Holley COMMANDER 950 - Manual (Page 71)

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Engine Hesitates When the Throttle is Applied
The following tuning will help alleviate hesitation when the throttle is applied. The flowchart (Figure 21) shows a graphical
representation.
- Injection volume map not correct. When the throttle is applied to accelerate, the area on the injection volume map that
the ECU reads from changes (rpm and load increases). If the next area on the injection volume map that the ECU reads
from is lean, a stumble will occur, even if there is a lot of acceleration enrichment.
The fix is to make sure that precise steady state mapping is performed at all points before transitional fueling and
mapping is tuned.
- If steady state mapping is done, and there is a hesitation when the throttle is applied, than the “acceleration enrichment”
under the “Fuel” column must be tuned. If there is a hesitation under a heavy load, increase the “Rate of Change of Map
Sensor”. If the hesitation occurs when the engine is in neutral, increase the “Rate of Change of TPS”. Use a combination
of the two for final tuning. The left portion of these tables are for slow changes in the TPS and the MAP sensors. The
right portion of these tables is for fast changes in the TPS or MAP sensors.
The fix is to increase the Acceleration Enrichment Tables.
- Increasing or decreasing the timing can affect acceleration. Increase or decrease the timing at different points and feel
the difference.
The fix is to modify the “Main Spark Map”
Cold Start Performance
The following is tuning help for when the engine is cold. The following flowchart (Figure 55) provides a simple graphical
representation.
Engine Runs Rough When Cold
The following will help cold engine startup.
- If the engine runs poorly when it is cold, the problem could be that the base injection volume map is too lean. Before
performing cold start tuning, make sure that the base fuel map is thoroughly tuned to be slightly rich of stoichiometric.
The fix is to tune the base fuel map after the engine is at operating temperature.
- After the base fuel map is tuned at operating temperature, if poor cold performance occurs, the coolant temperature
enrichment most likely needs modifications. This can be tuned while the engine is running until it operates smoothly.
The fix is to add or subtract coolant temperature enrichment while the engine is running until it runs properly
Engine Stalls Immediately After Startup
The following will help with problems after the vehicle is immediately started.
- If the engine stalls after it is started, the problem could be that the base fuel map is lean and/or the cold temperature
enrichment is lean.
The fix is to properly map the base fuel map and the cold start enrichment.
- If the base fuel map is correct, and cold temperature enrichment is correct and the engine still stalls after startup, the
most likely reason for this is that the afterstart enrichment is too low at the problematic temperature.
The fix is to increase the afterstart enrichment until the engine will remain running after startup.
- If the engine seems to struggle for air after startup, the “IAC Parked Position” most likely needs to be increased.
The fix is to increase the “IAC Parked Position”