2002 W210 E320 CDI smoke problem

[andy99]

Hello everyone - newbie here so please be gentle...

Have found a nice rust-free W210 with my engine of choice - the 3.2 straight six - and all is lovely. I went for condition over mileage so we're in the 150k club. 7 seater to fit all the kids in. Nice.

However... sometimes it runs beautifully, pulling strongly. Sometimes it does this with a fair amount of black smoke on part throttle. Sometimes it goes into limp mode and won't go beyond 3000rpm or kickdown. In limp mode there's no smoke. No malfunction shows on the dash. Restarting the engine sorts it all out - for a while - sometimes a mile, sometimes lots. Economy is indicated on the dash as 38mpg on the tank, but filling up I calculated only 32mpg.

Coming from a pretty agricultural but amazingly reliable Audi A6 with the 5-cylinder 2.5 diesel, I am somewhat at a loss to identify parts, let alone which bit is faulty. I am handy with a set of spanners and a multimeter... I have read many threads here about MAFs and EGRs and the things that can go wrong - flaps and hoses and the like - so I wanted to ask a few questions or get some points clarified.

1 - I'm convinced the turbo is fine as the black smoke is not always present.
2 - Can things gum up with disuse or gentle treatment? The car was used by an old boy to pootle around in so he probably never went over 2500rpm.
3 - Are there any simple unplugging/resetting routines I could try?
4 - The actuator arm on the turbo moves around half an inch under power - is this about right?
5 - black smoke is usually a symptom of an air leak after the turbo - where are the usual leaks on this system?

I prefer to do the easy and cheap things first - any advice before I start replacing bits and pieces?

Thanks for reading this far - your assistance is much appreciated.

Cheers,
Andy

 

[toby1]

Read my thread in my signature.

You've obviously done some searching already so you're probably on the right track. I''d want to have the fault codes checked first before wasting money on replacing parts willy nilly.

 

[Frontstep]

Hello everyone - newbie here so please be gentle...

Have found a nice rust-free W210 with my engine of choice - the 3.2 straight six - and all is lovely. I went for condition over mileage so we're in the 150k club. 7 seater to fit all the kids in. Nice.

However... sometimes it runs beautifully, pulling strongly. Sometimes it does this with a fair amount of black smoke on part throttle. Sometimes it goes into limp mode and won't go beyond 3000rpm or kickdown. In limp mode there's no smoke. No malfunction shows on the dash. Restarting the engine sorts it all out - for a while - sometimes a mile, sometimes lots. Economy is indicated on the dash as 38mpg on the tank, but filling up I calculated only 32mpg.

Coming from a pretty agricultural but amazingly reliable Audi A6 with the 5-cylinder 2.5 diesel, I am somewhat at a loss to identify parts, let alone which bit is faulty. I am handy with a set of spanners and a multimeter... I have read many threads here about MAFs and EGRs and the things that can go wrong - flaps and hoses and the like - so I wanted to ask a few questions or get some points clarified.

1 - I'm convinced the turbo is fine as the black smoke is not always present.
2 - Can things gum up with disuse or gentle treatment? The car was used by an old boy to pootle around in so he probably never went over 2500rpm.
3 - Are there any simple unplugging/resetting routines I could try?
4 - The actuator arm on the turbo moves around half an inch under power - is this about right?
5 - black smoke is usually a symptom of an air leak after the turbo - where are the usual leaks on this system?

I prefer to do the easy and cheap things first - any advice before I start replacing bits and pieces?

Thanks for reading this far - your assistance is much appreciated.

Cheers,
Andy

Well the clue might well be in the tootling around, some posher fuel and some very spirited driving is called for before you start throwing money at it.

 

[bob 6600]

As well as the advice above....

The MAF can be disconnected to see how it runs and eliminate it.

The EGR could probably do with a clean, it could be sticky and causing the limp mode.

 

[andy99]

Thanks for the advice -

toby1 - can the car log a fault without showing a malfunction on the dash?

Frontstep - it's had a tank of decent fuel and was driven in a spirited fashion (where conditions allowed!) and I thought a blast of full-chat turbo could shift some crud. Injector cleaner gone through too.

bob 6600 - the MAF connecter is the multipin on the left front of the motor (as I look from the front of the car) going into the black plastic arrangement (air cleaner?) Do I unplug this and start the engine or unplug while running and look for changes? What would I look for to eliminate it as the source?
The EGR is the silver cylinder on the inlet manifold with the odd rectangular box from the exhaust on the right as I look in? Is removal easy or not? I know they can be pretty messy but do they just need a clean and refit?

Sorry this has prompted more questions - it's my first Mercedes after many years of VW/Audi ownership!

Thanks,
Andy

 

[toby1]

Yes. Management light won't necessarily come on if in limp-home mode.

 

[bob 6600]

Mine has limped plenty of times in the past and never tripped the EML.

Yes that is the MAF connector. IIRC, when it limps, unplug it and see how it runs. If better then the MAF is duff. If you do replace, only buy a genuine Pierburg one.

Yes that is the EGR vavle (mixing chamber). It takes about an hour to remove (some bits are a bit fiddly) but it's not too difficult. Cleaning it is definitely beneficial and yes just a good clean. There is a thread on how to delete the EGR (search for thread by dieselman) to stop this coking up in the future.

 

[andy99]

Thanks bob -

Ok - so waiting for limp mode took ages - but it did eventually. I unplugged the MAF and jumped back in with the engine still running. Not worse or better - exactly the same. Tried a hot unplug once reset. Brought about the same mode. Fixed it by plugging in hot. Went back to normal.

Does this identity or eliminate the MAF from the search? I'm going round in logical knots trying work it out - obviously unplugging part of the engine will make it limp by if it's already in limp unplugging something won't make it better!!!

I look forward to sorting this!

Andy

 

[Naraic]

Clean or delete the EGR.

 

[andy99]

Been looking at dieselman's thread on egr delete - which seems like a plan. Looking at the cleaning option, does the inlet manifold need to come off or not?

 

[turbopete]

disconnecting the MAF on diesels often throws limp mode anyhow, hence you wouldnt tell the difference. mine failed on the 203 and i had permanent limp mode

 

[bob 6600]

Been looking at dieselman's thread on egr delete - which seems like a plan. Looking at the cleaning option, does the inlet manifold need to come off or not?

To clean the EGR - no

 

[andy99]

Thanks for all the advice folks - have performed the EGR delete (thanks dieselman and confirmation of Alex's wire colours) and all is good. Took around half an hour if you're handy with a soldering iron. No smoke to speak of (it is a diesel after all) warms up fine and not throwing a limp.

Result!

Cheers,

Andy