Mustang and Ford Performance Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter · #1 · (Edited)
Idle tuning help Vortech SC / Comp Cams XE270

I need some help with dialing in my idle tune. The setup is fairly common. Vortech supercharged with Comp Cams XE270 cams.

The engine will idle fine once idling, but the transition to idle is the problem.
When coming to a stop the idle will drop to 900-1000 and hang for a second or two, then it suddenly will drop and almost stall before catching itself and jumping backup up.
It will continue this a few times, then the idle will "lock in". It is like the idle catches and it is rock solid.
If I datalog it I can see the rpm oscillate in a perfect sine wave.

The IAC duty cycle is between .20 and .30.

The IAC Intergrator is nominal.
The timing clip is set to 0.
I've increased the dashpot predisposition and decresed decay at lower air flows. I've done about 10-15% each.

I'm curious if anyone else has this setup and what their predisposition and dashpot settings are?

Does anyone have any suggestions how to cure the hunting idle?
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #2 ·
Fixed. Just to close the loop on this and provide the information on what worked for me.
1. Put the throttle stop at the factory location. I've heard others say they adjusted the stop to give them 20%-30% duty cycle. I put it back to the factory setting and let the IAC duty cycle fall where it may. Dashpot and other factors are based off a factory default throttle opening and increasing the amount of air throws the them way off. And yes I know about the amount of air around the TB setting in the software.
2. MBT/Max Allowed Spark table. Change the lowest column for spark to below the expected idle speed. I changed mine from 900rpm to 700rpm. I idle at 800rpm. Add 5-10 degrees to the lowest idle rpm and load. So I increased spark at 700 rpm at .10 and .20 load. Increasing the spark increases torque and naturally causes the engine to push idle up when rpm drops instead of dropping off and stalling.
3. Set the idle spark to 0-5 and the gain to .5. If the gain is too low the spark will not "catch" the engine as it returns to idle, to much and it will hunt.

Hopefully this helps someone. Right now the car idles (bumps) at 800 rpm and more importantly settles to idle without stalling.
 

·
Administrator
Joined
·
9,417 Posts
Nice detective work there Bullitt!

Good to see a happy ending.


Ed
 
1 - 3 of 3 Posts
Top