Bogs down under throttle, slow to downshift
 

Car is a 1995 S320, 117 kmi. besides the noted issue it runs great. It has lately been down on overall power. Acceleration is suffering and even putting the pedal to the floor to down shift, feels delayed and weak. Thoughts? Fluids are good, plugs good, filters good, I think I need to get a air inj. pump soon. I only mention the air inj. pump because on a preious car I've owned, I had eliminated an inj. pump and the car ran poorly.

Please post.

Good acceleration is a product of fuel pressure & air mass info.

Any MIL lights? Do you use high octane fuel?

Low octane fuel can cause the knock sensors to retard the timing & reduce power.

Sounds like limp home to me.
Anziani

No codes
 

No CEL, no codes, or none yet. I'm guilty of using less than premium fuel, but never a ping or knock from the motor. I'm sure it's not in any sort of limp mode. I have cleaned the MAF with the appropriate MAF cleaner, as well as cleaning the IAT sensor. I did this after it started feeling slugish, no real difference. Maybe ran slightly smoother?
Please reply

Are the engine wiring harness and throttle body wiring original?

Wiring
 

Yes, all orig.

Many Mercedes mechanics won't touch models such as ours with driveability problems unless the original wiring harness has been replaced. There's a very good chance your problem may be with the underhood wiring.

I am not sure but I think it might be converter problem

Harness
 

I know about the insulation problem, where it basically crumbles off of the copper wire. I know that to my IAT sensor the insulation was shot. Looking up prices I see that I'm looking at approx $550. Is the known problem basically the wires and maybe a plug or two, which are sold seperately? I'm asking because I'm more than capable of pulling the harness on this straight 6cyl. and soldering in new wire &, shrink tubing all the connection. I've seen the illustrations of this harness and it's unjustified at that price, as well as not very big.
As for the throttle body harness, is that a seperate harness? or a couple wires?

I could buy several spools of wire, shrink tube, more solder, even a new iron, tape & wire loom. Relax at my work table while having a few beers doing this. When done have an extra $400. in my pocket, figuring an even $75 materials, $75 beer.:rolleyes:

The throttle body wiring is a separate harness. It's essentially a 12" pigtail of roughly a dozen wires coming from the throttle body that need to be replaced. I went through this exercise myself (successfully) a few years ago.

The link below illustrates how to fix the wiring in detail.
http://w140repair.com/ETA_Rewire.htmhttp://w140repair.com/ETA_Rewire.htm

+1 ... I just experienced this in my '95 bimmer. Power was way down but it ran smoothly and threw no codes (this is an OBD I car). A check of exhaust back pressure at the oxygen sensor bung would verify such a diagnosis quickly.

Harness and MAF
 

I'm planning on doing the engine harness, TB harness and a new MAF. My MAF is orig with 118kmi on it. I'd bet on a combination of the two, harness being the true culprit. Tend to lean away from a cat issue.

The secondary air injection pump has nothing to do with how the car runs. Its soul used is to heat the catalyst during cold start so they are ready quicker to reduce emissions. As far as poor performance, how is fuel pressure/pump draw? injector spray? engine harness? If you don't have to do a tailpipe sniff test, throw that pump in the woods and get the shorter belt. Don't spend money unless you need to, the MAF is an expensive guess, also you can take a razor and slice the throttle valve actuator's shrink wrapped harness and look at the internal harness's condition, the short out and take out the EA module on same vintage v12s.

I think your car still has the throttle-linkage-controlled control pressure cable, which may need to be adjusted.

Cable, Air pump, harness
 

Explain?


Yes, I agree about the air pump. Removal may be the better way if it ends up to be seizing up. I have to check it this weekend.

The harness definitly needs work. most likely the TB harness as well.

I mention the MAF because I've had old failing units not throw codes, not respond to a cleaning. But, when replaced made a big diferences.

The cable affects shift points. It was used on all models up until the mid 90's when the electronic transmission 722.6 came along. If the cable is broken or has too much slack, you shift into higher gears earlier, and you don't get downshifts when expected.

I wouldn't mess with that cable unless you had the correct procedure in front of you. You might piss the fuel computer off and put the car in limp home. Cleaning these early air mass sensors rarely yield any difference and they rarely failed. Do yourself a favor and go after the obvious before wasting your or anyone else's time.

OK, it looks like the 722.6 tranny first came to the W140 in 1996, so your car will have the control pressure cable and vacuum modulator. There is no limp home with those trannies, and the cable has no input to any engine computer. The cable should be adjusted to about zero slack.