[W126 Coupe] Help trouble shooting 87 560SEC hesitation at take off problem.

[Day . Ralph]

I had acceleration problems with both my 500SEC and 560SEC, especially when cold.  The car would seem to almost stall and lurch until it warmed up.  The other similar issue I had was just a plane lack of acceleration at anytime.  I replace the kick down module and that worked on the just plain bad acceleration but did nothing for the hesitation when cold.  Never could figure out the hesitation on either car, so now I have a CL55.

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 alal30319 at gmail.com
Sent: Monday, November 02, 2009 11:24 AM
To: Mercedes Coupes Mailing Lists
Subject: [W126 Coupe] Help trouble shooting 87 560SEC hesitation at take off problem.

All

I've been trying to trouble shoot my 1987 560SEC as it's having an odd hesitation issue between 600 rpm and 1200 rpm. It's pretty severe and makes crossing intersections hairy as the engine can choke out for a few seconds before it spins the wheels and hauls away. I've been trying to counter by keeping my left foot on the brake while revving the car so that I can avoid the hesitation.

Here is what I have done so far in an effort to trouble shoot the system.

 1.  Checked timing. Set to 27 degrees advance at idle (10xx rpm).
 2.  Checked sanity and make sure that I was on cylinder number 1 and that my timing light was working correctly.
 3.  Replaced black electronic device on the side of the fuel distributor with another one - no effect.
 4.  Pulled valve covers to check cam timing mark and both appeared within spec (chain will need to be replaced soon however as guide rails are black).
 5.  Checked throttle plate on air flow meter was in the right position and not too high, thus causing the flow of air to block when pressing on the gas - everything seems OK here.
 6.  Checked to see if the transmission was recently removed as this may mean the flywheel was incorrectly mounted - Transmission does not appear to be disturbed.
 7.  Switched ICU with a known good one - still have the same symptoms.
 8.  Replaced Bosch twin platinum plugs with NGK BP7ES - Did not cure the problem.
 9.  Adjusted mixture - No effect.
The car still has the green wire to the ignition unit which I understand must be old as new ones are black and can cause running issues so i'm going to try to replace that next.

Any other thoughts or insight would be gratefully appreciated.

With best regards

Al

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