SLK 230 Strange starting issue and supercharger not coming on until above 4000RPM

[SLK_]

Hi,

I'm a new member, but I've owned Mercedes for a long time and enjoyed owning my current 1997 SLK 230 Kompressor Auto for nearly 10 years.

Enjoyed it until recently that is... I have a problem that no one can fix and my garage suggested I join a forum for some advice as they are all out of ideas!

It all started a few months ago, when the supercharger suddenly stopped working on a long journey back from a holiday. It used to kick in at around 2000 rpm, now it only spins (slowly) over 4000 rpm. I took it to a respected Mercedes specialist who diagnosed on the 'STAR' machine a faulty Supercharger Clutch. My car is a early r170 model with a magnetic clutch. So, I replaced the magnet as suggested with a known working one. This, sadly did not fix the problem. Since then I have spent ££££ Replacing the following parts:

K40 relay (New)
Coolant Temp Sensor (New)
Cam Sensor (New)
Crank Position Sensor (New)
All supercharger hoses (Mix of new and good used)
Lambda Sensor (New)
Cat converter (New)
PCV (New)

The result of all this is that the supercharger still does not kick in at the correct rpm, but now I have another issue as well ! If I drive the car hard in manual mode or use the gearbox kickdown. Then the car will not start until the battery has been disconnected for a few minutes.

I've taken it to 3 garages in total and I am just desparate to fix it, because I really like the car.

The codes on the STAR machine are P0443, P1525, P0805, P0806 and P0135.

I really hope someone can help? I've had the wiring checked for oil and there is none. I've also had a new 'MOSFET' soldered on the engine ECU.

Thanks in anticipation, Katie

 

[Blobcat]

Hello and welcome,

@alexanderfoti might have some useful knowledge - he made a ‘96 SLK230K run very well indeed

 

[SLK_]

Hi Blobcat,

If anyone can help that would be amazing. I have searched the net for hours and tried everything I have found. It is such a strange issue. Could the not starting be a over fueling problem? Because the fuel economy has got worse and the car will start after the battery is disconnected and a few minutes rest, as if the engine is flooded? But why that would stop the supercharger from working I can't understand. May be the 2 problems are un-related?

 

[SL63 Mark]

Supercharger clutch does seem a likely cause, wonder if the “new magnets” have either failed, we’re not “new” or were not the cause in the first place ?

Perhaps get a different independent to look at it. Time for a second opinion, methinks, before you throw any more money at it. Sounds like they are playing “parts darts” with your money.

 

[Uncle Benz]

Sounds to me like a problem with the supercharger bypass flap. It’s a throttle plate unit close to the airbox, wire reinforced pipe goes to it. But really you need a decent independent to look at it to be sure.

 

[grahamcol]

Hi and welcome from a fellow SLK owner.
I Can't offer any direct advice or assistance but I'll be following this with interest and l hope these two issues get resolved.
As mentioned above, maybe best to find a different Mercedes specialist.
Good luck.

 

[SLK_]

Supercharger clutch does seem a likely cause, wonder if the “new magnets” have either failed, we’re not “new” or were not the cause in the first place ?

Perhaps get a different independent to look at it. Time for a second opinion, methinks, before you throw any more money at it. Sounds like they are playing “parts darts” with your money.

Hi

The supercharger clutch was changed for a 2nd hand part, as I could not buy it new. Mercedes Dealer told me they would only sell me the complete Supercharger as a unit which was ££££. I was told the magnet worked on the car it was removed from. I was also told by the specialist that they very rarely failed.

I tried jamming the clutch, so it always turned. However this did not work as the bypass valve stayed open, until over 4000 rpm, so no boost :-(

I have phoned another respected Merc specialist and given them the 'STAR' codes, but they say they need to see the car, which is perfectly understandable. But they are an hour's drive away. I am a bit reluctant to drive it that far, in case the problem gets worse and it breaks down. I have been replacing a lot of parts, just in desperation to get it fixed.

 

[SLK_]

Sounds to me like a problem with the supercharger bypass flap. It’s a throttle plate unit close to the airbox, wire reinforced pipe goes to it. But really you need a decent independent to look at it to be sure.

Hi,

Yes, I think it could be that, but before I get one I wanted to see if anyone had any other ideas, because the specialist and another garage told me it was working fine. I have replaced almost everything else ! So im thinking it must be the bypass valve. If not I can only imagine its a wiring issue ? Does anyone know if the 1997 SLK was affected by the wiring degrading issue that some 1990's Mercs had ? I cannot find a definitive answer on the net.

 

[Blobcat]

Hi,

Yes, I think it could be that, but before I get one I wanted to see if anyone had any other ideas, because the specialist and another garage told me it was working fine. I have replaced almost everything else ! So im thinking it must be the bypass valve. If not I can only imagine its a wiring issue ? Does anyone know if the 1997 SLK was affected by the wiring degrading issue that some 1990's Mercs had ? I cannot find a definitive answer on the net.

Not seen any SLK wiring degradation issues reported on the forum.

 

[SLK_]

Hi and welcome from a fellow SLK owner.
I Can't offer any direct advice or assistance but I'll be following this with interest and l hope these two issues get resolved.
As mentioned above, maybe best to find a different Mercedes specialist.
Good luck.

Hi,

Thanks for your good wishes. I love my SLK. They are sometimes maligned on some car forums I've read, but I think it is a great little car. I've replaced the springs and dampers on my car and it handles really well. It was great fun to drive when the supercharger worked. I am a bit reluctant to take it to another specialist as I already have the 'STAR' diagnostic codes and it has been to 3 garages (including the specialist), already. I just hope to find someone who has had this problem and successfully solved it, or found a mod to make the supercharger work.

 

[SLK_]

For added information, in case it helps some clever person to diagnose my cars problem. The starting problem only appeared after the garage had done a 'smoke test for air leaks'. The car failed the test badly and so a mix of new and good used supercharger hoses were fitted. The car then passed the smoke test, but the supercharger still does not kick in until over 4000rpm and now it won't start after a hard run, unless I let it sit a while / disconnect battery. I also had high exhaust emissions, this was fixed with a new cat and lambda sensor. The garage think all this suggests it is over fuelling, but they don't know why.

 

[SLK_]

Not seen any SLK wiring degradation issues reported on the forum.

Ok, that is a relief ! That was my biggest fear really.

 

[grahamcol]

Just thinking outside the box here for a mo. Strange that a battery disconnect and reconnect allows the car to start once more. To me this suggests possibly something electrical or electronic. I'd be checking ecu's for water damage and wiring for chafing or pest damage.
I agree these are fantastic cars and a whole lot of fun. Very much underrated in my opinion.

 

[SLK_]

Just thinking outside the box here for a mo. Strange that a battery disconnect and reconnect allows the car to start once more. To me this suggests possibly something electrical or electronic. I'd be checking ecu's for water damage and wiring for chafing or pest damage.
I agree these are fantastic cars and a whole lot of fun. Very much underrated in my opinion.

Pest damage to the wiring is a concern. We do get mice in the garage quite often. I haven't seen any damage myself, but it is a good suggestion, I will ask the garage to look when I take it in again. It once started without disconnecting the battery, it wouldn't start, but then did after it had been left half an hour. When I go to start it after a hard run, the engine turns and keeps turning after I release the key, but it doesn't start. If I drive it without using the manual gears or kickdown and keep the revs below 4000 rpm when the supercharger is now coming in, then the car always starts fine. It is like the supercharger coming on, causes a fault that then stops the car from starting until it has cooled a bit or codes are cleared by battery disconnect.

 

[SLK_]

Update:

The coolant temperature sensor was only replaced 2 days ago and I hadn't driven the car except back from the garage. So, not had a reason to restart it. But, having used the car extensively today, it appears that the not starting problem is fixed! Good news.

The supercharger is still not coming in until over 4000rpm though, so the car is pretty sluggish. If anyone has the answer I would be so grateful, I would love to have my car fun to drive again.

 

[grahamcol]

Thanks for the update. Hope it keeps starting!
The supercharger thing is a mystery. I summise it can only be the supercharger itself or sensor/module/component that tells the supercharger when to kick in. Hopefully you or someone will get to the bottom of this soon.
I presume you've looked at the American SLK forum in search of information?

 

[SLK_]

Thanks for the update. Hope it keeps starting!
The supercharger thing is a mystery. I summise it can only be the supercharger itself or sensor/module/component that tells the supercharger when to kick in. Hopefully you or someone will get to the bottom of this soon.
I presume you've looked at the American SLK forum in search of information?

Yes, thanks. I'm pretty convinced the coolant temp sensor was the non-starting issue. Interestingly, the non-starting happened weeks before the temp guage started acting erratically and it threw a diagnostic code. So, it must have been failing slowly for a while.

I've been reading as many forum's as I can find and looking on utube. As I understand it, the main engine ECU tells the magnet to come on to lock the supercharger clutch and make it spin. At the same time it tells the bypass valve what position to be in. This was why I had a new MOSFET resistor soldered in to my ECU, as they can apparently burn out and cause the clutch not to engage and the bypass to not function. But it didn't make any difference :-(

The fuel economy has worsened a lot, so whatever the cause it does look like it is over fueling. Would looking at the spark plugs tell me anything? They are a few years old, one of the few bits I haven't recently replaced.

 

[grahamcol]

Spark plugs can give an indication of over fuelling yes. I'd also sniff near the exhaust to see if there's a petrol smell.
Another idea perhaps is to take the car to a friendly mot place and get an emissions test done. An excess of hydrocarbons would indicate over rich running.
I do hope it's not the main engine ecu. If it is then you might be best off obtaining a replacement with the same part number (Dronsfields?). I have a feeling a new one won't be available. Even if you could source a new ecu, l expect it would cost an arm and a kidney.

 

[grahamcol]

Just another thought about the ecu if it comes to replacement. I've a feeling it might need programming to the car. Not sure on this so best seek the advice of others if it comes to this before you go further. Also l believe there are specialists around who claim to be able to test & repair ecu's.

 

[Botus]

may be of no help - but I thought it was common a 25p sensor gives up - and you can only fix it the approved way by buying the whole supercharger