S54 start problem

[João Silva]

Hi

I have strange starting problem BMW S54. 

Some times when craking wont start ( I notice when hot is worst), when the no start situation appends the engine start back fire in the exhaust. Stop craking try again without recicle ignition start right. Some times start first try.

First I suspect the crank sensor, replace whit oem part, no result. I try see trigger error when the problem occurs, in real time I not see noting, only when stop craking appears 2 trigger errors.        

 

Best regards

João Silva

[Adamw]

Please do a triggerscope capture when cranking and attach here.  

[João Silva]

Hi Adam

Thanks the replay. Another thing i dont know if help, this engine have NGK red cop coils

TriggerScopeLog.llgx

[João Silva]

Hi Adam

Do have some time analyse then scope.

Best regards

João Silva

[Adamw]

Yes, the problem is you have trigger 2 connected to the intake cam which has 6 evenly spaced teeth, so there is no unique event for the ecu to synchronise from.  

You need to instead connect the exhaust cam sensor to trigger 2, this has 6 short teeth and 1 long tooth so it has a unique pattern that the ecu can use to identify engine phase.  

The inlet cam can be moved to DI1-4.

[João Silva]

Thanks Adam

Is possible use only cam trigger? I ask because the engine not have wire in the exhaust cam sensor , someone cut the wire.

Best regards

João Silva  

[Adamw]

Do you mean crank trigger only?  If it still has ITB's then you could possibly connect the MAP sensor to cyl 1 intake port and use the MAP sync function instead of cam sync.  If it is single throttle that wont be possible.  

[João Silva]

Use the crank trigger and the cam trigger. If not possible I connect the exhaust cam sensor 

[João Silva]

I think understand. In my head the system function like this:

I have the S54 programmed in the ecu, the ecu fallow the oem trigger pattern in all engine, too synchronize the sequential injections and the cop the exhaust  position is need. The intel cam sensor is necessary only for the ecu know the cam real position to compare in the vvt target map, the exhaust cam sensor is need for the engine synchronization and if the vvt in cam is used also too confirm the vvt position.

My idea is correct?          

[Adamw]

A 4 stroke engine cycle is 720degrees (2 crankshaft revolutions), the crank wheel has missing teeth that occur every 360degrees, so if we look at the crank wheel only there is no unique event that the ecu can use to determine if the crankshaft is on its first 360deg revolution or 2nd 360deg revolution.  The same applies to  the intake cam - it has 6 teeth, 1 every 120degrees and all teeth are the same size, so again there is no unique pattern to identify position, the signal received at the ecu will look exactly the same on the first 360 crank revolution as the 2nd 360 revolution.  

The exhaust cam on the other hand has 6 short teeth and 1 long tooth, the ecu will receive 3 cam edges on the first crank revolution and 4 cam edges on the other, so with this information it can determine its position within the 720deg otto cycle.

For sequential operation, an ecu needs as a minimum: a crank position signal, and a cam signal with some unique event or other asymetrical pattern that repeats only once per cam rev.  

If you cant connect the exhaust cam signal to the ecu, then you could possibly swap the exhaust cam wheel to the intake cam (im not sure if they are mechanically interchangeable) or you could modify the intake cam wheel - for example cut 1 tooth off.