clutching, but no clutch?????????????
 

i have an 83' 300D. it sat for a couple weeks while i fixed a fuel line that was leaking(no big hurry). now when i get above 2200 rpm it starts to learch like it has a clutch engaging and dis-engaging. it does it on hard acceleration or easy. i'm guessing a vaccuum leak but dont know where to start looking(may be wrong all together). oddly, my 86' 300sdl has started doing the same thing, plus loses power going up a hill, to a crawl. and it wont shift out of overdrive unless you let off the fuel???
thank you for any and all assistance

It would seem to me that if all you have done is to work with the fuel system then that may be where the problem lies.. could the return line have been swaped to the fuel line, or some other easy to do (simple) fix?

Or is it that the engine is getting away from the transmission, that is does the car lurch along? or is the motor winding up as if you had your foot on the clutch?

Given the lurching regardless of how much fuel you're giving it, but only above 2200 rpm, that sounds fuel related. If the rpm only seems to exceed that expected at your particular speed when it lurches, that sounds like "slipping and catching" in the clutching mechanism, be it an automatic, hydrastatic or dry clutch. Yes, a vacuum leak will cause fuel draining back to the tank resulting in some air perhaps in the fuel feed or return system. I'm not expert in this, but I would think any air would work it's way through the system and the car would stop this behavior if you drove it for some time, say exceeding half an hour or so. As the previous forum member said, since it is the working on the fuel lines which immediately preceded the problem, this is where to determine if there is a problem. My 220D required hand pump priming to start if the car sat for more than a few minutes. I replaced all the braided line return hoses as well as the braided cigar hoses back at the fuel tank. The sure sign that I had a problem with failing hose causing the bleed back was that the hoses were wet with diesel (not dripping wet, but still wet with diesel). But, if fuel bleed back was a primary problem the car would be hard starting to one degree or another. At any rate, double check the hoses (and steel line) for signs of leaking diesel. With the car at a standstill when you run it above 2200 rpm is there any missing? I would think the lurching would be worse, in my opinion, when in high gear at low rpm when you give it a lot of pedal. But, if it only occurs above 2200 rpm under any load conditions, I guess this could possibly not rule out fuel problems nor slippage in the clutch mechanism (of whatever type).
So, check if the engine "misses" above 2200 under no load. Most likely, I would think, you have a fuel delivery problem. So, not only air in the system, but it could also be clogged filters, whether tank, primary or secondary filters. If they have some miles then put new ones in. Check fuel lines. Since this a new problem since you worked on fuel system, you need to rule it in or out first. If all is well, then check engine rpm during the lurching.

problem gone
 

under no load, the motor would rev and show no miss at all. it was only when driving, it would lurch like a clutch being pressed and released real fast, the motor would not rev, the rpm gauge was constant and steady, anyway, yesterday when i left work, it was fine, same this morning. actually more pep than i've had in a while. she still goes pretty good for 300k miles. 0-60 in 15 seconds this morning and no smoke at all. the leak i had was the braided hose off the tank.
thanks for the responses

Both Doing The Same Thing??
 

Did you fuel both these vehicles up at the same gas station close together?? Did you get bad fuel??? Seems strange they both decided to do the same thing at the same time

i used the same station i've used for some time now, fuel jumped 17 cents a gallon last night