95 LT-1 Idle Cell Comparison - Humidity?

[spfautsch]

I wasn't really intending for this thread to turn into a tuning workshop, but I appreciate the value of having your attention so what the heck. I want the tune to be perfect (eventually) but I want to know how to do it just a bit more.

These are the headers I have (link). Cats aren't currently installed, although I doubt they would do much of anything.

... If the 02s are mounted too far from engine than stock, there is some delay for the exhaust gas to reach the sensor and it must be fixed in the bin CL settings.

I'm aware of the 26FB integrator delay / transport delay table, and until just recently I had the values almost doubled from stock. They're back to stock now.

I did a bit of "visual" measuring against the stock exhaust system before taking it to the scrapper for this purpose. I can't find any pictures at the moment but if I'm remembering correctly the left bank O2 bung wasn't considerably closer / further away from the exhaust valves than they are through the header primaries. On the right bank the O2 bung was several inches closer because they tucked the cat much closer to the exhaust manifold.

In the grand scheme of things I'm not sure there's a lot of difference in transport delay though, when you consider the velocity of gasses traveling through a 1-5/8 tube versus the huge log manifold and then into the 2-1/2" exhaust pipe. But I'm open to suggestions.

The new 02s perform much better now, still the cross counts are little too low.

As mentioned the right bank has always been slightly lazy, but I'm starting to think this is a result of poor cylinder balance and improper injector characterization. Not to mention the old regulator producing higher than intended rail pressure.

To update the current state of affairs - since flashing the most recent prime pulsewidth tables using values from the correct conversion formulas, starts have been good so far. I suspect my old fuel pressure regulator has had me chasing my tail trying to find the injector slope "sweet spot" when in fact it was a moving target. I've been decrementing the 12B4C injector constant by 0x0001 with every flash and will continue until I see slightly rich OL numbers on the wideband. I suspect this will make the cross counts increase on both banks.

The engnie runs too cold to my linking at 78 degrees. The thermostat might need attention or the coolant sensor is not good.

I've had a 160F thermostat installed for several years. When I first bought the car it had numerous cooling system issues from all the dexcool sludge that had accumulated, so I put this in out of an abundance of caution. I see less need for that extra insurance now that I know the cooling system is 100% healthy. I understand the pros and cons of the lower temps, and I think I'll leave it alone until I'm happy with the state of the tune so a before / after comparison can be made when I install a OE spec 180F t-stat.

I see you got higher blms everywhere on the right side

Sorry, I'm not sure I'm seeing that (everywhere). Looking at the big log from earlier today stacked with the one attached from this afternoon I'm only seeing averaged BLMs on the right that are higher than 129 in cells 2 and 16-18.

Edit: I see what you're saying though - the right bank is on average lean of the right.

If you suspect a cylinder s cyl cut test can point which ones is giving trouble. Set the afr to 12.5 and start cutting cylinders with 5-10 second delay between them. Record how much the wideband readings change when a cylinder is cut.

That's what I've been doing minus dropping the AFR to 12.5. Nothing has really "jumped out" so far. I'll try to get a fresh balance test tomorrow.

Did you tried to lower the rpm and the advance for more stable idle. Stock cubes cammed lt1 idles happy at 650 at Park and 550rpm at drive. I doubt the 383 can`t keep stable idle at 750-850rpm with 20-25 degrees advance. At lower rpms the surge from bad tune is much more pronounced.
How is the idle ovespeed/underspeed spark retard/advance tables set. Having 1-3 degrees there offload the iac motor jumping all the time.

I've never been happy with the idle quality below 29 degrees spark or 900 rpm - I like to hear the cam, but I don' t like to feel it. I'm sure some of this is a function of cylinder balance. So hopefully this is something that will improve as I find the right individual cylinder trims. Unfortunately MBT is happening around 29 degrees so there's not much room for the underspeed idle spark control to do it's intended job.

Thanks to everyone for all your help and suggestions. I feel pretty confident now that all the problems encountered were not a direct result of the experimental ignition system, and that's what I was most concerned with.