Hey everyone,
I have an '85 300TD, which is my first diesel Benz, and I'm feeling very grateful for all the good info on the web I know there are many posts about glow plug issues on here, and I think I've done a pretty good job of working through the system to see what's going on, but can't see to get it fully resolved.
I had the issue where the light wouldn't come on only very sporadically or not at all - and the engine was starting very roughly. So, I followed the diagnosis procedure on Diesel Giant (Mercedes Diesel Glow Plug Repair) Everything checked out fine except the resistance test on the #5 glow plug. So, I pulled that plug, confirmed it was bad using my jump box, and replaced it. Still, the light wouldn't come on, so I unhooked everything from the relay, opened the relay to see if there were any signs of water or damage and didn't see anything. Put it all back together, including putting in a screw holding the bottom of the relay box to the chassis (it had been missing). Then, everything worked great for 2 days and the car started wonderfully! This morning, I get in and the light doesn't come on. I keep key in the glow position for 10 seconds or so, turn it off and back to glow and the light comes on. The engine then started fine w/ 40 degree ambient temp. Just tried it again and could only get the light to come on 1 out of 6 times.
So, now I'm stumped. Everything in the glow plug system tests fine electrically. I am wondering if it could have something to do with the ignition. I do have one other odd ignition system quirk - the HVAC system won't come on unless I turn the key very slightly back toward off while the car is running. It's almost an imperceptible turn, but it creates a clear click and the fan comes on. Could it be that there's something odd in the ignition? If so, I'm wondering why it worked perfectly for a couple of days after doing the work I did this weekend.
Any ideas would be greatly appreciated.
Thanks!
I have an '85 300TD, which is my first diesel Benz, and I'm feeling very grateful for all the good info on the web I know there are many posts about glow plug issues on here, and I think I've done a pretty good job of working through the system to see what's going on, but can't see to get it fully resolved.
I had the issue where the light wouldn't come on only very sporadically or not at all - and the engine was starting very roughly. So, I followed the diagnosis procedure on Diesel Giant (Mercedes Diesel Glow Plug Repair) Everything checked out fine except the resistance test on the #5 glow plug. So, I pulled that plug, confirmed it was bad using my jump box, and replaced it. Still, the light wouldn't come on, so I unhooked everything from the relay, opened the relay to see if there were any signs of water or damage and didn't see anything. Put it all back together, including putting in a screw holding the bottom of the relay box to the chassis (it had been missing). Then, everything worked great for 2 days and the car started wonderfully! This morning, I get in and the light doesn't come on. I keep key in the glow position for 10 seconds or so, turn it off and back to glow and the light comes on. The engine then started fine w/ 40 degree ambient temp. Just tried it again and could only get the light to come on 1 out of 6 times.
So, now I'm stumped. Everything in the glow plug system tests fine electrically. I am wondering if it could have something to do with the ignition. I do have one other odd ignition system quirk - the HVAC system won't come on unless I turn the key very slightly back toward off while the car is running. It's almost an imperceptible turn, but it creates a clear click and the fan comes on. Could it be that there's something odd in the ignition? If so, I'm wondering why it worked perfectly for a couple of days after doing the work I did this weekend.
Any ideas would be greatly appreciated.
Thanks!