Holley COMMANDER 950 - Manual (Page 42)

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Also make sure you listen for engine knock, especially in the peak torque area when you are changing timing.
If you drag race, sometimes putting in more timing in the map area where you stage and launch will help 60 foot times.
Usually, there is little to be gained with a few extra degrees of timing at WOT, so be somewhat conservative or you may
damage your engine.
A knock sensor is not designed so that you can run a lot of timing and let the knock sensor “pull it back to the best
timing”. All that will happen is that it will pull a lot of timing out and the engine will run worse than if you had the correct,
safe advance curve. Do not rely on it for performance. In applications such a towing, they are good to have if you get a
bad tank of fuel and are driving in mountainous conditions.
4. Idle Fine Tuning - The next area that will be addressed is fine tuning the idle. Getting a very smooth idle is sometimes
one of the most difficult things. The following tips should be helpful:
A. One of the best features of the Commander 950 for stabilizing idle is called “Idle Spark Control”. This is only used if
you have computer-controlled timing. Idle spark control is a feature in the ECU that will quickly raise and lower the
ignition timing automatically to stabilize the idle. If the idle moves higher than desired, the ECU will pull some
advance out to bring it down. If it goes lower than desired, it will raise the ignition timing.
1. To enable this feature, first go to the data monitor and turn the key on.
2. Note the position of the TPS and enter it here___________.
3. Next, go to “Spark” and “Idle Spark Control”. It asks for the Maximum TPS for idle.
4. Take your idle TPS value and ADD 5 to that value. For example if your idle TPS is 30, you would add 5 for a total
of 35.
5. Enter this value as the Maximum TPS for Idle. If this value is not more than 3-4 more than the real idle TPS
position, the idle spark control will not be activated.
6. Next, mouse click on the “Enable Idle Spark Control”. This will activate this feature. The idle spark “P” and “D”
terms relate to how fast the ECU changes the timing. These values are good for the vast majority of cases, so
don’t change them.
7. Next, start the engine. Look in the upper left corner of the fuel map. One of the features there says “Idle Spark
Active”. When it is active, it will be highlighted in red. This should occur at idle now. You can look at the spark
advance on the data monitor and see that the spark is changing quickly in small increments.
B. The next thing that greatly contributes to a smooth idle is having a fuel and spark map that is smooth in the area that
the engine idles. Note the map (Figure 23) above, the timing at idle is not flat. This causes the timing to fluctuate
and will make the engine surge. The spark map (Figure 24) below shows poor mapping at idle. If the engine was to
idle at 850 rpm at 44 kPa, the timing could be jumping between 11, 19, and 27 between the speeds of 400 to 1000
rpm. The area at which an engine idles should have a relatively flat timing area. It is fine to add advance as the rpm
increases, but when an engine is idling, the timing should not vary due to the map.
A similar rule applies to the fuel map. When the engine is idling, look at the data monitor at the Injector Pulsewidth
(Inj PW). It should not be changing much more than .1 - .2 milliseconds when the engine is idling. If it is, and the
engine idle is not smooth, then the fuel map is probably not smooth enough. Try to smooth it so the pulsewidth does
not fluctuate much. The following fuel graph (Figure 25) shows poor tuning at idle, which will cause the engine to
surge.