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  #1  
Old 02-04-20
arrow arrow is offline
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Default Cam sensor vs. crank angle sensor

OK, keep in mind I'm a layman ...............................

On a 6G74 engine, are the "cam sensor" and the "crank angle sensor" one and the same?

If not, a short description of the purpose of each would be appreciated.

Thanks.
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Old 02-04-20
erad erad is offline
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As far as I could see, the sensors were the same, but the leads and plugs were different in colour and length so that you could not confuse where to connect them. The crank angle sensor is used to determine the ignition advance. I never could understand what the cam angel sensor did, other than confirm that the camshaft was still rotating (ie the timing belt was not broken)..
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Old 02-04-20
Kingbrown Kingbrown is offline
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Quote:
Originally Posted by erad View Post
As far as I could see, the sensors were the same, but the leads and plugs were different in colour and length so that you could not confuse where to connect them. The crank angle sensor is used to determine the ignition advance. I never could understand what the cam angel sensor did, other than confirm that the camshaft was still rotating (ie the timing belt was not broken)..

My thought is that a four stroke engine has two rotations of the crank for only one rotation of a camshaft.
Without a cam sensor you wouldn't be able to establish whether you were at tdc on any cylinder's power stroke or its induction stroke.
Happy to be corrected.
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Old 02-04-20
disco stu disco stu is offline
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That was my conclusion as well. To me that made the cam sensor redundant as the ecu would know what the crank is doing based on the cam sensor.
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Old 02-04-20
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Kingbrown: I think that you are right. It must sense the one time when the Cam sensor picks up a signal saying No 1 cylinder is ready to fire and the crank sensor tells it when it is at TDC etc to fire the spark plug. Often I wish for the old days of a distributor and points - no electronics at all.
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Old 06-04-20
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Thanks for the replies which resolve my confusion and lack of understanding. Cheers ��
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Old 06-04-20
disco stu disco stu is offline
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Just realised I made a typo above. I meant to say crank sensor redundant, as the cam sensor would relay info on both
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Old 07-04-20
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Stu:
I think that the crank angle sensor is required because the exact crank angle position is required to get the spark at the correct time. The timing chain is tensioned by the tensioner and this means that the valves may be a little off position, but that doesn't really matter - all it needs to know is that it is either No 1 or No 4 cylinder at firing position TDC. In fact even this is irrelevant because No 1 and No 4 cylinders both spark at the same time anyway.
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Old 07-04-20
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Are no. 1 and no. 4 both are tdc at the same time, but on opposite parts of the cycle?

Good point that you have made. I was starting to think it doesn't matter, but it still needs to know fuel delivery times
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Old 07-04-20
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The firing order is 1, 2, 3, 4, 5, and 6. Thus 1 and 4 fire together - there are 2 HT wires in each coil. so 1 and 4 fire together, 2 and 5 , and 3 and 6 fire together. This is where I got stuffed up on my wiring after replacing the HT leads- I saw a number about 80 mm behind the coils, something like 251436, which I assumed was a a part number, but my wife eventually asked if the numbers had anything to do with the car not running. OOPS! I think she has forgottten it now, but I dare not raise it again.....
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