Looking to Buy a C230K W202 Model.. Help Please

[bored_welsh_lad]

Look at all this advice.. its quality.. cheers guys and girls.. just need to keep an eye out now

 

[vijilants]

Firstly, i have to confess I'm not an expert. Secondly, the experts to whom i have shown the car haven't solved my problems. The problems were that my fuel consumption seemed to be increasing over time (albeit at a very low rate). Secondly, the car used to idle at 700rpm on start from cold unless the outside temperature was very low - ie <5 degrees celsuis (say). Now it starts at 1,200rpm regardless of the outside temperature. Since cars use alot of fuel at startup to heat up the exhaust and catalytic converter in a mile or two, this 1,200rpm business started to bug me. Note that after the engine warms up the car would start at 750rpm straight off. Also, the engine temperature gauge seemed to climb to 85 slower than before. The car has been plugged onto the computer and symptoms observed but no-one could say what was going on as nothing had "failed" yet something had "changed". A new throttle actuator was fitted but at 24.5 degrees celsius ambient temperature, the car still started at 1,200rpm. I told them to take it off. I also saw some remarks from black c55 about o2 sensors and there are many comments about MAFs on the forum. So after 118,000 miles on the original MAF and original o2 sensor, I had them replaced yesterday. The MAF (if my understanding is correct) helps the ECU to decide how much air is getting into the engine. The o2 sensor helps the ECU to decide how much oxygen is left in the exhaust. Since the ECU is deciding the car needs to start at 1,200rpm, here are a number of possibilities...
1 Duff sensor data getting to the ECU (inputs)
2 Duff ECU (processing)
3 Duff equipment not properly carrying out the ECU instructions (outputs)
Well this is my view of the situation anyway.
So after the dealership I consulted failed to cure the problem I decided to embark on a little programme of staged replacement of parts, firstly those parts sending data to the ECU. So now I let things settle down for 2 weeks and see if I notice any differences. If the temperature still climbs lowly, I will have the radiator thermostat gubbins checked - it is supposed to allow circulation through the radiator only after the engine warms up - supposed to get the engine up to operating temperature quicker if it is not being cooled.
But it really is frustrating and I feel a bit like a blind man fumbling around.
So what I am trying to say - not very well - is that it is very difficult for even supposedly experienced people to understand what is going on. There are just too many bits involved to make identifying the duff bit easy.
If this doesn't cure the problem then the next candidate will be the coolant sensor/radiator thermostat. I will check the invoice and report back tomorrow.
Les

An unfortunate fact of life nowadays is that with a lot of dealerships, unless the computer tells them what's wrong, they simply start scratching their heads.

That's where a good indie that truly understands the mechanics of a car can help because they tend to be more experienced with the workings of the engine rather than solely depending on what a computer is telling them.

This applies especially to older models, as most dealerships cannot work on older models as they don't have the experience and simply don't know what to do with them.

Very few proper mechanics now exist in dealerships.

I had personal experience of this myself - I took my car in last year to the main dealer because I have a warranty and I at the time I couldn't be bothered to get my hands dirty, and a simple problem of water being pushed out of the overflow pipe took nearly three days to diagnose. They then proceeded to replace both the rad and the waterpump, and I am quite sure that the rad was OK.

The approach of replacing parts to eliminate a problem can become very expensive and can sometimes achieve nothing.

I would suggest you take the car to an indie that has a good reputation and use the money on getting the car diagnosed properly.

 

[sgtbob]

Thanks Dittrich. Very helpfull. I would be obliged if you could keep me informed of the progress of your investigation and outcomes.

Rob.

 

[DITTRICH]

I did use an independent before the dealership. The independent, a well known london based one, cleaned the throttle actuator, without any great success. Hence my trip to the dealership. I agree replacing parts without full knowledge of the problem cause is expensive but at 118,000 miles I think a new MAF and o2 sensor will improve my fuel consumption...

http://www.mbclub.co.uk/forums/showthread.php?t=44622&highlight=sensor+oxygen

As for the 1,200rpm idle from cold, sensors>ecu>throttle actuator. The ecu thinks it's cold. This morning it still started at 1,200rpm but fell quicker than before. My gear changes and throttle response have improved though which is nice. Next week the coolant sensor will be replaced, I think.

Les

 

[sgtbob]

How much was your o2 sensor to replace Dittrich??

 

[c955]

Im slightly worried about the mpg figures being quoted here! Ive never got 400 miles out of a tank ever in my c230K. Even when i drove to scotland, in 'W' mode, and did about 65 - 70 all the way there on the inside lane, only managed about 330 miles to a tank. Normally average about 290 - 300 (at a push) with a mix of town driving and short runs i.e. Liverpool/Manchester etc. When caning it in 'S' mode i can barely get 240 out of it? (btw its got a new MAF and new Cat and new throttle actuator so it cant be any of those affecting it?!)

Rob.

If it's any consolation, my driving is almost exclusively London-based in the C230K and I'm only averaging 23.5mpg over several tankfuls. So, I'd be happy with more than 300 miles when the light comes on...

 

[DITTRICH]

How much was your o2 sensor to replace Dittrich??

Okay you forced it out of me...

The invoices are difficult to follow (what a surprise!) but...

X MA000 540 60 17 291992/SENDER UNIT 1 @ 136.00
S MOT 1 @ 0.01 (This is real!)
A 07530302 (labour to replace sensor) 49.60 discount 47.41% = 26.08

All the above standard rated at 15% = 24.31

Grand total £186.40

I don't pretend to understand how this fits in with their 3+ tariff but my car responds better and shifts gear better. Still idles at 1,200 initially (for around 1m) then drops down.

Check the other link I posted where bigdusty provides another link which explains o2 sensors and how a duff sensor affects fuel consumption (badly it seems). The explanatory article is really very good.

The fact that your cat was replaced and you have crap fuel consumption might indicate a duff o2 sensor as the article states that the fuel mixture would be rich. Obviously this is all on the internet which is not necessarily the most reliable source of information but it seems reasonable from the opinions of the other posters on the linked thread.

Have fun

Les

 

[sgtbob]

Les. Thanks for all the help and info. Im toying with the idea of replacing it. Mine idled at above 1000 rpm this morning but then dropped down to about 500 - 600. I guess for that amount it may be worth just replacing it and seeing if there is any benefit. I take it that you had it done at the stealership?

Thanks again for your help.

Rob.

 

[DITTRICH]

As a further note, I came across my fuel records from my summer trip to scandinavia and over 1,810.6 miles London to Trondheim via Stockholm I averaged 33.9mpg. On the first leg to Stockholm I achieved an average of 34.0mpg. Maximum 36.9mpg and minimum 31.7mpg. Total fuel 219.76 litres. During the leg from London to Linkoping in Sweden I averaged 62mph (23 hours total less 5 hours rest breaks over 1122.3 miles). The conditions in Sweden were atrocious over the last 200 miles with driving wind and rain and low visibility. I regard these figures as reasonable for steady state motorway driving on the continent and were accurately obtained by brimming the tank to the very very top each time. Note it is possible to squeeze an extra 4+ litres of fuel into the tank of a c230k saloon after the nozzle first cuts out.
Les