Why is my performance dropping off? - Mercedes Benz SLK Forum

SLK R170 General Discussion SLK 200, SLK 230K, SLK 320, SLK32 AMG

 
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#1 Old 08-19-2015
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Why is my performance dropping off?

2000 SLK230 with 250K miles, runs great. Starts instantly hot or cold, 28 MPG in country driving with 55MPH speed limits and small towns.

But it doesn't seem to have the power it used to.
Got a 0-60 timer app for the phone, I have a 10 second 0-60 time now!
Air filter is clean, plugs and coils fairly new.

Recently cleaned the MAF after getting P0170 and P0136 codes.

I just ordered a change of supercharger oil, didn't know I needed that until I started reading about it here. Thanks!

I have a dashboard monitor that I plug into the OBD II connector, shows my boost. What should the peak boost be?

No surging, lagging, or difficulty starting. Probably running the original O2 sensors ( I have had it for the last 80K miles and I didn't change them).

Suggestions on where to look?
Thanks,
David
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#2 Old 08-19-2015
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#3 Old 09-02-2015
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Does your supercharger have a clutch? If so, check that it is engaging above 2000 rpm. If not, there is most likely a fail MOSFET in the ecu.
There is a cooling fan located under the ecu that pulls cabin air to keep the modules cool. The fan will fail without any indication and components in the ecu start failing due to heat. The first to go is the mosfet that switches the supercharger clutch.

I just made this repair on my wifes '98 SLK230 with 96K miles. Dealer wanted close to $4K! The repair cost me less than $20. New fan motor and replaced the mosfet. The mosfet had to come from china so I bought extras.

Good luck.
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#4 Old 09-02-2015
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Every 2 or 3K I put in the best non-ethanol 93 octane I can find. In addition, I put in appropriate, by the label on the can, amount of "TECHRON". Then I take it out on the highway and try to put 50 or so miles on it at 4K RPM. I then notice a real difference as the carbon on the piston and intake are cleaned off as well as the internals of the fuel delivery system........ God bless.....Dennis
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#5 Old 09-02-2015
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I have heard of around 8 PSI (0.55 BAR ) as being the expected stock boost(?).

And I think you're on the right track. When suddenly losing performance in a supercharged car while it runs good in general it's usually related to faulty boost pressure mechanics (valves/clutches/etc)
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