Making cams idle properly

[XR7-4.6]

Ok guys I need serious spoon feeding, tuning has never been my strongsuit but I generally learn enough to be dangerous with some direction if it’s explained to me like I’m a toddler. I’ve been datalogging and “tuning”( guessing and checking) to tame this condition but this is the best I got it and it’s still taking manual intervention to keep it from stalling after a very mild rev. It actually idles pretty good once it’s stabilized and in my datalog of this event the ISC duty cycle hovered around .35-.38ish.

This makes me think I should be focusing on Dashpot but I’m having an extremely difficult understanding it even with SCTs help sections and forum input (which has become incredibly limited by SCTs nuking of the Pro racer forum, EECtuning being down and Decipha’s site/forum speaking a completely different language from SCT).

Anyway, you tell me, in this vid I saved it from stalling every time it dipped to near 500rpm and at some point you can see how it stabilizes to the commanded 750 rpm. Even just a hint on what to log and what to mess with and what not to mess with in PRP would be helpful. Right now I’m in over my head

 

[theterminator93]

Log ISC_Integrator. It will tell you how much to add/remove from your idle airflow table to help dial in the idle from the IAC perspective.

 

[XR7-4.6]

Log ISC_Integrator. It will tell you how much to add/remove from your idle airflow table to help dial in the idle from the IAC perspective.

Yep I missed that one! What's your thoughts on the Duty cycle though? I had been reading to shoot for like .15-.25 where mine at idle is pretty consistently at .38ish.

 

[Grog6]

A mechanical dashpot is a damper like a shock, but near the end of travel, the piston lands on a trapped air cushion, that leaks off slowly, letting the piston hit end of travel. You seem not to arrest the rate of drop, as rpm's bottom out.

 

[theterminator93]

What's your thoughts on the Duty cycle though? I had been reading to shoot for like .15-.25 where mine at idle is pretty consistently at .38ish.

I honestly hadn't read much about it. You could open up the throttle blades a tad if you want to lower it, but I'd probably leave it alone unless there are other symptoms after dialing in the idle airflow.

 

[XR7-4.6]

I honestly hadn't read much about it. You could open up the throttle blades a tad if you want to lower it, but I'd probably leave it alone unless there are other symptoms after dialing in the idle airflow.

The rationale as I understand it in lowering the duty cycle is the ISC is less likely to surge down to the point it stalls as seen after I rev it up and let the rpm’s fall, and this should be done beforehand. I did a quick log a few hours ago and while the integrator is definitely not on target it’s not quite as off, but the absolute lowest the duty cycle went was .37 with a high of .59(which was probably when it was warming up commanding a higher idle).



I’m supposed to apply the data from the integrator to the ISC neutral/drive idle air sections in PRP, correct?

A mechanical dashpot is a damper like a shock, but near the end of travel, the piston lands on a trapped air cushion, that leaks off slowly, letting the piston hit end of travel. You seem not to arrest the rate of drop, as rpm's bottom out.

I understand it’s function and it’s mechanical equivalent but not so much on the digital end of things.

 

[theterminator93]

Yeah, add or subtract the ISC integrator value from the airflow #/min in the corresponding cell of the idle air table.

I don't know if drive idle air means anything with a manual, I'd probably just modify both to be safe all the same.

Depending on how "radical" your cams are considered, it may be worth looking into a slightly higher idle RPM. Mine aren't particularly lopey but I settled on the idle at 800 (factory, ironically) after trying 700 and 750.

 

[Grog6]

isc duty cycle is the iac pwm duty cycle; it's not a stepper, but a solenoid. those dips are where it's almost dying.

 

[Zep5.0]

I second the higher idle rpm. That's even pretty standard with a carb setup and cams. Otherwise your fighting the overlap too much.

 

[XR7-4.6]

I’m certainly open to increasing the idle speed as a last resort but if not for the transitions it actually idles really happy at 750 with no surge unless it’s induced by me

 

[Zep5.0]

I mean, it's sounds pretty damn good most of the time...

 

[XR7-4.6]

I mean, it's sounds pretty damn good most of the time...

Here’s the actual video of the screenshot I took from it this morning. It maintains rpm pretty much as good as the old cams did on this motor. I even clicked on AC and it didn’t upset it.

We’ll see tomorrow, I’m created a tune with a static ISC table and ignition timing locked to 15° like a spout plug and will unplug the TPS to try to get the duty cycle down with the set screw, then tweak the integrator. Hopefully that helps, if not I’m moving on to dashpot after

 

[XR7-4.6]

So I got the integrator to .00, also clipped the lowest idle timing to 15°. Definite improvement, not yet a solution as it still overshoots when the revs fall but it stabilizes substantially better, I think I’m on the right track.

Might try upping the idle timing again to 20° and see what that alone does before I try getting that duty cycle down

 

[Wile E. Coyote]

Not as intricate as you are getting, but when I cammed the red car and ran into this issue all I did was set a higher target idle. Fixed it

 

[XR7-4.6]

Not as intricate as you are getting, but when I cammed the red car and ran into this issue all I did was set a higher target idle. Fixed it

Just for shits I upped my idle to 800 via the optional parameters I put in my Xcal and it does indeed not stall when I rev it and take my foot completely off the throttle… but only just, it still nosedives to like 600rpm first and then surges a few times to the 800rpm idle, so I don’t consider it so much as a solution as much as a band aid. I mean my rationale is if it can idle as stable as it does at 750 but get so upset at finding that idle in the transition the tune needs more work. I’d keep this as a temporary solution but to make it drivable enough to take it to a local dyno who can fix it for me

 

[Wile E. Coyote]

Just for shits I upped my idle to 800 via the optional parameters I put in my Xcal and it does indeed not stall when I rev it and take my foot completely off the throttle… but only just, it still nosedives to like 600rpm first and then surges a few times to the 800rpm idle, so I don’t consider it so much as a solution as much as a band aid. I mean my rationale is if it can idle as stable as it does at 750 but get so upset at finding that idle in the transition the tune needs more work. I’d keep this as a temporary solution but to make it drivable enough to take it to a local dyno who can fix it for me

Mine is set to 850. And yeah if I'm free reving while it's cold it'll do that too, but when it's warm it doesn't.

 

[XR7-4.6]

Much progress! Swapped the throttle screw for a bolt and a jam nut yesterday but and got to work on lowering the duty cycle using it. Got it down to .20-.25 which is right about in the sweet spot, may adjust further after I redo the idle air integrator which is now way off; but check this out drops right back to idle without any hind of stalling. Still surges up a bit after but I think that’s the integrator being off