Volkswagen Jetta/Bora
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Hard start when cold

  #1  
Old 03-17-2015, 08:56 PM
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Default Hard start when cold

Jetta GLS. 2.0 Ltr. Engine code Bev. Gasoline engine. Replaced the fuel pump, fuel filter (W/ pressure regulator), ignition coil, wires, plugs. Same thing. Starts very hard when cold and it sits overnight. Needs to be turned over, key on off, multiple times before it will start. Runs and starts fine throughout the day, once started. Anything else I can check ? Loss of fuel pressure over night at the fuel rail. ( Connected to the Schrader valve ) Is there a certain amount of fuel pressure that needs to be maintained at the fuel rail for the engine to start? Or is cycling the fuel pump enough pressure. Leak down pressure is solid 50 PSI after 2 hrs. Thanks for the help.
 
  #2  
Old 03-25-2015, 05:48 PM
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In case anyone is interested I figured it out. Bad coolant temp sensor. On a cold start, (open loop) the PCM ignores the oxygen sensors and uses ECT, TPS, MAF, MAP, IAT, & BARO if it has one, for fuel mixture control. Once the oxygen sensors warm up and coolant has risen a certain amount, the PCM switches to closed loop and uses the oxygen sensors for fuel mixture control. Makes perfect sense that a mis-calibrated or faulty ECT would cause cold start issues.
 
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