1982 300sd glow plug circuit
 

Having trouble cranking unless block warmer plugged in. Glow plugs less than 6 mos old. Cranked very easy until recent cold weather snap(not really cold live in North Atlanta). Now won't crank even in garage w/o block warmer. Glow plug indicator comes on (don't know if this indicates anything). Purchased from MB mechanic and he said to check fuse and solenoid. However, cannot locate a fuse or identify GP solenoid. Looking for schematic and fuse panel/solenoid layout to troubleshoot from.

Would like a good shop manual. Any recommendations?

Thanks

Go to dieselgiant.com and follow his glow plug testing sequence. You need to check the resistance on each glowplug. Each should be less than 1 ohm. There's a strip fuse on the relay but if the light is working, I think this means that strip fuse is ok.

Thanks. The link is excellent. One more question. I have been getting the light but should the light go out before attempting to crank (like my Duramax)? I hope I have a bad solenoid. Otherwise, I don't have a good explananation for the dramatic change.

When you say will not crank do you mean the starter will not spin the engine over? Or the engine turns over and the car will not start. Solinoid usually refers to the starter. It is the component that makes the starter engage and turn the engine over.

Yes. The light is intended to indicate when an adequate glow time has been achieved, based on ambient temperature. In my experience, that indication is sometimes a bit optimistic.

I was talking about the relay that sends power to the glow plugs. The motor never fails to turn over but never wants to fire unless I have the block warmer plugged in.

The indication never seemed to want to go out. However, the MB mechanic I bought it from told me not to worry as he had just replaced all the glow plugs. So in the summer I just gave it about 10 seconds and it always fired right up. Temps below fifty and this does not work.

I would be kinda weary of the whole "I changed the glow plugs already" coming from someone that just wanted to sell the car at the time (not to say he's not honest or anything) but just because they were changed doesn't mean they (or at least enough of em) haven't failed. I'm in Cobb County outside Atlanta and yes it has been a bit nippy lately and I also had a hard start a few months ago with a perfectly good indicator working,etc but for some reason it would only start easily if I kept her plugged in if not in the garage. Sure enough I just went ahead and decided to give my 300SD the once over and flushed the coolant,changed the oil,PS Fluid and filter as well as fuel filters AND yes, the glow plugs...After removing them I tested each one (the jumper cable way to see if I'd get ANY glow) and only ONE worked!

I'm assuming the previous owner did replace them at one time (I guess but they were Beru which is usually a sign of origina from the factory ALTHOUGH I also use Beru so I don't rule out that they could be replacements but this time I replaced with the Bosch plugs) but anyway, now I KNOW the glow plugs (and glow plug relay) were replaced because I had an extra one and wondered if the GP relay may have been the cause of the other plugs going out from it malfunctioning. I haven't ironed all of those issues out yet but the new GP relay is doing fine and have had quick cold startups every time so far (but will still plug her up if I have to keep the family van in the garage and my other baby HAS to stay out when its 20 :)

Just my 2 cents but I figured if it starts when its plugged and warmed (like it would be if the GP's worked, you drove around and got up to operating temp, ran into a store for a few minutes, came out BUT the car was STILL AT OPERATING TEMP, the car would fire right up cause it doesn't need the GP's help to start as much as it would a cold engine), I'd replace the GP's AND as stated check em out first (I'm anal and already had extra GP's just in case...I also have an extra Alt,Starter,keep 5 primary and 2 secondary fuel filters and rotors,brakes,etc I'd buy new over the years so I wouldn't be scrambling to find em if one were to fail lol... Good Luck though