W220 hesitation on acceleration

[944S2cab]

For the last 2 months I have had a problem with acceleration on my 1999 S430 (petrol).

The engine is fine until I press the accelerator beyond approximately half way down at approx. 3500rpm, when it kicks back and seems to have run out of power. I had a fault code relating to the mass airflow sensor and I replaced it (with an aftermarket part as I intend to part-exchange the car). I cleared the fault code and it did not return.

The acceleration problem returned with fault codes relating to voltage on 3 coil packs. I replaced all 8 coil packs (aftermarket) and cleared the codes and they have not returned.

The acceleration problem returned and there was a fault code P0150 relating to the pre-cat left hand oxygen sensor. I fitted a new Bosch sensor and deleted the code but the acceleration problem is still there.

I have just serviced the car. It has new air filters, fuel filter and Bosch spark plugs.

I have obtained the following live data. The first reading is at idle, the second at 3000rpm.

Air mass volume: 8kg/h. 76kg/h

Air flow meter voltage: 1.21V. 2.1V

Throttle valve angle: 2.2 7.2

Injector duration 3.3 3.45 on both banks

Camshaft Hall sensor: 85-170 at idle, same at 3000rpm

Intake manifold pressure sensor: 0mbar 5mbar

Throttle position sensor signal 1: 4.41V 4.14V

Throttle position sensor signal 2: 0.57V 0.84V

Pedal position sensor signal 1: 0.31V 1.46V

Pedal position sensor signal 2: 0.14 0.78

Left O2 sensor pre-cat: -3% 0% voltage: 123mv 216mv

Right O2 sensor pre-cat -1% +1% voltage 641mv 69mv

My diagnostic kit will not give readings for the post-cat O2 sensors for some reason.

If any technician members could give me some guidance on what to do next (apart from take it to the local MB specialist) I would appreciate it.

Thank you.

 

[alabbasi]

MAF, plugs and pedal position sensor are usually the culprits

 

[944S2cab]

Alabbasi.

Thank you for that. I've already replaced the MAF and plugs so I have ordered a new throttle pedal position sensor.
I obtained more live data showing that the pedal position sensor readings increase up to 3500 rpm when the engine kicks back. I don't know what the minimum readings should be; my copy of WIS does not give that info.
I will report back after fitting the new sensor.

 

[944S2cab]

I fitted a new Hella pedal position sensor. It made no difference.
It then produced fault code P0170. Self-adaptation from the mixture forming.
Thinking it could be a blocked injector I cleared the code and poured a bottle of Wynn's extreme fuel system cleaner into the tank and drove the car. No difference. No fault code showing.
I then replaced the aftermarket MAF sensor with a new Bosch unit. Still hesitation and no fault code.
I found a post explaining how to reset the ECU after a MAF sensor swap. I did the reset and took the car out. This time I completely floored the accelerator and after kicking back and hesitating I kept the pedal down and the engine revved as high as 5000rpm. I did this a few times and it kicked back each time before changing down the gears and revving up to the red line. I drove home and checked for fault codes but there were none.
I noticed that there is slight movement at the component below the MAF sensor housing where it connects with the cylinder head. Could this be the source of an air leak?
I think it will have to go to the local MB specialist. I have run out of ideas.

 

[944S2cab]

I took the car out today and floored the accelerator pedal. It kicked back a bit then changed down a gear. I kept the pedal to the floor and it jerked and changed down another gear before revving up to the red line. I enjoyed the drive home after that.
While stationary at home it will not rev beyond 4000. Is this some kind of safety mechanism? Is it a normal characteristic of the W220?
I wonder if the fuel system cleaner has worked. Last night I treated the car to some Shell V-Power fuel. It felt much livelier when I drove it this morning. Perhaps it needs 97 octane.

 

[ivan1983]

I believe a lot of cars are rev limited in neural.

Have you played around with the behaviour when in manual mode , ie put it in 2 and see how it behaves above/ below 3.5k rpm

I wouldn't have thought 97 would make a difference. Inside of the filler cap will tell you the minimum ron rating

 

[944S2cab]

Inside the filler cap it says to use unleaded fuel only. I've been using Shell ordinary unleaded since I got the car earlier this year. It certainly seems livelier on 97 octane. Maybe the fuel system cleaner has done some good.
I have just taken it out and used 2nd gear in manual mode. The acceleration seems smoother with less kicking back, and it went to the red line.
Perhaps a change of transmission fluid and filter would make things smoother. The service history shows no record of these being changed.

 

[944S2cab]

I have changed all the transmission fluid and the filter. The fluid was black. It was probably 20 years old. (Not my fault. I've only had the car for a year). When I floor the accelerator the car now goes like a rocket all the way to the red line. It has never driven so well and the gearchanges are so smooth. I am driving with a smile on my face.