Mercedes Benz repair: Car cuts off after warm up, mercedes benz 420sel, fuel injection cleaner

Question
1987 Mercedes 420 SEL , 137K miles , just ran to Florida from NYC no problems ! On the return trip I poured in some fuel injection cleaner and octane booster! The day after arriving in NYC I went to visit a friend and left the car running , and when I got back to the car it shut off. It did not initially start up , but it turned over strongly , and after a few minutes it started up. It's been 2 months and this is occurring more and more, last night the car started and shut down 3 times in a row then it was fine again. I was considering changing the fuel pumps but I was wondering if this is a common problem with this make and model . Any advice is greatly appreciated.(I had the car tuned up and she runs great when she runs but.I explained the problem to the mechanic but he cannot diagnose the problem if the car is running.)

Answer
Here are the most likely issues.
I can not guess further without hands on.


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 420SEL
Part: Overload Relay
P2056-18124 Overload Relay IN STOCK $67.52  
  
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PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 420SEL
Part: Fuel Pump Relay
 Note:  Ten pin
 Year: -1989
P2037-34502 Fuel Pump Relay IN STOCK $144.40  

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Vehicle: 1987 Mercedes Benz 420SEL
Part: Reference Sensor
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   Reference Sensor
RPM
Located at flywheel.
Position Sender Unit
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   Reference Sensor
Position
Located at front crank pulley.  

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PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 420SEL
Part: Fuel Pump
 Note:  2 per car
E3000-95321 Fuel Pump Bosch IN STOCK $260.68  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc...


Vehicle: 1987 Mercedes Benz 420SEL
Part: Fuel Filter
Select one of the products from below  
 Image   Product   Fits
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   Fuel Filter
Optional 002 477 13 01 can still be used on early models with single fuel pump. New filter 002 477 44 01 is designed for tandem pumps where greater volume and dampening effect is needed.      
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   Fuel Filter
Optional with 002 477 17 01 .  

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PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 420SEL
Part: Voltage Regulator
 
F4010-39368 Voltage Regulator Bosch IN STOCK $33.26  
 
F4010-108169 Voltage Regulator Germany IN STOCK $24.68  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc...