Mercedes c220 diesel power problems!?

malk33

I have a 01 merc 220 diesel thats driving me nuts! It can be driving fine and for no apparant reason it starts pulling back and gets stuck on either 2000 revs or just under 3000 and wont accelerate(dangerous if overtaking!). Sometimes if I pull over and turn off the engine briefly and re-start its fine again. I brought it to an indy merc service garage and they said it was a pressure sensor(according to the on board computer) and replaced it at a cost of 500e but its made no difference.
Has anybody any experience of this?
The engine also wont start from cold straight away, have to turn the key until the plug light comes on and leave it like that for about 15 minutes before it will start in the morning. Not sure if the 2 problems are related. Its sluggish since this problem started and fuel economy has gone way down.
Any advice would be appreciated as garage doesnt seem to know what the problem is and by the time they've replaced several parts trying to figure it out, they'll have cleaned me out!!!!!!


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Mr.Diagnostic

Hi

I imagine they must have done a bit more than just replaced a pressure sensor for €500. The point you make about fitting parts is very valid. This is what I call “bolt on diagnostics” and is without doubt the most inefficient method to diagnose a fault. The pressure sensor is easy and quick to test, if you know how, so it should not be replaced unless confirmed as being faulty. In very rare cases if a fault is very intermittent it can make sense to fit a part that is suspect to try and avoid lots of hours being wasted.
The diagnostics would, in a case like this, only tell that there is a problem with a pressure signal, not that the sensor is faulty. The actual fault could be a bad connection or even totally unrelated to the error code since other faults can effect pressure signals. This is where the testing part of the process and understanding the system comes into play.

Your cold start problem, as described, does not make a lot of sense. I doubt very much that leaving the ignition on for 15 minutes is what gets it going.

Basically you have three symptoms. If they all started at the same time then they are most likely related.

It is difficult to know how to advise you. I don’t want to pre judge the garage based on what you posted but I suppose you may be better off getting someone else to look at it for you.

malk33

Just to clarify, I was charged 450 out of 700e bill for pressure sensor which I thought was excessive since I know this part only costs a fraction of this.

Your cold start problem, as described, does not make a lot of sense. I doubt very much that leaving the ignition on for 15 minutes is what gets it going.

This problem started weeks after the revs pulling back and if i turn the ignition from cold the car tries to start and cuts out straight away. I then have to keep the ignition turned for about 30 seconds while it struggles and splutters for want of a better description and eventually starts with a big plume of black smoke from the exhaust! However, if i leave the ignition turned to the heater on position for about 15 mins and then start the car it starts straight away.
Would the revs pulling back be caused by a malfunctioning mass air filter as ive read these cause problems in mercs and bmw's?

peasant

First things first ...when was your diesel filter last changed/checked ?

malk33

I'm not sure to be honest. The last time it had a full service a few different filters were replaced and problems still persist. I'll have to check. Would this be replaced/checked as standard at service??

peasant

not necessarily at every service ... sometimes there is a certain mileage guideline.

But if you had the problems pre-service I'd assume they at least checked your filter and as the problem was still there afterwards, it probably wasn't something as simple as the filter but some complicated electronic trickery.

Sounds to me like you need to find a diagnostics expert and not someone who just keeps replacing parts until the problem finally goes away

malk33

Sounds to me like you need to find a diagnostics expert

Where do you have to go to find one of those exactly!!!:D
I just find it amazing that you can go into a garage that specialises in servicing your make of car and leave the place 700 notes lighter and still with the exact same problem as you went in with. Surely Im not the only person whose ever had this problem! It seems to me that if you dont know what the problem is yourself they'll just keep replacing bits until they've either bleeded you dry or the car dies in the meantime!!
Sorry for the rant, Ive just been stung before! Had problems with my last car slipping out of gear and was told I needed new clutch which I got replaced only for the gearbox to go in it 2 weeks later:mad:

bbability

If you want the name of a good diagnostic fella pm me. That could be a couple of things and not just linked into the pressure sensor error as Peasant has pointed out. A computer with a could mechanic will get to the bottom of that issue.

Mr.Diagnostic

I would agree with the advice that you should find a diagnostic specialist. more so than a merc spesialist but can i suggest that you post back how it goes if you take that option.

good luck

malk33

Thanks guys will let ye know what problem was when/if I get it sorted.