Is mechanic a dingus? Vacuum problem with 115 glow plugs?
 

Glow plugs on the 220D were only working intermittently, like there was a short in the circuit, and I know the plugs are all good and wired correctly. Salt shaker would either cherry up on the first or second try or I might spend an hour trying to get them to glow. So I took it to a neighborhood shop that specializes in auto-electric, they have always been solid with my other vehicles (this is the first time I've taken the Benz there), but now after having the car for two weeks, dude tells me they believe there is a 'vacuum component' to the system causing problems and they are going to have to 'smoke it out'. I've been looking at schematics, and I see no vacuum lines having anything to do with the glow plugs. When I took it in, I had figured the gorilla knob was shot or there was a short somewhere else.

When the engine isn't yet running, vacuum = zero. Their 'smoke it out' procedure must involve cannabis. Did they check the blinker fluid too?

LOL!!!

Back on topic, I'd suspect that the switch that the glow knob acts on is bad, or the relay that it controls is bad. It won't be a "short", or you'd be letting another kind of smoke out...

I would tell them to cease work immediately and that I'd be picking the car up, with a tow truck if necessary.

I would imagine it's a very simple glow system on that car, so why not try do it yourself?

With the gorilla knob there is a fabric/rubber element that wears out and causes intermittent contact. If I remember correctly from when I changed one 'bout 30 years ago it is on or near the steering column under the brake master more or less. Simple to replace but hard to see.

Oh yes, he is a dingus.

Very strange indeed. I can only wonder about what that mechanic is confused about.

What it almost sounds like is a marginal connection. That when trying to make the circuit. A small amount of current may be flowing. Slowly heating the component until it expands enough to eventually make better contact.

Since it also is a simple series circuit. When it will not work it should be very easy to locate the issue. Maybe the mechanic and you could have a talk or print off this post and take it to him.

He for example could be confused by never running across a glow plug system in series. Or has not realized this one is. Plus as Tom mentioned there is a basic switch that apparently has a known failure rate in this older system.

Why I say strange as well. Is if he is coping with modern electrical systems in cars. This should have been a walk in the park for him.

Even with my extensive electronic and electrical background. Very modern cars electrical systems in cars do not make me happy. I might feel better about them if I worked on them a daily for a living.

In fact I almost see a time coming where some forms of electrical failures in cars will mean they are not worth repairing. Intermittent conditions especially.

OK, lets take this one bit at a time:

Does the fuse clear or wires melt when this " short " occurs? If not, there isn't a "short" and I'd call the car owner a dingus for using improper terminology.

They are thinking of a car with a vacuum engine shut off in the ignition switch. The operation of these 40 some year old cars is unlike any other car so give them some room. The smoke out procedure is used to find vacuum leaks. Google " vacuum smoke machine "


Did you provide the schematic to the shop? Did you interact with the shop explaining that the vacuum system pertains to the engine shut down system? The larger question is, it you know so much about the car, why are you taking it somewhere else for diagnosis / repairs?

The point of all of this is, one must be darn sure they get their facts straight before berating the knowledge of others.

This is so common with “mechanics” working on MB vehicles...

1. They have no idea what to do.
2. They read or heard somewhere that vacuum is used for the vehicles, so they associate everything with it...
3. They have no idea how to source a vacuum problem...

Go get your car. Don’t take it to them again, restrict their vehicle access to Honda’s...

Excellent info, thanks. Were you ever able to jury-rig or temporarily repair the rubber/fabric part or did you have to replace the whole knob? Asking because I'm hoping I can get it temporarily running while I track down the part number and find one for a reasonable price.

Thanks everyone for the input.

When I read "smoke out" I thought maybe the mechanic thinks he is working with Lucas Electric components.

As I remember the part is a rubber/fabric thing which you can hold in the palm of your hand. When it gets worn you cannot pull the switch closed. Temporary fix using baling wire or a zip tie might work.

I am a career electrician and over the years I have learned that 99% of the population uses the word "short" to describe any malfunction of an electrical system. Sometimes we have fun with it but usually just roll our eyes and get to work.

Yep. If the original poster said something like " I took the car to a shop but they need more information. " I would gently explain the differences between a short and an open. Instead he went right for " are they stupid? "

A person can be competent in their field with recent technology but unaware of obscure more or less obsolete tech, that does not make them a dingus.

If one put a professional automotive test driver in a Ford Model T they would have a difficult time making it move let alone getting it started if they never drove one. ( A T is operated way different than a more recent car )

There are too many people that call mechanics stupid but at the same time feel that they should know every minute detail of a 40 year old car.

I've got 40+ years in and around the car business coupled with 20+ in factory automation / industrial machinery. Robots , PLC equipment , CNC lathes- mills , stamping presses , press brakes , hydraulic and pneumatic systems are far and away easier to setup / diagnose / repair than most any car from the mid 80s and up.