Sprinter 311cdi backfiring

[PhilDonoghue]

Hi All hope someone can help,

I have an '02 Sprinter 311cdi with 300000 on the clock. About 6months ago it started occasionally losing power when going up hill and about to drop to 4th. Stopping and restarting (presumably resetting ecu) cured this and wouldn't happen for few hours or even days. Been on the computer at merc 3 times and always shows as low charge pressure fault but that is all.
Has been getting steadily worse and now has pronounced misfire and occasional backfire (which i didn't even know a diesel could do) especially coming thro low revs in 2nd and 3rd. This is present all the time for a few days and then runs perfectly for few days but like a bad marriage the good times are getting less frequent! Religiously change oil, oil filter, fuel and air filters so not that and put a spare intercooler on as that was getting old. No pipes leaking as far as can tell. Help I am loathed to give it to Merc and say fix it whatever as i know they are going to 'find' something very expensive. My gut feeling is it is something simple but I have no clue what. Any ideas?
Thanks in advance

 

[Sprint'n'Go]

Low charge pressure, presumably they mean low turbo pressure which would fit in with a reduction in power. Did they give any further explanation of what they meant?

I don't see how a turbo problem would induce mis/back firing as usualy the engine would run as a naturally aspirated unit without the turbo.

Could it be connected to the crank position sensor as I assume this controls injection timing? I was recently warned that if the twin mass flywheel fails badly then the engine would misfire as the sensor picks up its signal from the flywheel. Progressing that arguement further, have you had a clutch replaced and did this coincide with the start of your problems by any chance.

P.s did I hear you right, 300k since 2002? If so I must try harder.

 

[PhilDonoghue]

100,000 of them in last 6 months lol

Thanks for such prompt reply.
To be honest i know very little and knew even less before started trying to cure this. Think you right that low charge pressure relates to turbo as the list of possible faults it printed out all related to this but turbo is only thing dragging it along. At 3000rpm the turbo kicks in fine and drags it thro to the next gear. It is without the turbo that it has all the probs.
Will look up your suggestions thanks. Trying to get it sorted cheaply but think might have to bite bullet and give to merc.

 

[Sprint'n'Go]

Thanks for such prompt reply.
Trying to get it sorted cheaply but think might have to bite bullet and give to merc.

As Merc have already had a look at it 3 times but do not seem to be able to pin down a fault I would say they have had their chance. If you do end up letting a third party sort it then I would recommend you get out the phone book and find a diesel injection specialist that also has access to the necessary diagnostic computers (Merc and most merc independents use STAR diagnostics). I say this as a dealer has to cover all aspects of vehicle repair & maintenance while a specialist just sorts out problems like yours all day every day. Was your merc dealer a merc car dealer or a merc van/commercial dealer?

Despite the faults I have had with my current van, my previous Sprinter, a 311, was supremely reliable for the 80k I did, apart from one peculiar incident. I lost around half the power although I think it did not go into limp mode (I didn't know this existed at the time) The fault would reset itself when the engine was stopped then restarted and would not show again for days or weeks. The problem was with the vacuum pipes that operate the turbo actions. The same pipes also control the cab air recirculation and one had dropped off the air box. Pressing the recirc button would vent the vacuum and then knock out the turbo although this did not always seem to happen instantly hence the lack of association between the action and the result.
When I went to the dealer the technician went straight to the fault. He said they would normally have taken ages to find something that simple but stupid except it had happened to their breakdown support van the week before. It is definitely worth checking this, if I remember rightly there are 2 thin brown pipes that disappear up behind the scuttle panel between the air box and the passenger side wing and slide onto pipes on the air box using rubber sleeves at the join. I don’t know how this would cause a misfire, It didn’t in my case.
It is probably worth checking all these pipes at every join as it could be a weak/split joining sleeve at your mega mileage.

I think I would probably backfire if I had done 100k in 6 months

 

[psmart]

Hi Phil,

A thought on this: Backfiring is usually caused by an incorrect mixture not combusting (or not completely combusting) whilst in the cylinder then igniting in the exhaust.

If insufficient air was getting into the cylinders, then the MAF would detect this and shut the engine down into safe mode, but overfuelling, it may well not. Perhaps an injector or two is worn, faulty, sticking. As the common rail gets upto 1600bar, any fault on these injectors would see fuel getting into the cylinders and making a non-combustible fuel-air mix. 300,000 is a hellova distance, have you used a injector cleaner at all?

As SNG says, pop-in to a diesel specialist to get a once over.

 

[PhilDonoghue]

She's in at moment

Thanks guys,

Those are very much the lines we were all thinking on but have taken the advice and given it to an independent specialist. His first impression is the MAF but he says he will let me know in next 24. Will let you know.

Cheers

Phil D