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Discussion Starter #1
So I pulled my ECU on the weekend to replace the potentially bad S/C MOSFET.
However when I opened the ECU the inside did not look at all like I was expecting...
In the attached photo is anyone able to tell me which is the MOSFET for the S/C?
2661344
 

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See pics below...
 

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yep correct!
 

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see below
 

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Discussion Starter #7
So I pulled my ECU out again and replaced the MOSFET as identified by Subby_

Not sure if it worked or not.... IF the MOSFET has fixed the supercharger, how noticeable would it be?

Previously when I have tested the acceleration the car seemed to struggle to get to 140 km/hr. It seems now that I got to 130 (before I had to slow down) and the car was still accelerating and quite keen to go beyond the 140 as previously attained. But the power wasn't.... impressive. I didn't go WOOOOAH . Should I? Or is the power subtle?

Confused.
 

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Discussion Starter #8
Just watched some stock R170 acceleration tests on YT (manual admittedly) and I'm getting nothing lie they are.

S/C ain't working methinks.
 

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to test (keep the bonnet up so you can hear it or get someone to look);

with the car in N or P, bring the revs up slowly to 2-2500rpm you will here it click and start to engage from ~2,000rpm onwards
with the car in D it will be off at idle and turn on just above idle like 900rpm or so

if your car is stock and auto your 0-100 will be about 7.4 sec. 7.2 sec is for post facelift. those are the ballpark times, basically low 7 sec.
 
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this vid is from a forum member... this is exactly what it should look like

 
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Discussion Starter #11
Yes I think that's really the only way to be sure. My car is so loud though that I can't really do it at home.... I'll have to wait until I am out somewhere ;-)
 

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Discussion Starter #12
It's been raining today and I thought I'd turn off ASR and take advantage of it....

I noticed today especially that when my car is cold it seems to be extra spritely....

I don't normally drive to work, but did today due to the rain. Where I park leads up a tallish hill, and I turned up that hill it seemed to want to pull like a schoolboy. I was pleasantly surprised.

So to my mind 1 of 3 things is happening.
1) The S/C does work when cold, which I believe could be the case in certain models. But maybe not working when the engine has warmed up?
2) Turning off the ASR has some how sparked more like into the motor?
3) I'm imagining it all...

Subby_, your thoughts?
 

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what could be also going on is that the electromagnetic clutch itself has a short. unplug it and measure the resistance across the the coil it should be 2ohm or something like that from memory.

when mine failed i had to change the MOSFET & s/c magnetic clutch as my coil shorted in it (i guess thats what caused the MOSFET to blow). mine use to do the same from cold start the s/c would engage and then not engage after that.

ASR shouldn't have an impact unless its breaking traction it will cut throttle.

measure the resistance of the coil and post back (unplug at s/c)
 

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part no for new clutch is A1110970128 but its hard to find... if confirmed its gone, just get a whole second hand s/c unit (thats what i did) and strip it for parts. its more cost effective.
 

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Discussion Starter #15

part no for new clutch is A1110970128 but its hard to find... if confirmed its gone, just get a whole second hand s/c unit (thats what i did) and strip it for parts. its more cost effective.
Sweet thanks. I'll try and get to that this coming weekend.
Wrecked SLK's are scarcer than hen's teeth here so it could be a long wait if I need to replace the s/c.....
 

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same here in Aus. I get all my salvage stuff on eBay with most of it either coming from USA or UK.
 

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Discussion Starter #17
what could be also going on is that the electromagnetic clutch itself has a short. unplug it and measure the resistance across the the coil it should be 2ohm or something like that from memory.

when mine failed i had to change the MOSFET & s/c magnetic clutch as my coil shorted in it (i guess thats what caused the MOSFET to blow). mine use to do the same from cold start the s/c would engage and then not engage after that.

ASR shouldn't have an impact unless its breaking traction it will cut throttle.

measure the resistance of the coil and post back (unplug at s/c)
Subby_ I have to admit I don't know where to unplug the S/C. The only plug I can see that is readily accessible appears to be the same one (barrel connector with two pins) that goes to the bypass valve (which would make sense).

If this is the correct one I appear to be getting no resistance across the 2 pins in the connector.

Should I take a photo and show you which one I mean?
 

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This connector is for the s/c clutch - if getting no resistance reading on clutch side there is either a short or wire frayed (check and re-solder if so). need to take clutch off to take a look

2665831


This connector is for the bypass valve (for reference) don't need touch this one

2665832
 

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Discussion Starter #19
This connector is for the s/c clutch - if getting no resistance reading on clutch side there is either a short or wire frayed (check and re-solder if so). need to take clutch off to take a look

View attachment 2665831

This connector is for the bypass valve (for reference) don't need touch this one

View attachment 2665832
OK sweet thanks. I'm heading in the right direction. Next question then, is how to take the clutch off. No doubt there is a thread somewhere detaling this...
 

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the workshop manual says to take the s/c out to do this but it can be done in the car.

1) remove the radiator fan - this will give you heaps of room to work with. to do this undo the bolts to the expansion tank and move it to the side (no need to drain coolant). unclip radiator clips and unplug radiator fan electrical connector. gently wiggle it up - you will note there is a hose at the bottom of the fan which you can pop off. this makes more sense once you start to do it

2) undo the tension to the s/c belt tensioner. from memory its a torx socket cant remember which size. a long ratchet makes it easy to apply force to loosen it to slip the belt off. if not sure how the belt will go back on, draw a picture or take a photo at this point.

3) now this is the tricky bit is to undo the centre bolt to the s/c clutch. you can use a 8mm socket and use one hand to grip the front of the clutch while you turn to crack the bolt. if your grip is strong enough it can be done. the workshop suggests applying +12v to the coil so it clamps so you can undo the bolt. the coil may not be working correctly in this case and im confident you can get it off with hand. the bolt itself isnt torqued much like 8-10nm its just that it has thread locker on it making the initial undoing a bit hard.

4) once the bolt is out, slide a small allen key into the bolt hole - this is critical as you slide out the clutch face forward you will drop the spacer washers behind it. the allen key will stop them from dropping so you dont loose them. its important not to loose them as they set the air gap between clutch face and pulley.

5) now there is a circ-clip holding the bearing onto the pulley. get circ-clip pliars and take it out.

6) pull the pulley forwards with your hands - no special tools required it should slide off with your hands.

7) now you will see the magnet coil screwed onto the s/c snout. this is screwed on with torx bits again not sure which size from memory. unscrew it and thats the whole unit removed

at this point you can see if there is any damage done or wires exposed or frayed going to the magnet or if it has rubbed on the inside of the pulley etc
 
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