W126 Less Power at Top End
 

I am experiencing less ability to accelerate in my 85 500SEL at the top end. I still get good response 0-60 (for a V-8 saloon), and I get good mileage on road trips (~18-20 mpg).

But when I step on it, to pass trucks (yeah right), the response is not what it used to be.

I am thinking it is a fuel delivery issue. The kick-down, throttle, and engine all seem to be doing their part. I think she is just thirsty.

I have reviewed lots of posts on this subject (regardless of chassis) so I have a good idea I am on track with many things to evaluate/improve as DIY'er. But before I take this on as my next summer "project" ;) , I would like some input from the fellow enthusiasts and experts.

Info on the car:
>115k - seals are worn and I get a little bit of smoke when she starts up after sitting a day (future project)
>timing chain, O2 sensor, plugs, and some faulty plug wires were replaced at 107k (last year)
>fuel pump looks original, but is making noise. The dealer recommended not replacing [at this time].
> Service records from PO do not show any work on injectors/other items associated with fuel system.

Since the engine still runs quiet and smooth, I don't think a compression test is necessary, but maybe I'm wrong.

Where would you start?

Thanks in advance for the input ...... Michael