Puzzling Ignition Problem - PeachParts Mercedes-Benz Forum

RML · #1 09-22-2010, 09:09 AM

I am puzzled by this sequence of events: (It relates to my 84 300D)

1) My ignition lock tumbler has been hard to turn with one of my keys. Evidently I grabbed the wrong key yesterday. It turned OK in the morning, but when I went to go home from work, the key would not turn in the lock.

2) I had taken a can of spray lock lubricant and before inserting the key sprayed inside the lock.

3) I kept trying to turn the key, lifting up, pushing down, maneuvering it every which way. No go. So I called my wife and asked her to come and bring my other keys.

4) While waiting for my wife, I kept trying to turn the key and then started to smell a faint burning smell. A burning electrical wire type of smell. Not real strong but enough to get my attention. So I opened the hood and disconnected the battery. (I have a quick disconnect.)

5) My wife arrived and with another key she brought, I put it in the ignition and it turned with no problem. I connected the battery, but when I turned the key, there was no response. No glow light, no starter turning, nothing.

6) I checked the fuses but did not see a fuse blown.

7) My guess is that this is unrelated, but I will mention that my low fuel warning light has been staying on lately. I have a half a tank of fuel so it should not be on. It does not come on anyway when the fuel is low.

So is the apparent electrical problem related to my lock problem? Did the use of a spray lubricant trigger something? Is there is fuse somewhere else other than the fuse box? I did not see a fuse labeled "ignition switch" on the fuse box map.

Thanks for any suggestions.

Richard

micalk · #2 09-22-2010, 10:14 AM

You need to look at your ignition electrical switch and the wiring around it. Check the point-to-point connections from the battery to the GP relay through the ignition. There's not alot there so troubleshooting should be simple. Lube should not not have contributed unless you really flooded the thing, and even then it would be unlikely. The two assemblies are separate. Fuses would be after the ignition switch but I don't recall if GP relay and starter solenoid are fused. The one thing I would recommend is to replace your ignitio key tumbler. Sounds like it may be starting to go. You might consider replacing the entire lock assembly if the electrical switch is shot. A new electrical switch comes as part of the assembly and will alleviate any concerns with ignition key issues.

RML · #3 09-22-2010, 10:54 AM

Would I be safe in jumping the terminal box under the hood, on the fender, to get it started and home? Or would the ignition switch prevent this from working also? This may seem like an elementary question, but electrical stuff is not my forte. I will probably understand it a lot better after I have resolved this problem.

Richard

Daman858 · #4 09-22-2010, 11:07 AM

Unfortunately, these ignition switches don't last forever. I do believe that the smell you experienced was from the fluid you sprayed in there as I had the same problem years ago in a 240D. I was told by a long time Mercedes mechanic that the cause of ignition switch problems is too many keys and other junk on the key ring. The weight causes the key to jiggle around over the years thereby wearing out the internals. He said that, by far, most of the cars with switch problems that came into his facility were driven by women who have tons of junk on their key rings.
I would suggest that when using lock lubricant, just spray the key a bit and put it in the lock.

I agree with milkalk...a new ignition unit will do you just fine.

RML · #5 09-22-2010, 10:06 PM

I'll most likely take a fresh look at it tomorrow. My guess is that if it starts by jumping the terminals in the box on the fender under the hood, I will be able to drive it home, but I will need to shut it off with the manual shutoff.

RML · #6 09-27-2010, 12:08 AM

Well, I was able to start the car by jumping the terminal block under the hood. I got it home and parked it. The next day I tried it with the key again and the ignition switch works. The key only works when inserted one way. When turned 180 degrees, it will not let the tumbler go to the last position after the glow plug position. So I believe I need a new tumbler.

Note to self: Do not spray any liquid lubricants into the tumbler. As Daman858 confirmed, I believe this caused a temporary short. Seems like it did not do any lasting damage, so I got off easy this time.

BTW, I did not need to use the manual shutoff under the hood. The engine shut down normally when turning the car off with the key.

Thanks for the input.

Richard