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Post by snoopy11 on Apr 21, 2016 17:56:10 GMT
Ideas please.
Mrs Snoopy has a 2006 BMW 3 series euro box as a daily driver. It seems to have developed an intermitant starting problem.
99% of the time you press the starter and it goes.
Occasionaly you press the starter and it turns the engine but does not fire. If you wait 40 minutes and try again it generally starts as normal.
Any ideas what what this might be would be apreaciated as its confused me.
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Post by Penguin45 on Apr 21, 2016 23:29:11 GMT
Turning and nothing at all? Air, fuel, spark is the standard set of requirements, although these ghastly modern things have sensors and computers all over the place. No flashing lights, error codes?
Chris.
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Post by dave1800 on Apr 22, 2016 8:22:43 GMT
When it turns the engine over but doesn't start, does the rev counter move? If it doesn't then you need to check the crank sensor and its wiring. Look for any physical damage - the gap between the sensor and the crankshaft actuator is only a couple of mm in some cars. It could also be a stuck fuel pump, try hitting the fuel tank while it's cranking and do the same to the fuel pump relay. After that it's a process of elimination to see whether there is fuel pressure and ignition. Another common cause can be the alarm system.
Good luck
David
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Post by snoopy11 on May 5, 2016 18:18:47 GMT
It's done it again today. Unfortunately Mrs S was half way to work and 50 miles from where I was.
The only option was to call the man who drives the big orange tool box who on arrival plugged in his diagnostic computer and proudly declared that the water temperature sensor had a fault. It seems that the ecu thought that the car was overheating and was shutting off the fuel. I would never have found that. New one going in tomorrow.
As as a temporary fix it seems that the ecu can be fooled on start up by flooring the accelerator and then pressing start.
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Post by dave1800 on May 6, 2016 0:46:05 GMT
You can buy a blue tooth OBD2 plug on Ebay for around £10 and download a free program such as Torque to an Android mobile/ Pad (probably Apple as well?)and this will show many of the fault codes. Quite easy to use, plenty of Youtube examples to get you going. I'm surprised the check engine light was not on as most systems check for inconsistencies between sensors. The wonders of modern car electronics! Good to hear it is sorted David It's done it again today. Unfortunately Mrs S was half way to work and 50 miles from where I was. The only option was to call the man who drives the big orange tool box who on arrival plugged in his diagnostic computer and proudly declared that the water temperature sensor had a fault. It seems that the ecu thought that the car was overheating and was shutting off the fuel. I would never have found that. New one going in tomorrow. As as a temporary fix it seems that the ecu can be fooled on start up by flooring the accelerator and then pressing start. |
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Post by dave1800 on May 8, 2016 1:06:25 GMT
A few further comments. On a number of vehicles (I believe including BMW) flooring the throttle while starting actually turns off the injectors. It can be used to clear flooding as indeed it's a useful strategy with many carbs. It is a technique also used in diagnostics carrying out ignition checks instead of unplugging the injectors which can be difficult especially on the rear ones on transverse V engines (mainly US etc). If an engine does not fire, the fuel pump is automatically disconnected after a short time to prevent flooding. However if you try and start the car several times in a row or turn the ignition on and off which primes the fuel pump it is possible to create a fuel lock in a cylinder which could bend a rod. It's also not good for the cat so be warned.  While I cannot comment on the diagnosis you have been given, something doesn't add up, but there again that's the mysterious world of modern car electronics where every model seems to be different. An out of range temperature sensor would in theory either give too rich a mixture if it thought it was colder than it waa or too weak if hotter. Too far out of range should put the car in the "limp home" mode ignoring the sensor and activating the check engine light. It would be interesting to hear the outcome. regards David |
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