Yet another supercharger issues thread - Mercedes Benz SLK Forum

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#1 Old 06-18-2019
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Yet another supercharger issues thread

Hi All,


Having done some searching here, I think I've exhausted all reasonable options so am now looking for help.


I have a 1997 SLK230 R170 with clutch-type supercharger system.



Symptoms:


When I first bought the car, the supercharger was (mostly) working for first few minutes then (mostly) giving up once the car reached temperature. Sometimes it wouldn't engage from cold start, sometimes it would randomly work for a few minutes whilst warm then give up again. Now it doesn't work at all, even from a cold start.


If I disconnect supercharger clutch plug:


* Resistance of clutch coil is about 4.4 ohms
* Resistance of ECU end (battery disconnected) is about 69k ohms
* When ignition is on 2 or engine running, I meause 12V across ECU side of supercharger plug
* Yet SC clutch does not engage, can't hear a click, turns freely by hand with engine off, ignition on 2 (12V measured from ECU)


Recirculating air flap does nothing (always open). Measure 12V between power and ground, 0.5V between signal and ground from ECU end. Air flap doesn't make any noise, unlike the air intake throttle body.


I tried swapping the air flap for another one off eBay, still nothing. Can't be sure the replacement flap works either though.


One of the 15A fuses on my K40 was blown (sorry can't remember which one, but think it might have been the 4th from left (2nd from right) if looking at it such as the 40A fuse is at the top.


Replacing the fuse hasn't changed anything, hasn't blown again either.


I did take it in for diagnostics, unfortunately the garage wouldn't give me a list of fault codes. All they said was that it showed a recirculating flap error and that they ran a test of the flap using STAR and it wouldn't respond. They also cleared all the codes so I can come back later to see if any have re-appeared.


Unfortunately this car doesn't have OBDII (too old) and I don't have a multiplexer / interface box that can talk to it.



Based on the garage's advice I bought the eBay replacement flap/actuator (1110980009) but as I said it doesn't appear to have done anything.


Does anyone have any further advice? Is the clutch most likely not working?


Probably next up I'll try connecting the clutch straight across the battery. How have others managed this? Using alligator plugs? Directly on the pins or by cutting the wire insulation?


I might also rig up a test of the two recirculating flaps. I understand it should be 12V, GND and a pull-to-ground 45Hz PWM signal right?
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#2 Old 06-18-2019
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#3 Old 06-18-2019
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Hi,

I'm not going to be much help, but here are some observations from me ................

I don't think the 12V at the Plug is the issue, I reckon the PWM signal is going to be missing, due probably to another fault, which you need SDS to find.

Did you have to pay that Garage for the diagnosis, it seems to me they are hiding something, if you paid for diagnostic they should give you a print out !!

It could be something as simple as a bad IAT sensor so because of this sort of fault the ECU will shut down the S/C to prevent damage to the Engine.

I think @Turdo2 will know more about the 4 Cylinder S/C Motor than I do

HTH, Cheers Dave
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#4 Old 06-18-2019
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Originally Posted by Dave2302 View Post

I think @Turdo2 will know more about the 4 Cylinder S/C Motor than I do

yeah... I know how to rip it out and put in something better!

All I know, is when I had this issue I did 2 things:

1. re-do the solder on the K-40 (wasn't the issue)
2. cleaned the connector clutch plug (the one one right in front of the engine.

In my case, it was the plug. I had intermittent supercharger issues, until it just quit working all together.

I would definitely start by running a jumper wire to the connector!
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#5 Old 06-18-2019
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Quote:
Originally Posted by Dave2302 View Post
I don't think the 12V at the Plug is the issue, I reckon the PWM signal is going to be missing, due probably to another fault, which you need SDS to find.

Yeah, that's my thoughts too, although I paid 16 for the eBay replacement flap thingy so I'm not convinced that either one works. I'll probably rig up a bench PSU / Arduino / 12V transistor and make a test of the PWM response, unless there's anyone else here in the south of England who wants to let me plug my flap thingy into their 96-98 SLK to test it?


Quote:
Originally Posted by Dave2302 View Post
Did you have to pay that Garage for the diagnosis, it seems to me they are hiding something, if you paid for diagnostic they should give you a print out !!

To be honest, it's more that I didn't ask for a print-out. I think they were thinking I'd let them keep the car for them to fix. I'll call in and ask again to see if they still have a record of all the codes at some point later in the week. I know they said there were loads of codes to the point where they thought the best course of action would be to clear them then see what came back.


Quote:
Originally Posted by Dave2302 View Post
It could be something as simple as a bad IAT sensor so because of this sort of fault the ECU will shut down the S/C to prevent damage to the Engine.

The IAT is part of the MAF right? Does anyone have experince with the cheap Chinese eBay MAFs? The price difference between these and the Bosch ones is huge and I think mine currently has an unbranded one fitted. Also, my MAF was really really oily but I cleaned it and also cleaned the breather hoses / oil separator as best as I could using a can of electrical contact cleaner.


The breather hose from rocker cover to oil separator is also split / perished, I intend to replace this soon and would appreciate if anyone can advise the correct part number and where to source in the UK.
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#6 Old 06-18-2019
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Quote:
Originally Posted by Turdo2 View Post
1. re-do the solder on the K-40 (wasn't the issue)

I intend to do this anyway, I guess it can't hurt?




Quote:
Originally Posted by Turdo2 View Post
2. cleaned the connector clutch plug (the one one right in front of the engine.

Did this on my lunch break today.







Quote:
Originally Posted by Turdo2 View Post
I would definitely start by running a jumper wire to the connector!

Still interested in how others did this - by shoving 2 bare wires inside the connector and trying not to short them? Seems risky to me? Or maybe I should strip some insulation and use crocodile clips?
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#7 Old 06-18-2019
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Hi,

Well first up I would never fit any EBay Sensors on an Engine, most of them are Chinese junk, and if they do work outta the box they don't usually last long, yeah I know there are ones that go on for years, but there are more bad than good

Second hand parts that are genuine MB ones are normally OK, but of course you might have got a bad flapper, bit of a coincidence tho !!

I cut up old car wiring looms to get the tiny terminals and with heat shrink you can make up useful little flying leads for testing work

Also a split breather pipe could be causing un metered air and that could maybe cause ECU to shut down the S/C and Flap Circuits, like a limp mode ??????????????

I know for certain that sort of thing will shut down the Turbo's on V12 Motors and the S/C on V8 Kompressors

HTH, Cheers Dave
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#8 Old 06-18-2019
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Originally Posted by mickeyjaw View Post
Still interested in how others did this - by shoving 2 bare wires inside the connector and trying not to short them? Seems risky to me? Or maybe I should strip some insulation and use crocodile clips?
I T'd off the signal wire, that way the plug was still plugged in and grounded. then just ran a 12v wire to the battery.

I actually took a jumper wire with me on a trip just in case I needed to emergency make it work for a while.

If I recall, it wasn't so much the connector that was the issue, but the wires going into the connector. I'd check out that whole harness. I remember after making my jumper wire that it just started working and never had an issue since. I know it's not a solid solution, but that's my story!
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#9 Old 06-20-2019
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Status update:

Removed K40, found it has already been re-soldered! Touched it up anyway. Still no improvement.

Waiting on some alligator / crocodile leads to come today so I can try jumpering the supercharger clutch.

Car runs worse than ever, even more sluggish now. I guess that's because I left the negative lead off for about an hour while I re-worked the K40 and it's having to re-learn fuel trims etc?
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#10 Old 06-20-2019
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Update 2:


Today I went back to the garage on my lunch break.



Quote:
Originally Posted by Dave2302 View Post
Hi,

Did you have to pay that Garage for the diagnosis, it seems to me they are hiding something, if you paid for diagnostic they should give you a print out !
Turns out they were hiding something!


I don't think this software is MB Star / Xentry? Looks like some kind of generic tablet?


I'm guessing that there are probably other codes that this device can't read?
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File Type: jpg Diagnosis.jpg (43.3 KB, 4 views)
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#11 Old 06-20-2019
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Hi,

Yep, that looks like an Autel to me, maybe Maxi Sys, they are a good Generic, but still it will only see a max of 80% of all possible Codes so there may be another, but also there may not !!

Have you tried stripping down that connector that goes on the Clutch, and also the one on the flapper, wires often break off of the small metal terminal, well worth a look

HTH, Cheers Dave
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#12 Old 06-21-2019
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Quote:
Originally Posted by Dave2302 View Post
Hi,

Yep, that looks like an Autel to me, maybe Maxi Sys, they are a good Generic, but still it will only see a max of 80% of all possible Codes so there may be another, but also there may not !!

Have you tried stripping down that connector that goes on the Clutch, and also the one on the flapper, wires often break off of the small metal terminal, well worth a look

HTH, Cheers Dave
Do you have any info on how to disassemble/reassemble the connector? Any info on part numbers for replacement connectors in case i break one in the process?

The pins on the plug on the clutch are rusty as hell, could do with replacing the plug. In the meanwhile I'll try some diet coke to see if that cleans the pins up...

As for the flapper, well I've tried 2 different flappers and cleaned both with electrical contact cleaner. I'm tempted to make up a test jig with an Arduino to bench test my two flappers to rule out the bossibility both are broken, assuming I can't find somebody else nearby with a car I can borrow to test them.
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#13 Old 06-23-2019
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Next update: If I use alligator clip leads to connect the S/C clutch across the battery then it engages fine. Still no movement from the flapper.

If I use same leads to 'extend' the plug connection then still nothing (did this to confirm that it wasn't just poor connection between plug and socket).

What really confuses me is that I measure battery voltage across the S/C clutch pins coming from the ECU?

So it's like the ECU can't sink enough current to engage the clutch?
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#14 Old 06-24-2019
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Quote:
Originally Posted by mickeyjaw View Post
Next update: If I use alligator clip leads to connect the S/C clutch across the battery then it engages fine. Still no movement from the flapper.

If I use same leads to 'extend' the plug connection then still nothing (did this to confirm that it wasn't just poor connection between plug and socket).

What really confuses me is that I measure battery voltage across the S/C clutch pins coming from the ECU?

So it's like the ECU can't sink enough current to engage the clutch?
Hi,

The ECU will not even try and engage the Supercharger if there is a fault which there is at least one, Flapper or the Circuit to it.

If you find someone with SDS all of this can be confirmed by looking at Live Data, ("Actual Values"), it will also tell you if there is other codes that Autel is not seeing.

Also SDS has WIS / EPC.
EPC will help you identify the connectors that you need, part numbers etc, and likely in WIS it will tell you how / show where the little lock is on how to disassemble the Connector !!

Coke .........................
Buy a proper Aerosol Contact Cleaner spray from your local factor

Get WIS EPC Discs off EBay if you don't want to spend out on SDS, but tbh I can see a problem like this costing you more in wasted time and parts than just buying SDS and getting to the bottom of it first time

HTH, Cheers Dave
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#15 Old 06-24-2019
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Quote:
Originally Posted by Dave2302 View Post
Coke .........................
Buy a proper Aerosol Contact Cleaner spray from your local factor

Contact cleaner won't remove corrosion, only oil/dirt. The phosphoric acid in Coke will dissolve oxides, then you can do a final rinse with contact cleaner.



Here's what I do for corroded parts:


Step 1: Contact cleaner to remove oil/dirt.

Step 2: Coke, for a few hours to dissolve surface oxides

Step 3: Contact cleaner again, to remove coke residue
Step 4: Blow dry with compressed air





Quote:
Originally Posted by Dave2302 View Post
Get WIS EPC Discs off EBay if you don't want to spend out on SDS, but tbh I can see a problem like this costing you more in wasted time and parts than just buying SDS and getting to the bottom of it first time
HTH, Cheers Dave

Yeah, I have been seriously tempted to buy a laptop + C3/C4 multiplexer bundle off eBay. The problem is they sell for about the same as I paid for my car. If I could be 100% assured of re-selling for what I paid for it (minus shipping) then I'd do it. The other option is to use a local merc specialist who has the right gear, but he doesn't have an appointment until the end of July
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