I just recently had everything behind the manifold piece replaced with a "custom" unit (OEM was far too expensive), and now my engine seems to behave erratically at about 2800-3000RPM. It is almost as if the transmission is only half engaged and the tach "feathers" between 2800 and 3500 while at a constant speed and throttle position.

While working on the accessory belts, I disconnected and then reconnected a couple vacuum lines.

The ALDA has been adjusted before. The little fuel filter looks good but I do not know when they have been changed. The air filter is clean.

Also, the car is definitely not low on power. It really only surges at that RPM range with no change in speed.

I'm thinking the new exhaust system may be more restrictive and messing with the shifting mechanism?

Not too sure where to start with this one. Would appreciate any help. I'll try to take a video of it later.

Thanks!

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1985 300SD "The Saudi Prince"

http://www.conservativegentleman.com

I'd check the amount of vacuum going to the transmission modulator first since excessive vacuum will induce flaring. T into the line and monitor it as you drive.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I have a good used manifold pipe with the flex coupling in it that I will sell you reasonably.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Check your Boost Pressure; maybe the Waste Gate on the Turbo is opening.

I can't remember the name of it but between your Intake Manifold Pressure line and the ALDA is a device that will disconnects you from something. There is a Pressure Sensor for it on the Intake Manifold; look for a loose Electrical connection and trace the wire back to the device.

Over Pressure Relay Valve?

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the replies.

Well, I started with the obvious. Checked the trans fluid level (the car is new to me) and it is very low. Barely touching the stick. No leaks that I can find...

I couldn't get a video, but the shifts are a little soft and there is definitely some flare between 3 and 4.

I will grab some fluid in the morning and see if that fixes the issue. That's probably what's causing the problem, right?


Other than that, I love the car!

__________________
1985 300SD "The Saudi Prince"

http://www.conservativegentleman.com

Quite possible. But even if not it needs to be corrected.

__________________
2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)

These transmissions can be very sensitive to fluid levels sometimes. Hope that is it for you. Make sure you read the checking of transmission fluid proccedures carefully. Not rocket science but you want to do it right.

It didn't dawn on me that I was checking the level on my sloped driveway until I opened the shop manual. It wasn't quite that low, but still well below the line.

Put in some fluid and that solved the problem. The thing shifts like a dream now! I cannot believe I was so stupid. Wonder how much damage I did driving it 50 miles like that...

Thank you everyone for the suggestions and your help.

__________________
1985 300SD "The Saudi Prince"

http://www.conservativegentleman.com

What exactly is "custom" about the exhaust, if they used too small of pipe or poor quality restrictive muffler(s) it will indeed affect engine operation.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

No probable damage but check level frequently to accertain if a transmission leak is present somewhere. You were not stupid by the way as this particular series of transmissions can be very touchy about the fluid level.

The first time I experienced it it took me more than a few minutes to isolate the cause. My symptoms also where a little different as well.

I couldn't find a resonator and muffler piece reasonably priced so I had my exhaust shop whip something up. It definitely doesn't feel like it is holding the engine back.

Oh well. Thank you again. Onto the next problem!

__________________
1985 300SD "The Saudi Prince"

http://www.conservativegentleman.com

i sometimes feel redneck and wanna run a straight pipe on my SD (i really do!)
i wonder what kind of truck nuts would look good on a W126....