 relay work with this system?

Still trying to figure out how to swap a glow plug relay from an 87 300D into a 1991 350SD. Both car relays are out of their respective car.