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.

[kur4o]

Here is a starter pic of the intake manifold for reference for individual cyl trims. You can clearly see why in the stock applications #7 is always set at 0.9.
WIth long tubes with different lenght primaries there is considerable difference in cylinder efficiency. The longer the tube the more air it draws. SO the difference will be how much readily available air is left for cylinder to draw from the intake passage and how much vacuum is made in the exhaust tube.

If you haven`t equalize the stock intake passage holes, you can start with the stock cyl trims settings and work from there. The idea is to find out which cylinders draw more air and which ones` less, Than adjust the fueling.

I always wondered why the CL worked for you at idle even at that cam and didn`t experience the dreaded enleanment at idle CL. When you mentioned that the 02s were down the pipe, I checked the bin settings for your calibration and it is seems like it is preset for some headers already. I will test them as soon as possible and will report how it does with midlenght slp headers.
You can still make some tweeks to get more crosscounts at off idle cruising.

MBT is ideal at wide-open throttle (WOT), but not desirable when the engine is at idle.

per wikipedia.
Too much heat in exchange for really lean mixture to utilize the extra spark advance. Maybe that`s why you are getting that unburned fuel smell. The afr is too fat for the advance and the fuel can`t burn and it is dumped in the exhaust.

I agree and terminal_crazy also reported similar results.
I have also zeroed the underspeed tables and the result was a disaster in idle quality. So I increased it to a max of +-2 degrees. It really smooths and offload the IAC valve from constantly adjusting.

The only reason I see for idle rpm increase is if the engine stalls at take off or it gets unstable at near idle conditions and is trying to die. Also the lower map readings you get are because the higher rpms. I am sure that the map will jump around 45-50kp area if you lower the rpms by 100. It takes alot of tuning to get it right with no surging but the results is clean and efficient combustion.

I also have 160* thermostat but never have seen under 80-81 C degrees cruising even at colder weather. I can suggest to leave the thermostat and increase the fan points. At colder weather block part of the radiator. Just for sake of experiments try the idle quality at 90*C and see how it calms and quiets down. I have never run it hotter but can imagine stock at 100*C. There is one very nice settings for fan temp with mph threshold. You can set higher temps with low speed cruising and colder settings with high speed performance trips.

Sometimes it is better to tune by feel and sound. The preffered method is also seat in the pants tuning.

[spfautsch]

When you mentioned that the 02s were down the pipe, I checked the bin settings for your calibration and it is seems like it is preset for some headers already.

Am I correct to interpret that to mean the O2s are in the manifolds on other LT1s? That would explain a lot of the difficulties f-body guys have with headers.

per wikipedia.
Too much heat in exchange for really lean mixture to utilize the extra spark advance. Maybe that`s why you are getting that unburned fuel smell. The afr is too fat for the advance and the fuel can`t burn and it is dumped in the exhaust.

I would suggest you search "spark hook test". Maximum Brake Torque is the spark advance where, with all other variables removed (speed and AFR) the most torque is generated, and consequently the lowest resultant manifold pressure. Adding more spark advance beyond MBT for a given mixture yields no additional torque. This is why you want spark at MBT everywhere except at idle, because the underspeed adder can't increase engine speed if you're already at MBT.

The only reason I see for idle rpm increase is if the engine stalls at take off or it gets unstable at near idle conditions and is trying to die.

I've never attempted to get it to idle below 875. The cam lope shakes the entire car and I'm not a fan of it. If I can find any improvements with cylinder balance I may attempt to work on lowering idle speed and spark.

Also the lower map readings you get are because the higher rpms. I am sure that the map will jump around 45-50kp area if you lower the rpms by 100.

I was under the impression lower map at idle was the goal, not higher. ???

It takes alot of tuning to get it right with no surging but the results is clean and efficient combustion.

When you write a book I'll be the first in line to purchase it.

[spfautsch]

cut test can point which ones is giving trouble. Set the afr to 12.5 and start cutting cylinders

Is this something that's only possible with your v4 patches? The fork of eehack I'm using has the cylinder disable button group greyed out when AFR is overridden, but when I commented out the line that greys them out and tested it seems like the AFR reverts back to the tune default when a cylinder is disabled.

As a workaround I changed the OL AFR target to 13.2 in all the cells I thought would be affected. I should have gone one temperature band higher, the result was 13.4-13.6 during the balance test. In the attached log it starts at timestamp 4410 and I disabled the cylinders in numerical order.

bal-test-2019-09-25.jpg

If you watch the narrowbands, it looks like the right bank is robbing fuel from #3 pretty efficiently as both sides go flat when it's injector is disabled. I'm not sure what this means (if anything).

Other than that I don't see any really obvious red flags except that MAP took a nosedive after #6 had been disabled for a few seconds.

At the end I played with idle speed and spark and managed to get a reasonable idle at 800 with 25-26 degrees advance (albeit at 13.4:1 OL afr). But then I let it revert to closed loop and couldn't tell much difference. I guess I need to try these settings out in a tune and see how it feels as it's warming up.

The attached log is about 80 minutes of mixed driving in closed loop until I got in the driveway and played with cylinder balance and then idle. If you look at the CL Performance tab on analysis in eehack note that my two primary cruising cells (2 and 6) seem to trade places - in cell 2 the right bank is lean, and in cell 6 the left bank turns lean. The BLMs almost trade places.

On an unrelated subject, I think I came up with a semi-reasonable method for working out the cranking prime pulse tables. I need to clean up my worksheet and write up a how-to for you to look at and see what you think. What I did is took the actual pulsewidths after the floats have been converted to hex and calculated the sum of the actual fuel charge for the first two pulses. Then I adjust one or the other until the summed fuel charge most closely matches the desired sum. It seems to be producing decent results. I've seen folks mention running 80lb Ford Racing injectors in this application, and I have to wonder how they've managed to get crank fueling dialed in with no more resolution than is available here.

[spfautsch]

Hot target idle speed set to 800rpm with 26 degrees. Idle over and underspeed tables restored to original. Also added a bit more fuel to 2, 4 and 6 trims. Bin included with log this time.

Cold start this morning was great. No problems whatsoever - sitting idle was great but I might have felt a slight amount of surge at ~20mph before pulling in the parking lot at work. This is the first 50+ mile log I can recall with zero knock events.

The idle BLM split didn't improve much but the cell 2 split is slightly better. Still significantly fewer cross counts on the right. Planning on pulling the throttle body tonight to see if anything might be clogging up the 2 and 4 idle ports.

If nothing breaks and warm / hot restarts are ok I'm going to drive this a while and see how it performs. If I change anything it will be continuing to reduce the injector constant gradually as PE seems lean.

Hoping to work on SD VE tables this weekend.

[kur4o]

Great you are having serious progress.
The afr target and cyl cut use the same byte in mode4 message and are exclusive.
v4 has the same limitation. In v4 you can change the cyl trims on the fly.

The cyl balance test wasn`t very reliable. The fans skew the map readings and afr is moving a bit and is not too fat. The wideband is almost topped at 16.5.
A new test with constant variables will give better picture, since you also change the rpm target.

The cut test produce some good results showing some lean cylinder on the right side. Could be #6 since it is the one that fires after #3. More air left for #6 to draw. Or it could be #2 the companion firing cylinder of #3.Generally all of the right side calibrations have more fuel added. I checked the bin and the trims looks really conservative. It is not uncommon to have 5-10% difference even with stock form.
I ended with this settings in firing order.

1.070
0.984
1.031
0.938
1.039
1.008
0.977
1.047

The result of drilling the passage holes even. #1 had much smaller hole since it draws much more air and now I got it at 1.07.
I tried to get them better with wideband test but failed. The test looked better and even but the feel and sound of the engine sucked so I revert to the best feel.
I always have 1-3 problems cylinders that didn`t react to changes as expected. I am planning to play more with them if I have the time. I suspect you need much more air on the right side for some reason. It could be 1 cylinder leaning or it could be mutiple.

As I remember the passage goes to mid of the intake plug and than goes to both sides center and than goes to intake ports. 2 90* turns till it reach the ports.
#2 and #4 have the shortest path. #6 and #8 the longest. #7 fires after #5 and for #7 there is almost no air left. Also there are 2 different designed intakes. the one have a center plug the other doesn`t and there are some other visible changes in the bottom shape. Do you remember which one you have.


I noticed that the rpm and map blm boundaries are also higher in the bin. The crosscounts could be lower because of the different settings in the vette bin. I will try the settings and compare the results with some older logs.

[kur4o]

I couldn`t resist and made a quick log with the vette CL settings. To my surprise it worked perfect with SLP midlenght headers and GM 846 cam. The right one is a little shorter and the 02 bung is the header flange, the left is longer and the 02s is down the pipe, like 8-10 inches down the flange. SO there is considerable difference in the 02s placement.

So GM had perfect CL idle settings for radical cams and headers all the time and nobody noticed. Now I will have to ditch my Open loop idle patch, but first I will do some driving and see how it goes on the road.

Later I see what settings are changed and make analysis how it works in the bin.

[spfautsch]

So GM had perfect CL idle settings for radical cams and headers all the time and nobody noticed.

Knowing that the CL logic is controlled by a PID type feedback loop, I'd always wondered why no-one having these problems was discussing changing the gain and proportional tables.

[spfautsch]

The afr target and cyl cut use the same byte in mode4 message and are exclusive.
v4 has the same limitation.

So changing the Target AFR table is the only way to lock AFR for this test?

In v4 you can change the cyl trims on the fly.

I may break out a mouse and make a serious effort to utilize it this weekend.

I have a few interesting items to report from last night's changes. First I tamed down some of my individual trims on the right bank because I was smelling fuel at closed loop idle. I also took a good bit more out of the injector constant which is now at 41.88.

The first thing that I noticed is that startup went to hell when it was starting almost perfectly yesterday afternoon prior to the individual trims change. So I think I was on the right path and removing fuel from the right was a mistake. It seems to me (and this is just a theory) that the prime pulses have to be spot-on to get the usual immediate fire and run we all know so well with this setup. I had just never considered that the individual trims were applied to the prime pulses.

Also, this log of my morning commute compared to the other three days has the lowest difference between cross counts bank to bank - 7218L, 6010R of 31811 records. I don't know if this is coincidence or a direct result of one of the things I changed - it is pretty humid and there are spot showers popping up today. I guess I need a weather station in my car.

Lastly, AFR at PE is closer to commanded than ever, so I think I'm pretty close to the right injector slope.

The cyl balance ... The fans skew the map readings

I've been forcing the fans on low because I don't want them kicking on during the test and changing accessory load. I assume this means your method is to force them off?

The cut test produce some good results showing some lean cylinder on the right side. Could be #6 since it is the one that fires after #3. More air left for #6 to draw. Or it could be #2 the companion firing cylinder of #3.

I'm not sure it matters but my assumption is that #4 is the one robbing fuel from #3 because it's adjacent in firing order and closer to #3 injector than #6. It will be on the intake stroke while the #3 injector is firing, whereas when #6 is on intake #3 would have just finished depleting any fuel left in it's intake port. I think #6 is what's robbing fuel from #5 because it also has the same relationship as 4 to 3.

Generally all of the right side calibrations have more fuel added. I checked the bin and the trims looks really conservative.

I arrived at this after setting them all to 1.0. I tried using the stock trims at one point and it wasn't good, but I could have had other things way out of whack at that point so I'll revisit that this weekend. I feel like I'm going to spend 90% of my tuning time nailing down the cylinder trims.

there are 2 different designed intakes ... Do you remember which one you have.

I think I have a picture with the oil shield off somewhere. Will update if I can find it.

I noticed that the rpm and map blm boundaries are also higher in the bin.

I did customize the BLM boundaries when I first got it running as a 350 with this cam. I may revert this back and see if the BLMs are better distributed. It seems like 95% of normal driving falls into two or three cells. But I suspect this is just the nature of running a built engine on the street.

[spfautsch]

Reverting to trims from previous tune and then adding a slight bit to 1, 2 and 4 caused noticeable improvement to starting and idle sound. Also it seems to have much more torque when I let the clutch out too fast and bog it down towards 400 RPM.

Edit: Also, surge feels almost non-existent. When I pulled in the parking lot I left it in 2nd and let it slow down until it started bucking. I didn't log it but it was perfectly smooth down to what seemed to be idle target (800).

Sorry to quote myself but I had a revelation while out getting some air.

... my assumption is that #4 is the one robbing fuel from #3 because it's adjacent in firing order ... I think #6 is what's robbing fuel from #5 because it also has the same relationship as 4 to 3.

It may seem counter intuitive, but what if the way to get more fuel to #4 and #6 is to also increase fuel to #3 and #5?

Here's a back of the napkin sketch of how I envision parasitic fuel flow in a gen 2 LT-1.

1 -> 2

3 -> 4

5 -> 6
  ^
7 ⅃  8

Obviously all these dynamics change when the throttle blades open, but maybe the way to get perfect balance has less to do with the size of the idle feed holes and more to do with parasitic flow.

[LeMarky Dissod]

I did customize the BLM boundaries when I first got it running as a 350 with this cam. I may revert this back and see if the BLMs are better distributed. It seems like 95% of normal driving falls into two or three cells. But I suspect this is just the nature of running a built engine on the street.

You should [continue to] customise the BLM RpM and MAP boundaries, based on how you'd drive if you were trying to achieve better MpGs.
The OEM boundaries are silly even for a bonestock car doing the EPA's CAFE MpG test, nevermind driven normally, nevermind modded, etc