Hello,

We recently got a 1984 300SD with 248k on it. It seems to drive fine, I just replaced the front pads 'n rotors. It's been runnning fine for a month and then right after I put the brakes on the car won't start. It turns over a little slow, but never starts. I thought the battery might have gotten low because we left the key in the ignition with the electrics on for maybe 30 mins. We tried for ever to try to jump it with my VW and it still won't start.

I checked the resistance at the glow plugs and they're all reading around 6-8 ohms. I read up on here and it says they're supposed to be around 1 ohm, or less. Is it possible that by leaving the ignition on we fried the glow plugs? The fuse is fine in the GP relay box, and you can hear the relay clicking when you turn the key. The dash GP light works the same as it ever did, it turns on for a little while when you turn the key, then goes out and lets you know its time to start.

Also, it was starting really hard before this problem occured. When you started it in the AM it sounded like one of the cylinder's wasn't firing. If I gave it just a slight touch of the throttle while it was warming up it was smooth. I'm guessing that means one of the plugs wasn't working?

Please, do tell.


Thanks!

 

When u left the key in, was it in the number 3 position? If so, nothing should have happen if your glowplug relay is working proper. If it wasn't then it provided juice to all plugs and left them on. On your car the glowplugs run for 45 sec. then shut off, (Thats why it seems like all cylinders are not running at startup) newer MB diesels glow is for 90 sec to 120 sec,(lot smoother startup) check your relay, there is a fues in there that looks like a band of aluminum. See if theat went. Also I'm not to sure as far as Ohm readings on your glow plugs. The way I check my glow plugs is a test light. If it is bright good, if dim or not at all, shot. Good luck.
Rob

 

I just checked the fuse and relay, they're OK. I had a helper turn the key to activate the glow plugs and I observed 12v at the the glow plug for about 45 seconds like you stated. Are the plugs supposed to get hot to the touch when they're working? On a 1978 240D I used to have, I touched the common rail for the plugs to see if they were working and got a nasty burn. On this car there's no common rail, but the plugs are cold as steel. Is this any indicator of the plugs not working?

I want to make sure its not a fuel problem or otherwise before I order new GP's.

Thanks.

 

to see if it is fuel, make sure there is fuel in the prefilter, then while someone is cranking it over, crack the nuts on the fuel lines on each injector. this will not tell you if you have bad injectors, but it will let you know if fuel is at least leaving the IP.
you said it is cranking a little slow, you may have a bad cell in the battery, or your starter could be getting weak. while the injectors are energized, what is the exact voltage? with a digital voltmeter, you should read 12.0 volts while GP are energized. also when cranking the motor, the voltage should not drop below 10.0 preferably stay above 11.0
since you were having trouble starting before, I bet you have clogged injectors. you have ohmed out the GP's so that is most likely not the problem.
John

 

Thanks for the info John.

Can you confirm what the resistance is supposed to be at the GP's? I read somewhere on the net and someone said it should be around 1 ohm. I measued 6-8 ohms. I'll check for fuel at the injectors this weekend, hopefully the weather clears up. From your post, I'm guessing if I just crack the fitting on the Injector while the motor is cranking fuel is supposed to spit out of the there?

I was reading just under 12v at the battery without any load. I think I'll get a trickle charger to bring the battery back up to par... we've got three old german cars in the stable now (only one of which is running) so I'm sure it will come in handy.

I ordered the CD manual off ebay, it should show up soon. I hope that thing has some good info in it

 

i have a 85 mercedes 300sd that needs new glowplugs, i'm not an expert in cars or engines but i know enough that i think i could do it myself...with some help, does anyone know how to install glowplugs or can show me a site that will give me instructions?

 

easy jsut take them out and replace them like u would a spark plug