loss of power on acceleration

[richard@focal.co.uk]

Hi
I dont know if anyone can help me re the following symptons re my S320CDi

THe car limps along at 2000 revs until speed gets to a level whereby rev counter goes beyond this – 65 – 70 mph
It will not allow me to kickdown to accelerate away at low speeds/gears
It occassionally blows grey/black smoke from exhaust – when going up hill or when putting strain on the engine
It only goes to 3000 revs max when accelerator pedal pushed when car in neutral or park
Does not appear to affect fuel consumption
no funny noises coming from the car when driving.
no malfunction light coming up on dashboard

Any help out there would be greatly appreciated. This is a problem I have had on and off since buying the cars 2 years ago and I need to rectify this once and for all

Thanks all and regards
Richard Knight

 

[television]

Hello Richard, you have all of the symtons of a faulty MAF filter.

Malcolm

 

[richard@focal.co.uk]

faulty MAF filter

Hi Malcom
Thanks for prompt reply - is the MAF filter an expensive job to do?
I will keep you posted
Regards
Richard Knight

 

[Cnics]

If you look at the top of the list on this part of the forum you'll find instructions for cleaning. This may help you.

 

[television]

Hi Malcom
Thanks for prompt reply - is the MAF filter an expensive job to do?
I will keep you posted
Regards
Richard Knight

Hello again Richard, they are on Ebay £65 or you can buy the insert from any Bosch agent / dealer much cheaper than from MB. you will find it at the other end of the air intake box, you could also try and clean it as the thread under engines.

http://forums.mercedesclub.org.uk/showthread.php?t=18298


Malcolm

 

[khanie]

Its a very easy job if you want to replace it - one screw and one clip. A genuine MB one is around £250, a generic one about £50-70. I bought a generic one and it solved the problems I was having with my E230.

At the top of the 'Engine, Drive and Fuel' section is a whole set of brilliantly straight forward instructions on how to clean it if you wish to try that before buying a replacement.

Mark.

 

[richard@focal.co.uk]

Malcolm
My mechanic friend changed the MAF. No lack smoke now, but still wont go above 2000 revs in drive. I can change down and can get to 3000 revs through tiptronic but no acceleration or kickdown. Any other ideas - going back in tomorrow
Thanks

 

[richard@focal.co.uk]

MAF changed - no black smoke, still no power above 2000 revs. kickdown not working. Can go through auto gearbox and by changing down give revs up to 3000 but still not working properly. Any other ideas from anyone
Thanks

 

[John Kerr]

I have the same problem myself on 220 CDI.No fault codes showing up on diagnostics.If you find the problem please let us know.

 

[psmart]

As mentioned to John, there are several potential areas here, which I discovered whilst diagnosing a fault on my car. Im armed with diagnostics so Ill list the items which show up and wont show up (at least according to my tests) on diagnostics.

Items which will show up:
1) Fuel pressure in the Common Rail Bus.
2) EGR Control Valve Transducer
3) Turbo Control Valve Transducer
4) Boost Pressure Sensor
5) MAF (occasionally)
6) Charge Temperature Sensor
7) Fuel Injectors.

Items which wont shop up:
a) Blocked or failed Catalytic convertor/exhaust. Will show up if it is severe enough to cause the ECU to sense an out of parameter boost pressure due to air/charge not being able to freeflow.
b) Blocked inlet manifold (a thread from June/July described a strip down for this job, cant seem to locate it). Again, as per 1, it wont show up on diagnostics unless it causes a sensor to go out of parameterisation.

The interesting points are black smoke, a sign of over fuelling or insufficient air (b above). No diagnostic information (John Kerr), a or b.

2000-3000 rpm could be due to the ECU going into safe mode, or because these are forced induction engines, a boost pressure not being developed; or boost pressure not reaching the combustion chambers; or back pressure preventing boost from forming a correct expansion/explosion in the cylinder. In some of these scenarios, you'd expect a sensor such as the MAF (sensing air flowing over it and temperature of the air), boost pressure sensor registering a fault, but on my tests, these didnt reliably, ie. I could block the exhaust system, rev the engine and no fault would be logged.

There was a thread on a sticking EGR valve, which allows hot exhaust gasses to flow directly into the inlet manifold (via a cooler) which could get stuck, and could kill the combustion process. This wouldnt necessarilz show up as a fault because the transducer opening the valve does not detect it and I didnt come across any other sensors in this area (please correct me if I missed one).

Food for thought. Try the simple things first, whip off the air filter, remove the spring loaded clamp connecting the Turbo to the Pre-Cat and prize apart, then rev the engine. If it is still limited to 2000-3000 rpm, then its not the exhaust. Check the movement of the Turbo Actuator arm when the air filter is off, is this arm pulled down when the engine starts up, and does it fluctuate as you rev it, if it doesnt, then you have an actuator/vacuum/Turbo Boost Control Valve failure. (should show up on diagnostics, but as with most things, sometimes it just doesnt happen). If the Turbo actuator arm is spinning up, then get a vacuum guage, unplug the Charge Temperature Sensor, shove the vacuum guage into it and rev the engine to verify a boost is occurring (negative, then positive swing on the guage upto ~1 bar). If the boost is occurring, then it looks too much like something with the inlet manifold flaps or the EGR which will involve a strip down of the EGR or the inlet manifold, but please scan for the threads which list this procedure (its not easy, involving removal of the Common Rail, injector feed pipes etc etc).

Hope this helps, but the CDI's are not too complicated engines, fairly logical, just need to logically go through the scenarios until you hit the problem.

 

[richard@focal.co.uk]

Hi
Thanks for all the feedback - will let you know the outcome as soon as known
REgards

 

[eGuru]

Had a similar problem last year. Fault happened to severed vacuum pipe on EGR valve, I think (Will need to dig out the invoice).
Car has run fine ever since.
Jay

 

[Uncle Benz]

I fancy the EGR or boost control valve as Psmart has said. They are actually the same component. There are two of them and the EGR one will give precisely these symptoms. Is the car bad all the time? I have changed a couple of these valves now, and the ones I have seen are OK when the car first starts off, but then quickly go bad giving the symptoms you describe.

They do generate fault codes as mentioned. Have you had the codes read on your car? Maybe find a specialist to check this for you.

If you want to find the units, they are black and have 2 pipes on the top and one on the bottom with an open small filter on it alongside a two pin wiring connector.

 

[richard@focal.co.uk]

loss of power - problem solved

Thanks for all you help and advice.

We changed the MAF but still no change. Less black smoke but that was about all. It turned out the pipe the plugs into the intercooler had come adrift and the cup that holds the pipe had broken, so a new pipe, new intercooler, a £500 bill and 2 days of searching, we finally had the problem licked.

Car runs well again and have even managed to squeeze another 4 miles a gallon. Thanks again and hope this might be of help to some other members out there

Regards
Richard

 

[television]

Thanks richard for posting back, sadly I found some reference to this a few days ago, but I could not remember what to do with it or who posted the problem.


Malcolm

 

[hs500]

Have a similar problem .... already changed the MAS, no change. Got a diagnosis done and the computer pointed to a Accelerator Pedal limit sensor. anyone know what this is?