[W126 Coupe] Hesitation from 60C to 80C

[Jason Mavris]

The Modulator Valve  on drive side of the transmission could be the issue. Cracked cap, bad line or bad valve.  We use to have a 87 420Sel, that had the same problem.  The mech could not figure it out and said well with 235K its probably the tranny, she's due.  Long story short I replaced the modulator valve and the vacuum line that connected it. Car shifted perfect till we sold it with 298K.   It was the original transmission.    

Jason 










  ----- Original Message ----- 
  From: Day . Ralph 
  To: Mercedes Coupes Mailing Lists 
  Sent: Monday, February 09, 2009 6:40 PM
  Subject: Re: [W126 Coupe] Hesitation from 60C to 80C


  Kelly,

   

  Can you be more specific?  I got rid of my 1984  because of this, bought a 1991 five years ago, and am getting rid of it because it has now develop the same problem.  The cars are wonderful, but this borders on safety.  I am reluctant to sell it to anyone.  My certified Mercedes mechanic cannot figure it out either.

   

  Ralph D. Day

  Senior Program Manager/ASQ LSS Certified Black Belt

  MDA Master Black Belt

  Dynamics Research Corporation

  (301) 275-9030 (cell)

   

  From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Kelly Frink
  Sent: Sunday, February 08, 2009 12:54 PM
  To: 'Mercedes Coupes Mailing Lists'
  Subject: Re: [W126 Coupe] Hesitation from 60C to 80C

   

  Vacuum 

   

  From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Matt Jurcich
  Sent: Sunday, February 08, 2009 12:41 PM
  To: mbcoupes at mbcoupes.com
  Subject: [W126 Coupe] Hesitation from 60C to 80C

   

  Hey all,

  My 89 560 SEC (110k or so) runs and shifts fine from cold until about 60C.  It starts to hesitate, tranny shifts way late (it's scary if you're on the freeway and can't keep speed!) but then when the temp gets up to 80C (running temp) the power comes back and shifting is normal.  Car is completely fine until it cools off.

  I changed the fuel pressure regulator, had my fuel filters changed at the pumps about a year ago, tranny service a couple of years ago, changed plugs, rotor and dist cap last year.

  Any suggestions?  It seems like some temperature sensor that's flaking out......

  Thanks.

  -m

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