Turbo Seems Fine--No Power below 2k rpm

[dave_zook@hyper]

It seems to have happened kind of suddenly but my 85 300SD has very little power until it gets to the 2k range and then the turbo kicks in and I get some accelleration. So my thought is that the Turbo is fine but I can't explain the loss of power from a full stop. I understand that this car is not a dragster but it had more umph until a few days ago. Now it seems like it will never accelerate to the 2k mark. After that, the turbo kicks in but it feels like it is going into passing gear instead of a smooth take off. I am a real newbie when it comes to these cars so any help would be appreciated.

Thanks

[MercFan]

I've experienced similar symptomps when I first bought my car 1 month ago... Here's what I did (per advice from this forum):

1) I checked the condition of the Banjo bolt (on the BACK of the intake manifold - I unscrewed it and cleaned the gunk out with a break cleaner as it was really plugged up.

2) I replaced the pressure line from the banjo bolt to the switchover valve on the firewall. Disconnected and cleaned the switchover valve with break cleaner, dried it out and reinstalled.

3) I cleaned the overboost protection valve on TOP of the intake manifold.

4) Finally, I replaced the pressure line from the switchover valve to the ALDA itself. That cured MOST of my performace problems...

Still I had trouble accelearating from dead stop - for that I ended up adjusting the ALDA aneroid valve on the Injection Pump - in my case I've turned it 3/4 turn CCW and the performance improved (though the mpg suffered)...

Also, if you haven't checked/replaced the fuel filters it may be time to do that - I would check those as well.

Do a search on performance loss on this forum - I've seen several posts that helped me solve some of my issues with performance.

James

[dave_zook@hyper]

Thanks, James

I will check on all this.

Dave

[SD Blue]

It sounds as if your car may be starting off in 2nd gear. Check your linkages and see if there is any malfuntion. I had a C-clip break on mine. Also check for slight tension on the bowden cable. If you take it loose at the ball link, on the linkage, and pull till you feel a little tension, it should be close to lining up with the ball.

[dave_zook@hyper]

You know, Sam, that sounds real plausible. I will check the linkages. All of those are on the tranny under the car? If the linkages don't line up what do I do?

Is there a good manual for the 300SD? I have been looking all over the place and can find no books at all.

[SD Blue]

No, the linkages I am speaking about are up top near the air filter housing. http://articles.mbz.org/transmission/adjust/

There are no on-the-shelf manuals for the W126. Haynes has one for the W123 that covers many things but for more complete coverage, you will need to go to the factory CD, available at MBCA, or on-line http://mb.braingears.com

[P.E.Haiges]

Dave,

Have U tried shifting the gear selector into low, accelerating and comparing that acceleration to starting out in Drive?

That might U tell if the trans is starting out in low gear or not.

P E H

[dave_zook@hyper]

That's a good way to test it. I will try that this morning and see how I do. The transmission has been a bit sluggish when I shift to reverse it seems to take a short amount of time for it to engage.

I also do need to check all the filters and banjo bolt and all that but it really does feel like I am starting off in second.

Thanks, I'll let you know how the test goes.

[SD Blue]

What about the fluid level?

These cars seem to be very sensitive to this.

[MBeige]

Check the throttle linkages. Most of the time there's a single 10mm screw on the turbocharged models that get loose after some time. Follow the rod that comes from the firewall into the stop lever area. Look around for a 10mm screw.

Adjusted that and power went back on mine. I even had to downshift to S just to get by when I didn't see that.

[Old300D]

Another thing to consider is a flow restriction, either in the intake or the exhaust. Make sure your air filter is clean and your exhaust is open.

[dave_zook@hyper]

Well, Guys,

I just got back from trying out the suggestion to shift into low to start and see if that made a difference. It did not. I will check for that adjustment screw and also look to see that the exhaust is open and there is no air restriction.

The other thing that I will try is to replace the fuel filter and make sure the fuel lines and the banjo bolt are clear.

I did notice that at idle, the oil pressure went down from three to two but as soon as I stepped on the gas, it went right back up again.

Thanks for all your help.

[wahlspyder]

Have you found the solution to your problem yet? I seem to be experiencing the same thing - if I start on a hill it won't even pull itself.

[my123ca]

It could be a california car with an ARV on the turbo. Some have disabled the valve to get an immediate response from the turbo.

[Jmana]

What is an ARV? Mine is from CA also, and it doesn't seem like the turbo kicks in early enough. Please inform me on how to disable this.