[C32_AMG_UK]

Hi All,

So, I just picked up an SLK230 Auto this week (1999 UK Car with 94,500 miles). The engine doesn't make any nasty noises and the gearbox seems to change smoothly but:

1. The car has very little power
2. The engine develops a misfire at high revs (5000+)

After reading a lot of information on the internet I am lead to suspect the MAF Sensor. Here is what I have done so far:

• Observed the Supercharger Clutch and confirmed it does NOT engage at all.
• Started the engine without the MAF connected - no difference in running.
• Found a third party "performance module" scotch locked into the wiring coming from the MAF sensor - removed this.
• Left the battery disconnected overnight.

This morning when I reconnected the battery I drove the car up the street and it started running very rough (misfiring). Upon switching the engine off and back on it went back to it's "normal" powerless self.

I don't believe this is in any way relevant to the engine problem, but just in case it is - the BAS/ASR light is constantly on and the lock-to-lock calibration process does not clear this. The ABS light comes on intermittently, but there are no further warning lights. Another issue that I don't believe is relevant is that the heater blower runs on full power all the time and the fuse has to be removed to stop it.

I'm thinking of removing the MAF sensor tomorrow evening and cleaning it with electrical cleaner. Given the symptoms, do you think I am on the right track? Any advice would be much appreciated.

Thanks, Adam

 

[Mike C 3039]

You may not be aware that the EMS on these cars limit the revs in neutral to about 5000 rpm. At the rev limit the engine sounds like it has a major ignition fault.

For everything else I'd reset the codes, run the car then look at any codes that reappear before taking any action. Years ago I bought a Chinese 32 pin code reader for about $A130, since then its saved me thousands of dollars - you really can't work on a R170 without one.

 

[C32_AMG_UK]

You may not be aware that the EMS on these cars limit the revs in neutral to about 5000 rpm. At the rev limit the engine sounds like it has a major ignition fault.

For everything else I'd reset the codes, run the car then look at any codes that reappear before taking any action. Years ago I bought a Chinese 32 pin code reader for about $A130, since then its saved me thousands of dollars - you really can't work on a R170 without one.

Thanks Mike.

I'm aware of the rev limiter, this feels like something else. A good description is probably "when driving up the motorway with your foot flat on the floor the car gets to over 5k revs that starts to misfire, unevenly rather than the even pattern produced by the limiter. Eventually it works it's way up to 6k then changes gear".

Cheers for the advice on the code reader, I've read about the Chinese ones and wasn't 100% sure. I'm taking it to a friend next week to see if his diagnostic gear can read it, if not I will have a look at what I can get my hands on cheap. Certainly can't afford a genuine Merc Multiplexer!

 

[John Jones Jr.]

First off get the fault codes read. And fully delete the mod that's connected to the MAF wiring.

Besides doing that, I'd change the MAF regardless unless it looks recent and is a Bosch or Pierburg unit - they are a long term serviceable items i.e. 80/100k miles.

Check for oil residue on the MAF itself and in boost pipers, if there is oil sort that problem first (see threads on here for that re: engine breather/PVC valve and hoses).

After that you could have a K40 reply problem or even a fault within the engine ECU, again search for the many threads on here for detailed info on both of these.

As for the ABS/BAS fault it could several things. I've had a faulty brake light switch and BAS brake servo sensor causing this issue previously but the fault could be caused by an ABS sensor, BAS control unit etc.

 

[TRabe]

I had the fan running, supercharger disengaging and all sorts of codes, turned out to be an identical looking maf with different air temp sensor properties. Got a pierburg 7.22684.09.0 and all sorted out. Also had the BAS/ASR light constantly on. Turned out to be the brake light switch.

cheers,
Tor

 

[C32_AMG_UK]

Supercharger Success!

Hi All,

Thank you for all the advice. Here's the next couple of chapters in the story.....

I removed the MAF and cleaned it with electrical cleaner. There was indeed some oil residue in the air intake pipework so I intend to clean out the oil separator etc as per the other threads (Thanks John).

Cleaning the MAF made no difference to the car so I invested in a Chinese multiplexer with Carsoft 7.4. This gave me fault codes P1235 and P1236 from the ME module. It also confirmed the suspicion of the Brake Light Switch for the BAS light so I need to source one of those and fit it.

I cleared the ME fault codes and they came straight back without the engine even being started. So, this evening I removed the K40 relay and soldered the usual suspect top left joints. Put the car back together and took it out for a ride, I could feel straight away that the Supercharger was working :grin but the car was running very rough. Drove it for a few miles and it smoothed out then drove great with plenty of power. I've read that the MAF can cause rough running from cold so if it keeps doing that I will replace it (unless anyone has any other ideas?) but the good news is there are no fault codes coming up on the ME module now apart from "Stop Lamp Switch".

A couple of other observations I made were:

• On the odd occasion the gearbox is a bit slow between the gears under hard acceleration. It gets to the top of the rev range, deselects the gear then hesitates before engaging the next gear. It only did this a couple of times but I'd like to know what causes it. Is it worth changing the gearbox oil?
• Heard a noise around 1500 rpm - it's a familiar noise - the slight squeak from the supercharger pulley bearing. We had to replace this on our old C32, I'll keep an eye on it and replace if and when it gets worse.

Anyways, I am much happier now I have power :grin Thank you again for all the advice.

 

[John Jones Jr.]

Great news!

What I would do is disconnect the battery for 30-60 mins and let the engine ECU carry out a 're-learn' since fixing the K40.

I can't comment on gearbox (other than I'd change the oil and filter regardless) but the squeaking noise could be from a drive belt, belt tensioner or idlers, usually they get a bit noisy as the miles are racked up or from lack of use.

As for the oil reside in MAF, don't forget the PCV valve, breather jets and hoses under the inlet manifold.

 

[Subby_]

gear box oil is definitely worth it, even if you just drop the pan and change 4lts of it. I have done that heaps of times in my car. about a year ago i took my car to a transmission shop to get a machine to fully flush and change the transmission fluid from the system. ended up using Fuchs fluid for the 7speed (backwards compatible for the 5speed)

Titan ATF 4134 | Fuchs Lubricants Benelux

very good shifting even after punishing it around the track

also since you have car soft reset adaptions on the EGS (gearbox) and drive it gently for a bit to re-learn shifts etc.