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1999 SLK230
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Discussion Starter · #1 ·
Hi all,
I purchased my 99 M111 car a couple of weeks ago and after doing a massive maintenance overhaul, am getting acquainted with it.

The car has a Kleemann boost kit, and the previous owner has a very DIY cold air setup on it. I've got the parts on order to revert back to stock airbox, but wanted to present an interesting issue this car is having.

When I go full throttle, the car will pull very hard to redline (5mt). If I shift and continue WOT in the following gear, at almost exactly 5k rpm the car hits what feels like a boost cut. Power stops like hitting a wall and the supercharger audibly shuts off, not returning until the car is restarted. If I shift at 4900 even, there is no cutoff.

I'm definitely going to start with that airbox, but I figure my next step is either the MAF or the bypass. Just wanted to see if anyone has had this experience prior to tossing parts at it.

Thanks!
 

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2003 R170 SLK230 used /abused daily
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87 Posts
We will try this , @Alex.M-oneeleven . I think you need a tune, you didn't say how big a pulley was put on, so its differcult to work out the amount of overboost you are getting. You are hitting a limit 1k short of the 6k these engines pull, and the S/C will go till it blows, so is that a rev limit . Does the ECU think you are at 6k by air volume when you are actually at 5k? So a tune to sort it out
 

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1999 SLK230 turbo
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690 Posts
Thank you @elphie 🙂, to me this sounds typical of the stock MAF sensor topping out.

What happens with these cars I've experienced it myself. Is when you use something like a larger crank pulley or even like the Speer pulley, it overdrives the Supercharger just enough to top the MAF voltage out. If I remember our stock MAF's read between 0 and 5 volts, basically it's sort of set to a boost limiter. So when you overspin the SC it hits 5v too soon sometimes causing a very unpleasant bucking or misfire type situation.

However all is not lost... What we did when we used the crank pulley was a BMW E39 M5 MAF sensor a genuine Bosch one of course, we removed the element from that M5 MAF and fitted it in our stock housing. That is a awkward job as Bosch use security screws, but we just cut a slit into the screw head so a glad head screwdriver would fit. We used a dremmel to do that be careful.

Also it's worth remembering that when you up the boost you need more fuel too, what we use for that is a VW 4 bar fuel pressure regulator straight swap and easy to get hold of. I do not recommend a 5 bar fuel pressure regulator as that affects spray pattern and also puts a greater load on the injectors, if you find yourself needing more fuel even after a 4 bar fuel pressure regulator I recommend Saab B204 high pressure turbo injectors or VW BAM injectors. The issue with a injector swap is they are shorter than stock and will require injector top hats to extend them.

Hope you find that helpful
Cheers 😃
 

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1999 SLK230 turbo
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690 Posts
@Alex.M-oneeleven I'm just wondering why you didn't use a zener as a MAF clamp. I'm certain there is s good reason;).
We did on the Slk with the turbo but our experience of using that method was that it turned the throttle into an on off switch, now we haven't tried that method on a SC car as back when we had the overspun chargers we were fairly new to the game 7/8 years ago. So the zenner method may work on a SC car better than a turbo car we were at 1 bar though. I only like to recommend what I know works, and because of our experience with the zenner diode clamping method I couldn't be sure it would work with desired results. However if anyone that has used that method and knows if it works wants to recommend it feel free 😃. Just like I say most of my advice is based on personal experience so if I haven't tried it or haven't had good results from it I don't like to suggest it Incas it's not sound advice. Also for the less technologically minded folk changing the MAF element is a easier idea to comprehend. Also I give far to much of an explanation every time 🤣😂🤣😂🤣
 

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2003 SLK230
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666 Posts
I think Alex is likely correct. If it has both the larger crank and smaller pulley on the SC, you might try removing one and using the stock one. That might slow it down a bit to keep from maxing out the MAF. You'd still be a little quicker than the completely stock set up. One other thing to investigate is whether the previous owner re-mapped the ecu. If he/she did the pulleys and modded the air box, there's a fairly good chance they re-mapped as well.
 

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* Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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Also I give far to much of an explanation every time 🤣😂🤣😂🤣
I got that affliction too, you see the reason is ......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... :ROFLMAO: :ROFLMAO: :ROFLMAO:
 

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1999 SLK230 turbo
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690 Posts
I got that affliction too, you see the reason is ......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... :ROFLMAO: :ROFLMAO: :ROFLMAO:
Pahahah 🤣😂🤣 oh Dave that cracked me up 😂
 

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1997 SLK230K
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577 Posts
@banana170, I'm only speculating here but following @Alex.M-oneeleven excellent description of the way the MAF goes into limp mode when the output hits 5v. It seems it does this because it thinks there may be something wrong with the MAF. The usual method for overriding the limp mode seems to be fitting a zener. Usually a 4.7v zener is used. Why? Because it's a common size and they usually have a 5% tolerance so if you get one at the extreme end of the spectrum it's still below 5v. Of course at full throttle the fuelling will be out I guess using this means of avoiding limp. Kleeman use a different method. They simply pop a resistor in the line. This will reduce the output voltage over the whole range. I'm wondering if either you have an issue with your MAF or has the wrong size resistor been fitted?. There is quite a lot of info on BenzWorld including flashing the ECU to eliminate the need for clamping. I did wonder if you could measure the MAF output whilst on a road test?
Of course I might be talking through my hat in which case I'm sure I'll hear soon enough:rolleyes:

PS. Maybe I should have said no resistor has been fitted.......
 

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1999 SLK230 turbo
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@banana170, I'm only speculating here but following @Alex.M-oneeleven excellent description of the way the MAF goes into limp mode when the output hits 5v. It seems it does this because it thinks there may be something wrong with the MAF. The usual method for overriding the limp mode seems to be fitting a zener. Usually a 4.7v zener is used. Why? Because it's a common size and they usually have a 5% tolerance so if you get one at the extreme end of the spectrum it's still below 5v. Of course at full throttle the fuelling will be out I guess using this means of avoiding limp. Kleeman use a different method. They simply pop a resistor in the line. This will reduce the output voltage over the whole range. I'm wondering if either you have an issue with your MAF or has the wrong size resistor been fitted?. There is quite a lot of info on BenzWorld including flashing the ECU to eliminate the need for clamping. I did wonder if you could measure the MAF output whilst on a road test?
Of course I might be talking through my hat in which case I'm sure I'll hear soon enough:rolleyes:

PS. Maybe I should have said no resistor has been fitted.......
Excellent explanation, I think we had so many issues because we were 1+bar and we had other things going on also. But that is a better explanation than I could have given, we got very close to figuring out a Audi V8 MAF that would have most likely worked above a bar but we never got to testing it I'll see if Ben still knows the part number. It took sooo much research 🤣
 

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1999 SLK230
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Discussion Starter · #11 ·
Apologies, hadn't even realized I had responses here and I check to see a plethora of helpful suggestions/advice!

The pulley kit is one of the old Kleemann ones for the pre-2000 M111, the G1 boost kit to be exact. So, the car only has an oversized crank pulley. It also gets heinous fuel economy, so I suspect fueling may have already been tinkered with in some aspect. Always tricky to work backwards with cars modified by previous owners.

Knowing this owner, despite the airbox modifications and pulley kit, there is likely no tune. I was told the car was maintained and received with a tired water pump, entirely collapsed oil filter, leaking magnet, etc. Effectively a "look pretty, pretend it's nice" car.

I fortunately work for a Euro parts supplier here in the US, so I will definitely give the BMW maf a shot as it seems easy enough.

I wouldn't quite call the cutoff a bucking or anything violent, more of an immediate limp mode type cut; like hitting a rev limiter, except at 5k. Following that moment of failure, the car drives perfectly fine, it just is no longer using the supercharger (and embarassingly still feels faster than my prior build).

Thank you all! I am not going to mark this as solved just yet, as it seems odd that I am able to fully rev out second but hit boost cut in third (though obviously, more load in third could mean more boost). Will update with any discoveries, and would love any more insight.
 

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Discussion Starter · #12 ·
@banana170, I'm only speculating here but following @Alex.M-oneeleven excellent description of the way the MAF goes into limp mode when the output hits 5v. It seems it does this because it thinks there may be something wrong with the MAF. The usual method for overriding the limp mode seems to be fitting a zener. Usually a 4.7v zener is used. Why? Because it's a common size and they usually have a 5% tolerance so if you get one at the extreme end of the spectrum it's still below 5v. Of course at full throttle the fuelling will be out I guess using this means of avoiding limp. Kleeman use a different method. They simply pop a resistor in the line. This will reduce the output voltage over the whole range. I'm wondering if either you have an issue with your MAF or has the wrong size resistor been fitted?. There is quite a lot of info on BenzWorld including flashing the ECU to eliminate the need for clamping. I did wonder if you could measure the MAF output whilst on a road test?
Of course I might be talking through my hat in which case I'm sure I'll hear soon enough:rolleyes:

PS. Maybe I should have said no resistor has been fitted.......
I may investigate this resistor as well. If I don't have it in there already, it should be something I can DIY. If it is in there, sounds like a new OEM maf may correct the issue.
 

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1999 SLK230
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Discussion Starter · #14 ·
Just chewing the fat, but you have double checked MAF is clean and working?

I'm not a builder/modifier, just a forum mod, but higher demands would make me want to be sure MAF is all good. Simple part, but dramatic effect when it has issues.
I wanted to revert the airbox ASAP and go from there, as a full-boost lift off the throttle was blowing this kid's plumbing off 7 out of 10 times. He did the same modification as seen on this forum with a K&N on intake and a jet ski filter on the bypass, but the flange he used doesn't fit and the torx bolts are backwards and not threaded to anything. I can do without the neat sound effects if things work properly and safely.

Maf inspection will probably be done tomorrow night though. This car is very much a secondhand head-scratcher, so I'm finding odd little tidbits of missed maintenance along the way.
 

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1999 SLK230 turbo
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Hmm it just disengages the Supercharger and does it sort of smoothly, that leads me to believe that it is indeed mix related it could be running out of fuel at the top end. I know you said it gets poor gas mileage but it doesn't necessarily mean that it's getting the extra fuel at the right point if that makes sense. The likelihood is it's MAF or fuel, just normally when it's the fuel it cuts the spark if I remember right resulting in the brutal bucking. So I would definitely be inclined to start at the MAF and work from there as when the MAF can't read (fails) or just tops out it throws the ECU into its like safe mode protocol where it disengages the charger and opens the bypass valve, it also goes to a fixed target fuel trim map so the engine essentially goes NA in limp mode. It does this simply cause it can't calculate the fuel air mixture. So part Throttle it used the MAF and WOT it uses the O2 but because it's a load based system it switches between the two under WOT it is worth checking your O2 is good also if all else fails.
 

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* Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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there is likely no tune.
Thing is this, it is very difficult to find folks who can tune the early ecu's, the only decent ones are expensive and that is for a reason, they have had to spend considerable time hacking thousands of lines of code to work out a "Definition File" so that they can tune hundreds of parameters. That takes months of paying expensive engineers, months of testing etc etc.

So no, they aren't being greedy, as some previous threads have suggested, I have spent a lifetime modifying all kinds of Engines / Vehicles, and decent mods that work do cost ;)

So, what Alex says is correct, I personally would not cap the MAF with Diode / resistor etc, and I definitely would not delete it's monitoring, it is saving you from melting a piston ore even worse.

Alex is once again correct, you have to up the fuelling as well. Since you can't cheaply tune the ECU, his solutions of Fuel Pressure Reg and Injectors is way to go, but you can forget Economy 🤣

The first thing I would do if I were you is install an Innovate Wide Band Lambda set up to see what AFR's are doing and that will also enable you to Datalog too ..................

It is the only way without risk. On boosted Engines we used to also run EGT measurements on each cylinder, but we were using well over 2 Bar Boost and getting 700 + Hp on YB Cosworth Motors, and 24V V6 BOB Cossies ;) We were blowing Cranks out the bottom of the Blocks, because the Main Bearing Housings were the "weak" point even with 6mm Steel and also Cast into Sump Girdles :ROFLMAO: 800Hp through a Cologne Ford V6 Bottom end is serious :censored emoji:

HTH ;)
 

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1999 SLK230 turbo
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As @Dave2302 says this is what will happen if your fuel goes too lean for too long.
VID-20210328-WA0000_exported_30592_1616935817075.jpg

That is one of our old M111.975 pistons from our turbo Slk. Dave's comment about a innovate wideband is sound advice as the handheld unit has datalogging capabilities, this helps immensely with setting up your fuelling. It's far easier with data logging to see exactly at what load and revs you need the fuel at.

Also Dave is correct about the tuners I myself am guilty of using the term "greedy" before but he is 100% right the time and effort that goes into a definition file alone is insane to comprehend then you have Dyno tuning to make sure the map is safe. We remapped my stock Clk and the Slk blindly meaning we had no definition file only an AFR and we got lucky very lucky but it isn't safe, it's also still super difficult to do.

But to be fair to the Bosch ECU it is very good at adapting, so you can get away with upping the boost along with the fueling up to a certain point which I think is around 0.8 bar. After that is where the MAF clamp ide comes in but I have no experience with that method having the desired affect.
 

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* Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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Hows about this for over-boosted, this pic hit my inbox in a very a timely manner this morning, it brings a whole new meaning to the term "Blown Small Block Chevy" :ROFLMAO: ....

clickable :-

 
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