I got so much help here, so I whant to contribute with my experince.

I went thru 4 years of frustration with my setup. Trying to tune it good in closed loop.
The only way I could get part time throttle to work, whas to run the car in open loop all the time.


Symptoms were, bucking, hesitations at low map / low rpm operation.
And total fail at the anual "sniffer test" here in Sweden..

The 6spd amplified it ten times. No torque converter to smooth it out..

My setup whas:

1991 6spd vette
730 ECM

forge 355
Jegs 195cc heads
Converted Lt1 intake
Headers


What I did to "cover it" whas:

Adjust "throttle follower", so that the IAC hold rpm longer when you released the throttle in stop and go traffic etc.

Crazy amount of closed throttle timing abow 1000rpm ( the car alsmot drove it self with throttle closed ).

I also adjusted the PID, that made a big diffrence, but no cigarr.

The main problem where lean condition under 2000rpm and low MAP.
( I could hear popp and cracks in the exhaust during normal driving )

I could not tune that out in closed loop. The BLMS keept fighting me all the time.

I enden up disabel "closed loop" and tuned with a wideband in "open loop".
Dident care about lambda 1. I gave the engine what it whanted.
If it feelt good, I whas happy.

What I think is the problem with the LT1 intake, is air distribution to the back cylinders.
When I looked at the plugs, the rear always hade less carbon buildup on them vs the front.
I also used a temp-gun to look at the exhaust manifold.
Result whas the same. Hotter at the back vs the front.

The LT1 code even has a "injector offset" for this, I seen it now on its DEF file.

ALso LT1 had problem with "split BLMS".
The intake acctual has tiny air distribution holes, going from the IAC area in the TB, to each cylinder.
The stock TPI TB needs to be modfied to utilize this.
I did it, idle quality did improve.

If I know back then, what I know now. I would NEVER use that intake especially with a matched LT1 cam ( hot cam ).

I dont know if the conversion is still something people do.
But at least now, when someone is searching for it, perhaps this thread pops up...

Cheers

 

Sounds very similar to what I went through with my Miniram.

I've got mine to where it idles quite nicely and has great throttle response off the line, thankfully. But yeah, it took quite a bit of massaging of the tune. There were times I considered getting rid of it, but I absolutely love the torque curve on this thing...

I'm also running an automatic with a factory LT4 converter that feels pretty tight. So I also had to deal with this balancing act of getting it to idle nicely at a RPM low enough that it doesn't make the car want to creep forward while stopped at traffic lights.

One thing that seemed to work wonders on throttle response was activating the switch for "Reset Integrator when AE in progress". The ECM seemed to be "fighting against" the AE since the integrator would react to the momentary increase in fuel during throttle position changes. It was like a viscous cycle... keep adding more fuel on AE to compensate for ECM taking it out, but the more you add, the more the ECM tried to pull it out. Activiating that switch seemed to neutralize that effect.

I had also went back and rebaselined using a lot of the factory LT1/LT4 calibration ($DA3 mask) manually re-entered into the $8D mask. Timing, VE, AE, MAT, DFCO, CCP, everything.... etc... I had originally started with ANHT (for large cap dizzy) and the $DA3 values "out of the box" worked better than months and months worth tweaking on the ANHT. Then with minor tweaks to the $DA3 values, it seemed to settle into place, which is where I am now.

At one point a while ago, I conquered the split BLM thing, but the contraption I came up with didn't quite work out for long term use as I had hoped. I was attempting to mimic the LT1 internal design...

https://www.thirdgen.org/forums/diy-...ram-split.html

I actually still have the set up on the manifold, just plugged up at the intake port But lately I've been thinking about resurrecting it though to see what I get with my better tune that I'm running now.

 

"Good" to hear that my observations is not a isolated problem.
I whas going nuts over this.

I also used $DA3 values and tried to copy them over to the 8D mask. I acctual liked the timing tabel, and did a complete copy paste from the DA3 to the 8D.
( hade to mod it ofcourse, as the 8D mask has smaller steps in the RPM area etc)

But the 8D code also lacks the "injector offset" tabel, wich I think is a major problem for short runner design using bank to bank injector sequnce firing.

Special when the 02 is on the collector.

Open loop did it for me. I gave up on closed loop with my combo.
I just dont think the 8D can handel it.

Im now back using TPI design intake, and a milder cam and the 8D.



Open loop whas the answer to me.

 

Sequential is really the best answer for that type of thing IMO.
Individual cylinder control could do it.
(I want that too )

 

Agreed.

But in my case, a "injector offset vs MAP/RPM" would have cured it.
It whas the 2 rear cylinders that whas lean from idle to around 2300rpm.
After 2300rpm the air distrubution seemd to even out.
It whas like hitting a switch.
The INT settled and all hesitation, crack and "popps" from the exhaust where gone and the car pulled like train..

Also the exhaust temp did equal out abow 2000 rpm..

 

I have a 350 with afr195's and a miniram and a faily large cam for my setup, automatic trans though but I really didn't have any problems tuning it.

when you say injector offset what table are you talking about?

The table I wish $8d had would be injector phase angle timing, I really think that would help smoth out my lumpy cam.

I wish I knew assemble so I could find out how $8d calculates injector timing angle. (before, middle or end of injection and what fixed angle it is set to) to see if a table could be added.