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Matt
Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 21599
Experience:  BEng hons Mech engineering, in auto industry 22 years
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i have a bmw 323i automatic which will not start it was fine

Customer Question

i have a bmw 323i automatic which will not start it was fine one day then the next day would not start I have replaced the crank and cam censors and have spark to the plugs can anyone help?
Submitted: 2 years ago.
Category: BMW
Expert:  Matt replied 2 years ago.
Hello

you say you've checked for spark ? can you tell me if you have spark or not?

If there is a spark and its still not starting then its likely that the ECU isn't opening the fuel injectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.

If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If you remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly

If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.

You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are opening then there’s a problem with the pump or the filter or even the pressure regulator


Could also be incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will never add the 'cold start' extra fuel required if the car starts OK when warm then I 'd look into changing the sensor.

Customer: replied 2 years ago.

Matt

Have spark to plugs. removed the ecu to check for obvious damage etc but all looked fine just have to wait for the "assistant" to turn up lol

Expert:  Matt replied 2 years ago.
Hello

if you have a multimeter then try measuring for 12V at the ECU fuse in the engine bay fusebox
Expert:  Matt replied 2 years ago.

hi

do you still need help with this?

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