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Starting problems when warm | AUDI
Hello, I hope someone can help me. The problem is the following: As soon as it is above approx. 23 degrees Celsius outside and the car is driven and then stands for longer than 15 minutes, it hardly starts the next time, unless you accelerate, then it starts sometime. But then it runs completely normally. If it is cooler outside, the problem does not occur, no matter how long you drive or stand. The following has already been replaced/checked: Fuel pressure regulator, fuel pressure, fuel pump, crankshaft sensor, camshaft sensors, temperature sensor, fuel tank vent valve. Hope for help! Thank you!
Engine code: AQJ
Transmission code: EFN
Fault memory empty
AUDI
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Comments (14)
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Hans P. Audi has a dual temperature sensor for the coolant.... One sensor is for the display and one sensor is for the ECU. Check with VCDS or similar to see if the values are identical. The sensor often fails and can cause such a problem...
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Roland L. Hello. The sensor is new and the values read out are correct
Franz K. The first thing that comes to my mind is vapor lock. I believe that happens when the fuel check valve is defective. But unfortunately, I don't know where it's installed on your car. 🤔
Hans P. I missed the sensor in your post above... Sorry!
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Roland L. We suspected that too, so we installed an external check valve in the line, but unfortunately that didn't help.
Frank M. Have the fuel injectors and return flow rate been checked?
Roland L. No, that hasn't been checked yet, but it shouldn't be temperature-dependent, as it otherwise runs absolutely smoothly and starts great, unless it's over about 23 degrees Celsius.
Alexander W. Does it really have something to do with the outside temperature or does the problem also exist when the engine is warm? You should visualise the camshaft and crankshaft signals on an oscilloscope when the fault occurs, you may find dropouts there. Is the fault memory empty? Has the sensor wiring been checked under load and is it OK?
Roland L. Yes, it really depends on the outside temperature. If it's cool outside, there's no problem, no matter how warm the engine is. The crankshaft sensor has also been renewed. The wiring looks okay so far, and wiggling the cables/connectors during the starting process didn't change anything. The error memory is empty. Unfortunately, an oscilloscope is not available, but I'll see if I can find one.
Hans P. Was the outside temperature sensor also replaced?
Roland L. No, I didn't replace it, but it seems to be showing the correct temperature. But it doesn't interfere with the mixture preparation/engine management, does it?
Konstantin L. Several things come to mind immediately, depending on what he has installed.
Altimeter, intake air temperature sensor (air mass meter can contain both)
Engine control unit (cold solder joint)
Those are the things I would check next.
Frank M. Can any decent workshop show testers...
It was the fuel tank vent valve. I don't quite understand how it was related to the problem, but we replaced the valve and the problem has been resolved since then.