1999 Subaru WRX


Nick Maple

January, 24, 2010 AT 4:10 PM

Electrical problem
1999 Subaru WRX 4 cyl All Wheel Drive Manual

Is the ignition module and engine computer the same unit on DIS systems?

How often does the ecm reads the input from the CKP sensor and (CMP) sensor?

Another question, Once the ECM knows what stroke and (TDC) cylinder #1 is on from the 2 sensors, the ECM automatically does a sequence? Theres no sensors monitoring any of the other cylinders to know what there (TDC) and to know there stroke. Is the ECM already programed to fire automatically in a certain order, once it knows the number 1 cylinders position?


4 Answers



January, 25, 2010 AT 2:43 PM

According to my software the Ignition control is integrated into the ECM. The wheel that the crank sensor reads off has a specific number of teeth, with a larger space to determine #1 with. After the CKP sees the reference point (#1) it knows through programming that the next spaces signify specific cylinder TDC's. It determines misfires when it takes longer for the next reference spot to arrive at the sensor. The timing isnt necessarily controlled per cylinder. The cam and crank sensors are constant input, they never stop reading the data from them


Nick Maple

January, 27, 2010 AT 1:09 PM

Are crankshaft reluctor wheels and trigger wheels the same??

when i search for crankshaft reluctor wheels and trigger wheels these two seem to always come up.


in picture # 2, i see the reference point the missing tooth,so that indicates "TDC"..........but for picture #1 how does it read cylinder # 1 when its a "TDC? i dont see any missing tooth on the wheel, or maybe it's just a wrong wheel they posted on "Google"??



January, 27, 2010 AT 3:17 PM

The pic is kind of fuzzy, bu tif you look at the teeth on #1 they are combinations of long/short teeth. So when the PCMi sprogrammed, it may see that 2 long then 2 short indicate #1 for a specific cylinder. Some even use cam sensors in conjunction with crank to find #1. Some meanufacturers do it different than others.


Nick Maple

January, 27, 2010 AT 4:17 PM

The teeth's are definitely different. what the purpose for this........does it identify each individual cylinder at "TDC"?

Is this the type of reluctor wheel that is comprised of four 90 degree segments. Each segment represents a pair of cylinders at TDC. This pic is from a "GMC" i'm thinkin 8 cylinder.


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