S320 cdi smoke

[peterfau]

S320 cdi NO smoke anymore!!

S320 cdi smoke

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May 2000 S320 cdi 59K Miles FULL SH

the car is very smokey under load (Boost) with big puff of black smoke (unburt fuel). Peformance is perfect, idle even from cold at -6 Deg C ambient is sewing machine sweet.

So far I have had
1. the air intake system checked for leaves etc, new air filter.
2. Tank drained and new fues filter. as i always fill from the same private tank ( suspect fuel),
3.New fuel from new source.
4. Fuel additive for diesel engine/injectors cleaning.
All to no avail, it still smokes.

Had full engine diagnostic check (MB equipment & technician), which showed no faults!! The only slight varience was that injector on cyl no 6 gave a reading of 1.15 all the others were between -0.7 and +0.8. I am told that a value of 5.0 is required to warrant an injector replacement.

Just this morning for the very first time, on a very short journey, the car felt like all turbo boost was gone but when I restarted the car it was fine, but smoke was still there.

I now suspect the MAF but have no solid reasons, just a lack of new ideas!! ( In the last twelve months wife's AudiTT with only 20K on it plus daughter's VW Gti 26K both needed them!!)

Any ideas?

 

[Dieselman]

It could well be the MAF but this should have been picked up during the diagnostic session.
Alternatively it could be that the EGR valve is opening too much or is stuck open.

 

[peterfau]

Disconnected MAF, still smokey and will not rev beyond 3K with no power! will have EGR tested next. Should this not also have been picked up by diagnostic check?

 

[peterfau]

Sorry I should have asked, how is the EGR valve tested. Looking on the web, info seems to suggest that it (they?) are cast into/located in the head casting. Any help/info would be appreciated.

 

[jimmy]

Disconnected MAF, still smokey and will not rev beyond 3K with no power! will have EGR tested next. Should this not also have been picked up by diagnostic check?

The engine will not rev past 3Krpm with the car stationary, it's a safety feature.

I used to get a puff of black smoke when pulling away from stationary, I blocked off my EGR valve by placing a ball bearing in the vacuum pipe and this has reduced/stopped the black smoke. I occasionally operate the EGR valve by sucking on the pipe to prevent it seizing.

You must first check to see if yours is stuck or not.

Obviously you have checked the air filter?

I have a tuning chip fitted to mine and that makes it smoke alot under hard acceleration, I can tell from easing off the gas pedal a touch and the smoke stops that the engine is being overfuelled.

Do you think your car could have been chipped at some point? Have you owned it from new?

 

[peterfau]

Thanks Jimmy. When I follwed up on Dieselmans EGR suggestion, I see that this "clever wrinkle" does not work on the Cdi engines as they have a fully electronic injection system and need the feedback. I have owned the car from new and it is not chipped, with 500mn of torque it doesn't suffer from a shortage of grunt (when in full health).

How do you check these new in-head cdi EGRs?

Peter

 

[peterfau]

Yet another PS! This past winter has been colder than those of the last couple of years, but as I travel to work by the same route every day, I THINK I have noticed that the car takes longer to heat up. I am at a pub rather than a hospital by the time the cc starts to deliver warm air!!

 

[fuzzer]

Yet another PS! This past winter has been colder than those of the last couple of years, but as I travel to work by the same route every day, I THINK I have noticed that the car takes longer to heat up. I am at a pub rather than a hospital by the time the cc starts to deliver warm air!!

I would assume these are landmarks rather than destinations on your journey ?

 

[guydewdney]

odd - on a 'normal' old style deisel the extra smoke = more power. this is usually regulated by a 'smoke control screw' on a deisel pump. but yours, being cdi wont have this to my knowledge.

timing can give these issues - but again the ecu should pick these up.

blocked exhaust can also do this - does it get thrashed once in a blue moon?

black smoke isnt unburnt fuel, its just the by-product of a deisel combustion. its always there, just not enough to see.

so - my suggestion is the car is overfuelling - possibly to compensate for being 'cold' - is the engine temp sensor correct? a new one is 16 quid for my V8 CL420, i suspect yours is the same. mine is 011 542 51 17

theres a 004 153 31 28 sender unit charging pressure on the inlet manifold.

theres a 000 542 28 18 temperature sensor intake air on the inlet as well.

theres a 611 078 01 49 valve, pressure control (controls the fuel pressure - if its stuck, it will deliver too much fuel) on the end of the injection rail

cant find an engine temperature sensor (sender in MB speak)

all these senders can go dowmn, and are worth checking.
(as an aside - if anyone wants lots of grunt from a normally aspirated deisel, turning said protected screw in 1/2 a turn gives almost 50% more power - and lots of smoke)

 

[Dieselman]

I still think it could be the MAF.

The engine won't rev if it's disconnected because the ECU adopts limp home mode.

The MAF output can be measured either with the MB diag machine or a digital voltmeter.

Before condemning any parts run some injector cleaner through the engine or have the injectors tested.

There is a possibility that there is a split in an intake duct losing air but still fuelling the engine as the air is still passing the MAF.

Here are my values for my maf measured with a DMM.

http://mbclub.co.uk/forums/showpost.php?p=35102&postcount=35

If feeling handy you might want to clean the injectors using a pressure pump, a 12v connection and some white spirit.
Pressurise the white spirit and rapidly make and break the 12V to operate the injector. If one is dribbling it will cause a lot of smoke before a loss of performance. Also this may lead to cylinder cooling due to the extra fuel.

 

[peterfau]

Thanks Dieselman.
the full diagnostic shows no faults other than 1 injector reading of 1.15. with 5 being the fault level, it was decided that this was not the problem. 3 different brands of cleaner additive have been tried. Even from extreme cold, the engine runs absolutely smoothly even at idle, no hunting or lumpy tickover ( I am told a leaky injector or bad spray pattern would give these symtoms)

When the car had about 17K miles up, it blew an air hose on the pressure side of the turbo, causing all boost to be lost. this was repaired under warranty.

Your suggestion of a leak somewhere on the air inlet system is certainly worth investigating thoroughly. I will now have the full air inlet tract from filter box onwards checked for splits or leaks. While this is stripped down, is this the same side that will allow the EGR to be checked? what checks could/should be performed on this unit?

 

[peterfau]

I Eo

 

[Dieselman]

Your suggestion of a leak somewhere on the air inlet system is certainly worth investigating thoroughly. I will now have the full air inlet tract from filter box onwards checked for splits or leaks. While this is stripped down, is this the same side that will allow the EGR to be checked? what checks could/should be performed on this unit?

The EGR valve is housed between the intake ducting and the inlet manifold. It's a vacuum operated valve. Suck on the pipe to open the valve then let it snap back. If it snaps back it should be working ok.

You could well have a MAF problem here.

 

[peterfau]

Dieselman

The MAF is showing no fault on a full MB diagnostic, so it looks like it is now between an EGR issue or as you suggested earlier a leak in the induction system after the the MAF causing excessive fuelling due to the cylinders not actually receiving all the air sensed by the MAF.

 

[Dieselman]

Dieselman

The MAF is showing no fault on a full MB diagnostic, so it looks like it is now between an EGR issue or as you suggested earlier a leak in the induction system after the the MAF causing excessive fuelling due to the cylinders not actually receiving all the air sensed by the MAF.

Be aware that the MAF will virtually never record a fault code, it just doesn't perform to spec and has to be tested specifically for this. did the dealer take readings for the MAF?

 

[peterfau]

Thanks Dieselman

Just back from a week in the sun. While I was away the inlet system was checked for air leaks and all appeared OK also the EGR was checked for functionality, sticking etc all appeared normal.
I had a trip of some 40 miles this morning and a funny thing happened, the car had no power and would not rev beyond 3K. In fact it drove the same as when the MAF was disconnected, in the earlier test!! I pulled over, switched engine off, set and cancerlled the alarm, and hey presto fault dissapeared when immediately restarted, except for the smoke!!

I am now going to try a new (loan) MAF. what do you think??

Peter

 

[Dieselman]

If the power is ok for the first few minutes then dissapears ensure all vacuum connections have been made good after the checking. If the EGR valve is not operating the turbo wastegate will be released so there will be no boost.

If you can borrow a MAF then do so, alternatively it needs testing.

A full flow test of the injectors would be interesting if not fixed by the MAF.

 

[Dieselman]

odd - on a 'normal' old style deisel the extra smoke = more power. this is usually regulated by a 'smoke control screw' on a deisel pump. but yours, being cdi wont have this to my knowledge.


black smoke isnt unburnt fuel, its just the by-product of a deisel combustion. its always there, just not enough to see.

Visible smoke shouldn't be apparant on any engine when cruising. The visible smoke is caused by overfuelling usually when accelerating.

If the air fuel ratio becomes richer than stoichiometric ( 15:1) then the engine wil produce less power and create smoke.

As there is no control over air quantity on a diesel they nearly always run lean so no smoke should be visible. They are leanest at idle which is why they make the knocking noises associated with diesels.
A diesel will only run at stoich. when accelerating hard or running at full power.

 

[peterfau]

Dieselman

it happened again this morning. It appears to occur straight from start-up and not when it is running normally, boost comes back after switch off/ delay/alarm activation etc.

 

[peterfau]

New MAF fitted yesterday, still smoking!! What about replacing or blocking off the EGR?