R170 SLK 320 cutting out under hard acceleration

Tony.T

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I've had a few running problems with my SLK 320 (2001 R170)

In march it was misfiring over 4000 rpm, each time the CEL came on. My local garage downloaded fault codes which suggested that some cylinders were misfiring.- well we knew that:p

Anyway, they cleaned the MAF sensor and all was well for a week, then the problem re-occurred. We decided to replace the MAF sensor, and again all was well (in fact the car had never drove so well)

Now however, if I try to accelerate hard, it starts off ok for about a second, then the engine momentarily cuts out (Not a misfire but a total cut out) this only lasts for a split second and then off we go with no further problems.

If I accelerate more gently then there is no problem and it rund happily right past 5000rpm.

Any ideas? Anyone had this and found the cure?
 
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Tony.T

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Forgot to say, when the engine cuts out the CEL does not come on
 

television

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As Jib, thats the important bit
 

Scoob

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ECU could be thinking the car is over-boosting, hence the cut-out. I'm not sure how Mercedes handle over-boost situations...Fords blow up* (like my Focus lol) my Impreza just opens the waste gate (a better solution that Ford's methinks) so the power (boost) bleed away fairly safely.

The MAF is critical here, so find out all you can about it. I'd suspect that an incorrect MAF could be showing a lower air-flow than is actually occuring, so the turbo keeps working, eventually triggering an over-boost scenario. This is pure speculation on my part, but I've had experience with similar on other cars.

Possibly, over an over-boost situation, the ECU then limits boost the rest of that session. Hopefully some of the veteran Mercedes owners here can advise.

Best of luck getting to the bottom of this one.

Scoob.

* Just kidding for the most part, mine did go bang, but obviously something else was wrong for the overboost to occur in the first place. It drives lovely now.
 

jibcl500

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This SLK 320 doesnt have a komp or turbo so I dont think he needs to worry about over boost!

jib
 

Scoob

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This SLK 320 doesnt have a komp or turbo so I dont think he needs to worry about over boost!

jib

Heh, ok. Did I mention I don't really know Mercs so well yet? :)

I the MAF could just being going off the scale expected by the ECU? Or simply glitching and showing NO air flow...MAF are buggers, no matter what car they're on.

Scoob.
 
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Tony.T

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Thanks guys for the replies!

Now I know I'm going to get shouted at but I bought the MAF off e-bay from a UK supplier, it has a 12 moth warranty and so far they have been very helpful. If it comes to it I'll buy a bosch unit and if that works ok I'll return the other one for a refund!
 

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Yes it will have to go back, ask your local Bosch agent in your town or ECP
 
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Tony.T

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Yes it will have to go back, ask your local Bosch agent in your town or ECP

ECP are doing a genuine Bosch unit at a discounted price- think I'll have to order one. £140 delivered- anyone know of a better deal?
 

c15htn

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Thanks guys for the replies!

Now I know I'm going to get shouted at but I bought the MAF off e-bay from a UK supplier, it has a 12 moth warranty and so far they have been very helpful. If it comes to it I'll buy a bosch unit and if that works ok I'll return the other one for a refund!

I did the eBay thing once too........ lasted 25minutes lol!!
Get the Bosch one from ecp, I did and fitted it in the car park - seriously good result :lol:
 

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The actual sensor in the tube can be bought for about £75 if it has a Bosch part number on it, that makes the plastic tube the most expensive bit of tube in the world
 

alexanderfoti

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Mine has a rough idle and hesitation . The maf part is 140 from ecp on deal :(

Sent from a mobile device
 

television

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It should not effect idle I think, when bad they can cause the engine to stall if you press the throttle, but they can fail in all kinds of ways
 

c15htn

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It should not effect idle I think, when bad they can cause the engine to stall if you press the throttle, but they can fail in all kinds of ways

Oh yes it can I'm afraid..... mine idled really lumpy when it was warmed up, probably running a bit rich is guess, when the MAF was duff...... and the cheap eBay version didn't idle at all lol! :shock:
 

alexanderfoti

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It should not effect idle I think, when bad they can cause the engine to stall if you press the throttle, but they can fail in all kinds of ways

It idles normally with it unplugged :)
 


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