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2000 ML430
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12 Posts
Discussion Starter #1
I recently purchased a 1997 SL320 under the potentially mistaken assumption that the six would be more reliable and cheaper to maintain than the 8 or the 12. I love the car but the transmission behaves very differently than I expected and I hope it is not "normal".

When I purchased the car it had a pretty good oil leak at the passenger rear and thanks to this board I knew in advance that the head gaskets on these cars are simply prone to failure and not much to worry about. I got a very good deal on the car because of the oil leak in any event and I actually drove the car carefully for about a month before I had the head gasket replaced at the dealer. Now that the car is not leaking oil I am starting to push it a bit and hence this issue has presented itself.

When the car is cold the upshifts from first and second are delayed to warm the engine and the catalyst faster and this seems to work normally with slightly elevated shifts. I do notice when the car is cold that a shift at more than 60% throttle results in a slight engine misfire for a second but this only happens in the first minute of driving and then goes away. It would appear that MB retards the engine timing a bit during the shift to reduce engine torque to the transmission and this timing retard may be the culprit on the misfire.

When the car is accelerated at full throttle cool/warm or fully warmed up the car will not upshift from first to second and the engine rpms hold perfectly steady at about 6000 rpm with no miss. It feels like some sort of rev limiter but 6000 is well below the redline of the engine. If I lift just enough to not engage the downshift switch under the accelerator pedal the car will still not shift out of first. When I finally lift the pedal a bit more and the throttle angle is less than 100% the car then upshifts fine.

The check engine light is not on and there are no codes stored. I also recently had the brake switch replaced which had caused the ASR MIL and otherwise the car runs excellent. I also recently replaced the spark plugs and wires with no effect.

Any ideas on what else could be the issue either in the transmission (shift sensors) or the engine (faulty speed sensor maybe). I also checked the engine harness and the wiring loom all appears new but I did not open the loom to inspect the actual wires.
 

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Registered
2000 ML430
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12 Posts
Discussion Starter #2
Update on shift and rev limit issue

Replaced the fuel filter today as a token gesture. Code retreive resulted in a P0170 fuel trim diagnostic trouble code. I data logged the car and the long term fuel trim is maxed out at 32% and during full throttle acceleration the short term fuel trim maxes out at 25%. Still not exactly sure if this is really a fuel supply issue or whether the air flow meter is way off. Either way it appears I may be back to the dealer.
 

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Registered
2000 ML430
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12 Posts
Discussion Starter #3
final solution

Final resolution on my lack of power was a new air flow meter. In the end the only give away was that the long and short term fuel trim were maxed out during acceleration.
 

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1991 500SL
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19 Posts
Re: final solution

Final resolution on my lack of power was a new air flow meter. In the end the only give away was that the long and short term fuel trim were maxed out during acceleration.
I had a simililar problem with my 91 500sl, it was a problem with the transmission. Replaced filter and fluid - fixed!
 
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