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2001 R170 SLK230K 6M Sport
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Discussion Starter #1
First off, the details.

2001 r170 sport 6-speed manual, 98k miles.

220mm Crank pulley
67mm supercharger pulley
Custom welded air intake pipe with K&N filter
Ported supercharger
Supercharger plenum baffle delete
BKR7E spark plugs
Stainless 63.5mm exhaust with two chamber muffler and high flow catalyst
Custom stage 2 tuning
Progressive LSD

Now, I'm having some issues. I can't seem to pinpoint if its an age/wear problem or a tune issue.

At top speed, I seem to be limited to 120-121 mph. At that point, the ecu pulls back throttle and I instantly get a DTC for (p0243) "turbo/supercharger waste gate solenoid A" and p0103 "mass air flow circuit high input". This is followed by a immediate power loss and it happens EVERY time I hit the speed governor. The only way to correct it is to shut the car off, turn the key to "on", not run and let the ECU do something under the hood for a moment. It will return to normal if you allow 30 seconds or so after the key is turned to "on" before starting. If you start immediately the diverter valve seems to be commanded not to operate. As you can imagine, I time trial this thing and having a mid-heat shutdown isn't convenient.

I'm assuming this is due to the large increase in air flowing into the engine with the modifications made. What now? Can this be corrected?
 

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1998 SLK 230
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2,631 Posts
That sounds like its hitting limp mode because the MAF has its flow maxed out. i.e. it is hitting over 4.85v, and the ECU will open the bypass valve fully to dump boost to save the motor.

Remember the ECU and MAF don't know about boost it's calculated by the flow. I believe this can be fixed in the tune depending what the tuner can access or setting a MAF clamp so it pegs the voltage at just under the limp setting and as long as you have fuel to accommodate the boost to keep the air/fuels good it won't go into limp mode.
 

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2001 R170 SLK230K 6M Sport
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30 Posts
Discussion Starter #3
Can this be done outside of the tune? Like with some sort of voltage regulator?
 

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1998 SLK 230
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It can be done 2 ways

1) using a diode - google MAF clamp diode. this is the cheapest way but is non-user adjustable
2) using a 3rd party product such as VC3-100 Voltage Clamp | this is adjustable
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #5
Nice.

Thanks bro.
 

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1998 SLK 230
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2,631 Posts
I also forgot to add that the bypass valve itself could be faulty. It's not a cheap part (I'm pretty sure you can only get them second hand now)...

this exact issue has been solved by replacing the bypass valve, so keep that in mind when troubleshooting.
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #7
So I purchased enough supplies to make 10 MAF clamps for people if they want one. I'll make them up and I'll only be charging postage to anyone.
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #8
FYI, just reading through your mod list in your signature and noticed something for MY2001+ owners who are modifying.

Post facelift models don't require an adjustable FPR. My fuel pressure has been maintaining constant pressure throughout the load range on a dyno without hesitation. The car is making 316 hp and 298 lb.ft. right now with methanol and a heavy dose of timing advance on 12-13 psi. On 93 pump gas it maintains 258 hp and 250 lb.ft. safely at the highest boost level.
 

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1998 SLK 230
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Mine can run ok with a 4 bar fuel reg but it performs a lot better with a 5 bar. I have noticed it kills my top speeds when doing track days running a 4bar. same parts of the track I would be hitting 175km/h with a 4 bar fuel reg (air-fuel around 12.2 slowly creeping to 13) and when I am on a 5bar fuel reg (air-fuel 10.8-11.2) 185+km/h.

what I have realised in my case in the hotter climate (Australia) running richer cools the cylinder temps down a lot more and stops the engine pulling timing which cuts power.
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #10
Yeeeah I literally just went to the Dyno down the street after fabbing up a new CAI and now I'm leaning out after 5k rpm. That being said, it Max's out the MAF at 4700 now and pushed 14 psi today.

Guess I need to figure out my fuel pressure....
 

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1998 SLK 230
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Yep, that's exactly what happened to me... it pulls like a train then top-end it doesn't feel like its pulling any more as it's running out of fuel.

You only notice power drops top end etc... you won't notice it for 0-100km/h, etc.

eg. for me

0 - 140km/h = 4 bar fuel reg (11.2 - 11.5 sec), 5 bar fuel reg (10.3 - 10.5 sec)
80 - 120km/h = 4 bar fuel reg (4.2 - 4.5 sec), 5 bar fuel reg (3.5 - 3.7 sec)
80 - 180km/h = 4 bar fuel reg (around 14 sec), 5 bar fuel reg (around 12 sec)
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #12
Yep, that's exactly what happened to me... it pulls like a train then top-end it doesn't feel like its pulling any more as it's running out of fuel.

You only notice power drops top end etc... you won't notice it for 0-100km/h, etc.

eg. for me

0 - 140km/h = 4 bar fuel reg (11.2 - 11.5 sec), 5 bar fuel reg (10.3 - 10.5 sec)
80 - 120km/h = 4 bar fuel reg (4.2 - 4.5 sec), 5 bar fuel reg (3.5 - 3.7 sec)
80 - 180km/h = 4 bar fuel reg (around 14 sec), 5 bar fuel reg (around 12 sec)
Mine continues to pull like crazy, it just leans out and trips the MAF limit.

Also, I logged iat, boost and MAF cfm with the stock intake, stock intake with the forward duct removed and an open air filter.

Stock airbox with duct had the highest boost level, highest iat and lowest cfm.

Stock airbox witbout duct had medium boost, lower iat and mid-cfm numbers.

Open element air filter has lowest iat, highest CFM and second highest boost pressure.

Also, the MAX iat recorded on a very hard wot pull through all gears to redline, the highest was 112. Our intercooler works quite well considering. Miata owners with intercooled aftermarket blowers see 150 easy.
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #13
By the way, my M45 is noisy after removing the silencer plenum. At the time, I didn't do any porting yet, just changed the pulley and fluid. After, the supercharger makes a rattle sound at idle, but is gone when driving. The pulley spins freely by hand and gives no indication of any problems, other than the sound. It's not loud, but can be heard.

It didn't do it before and I've checked all the bearings to find them perfectly fine.

I have verified the noise to be isolated to the supercharger by removing the drive belt and running the engine.
 

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1998 SLK 230
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yes, I agree with the intake... the stock box the car struggles to breathe. what people forget that this is a roots blower, so any restriction on the intake side it has to work harder to pump the air.

also, low IAT is a result of porting the s/c, if you had it stock they would skyrocket especially in higher boost.

with the supercharger noise, I am pretty sure the plastic coupler is worn inside the snout. it's very common. google "supercharger coupler" and you will see. I haven't opened up an m45 but I'm pretty sure they would use one. this would be the culprit.
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #15
yes, I agree with the intake... the stock box the car struggles to breathe. what people forget that this is a roots blower, so any restriction on the intake side it has to work harder to pump the air.

also, low IAT is a result of porting the s/c, if you had it stock they would skyrocket especially in higher boost.

with the supercharger noise, I am pretty sure the plastic coupler is worn inside the snout. it's very common. google "supercharger coupler" and you will see. I haven't opened up an m45 but I'm pretty sure they would use one. this would be the culprit.
It looked fine to me, I pulled it, cleaned it and it fit back in without issue.

EDIT: by god, you're right. I DID notice the center to be oblonged. Ordering a replacement now.
 

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1998 SLK 230
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The other thing that can cause rattle is if there is too much play in the rear needle bearings in the case. (this can be a bit hard to check). I think they are a bit harder to replace in the m45. if not already done (give the miles on the car) I would swap them out.

I had an issue with my m62 last year where it would make a funny noise low rpm (but fine when spinning full RPM) and I swapped out my needle bearings in the case and it went away
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #17
The other thing that can cause rattle is if there is too much play in the rear needle bearings in the case. (this can be a bit hard to check). I think they are a bit harder to replace in the m45. if not already done (give the miles on the car) I would swap them out.

I had an issue with my m62 last year where it would make a funny noise low rpm (but fine when spinning full RPM) and I swapped out my needle bearings in the case and it went away
When I had it apart I checked the lobes for radial and axial play. There was none. The bearings are quite good. I'm sure the coupler is at fault.
 

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1998 SLK 230
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Yeah I would replace it (coupler) as its a wear and tear item. not too expensive.

Are you running the recommended s/c oil for Eaton's too? some people run regular gear oil in them and that causes issues with the high rpm
 

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2001 R170 SLK230K 6M Sport
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Discussion Starter #19
Yeah I would replace it (coupler) as its a wear and tear item. not too expensive.

Are you running the recommended s/c oil for Eaton's too? some people run regular gear oil in them and that causes issues with the high rpm
I just ordered one from Dirossi superchargers for $10.

I'm running ACdelco supercharger oil.
 

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1998 SLK 230
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That sounds good, running ACDelco s/c oil myself
 
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