First off a little bit of info. I do not have a stock truck cam. current cam is 208/216 .500/.500 113lsa. Startup idle, throttle response and no dying on hard stops was fine with just the cam swap. Next came a Whipple super charger which made a harder startup (hunting a lot for idle) but there were no additional symptoms after the SC and cam such as dying at hard stops.
Now, I designed and built an intercooler setup for my Whipple twin-screw SC. Startup is even worse as it will die on the first two startup tries before it even gets a chance to hunt big time for idle on the third try. Also, the most anoying part, the truck dies at stops. ***It only dies from first gear stops before it has a chance to shift into second gear. If I come to a hard stop when I had been running in second gear, it will not stall out and things are fine.

Here is what I have concluded and worked on:
Over the modification period of the truck, the intake air has had to take a longer and longer route before it finally gets into the intake manifold. i.e. through a SC now through a SC and intercooler and some plumbing to get to the intake manifold. To address the dying at stops situation, I adjusted the Airflow Decay in Drive table in LS1edit...to my suprise even at maximum input values the rpm's would still drop and the truck would eventually die--comming from a first gear stop only I next logged the IAC readings from a second gear stop that works just fine, versus coming to stops in a first gear scenario. The IAC counts are much higher in second gear and do not decay as nearly as quickly as a stop in first gear. My idea is that it is allowing more airflow through the IAC coming from a stop in second gear than compared to the amount of air the engine gets coming from a first gear stop.
I have tuned all of the Airflow tables in Edit with no luck. I am pretty sure I just need to keep the IAC open longer when stopping from first gear. I thought that is what the Airflow Decay in Drive table was for, but it did nothing -even with the maxed out values in the table Is drilling a hole in the throttle body the only way to cure this? Wouldn't drilling a hole have an effect of a higher idle as well though?

Any help is greatly appreciated as I am pretty stumpped here

 

ttt, need some help please

 

What are your IAC's at idle in park and at idle in gear? Also, is the throttle body dirt free? What is the idle engine speed? Grime buildup around the edges of the throttle blade and air bleed hole can cause similar issues that you are experiencing.
I don't know why, but trucks seem to require higher IAC values than cars. IAC values in park with air off should be around 50-60 counts.

Good luck,

Richard

 

The throttle body is absolutely spotless, as is the IAC sensor. I have idle set to 650rpm in drive for AC on and off and 675rpm in park for both AC on and off. My IAC in park with air off reads 51-54 -jumping between that range.

Before the motor dies, the IAC opens up more, but it is like it is never enough to keep the engine running. I have tried increasing the Airflow Decay in Drive table because this seems to fix the problems of this sort in LS1 motors, but it did nothing on my truck.
Is there a way to increase the IAC value when coming down from first gear to keep the engine from dying?
Thanks Richard
Ryan

 

Okay here is what it does. Notice just before the shift into second gear, I hit the brakes. At that point, the engine rpms fall and at the same time, the IAC rockets to 125 to try and save it. I think the IAC might be maxed out at this point and the engine is still not getting enough airflow. In this graph, green is engine RPM and blue is IAC

It does not do this behavior from a second gear stop because the IAC seems to hang at a high number for a much longer time rather than falling (like a first gear stop) and then maxing out in the open position to try and save the motor from a stall condition.

 

could you have an intake leak? (like in a hose going from the SC to the manifold)

i know my old car would die when i had a leak in one of the hoses (91 tsi awd)

 

those pics are kinda dark, and im not too familiar with what kind of bypass valve does the roots blower have built into it?

if it does not have one, you need to have a bypass across the intercooler when not in boost, (most likely a large race style) otherwise you will get pressure waves bouncing around, and cause drivability problemd, like the ones you are having.

please post some info on the TB/MAF placement, and bypass/blowoff valves on your setup, and i'll try to help.

Thanks

Ryan.

 

I have checked for leaks everywhere in the system, and there are none -no vacuum leaks.

The throttle body is on the intake side of the blower and the MAF is right before the throttle body. It is a draw through system. The blow off is on the SC itself. It is on the pressure side of the SC and blows off inside the SC case to the non pressure side of inside the supercharger casing. Kind of a wierd setup I know, but twin screws are like this.

I am pretty sure it is a tunning issue. I just somehow need to give it more air in a first gear stop. Either there is someway to tune for that in Edit or if not I should drill the throttle body..?

 

FWIW, isn't 650 Idle speed a tad low in drive??? Your going to need some additional RPM's to turn the Whipple.

 

The bypass valve in the SC blows off all of the boost until at 70% or greater on the throttle position sensor.
What do you mean by adding some additional rpms to turn the Whipple? I know you are on a 427ci now, but what does the Radix tune have a car idle at?

 

Ryan:
Have you tried adjusting the throttle blade screw? Your IAC's in park are right on for a truck engine, but the intercooler is acting like a big plenum and the IAC system can't adjust to the vacuum swings quickly enough. You might try opening the throttle blade to bring the IAC's down to 25 or 30 counts. That'll give the IAC more range of adjustment. WARNING: don't let the throttle blade tip past 0% or you might leave the idle trim cell.


Good luck,
Richard

 

I've got a cam with about 30 degrees more of duration but mine idles at 975 pretty nicely. Seems like you've tried just about everything else. Try bumping it up to 800 or 850. WCCH might be on to something there, but I'd try raising the idle first. In the long run it will make IAC adjustments easier.

 

Hey Richard is this 0% on the TPS readout? If I do this would it make the engine idle higher?

I really would like to stay at a low idle speed. I know I am starting to get beyond this point, but I need decent fuel milage. When I am sitting in traffic, I don't like to be revving really high and using lots of fuel. (for emissions testing that would also be a dead giveaway...although I could retune for testing day i guess)

 

As long as the TPS is at 0% your ok.
Next, I would try raising the timing 2-3º between 400-1200 rpm. Do this in the "High Octane Spark Table".
Your idle speed should be fine with that cam. My wife's truck idles nicely at 650rpm with a Comp Cams 214º on 112ºlsa. I don't think there's any need to raise the idle speed.

Keep us posted on your progress Ryan.

Richard

 

Okay, got it fixed!!! I first tried cracking the throttle body to decrease IAC so it would be able to open up and let in more air when I stopped. Theoretically this works; however, it still was not giving the IAC enough to save the engine from dying. And in fact, I really screwed it up because I had it right on the edge of 0.5volts and 0.6volts on the Throttle Position Sensor. I was unaware of how close it was (my bad). When it got to 0.6volts at a stoplight on the street it would start to hunt for idle and die on its own. That sucked! So I put all of that back to stock.

HERE is what did work: Inside LS1edit v1.3...again, version 1.3 there is a new table under Engine Cal.>Idle+Limiters called "Throttle Cracker" The values at a stop are zeroed out. Well I increased the first two rows and colums (upper left four boxes) to a value of 2.00 and things work great now!!! I guess this will kind of be my "crutch" until the new cam with 117.5lsa goes in.
I hope this can help anyone else with this problem. And thanks to you guys for your input also.
Ryan

 

Thanks for the update Ryan. Your feedback is duley noted. Good luck with your ride.

Richard