Engine breaking down 4500rpm - Mercedes Benz SLK Forum

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#1 Old 03-01-2013
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Engine breaking down 4500rpm

Hello All
My problem is somewhat baffling!
When i drive my 1998 SLK230K and stand on the accelerator pedal somewhat firmly, when the engine revs are at about 4500 the engine will develope a stutter or miss (sometimes i can feel the same miss when driving normally around town but very rarely and usually when the ambient tempreature is around the 35-45 degrees C.). Other wise, under gentle acceleration and normal driving it performs fine.
When i shift the auto transmission into 1st gear and manually change as my speed increases the motor begins to break down at around the 4500 revs in all gears.

Can any one shed some light on this issue.

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#2 Old 03-01-2013
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Any trouble codes? I would suspect the MAF as the most likely suspect. But in any case if it were a coil, etc. It should throw a code.
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#3 Old 03-06-2013
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Disconnect the electrical cable from the MAF and test it at full throttle. If it respons OK and the fan operates all the time you have a MAF problem. Clean it with a good MAF or contact cleaner, reassemble it including the electrical cable. Should be OK.

Good luck
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#4 Old 03-08-2013
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Thanks Davronoe
I disconnected the wiring connection as you suggested and took the car for a run around town.

The motor struggled to run and accelerate, but it reved right out to 5.5 rpm

So you are probably correct it is the MAF.
When i disconnected the wiring i found two of the wires in the loom had the insulation worn away by the pulley next to the MAF on the engine, has a radiator hose rub through a couple of months age as well.

I am going to fix the wiring and give the MAF a good clean up as well. it may only be the wiring shorting out i hope.

I really appreciate the help thanks.

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#5 Old 03-09-2013
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Two Problems

Hi Wheels52,

It sounds like you have two problems. One is the MAF cleaning and second is the bare wires - if they are touching the pulley it would act as a problem intermitently. Fix the wires and see what you have. If it is necessary to clean it there are video's to show you how to do it. BUT two items the videos don't tell you is;

1) after you remove the MAF look through the tube. The screen you see is not the sensor that needs to be cleaned (clean it anyways).
2)The item that really needs to be cleaned it the sensor that is explained below. I cut and pasted this from another blog of mine.

"I want to add something to this cleaning that may be helpful to those who tried to clean the MAF unsucessfully.

I have a 1999 230k that refused to go over 3000 rpm at more than 30% (approx) throttle. Read on another post that if you disconnect the MAF the engine should run OK and the fan will run continuously. I did this and my car ran just as this said. Ran great and the fan ran continuously. I tried to clean it twice before without success.

Today I was determined to find why the MAF would go bad - if it really did? I was not convinced that this part could go bad unless it was physically damaged.

Besides the regular cleaning as indicated in this post I also removed the sensor by removing the two screws holding it in the air tube. It is sealed with an "O" ring but easily pried out with a screw driver. I noticed an arrow designating air flow and a sensor wire down inside this housing. I cleaned the wire with contact cleaner and a "Q" tip. And more cleaner.

Put it back together and took it for a ride. IT RAN GREAT - 6000 rpm at full throttle.

At $400 plus for a MAF it is worth it to me to try other alternatives.

Good luck"

Let us know how it turns out.
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