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Discussion Starter #1
My ML has been somewhat inconsistent in starting for almost a year now and it has been to the dealer I guess 3 times to address the issue but to now avail. Perhaps someone in the community may know what's going on…

Here is a video link to my truck starting rough (almost 10 secs for engine to turn)

I can't reproduce the problem on demand, it happens when it likes to. Outside temperature doesn't seem to be a factor - as you can see it was 12.5C (54.5F) when I recorded this. And I've had it stutter with 20C (68F). I thought it happens if I don't drive the ML for a couple of days, but nope, doesn't matter.

My boyfriend thinks it has something to do with the glow plug, but heck, I'm a woman… glow what? Today the glow lamp came on… first time ever, it went off, but now the check engine light is on. Hmm…

I called my Service Advisor and he said the glow plug has nothing to do with the current rough start I'm experiencing. OK… but doesn't the glow plug help start a diesel engine?

I'm hoping someone out there has some advice for me. My warranty just expired in October :( but fortunately the work order on this is still open, and so the investigation continues… I'm starting to lose faith in the dealer…

Thoughts?
 

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Starting a diesel is somewhat different from gas engines. Diesel engines have a "glow plug" to somewhat heat things up before you start cranking. Posting this video was a good idea coz you just demonstrated a very common mistake. Whenever you start your "diesel", you should turn the key to "on" and wait for that glow indicator light (the one on the right that looks like a coil or spring symbol) to turn off. It should only come on for less than a second. Then and only then should you "start" or crank the engine. These instructions are in the owners manual.

I've only owned my 07 CDI for less than a year - this is my first winter and I have not seen that glow indicator last for more than 2 seconds even in 30 degree F weather. I hope this helps.

Im using the term "glow plug" loosely. Some other forums indicate our W164 might even have some type of spark plug. But the starting procedure have been the same for Mercedes diesels since the 80s.

The problem wont show up in the dealer because the engine is already "warmed up" by that time. Pre-heating is generally most important when the engine is cold.
 

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I was under the impression the glowplugs warmed things up in milliseconds, not seconds? When I turn my key, it seems to occasionally delay the actual starting momentarily. My assumption was this is glow plug related.

Your idle seems to be pretty terrible too.

Could this be a fuel pump issue, do our engines create enough suction to operate without the in tank pump operating properly?
 

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Discussion Starter #4
Starting a diesel is somewhat different from gas engines. Diesel engines have a "glow plug" to somewhat heat things up before you start cranking. Posting this video was a good idea coz you just demonstrated a very common mistake. Whenever you start your "diesel", you should turn the key to "on" and wait for that glow indicator light (the one on the right that looks like a coil or spring symbol) to turn off. It should only come on for less than a second. Then and only then should you "start" or crank the engine. These instructions are in the owners manual.

I've only owned my 07 CDI for less than a year - this is my first winter and I have not seen that glow indicator last for more than 2 seconds even in 30 degree F weather. I hope this helps.

Im using the term "glow plug" loosely. Some other forums indicate our W164 might even have some type of spark plug. But the starting procedure have been the same for Mercedes diesels since the 80s.

The problem wont show up in the dealer because the engine is already "warmed up" by that time. Pre-heating is generally most important when the engine is cold.
Ahh… good points raised. I did have the discussion with the Service Advisor a while back - "Am I doing something wrong when I start?". He goes nope, just turn the key and start. He drives a CDI too, so he should know. :)

I have parked my truck at the dealer over the weekends for the Monday morning starts and the problem has shown up one time, but they weren't able to address it.

One time the problem was attributed to a dirty air filter and "stuff" because my service was 1000K over… Another time they "reset" some program which seem to be their usual way to address unknown issues.
 

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when you turn the key to the on position you should hear the electric feed pump humming. its located under the right rear seat. No hum no start. Assuming they changed the fuel filter I would suspect the pump. Mine took about a year to hard fail. The engine will not start without the feed pump operating. It delivers fuel to the engine driven high pressure pump. Mine left me stranded in parking lots several times. I begged the dealer to change it while it was under warranty but they flat out refused. So I got to pay $430 and do it myself. hopefully yours wont leave you stranded in a bad spot. It could be water in the fuel but a filter change would solve that. Good Luck.

Scott MacMoyle
 

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Having said all that.. You should still wait longer for the glow lug light to go out. You could even wait an extra few seconds before starting and see if it make a difference.
 

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Discussion Starter #7
I guess I should update the thread on what has happened since the last posts..

The situation actually got worst - which is a good thing.
I was in an underground parkade and when I turned the key, the glow light came on and stayed on.. Strange, this isn't supposed to be like that as I drove the car for 30mins earlier and was parked for 2 hours. Not knowing what to do I turned off the engine… Turned the engine back on and guess what, I had both the Check Engine and pre glow lights illuminated! Darn it, I have to go home, I'm driving it!

Both warning lights went out eventually. But the good thing is that it left an error code for the dealer to look at.. Finally!!!

So, they replaced the ECU and some other stuff which I don't know exactly as I never got the bill. It was a $1800 but was "waived" off as a courtesy because they never could fix the problem and it was just past the warranty expiry..

I now make sure the preglow lights goes out before I turn the engine fully.. It has been good so far..
 
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