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Old 05-19-2006, 06:40 PM
Join Date: May 2006
Location: Denver, CO
Posts: 25
Question Bad MPG and slow shifts in 83 240D

I just bought a 1983 MB 240D and I only got a best of 28 MPG on a road trip. I was driving pretty fast and pushing speeds up to 85 MPH, but it still seems like a bad MPG for a 240D. Does it have something to do with the idle speed control being too low or too high? The car sounds really loud at that speed (80-85 MPH) and feels like it needs a higher gear, is it just geared low?

Also, the car does not want to shift down without manually moving the gearshift from "D" to "S", or from "S" to "L" at really low speeds. From a standing start, it does not feel like it's getting full acceleration and engaging in first gear. It does not slip, but shifts harshly. The downshift button beneath the gas pedal when the pedal is floored does not trigger a downshift either. Any advice?

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Old 05-20-2006, 10:55 AM
t walgamuth's Avatar
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 35,595
i am no expert on auto trannys but your mileage looks really good for the speeds you are driving.

it is not a 1800# economy car with a 1200cc engine and six speed manual.

tom w
[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.
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Old 05-20-2006, 06:42 PM
dmorrison's Avatar
Registered User
Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
28MPG at 85MPH is good for the 240D. If you want better gas mileage slow to 55MPH. It will do much better. Add a injector cleaner to make sure the injectors are clean.

Your downshift problem is a vacuum issue. the 722.1 transmission uses vacuum signals to shift. It does not have a downshift cable as the 300D and 300TD does.

Do a search on vacuum systems. You want to replace all the vacuum connectors (2 way,3 way and 4 way connectors) make sure the other vacuum systems are not "stealing" vacuum and check the vacuum output of the vacuum pump. Make sure all those are working correctly, then if all is OK then you may have to look at the vacuum control unit on the rear of the Injection pump. this controls the transmission shift. But at $165 I would check all the other vacuum systems first.

To get the 240D to downshift we have to floor it, or make the car downshift. I drive the diesels differently then a gas car. Just the nature of the beast.

1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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Old 05-21-2006, 10:15 PM
C32AMG's Avatar
Registered User
Join Date: Mar 2004
Location: new york/orange county
Posts: 639
That 722.1 transmission should have a control pressure rod which is part of, attach to the angle lever on injector pump. Itís a push pull set up, look for the rod on the passenger side of the engine going down to the transmission, make that rod shorter by turning the ball socket. You may need to set up/ adjust the linkage rods.

To check the kick down solenoid and electrical circuit. Open the passenger door with the ignition on depress the throttle pedal to full throttle , you should a hear click at the side of the open door, if not , blow fuse or open wire to the solenoid, bad solenoid or the pedal is not fully contacting the KD switch or a bad switch under pedal.

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