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when my car's engine is cold, it turning on immediately. But when it is warm an turn it off, then after 20 or 30 minutes need long start for turning on. where is problem? my car is peugeot 405 made in 2001 with magnet mailer ecu. I replace the rpm sensor but nothing changed.

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    We need more information to be able to answer this - what car is it, what year, which engine does it have. – Nick C Mar 21 '17 at 13:51
  • Welcome to mechanics.SE! We're glad to see you here. This problem is rather broad: what have you tried and what tests have you done? – anonymous2 Mar 21 '17 at 13:51
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It sounds like the car is unable to maintain sufficient pressure in the fuel rail.

Have a look at this answer for more details on potential causes for hot start problems.

The reason why this happens only for hot starts is because the fuel is more likely to vaporize as temperature increases. In order to avoid vaporization problems the fuel lines are expected to be pressurized during a hot start.

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    Also check the fuel line itself. If it is too near a hot spot and lost some sort of shielding, when you turn the engine off, no more fuel is flowing and the heat could cause the fuel in the line to bubble kind of like a vapor lock. You will have to crank until the bubble clears. – Blackbeagle Mar 22 '17 at 21:13
  • May be due to fuel pressure sensor malfunction? – M.K. Dadsetani Apr 4 '17 at 7:06
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The rpm sensor was a good candidate.

I would consider the following tests:

  • Start it warm with opened fuel filler flap.
  • Clean the contacts of every temperature sensor and the crankshaft position sensor (Plugging them out and in several times).
  • Does the exhaust fume smells like petrol? (Attention: Health hazard!).
  • Spray start-pilot while starting the engine. Does the engine start?
  • Are the spark plugs wet afterwards? Could you post photos of your spark plugs?
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There is not enough information as others have indicated, however, the most likely cause is that the vehicle has a bad sensor that is telling the computer that the engine is warm when it is not so it doesn't enrich the mixture sufficiently. No choke is used on these cars.

If the car is real old '70s or before, the mechanical choke would cause this type of problem because it would stay hot while the engine needed more choking to start. Or the choke would stick. This is for info only - this vehicle is a 2001.

  • Bad sensor, or some vehicles need to have the ecu updated to resolve this problem. – Solar Mike Mar 21 '17 at 14:51
  • Yes, to ECU possibility. Blackbeagle and Zaid suggested that fuel will be vaporizing and/or vapor locking. The temperature should be lower than that by 20 - 30 minutes. Also if the OP tests by turning the key on, then off then on again and attempting to start, the engine should start immediately if low pressure is the problem, but has not experienced any run-time issues. The most likely is that the temperature is being read incorrectly and the fuel mixture is too lean. I don't see how the RPM sensor would have any effect either. – JDubya Mar 23 '17 at 4:34

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