IDM Over-Clock



While working on a way to get the code out of the IDM i had a question. This question is, what happens to the IDM output when we change the crystal frequency? Initially i suspected that lowering the frequency would increase the allowable pulse width under high RPM. This speculation was based on a program model that used the timer as reference. Thus decreasing the frequency would increase the amount of time between events. Experimental data has proven that this is not the case. In fact lower frequencies seem to make the problem worse. With that data i then increased the clock frequency to find that it improved the pulse width by a small percentage.


As can been seen here the maximum frequency is 12mhz.



The table below gives the cut-out of a factory IDM running 8mhz and a modified IDM running at 10mhz. This data was extracted by running through various pulse-widths using the ecolyzer, a new program which was written to sniff these numbers out and 4 injectors. The data was exported as CSV and the imported into open office to perform the calculations. The spread sheet can be downloaded below.

RPM

8mhz cut-out

10mhz cut-out

Sig dev

PW diff

3000

4.21

4.37

3.66%

.16

3099.17

4.05

4.21

3.80%

.16

3199.66

3.9

4.06

3.94%

.16

3295.26

3.77

3.93

4.07%

.16

3396.74

3.62

3.78

4.23%

.16

3498.13

3.5

3.66

4.38%

.16

3598.85

3.38

3.54

4.52%

.16

3698.23

3.26

3.42

4.67%

.16

3795.55

3.16

3.32

4.82%

.16

3898.13

3.06

3.22

4.98%

.16

3997.87

2.96

3.12

5.13%

.16

4093.89

2.87

3.03

5.28%

.16

4194.63

2.78

2.94

5.43%

.16

4290.62

2.7

2.86

5.59%

.16

4391.1

2.62

2.78

5.75%

.16

4496.4

2.54

2.7

5.64%

.15

4595.59

2.47

2.62

5.79%

.15

4699.25

2.4

2.56

6.25%

.16

4795.4

2.34

2.5

6.41%

.16

4895.56

2.27

2.43

6.58%

.16

5000

2.22

2.38

6.73%

.16



As you can see from this table the 10mhz crystal adds roughly .16ms of pulse width regardless of RPM and PW. This suggests that the PW limiter is a state machine.

Here is an open office spread sheet with the above information. And Here is a PDF.




This modification is very easy. Simply locate the crystal (metal can) and replace it with a 10mhz version. I suspect that a 12mhz crystal will give .32ms increase but i have no experimental data to back this theory up.