W164 ML280 - Starting Problems

[cwpaters]

My ML280 over the last week has been taking a few secs sometimes 5 of turning over until it actually starts then i am getting a big plume of smoke out the back!

I have just been thinking i could try do test on the glow plugs with a multi-meter? but then i read somewhere online that the glow plugs dont have anything to do with the starting of the engine which i found to be weird? this was on a c270 thread though?

this morning was pretty cold and my wife said she though the car was not going to start!

any help or other suggestions to test would be much appreciated?

 

[grumpyoldgit]

I think you may have misread, or someone has given false information regarding glow-plug purpose. However, the information could also relate to a hot engine. They are needed to assist starting in cold weather.

When a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel. The glow plug is an electrically heated wire (think of the hot wires you see in a toaster) that heats the combustion chambers and raises the air temperature when the engine is cold so that the engine can start.

Get the glow plugs checked, it is quite common for one or more to fail.
The plume of smoke you are seeing is probably the accumulation of the unignited diesel which is injected into the cylinders with every rotation of the engine while you are cranking it. Diesel ignites by the heat caused by compression alone.

 

[BlackC55]

It is very likely to be caused by the glow plug control unit.

 

[cwpaters]

Grumpy - that's exactly what I thought that's why I couldn't understand the piece I was reading! I will check the resistance when I manage to get my hands on a multimeter! Someone said to check the resistance? Ohms

Blackc55 - sounds expensive? Best doing the trial of elimination first though?

 

[BlackC55]

Not at all.
They are tricky to diagnose as they don't always give codes.

I would be pretty sure that the glow plug unit is faulty. We have done many for this fault.

 

[cwpaters]

Thanks for your reply again blackc55!

So once I test them tomorrow night when I get a multimeter and if all is ok, how easy is it to change out the control unit?

 

[thecolonel]

how did you get on with this? interested in whether it was the GPs or the Module?

 

[Terry_]

Glow plugs will usually only fail individually and this will not cause hard starting
The module will cause hard starting as they will make the preheat fail on all cylinders, and the 642 engine does need preheat.
We have, however , seen injectors producing excessive leak off on these engines too. It's best not to take a punt on a glow controller and have it checked

 

[mbenz1]

Most likely it is the glow plug module. Exact same symptoms happened in my dad's E280 CDI when winter started last year. Changed the module and no problems since. Its worth doing a STAR diag. to reveal the problem.

Glow plug modules failing in the OM642 V6 is pretty common

 

[thecolonel]

Interesting, my 280 ml has the glow plug bulb stay in for 1min or so after start up. Diag shows cyl 6 glow plug faulty. It also can on occassion take 2-3 secs to fire.

Will swap out cyl 6 plug first and see if that solves, if not will be looking at a module i guess. Just hope they are pnp and dont require some daft programming on STAR etc.

 

[E270 Owner]

On the 270's you were reading about......
What can happen is a glow plug goes short circuit and blows a fuse link in the glow plug relay, you replace the glow plug but still have a fault in the glow plug relay circuit due to the link being blown so the glow plug never heats and shows a fault code.

You can open the glow plug relay and solder a new fusible link in untill you can get a replacement relay unit.

Not sure if its the same on the 280 as the 270 though,

http://www.mbclub.co.uk/forums/elec...-relay-module-028-545-4032-a.html#post1792000








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[chrisjj1982]

i put new glow plugs in my ml270 last weekend because the glow plug would go off then come back on for a min.

 

[DaveyLC]

I have been having cold start issues: My W164 ML320 would turn over for a good 5 seconds or so before starting and then it would run rough for a few seconds. Once it was warmed up it would start on pretty much the first turn of the engine.

My initial thoughts were it was an air leak on the fuel lines but a good way to check this is to turn the ignition on and off a few times before starting to allow the primer pump to pressurise the system fully.

I tried the trick above one cold morning and it made no difference, I decided to do a diagnostic check (Even though the MIL light wasn't on): low and behold there was a P0670 error stored which generally means the glowplug controller module/timer is stuffed! (P0671-P0676 would be individual plug faults).

I opened up the module and straight away I could see that it was burnt out on the input voltage side as several of the little fuse-able links were broken (sorry I didn't take any photos).

The original glow plug module has be replaced with a revised item (A 642 900 58 01) which is strangely much smaller too.

I ordered the replacement module (£118 delivered) and before fitting I tested the glow plugs to make sure that one hadn't failed and it would eventually destroy my new module.

Testing them with the module removed is VERY SIMPLE! On the connector you'll notice there are 6 (grouped together) thicker black wires each with a different colour line running down them, you simply use a multi-meter to test the resistance between each wire and ground (negative): It should be around the 0.7ohm mark.

I hope this helps someone

 

[T25JHW]

Gents,
I have a similar issue - takes 3-5 seconds to start when cold. I performed the checks on the glow plugs and module and all is fine (thanks to the detailed info above). Any other assistance? as l guess it must be a fuel issue? Car is fine when warm.

 

[kid-jensen]

DaveyLC,

I see you have a Memoscan (U581?)...

Do you recommend it for Mercedes-specific fault finding? I'm thinking of stuff like the Parking sensors and maybe some real-time monitoring of engine paramenters that you wouldn't get with most generic readers..

Should I get one or spend a bit more for a Mercedes-specific device?

 

[DaveyLC]

The model I've got is only good for engine fault codes and live engine data. I'm not sure any of the cheaper scanners like these can do much with body related faults.

 

[kid-jensen]

DaveyLC,

Thanks for the quick reply..

I'm still trying to find a diagnostic device thet does it all and costs about the price of a round..

So far I'm undecided between the iCarsoft i980 and the Delphi DS150...just need to do a bit more research.

 

[DaveyLC]

So much R&D has to go into the high end scanners they end up costing a fair bit.

 

[JamesOverton]

Mercedes Benz Diagnostic Tool ,Multi System Scanner iCarsoft i980 designed for Mercedes Benz cars - scantool-direct.co.uk

Looks pretty good for under £100

 

[Awais93]

Hi I purchased a dell laptop with the Delphi software and also got the hardware and it serves lots of functions for most cars including the om642
Air filter reset
Reset adaptions
Throttle learning
Reset maf data
Zero calibration
A lot of live data
Injector programming
forced dpf regeneration
Adaptions for transmission
Reset shifts (although I wouldn't mess with this as it takes long to put right )
Transmission oil temp which is really useful when filling up the atf to get a accurate reading of temp
Plus service resets
And many more features