IAC counts, Drilling TB, TPS voltage...
IAC counts, Drilling TB, TPS voltage... Got a Cam only 5.3 TSP 228R.
I see a lot of people that look down on those who drill TB blades to get more air. On this truck I decided I was going to try to do it without drilling. Pulled the TB and flipped the blade screw for better adjustment. Left the key on and cracked the blade till I had .76V on the scanner (.4 Throttle position) and I'm not getting nearly enough air. IAC counts are 200+ without the a/c on.
How are yall getting away without drilling?
You dont have hardly any TB adjustment with the screw without getting too much TPS voltage.
I see a lot of people that look down on those who drill TB blades to get more air. On this truck I decided I was going to try to do it without drilling. Pulled the TB and flipped the blade screw for better adjustment. Left the key on and cracked the blade till I had .76V on the scanner (.4 Throttle position) and I'm not getting nearly enough air. IAC counts are 200+ without the a/c on.
How are yall getting away without drilling?
You dont have hardly any TB adjustment with the screw without getting too much TPS voltage.
We have never drilled a single TB blade. If the voltage it out of range sometimes you can clock the TPS just enough to get it in range but thats not very often. What all have you changed in the tune for idle? There a couple tables that affect the IAC, if they aren't right you won't be able to get the IAC counts down.
On a cable TB unmolested, you can get enough air
through the IAC channel for any well tuned motor.
But that's a problem, getting idle tuned right, especially
with a high overlap cam and trying to stay closed loop.
I'd break the problem into two parts - first, get idle
mixture right and spark too; focus on minimum MAP
and not a wideband mixture reading, because LSU4
type widebands are just as spoofable as the stock
narrowbands. Use a scan tool with real time controls
so you can bump commanded AFR, commanded spark
and commanded IAC position and find "the happy
place". Prove to yourself that adequate idle airflow
can be had, with room to spare.
Then deal with the closed loop trimming making your
idle AFR ridiculously fat, thus needing excessive idle
air to live. Part of this may lie with the low end of the
VE table, but also the O2 sensors' miserable ability to
deal with more than expected residual oxygen in the
exhaust (thanks, Mr. Stage 4 cam, whatever the hell
that means).
Meanwhile, back in your Happy Place of Idle, take a
few notes about where your NBO2 voltage is sitting
and what the airflow is, so you can try and touch
up the O2 sensor voltage target vs airflow mode
table, try to get it trimming to real target instead
of stock-arbitrary one. Or maybe defeat idle-range
fuel trimming altogether, if too much variability w/
driving history and environment.
through the IAC channel for any well tuned motor.
But that's a problem, getting idle tuned right, especially
with a high overlap cam and trying to stay closed loop.
I'd break the problem into two parts - first, get idle
mixture right and spark too; focus on minimum MAP
and not a wideband mixture reading, because LSU4
type widebands are just as spoofable as the stock
narrowbands. Use a scan tool with real time controls
so you can bump commanded AFR, commanded spark
and commanded IAC position and find "the happy
place". Prove to yourself that adequate idle airflow
can be had, with room to spare.
Then deal with the closed loop trimming making your
idle AFR ridiculously fat, thus needing excessive idle
air to live. Part of this may lie with the low end of the
VE table, but also the O2 sensors' miserable ability to
deal with more than expected residual oxygen in the
exhaust (thanks, Mr. Stage 4 cam, whatever the hell
that means).
Meanwhile, back in your Happy Place of Idle, take a
few notes about where your NBO2 voltage is sitting
and what the airflow is, so you can try and touch
up the O2 sensor voltage target vs airflow mode
table, try to get it trimming to real target instead
of stock-arbitrary one. Or maybe defeat idle-range
fuel trimming altogether, if too much variability w/
driving history and environment.
assuming everything in the tune is correct, and the motor still isn't getting enough air (aka max iac counts) there are 2 methods. crack the blade and clock the sensor back to the correct voltage, or drill the blade. I had a 408 with a 247/255 cam, heads, and ported fast that couldn't get enough air no matter what we did. I reluctantly drilled the blade and tuning was a breeze from there once we got the IAC counts down to the 60-80 range.
