Mercedes: 1989 Mercedes 420SEL, mercedes 420sel, mercedes benz 420sel

Question
San Francisco, CA.  Thanks so much, I'll pass this on to my mechanic. He's working hard on diagnosing and is concerned about buying parts he can't return if need be.  He was happy to have some input.  Karen
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Followup To

Question -
My 1989 Mercedes 420 sel (120k miles) won't start after I've taken it on a couple of short errands and has stalled out in traffic.  It sometimes starts after 20 minutes.  Mechanic says when it doesn't start, it's not sparking.  It feels like it's about to turn over when you start it, but fails.  Mechanic has ruled out fuel system and is looking at ignition system.  The car has a new distributor cap, new spark plugs, new fuel relay.  Any ideas?  Thanks.

Answer -
Where are you?

Chassis W126.035
Engine M116.965 V8
Model 420SEL
Years 1986-91

Best guess, without hands on.

Crank position Reference Sensor feeds signal through the Overload Relay = if the relay is marginal you have issues.
Replace both ten AMP fuses in the Overload Relay with new.

Picture of Overload Relay
http://catalog.eautopartscatalog.com/mercedesshop/sophio/image.jsp?title=Overloa

Ignition Coil weak, old, failing.
Ignition Control Unit seal breached = internal corrosion.
Alternator voltage spiking, weak, old, failing.
Reference Sensor signal weak, old, failing.
Overload Relay weak, old, failing.
EGR Valve leaking.
Catalytic Converter plugged and/or failing.


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1989 Mercedes Benz 420SEL
Part: Reference Sensor
 Note:  Position
Located at front crank pulley.     
F6010-12104 Reference Sensor Beru IN STOCK $55.86  

F6010-12104 Reference Sensor IN STOCK $55.86  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=cata


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1989 Mercedes Benz 420SEL
Part: Catalytic Converter
 Note:  50 States
After-market" OBD II Catalytic Converters Not Legal for Sale in California 1995 On!     

H3000-74199 Catalytic Converter Federal Only A & B Auto Parts IN STOCK $568.80  
  
H3000-49563 Catalytic Converter Federal Only Bosal IN STOCK $532.33  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=cata

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1989 Mercedes Benz 420SEL
Part: Ignition Coil
F3000-34902 Ignition Coil Bosch IN STOCK $133.29  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1989 Mercedes Benz 420SEL
Part: Overload Relay
 Note:  
Aluminum cover with bracket : contains (2) 10 amp ATC fuses on top .     
 Year: 1988-
P2056-18126 Overload Relay Germany IN STOCK $74.77  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc

Answer
Hello Karen
The thought of a domestic mechanic trying to repair your car is frightening, and costly.
Here are alternative MB mechanics in your area.

You might try this fellow, he is a mobile MB master technician.
http://www.theworkshopmercedesbenz.com/Coverage-Area.htm

Mechanic in San Francisco, CA
http://www.mercedesshop.com/shopforum/showthread.php?t=149335