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[ziadalmahmoud]

hey guys,

a few questions came to my mind while coming back from work..

when starting the engine, if the crank sensor isnt working, i would assume that the engine wont fire.. but would the ECU still give signal to injectors to inject fuel?
in this case would continous cranking with no firing flood the engine?

Incase of a faulty crank sensor, if the sensor gives a signal in the wrong time, and the firing happens in the wrong time, would the engine start (maybe lumpy)? and would the ecu recorrect the timing automatically?

any thoughts?

[ians]

I think faulty crank sensor is most likely to cause the ECU not to fire.

Is this a hypothetical question or do you have a real problem?  If so what are the symptoms?

[ziadalmahmoud]

yeah i would expect the ecu not to fire, but im just wondering if the ecu would still inject fuel in the engine.

read somewhere that ecu usually fires when it reads the first crank sensor signal that follows the cam sensor signal. thats when the ecu knows that the engine is in TDC. so im thinking if the sensor gives a wrong signal, it might start the sequence of firing in the wrong time, hence starting lumpy. but is there some auto correction done by ecu after starting?

my question is based on an intermittent problem that ive been facing.
some 6 months ago, car had some hard starting problem, both when cold and hot. it was intermittent, sometimes the car would start normal, and sometime i would need to crank it some 6-7 times for it to start, and once it does it starts lumpy with plenty of black smoke for around 15 seconds, then the engine slowly goes back to its normal tone. problem was only starting.
Took the car to mechanic, he advised that injectors are leaking, and when car is off for some time, the engine would get flooded and choke at starting. So he replaced the set of injectors with used ones. After that the car never had a single starting problem until 5 months later (last week), thats when the same problem started to appear again. Intermittent. When cranking, it cranks with some random firing in the first couple of seconds, then it starts to fire continous, then when i release the starter, it dies (unless i give it gas, and thats when it starts lumpy with black smoke for 10-15 seconds then clears).

few days back, car had this problem, yesterday and today it started as if nothing is wrong with it. already got a new crank sensor and old injectors are under cleaning and testing. tomorrow will be replaced.