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Discussion Starter · #1 · (Edited)
MY 2003, 525i m sport wont start when it is warn. It was attended to by the AA who told me that the battery voltage is 12.5v which is considered good. He try to start the car but it would not start. However, when he attached a jumper cable to the battery pionts in
the engine bay the car start on the first turn of the key. He recommended changing the starter motor which I did but the problem continues (the car start first time when it is not warn and never cuts out, however if you turn the ignition off after it has been running for a while it will not start). All the electric work. The AA also provided me with two fault codes which are P0171 and P0174.

Can anybody provide me with some form of solution?
 

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These codes identify a lean condition. Check the battery terminals for being clean. Have the fuel pressure measured when the engine is running, and at temperature. You may have a failing fuel pump.
 

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My experience of cars not starting when warm (2 cars) has always been related to engine temp sensor. ECU gets the wrong temp, adjusts the mixture for the incorrect temp and the mixture is that far of it won't start. May also explain the lean fault codes you have.

The right diag tools/scanner should be able to check the temp sensor value and track how it changes with cold/hot engine. Temp sensor shouldn't be too expensive (even in UK) and fairly easy to change, so probably worth checking.
 

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A lean condition can be caused by a vacuum leak, MAF or a failing fuel pump. The former is far more common. A vacuum leak often results in starting or idle problems. our problem is only with a hot start because the computer commands the fuel injection to inject a richer mixture during a cold start, compensating for the lean condition. Under hot condition, the fuel mixture is too lean to ignite. If you are below 50% charge, you can begin to expect to see starting problems. You might get away with one of these issues but the combination may be causing your hot start problem.
 

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Discussion Starter · #8 ·
Guys I am not mechanically minded, I have always taken the car to the shop for it to be worked on, not that I have ever had any problems with it apart from changing altenator, brakes and servicing. However, given the financial crisis I decided to have a go myself. I have taking all your suggestions on board but what is not clear to me is why the car will only start with a jumper cable from the points in the engine bay even when it is hot. Clearly if this was a fuel pump issue it would not start any at all.
 

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That is correct. Your problem may not have anything to do with your fuel pump. Then again, it may. Do not expect to get a solution to every problem over the internet. While any internet diagnosis is somewhat of a guess, the battery certainly appears to be part of your problem, since jumping the car corrects the problem. It is clearly weak. Compound the battery weakness with a lean condition and that is why your car can only start with a jump when hot. While a lean condition can be caused by a failing fuel pump, it is NOT the only cause. That is why I suggest you investigate a vacuum leak, which is a much more common cause of the lean condition. Am I right? Who knows? :dunno: But at least this is a logical diagnosis based on the information provided. There could be another reason but this is a starting point for your troubleshooting. Good luck.

Please report back what you find.
 

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Discussion Starter · #10 ·
Guys thank you all for your support. The car is starting as and when I attempt to start it. I have not done anything to it but it is working prefectly again apart from the EML came up on the dash. Made appiontment with garage to service and inspect.
 
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