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Thread: 95 LT-1 Idle Cell Comparison - Humidity?

  1. #31
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    I should say you are running really lean on startup.
    Don`t forget you are spraying cold fuel straight in the cylinder, There is not enough time to evaporate and it should be extra rich to run smooth.
    The engine doesn`t make enough power and wants to stall, drawing more unused air, making things worse, that`s why you are seeing 160 iac and high map and low rpm. The engine is fighting to run.
    It gets a liitle better when the 02s start to climb.

    Compare that with high humidity and possible weak spark not having enough energy to ignite the lean humid mixture.


    Engine is not making enough power to stay running.

    Maf doesn`t play at engine starting at all it is the crank VE table that matters.

    And that 02s are like frozen they should be jumping like mad from rich to lean. There is something very bad happening there. Load the stock CL settings and see if there is some improvements.
    If you still can`t dial the idle closed loop, I have a remedy called Open loop idle patch.

    You should also investigate the controversial readings between narrowband 02s and wideband readings.

  2. #32
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    I should say you are running really lean on startup.
    ...
    The engine doesn`t make enough power and wants to stall, drawing more unused air, making things worse, that`s why you are seeing 160 iac and high map and low rpm. The engine is fighting to run.
    It gets a liitle better when the 02s start to climb.

    Compare that with high humidity and possible weak spark not having enough energy to ignite the lean humid mixture.

    Engine is not making enough power to stay running.
    Now you're making sense. I'll give it a try.

    Quote Originally Posted by kur4o View Post
    Maf doesn`t play at engine starting at all it is the crank VE table that matters.
    I understand that - the startup / cranking fueling tables are well out of the picture after the first 8-12 logged frames of startup. But immediately after those initial frames the MAF and Injector constant pretty much run the whole show. Agreed?

    Quote Originally Posted by kur4o View Post
    And that 02s are like frozen they should be jumping like mad from rich to lean. There is something very bad happening there.
    As I mentioned previously, I think I've raised the injector constant enough to cause this. In the first post, both frames (43kpa and 48kpa) were taken with 42.036 for the injector constant. It's currently at 43.547. I suppose it's possible the injectors flow less than 42, or my dwell problem was wholly to blame and I've moved it from rich (or ideal) to lean fighting what I believed to be a problem of too much fuel and not enough air.

    Quote Originally Posted by kur4o View Post
    Load the stock CL settings and see if there is some improvements.
    If you still can`t dial the idle closed loop, I have a remedy called Open loop idle patch.
    If you would, take a look at these logs and critique the closed loop behavior. The 43kpa idle frame was taken from one of these logs, and the only closed loop setting I've changed since is the Stoich AFR Target.

    Quote Originally Posted by kur4o View Post
    You should also investigate the controversial readings between narrowband 02s and wideband readings.
    I'll worry about that another time. As discussed in other threads it's using the D27 analog input with the default ADC output settings. It's also mounted about 18" downstream from the narrowbands in the X pipe. It doesn't get hot enough from idling alone for me to use for calibration purposes.

    Edit: Acutally the x pipe is more like 24" downstream of the header collectors.

  3. #33
    Fuel Injected! Terminal_Crazy's Avatar
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    Hi Scott, I know you know what you're doing.

    Have you played with injector startup PW and crank VE tables.

    Mine cranks right away now cold but doesn't always fire right away when warm... but is ok hot.
    I can't tell whether it needs more or less fuel, Probably more.

    Just played back a log starting. My IAC starts at 130 & drops to 108 as soon as the motor fires, then drops as motor warms up.
    I've lowered most of the tables re IAC and nothing is set that high.
    IAC keep alive :20
    present motor position loaded at reset : 40
    Park position crank offset vs coolant
    -4 20
    8 21
    20 21
    32 21
    IAC Initial position
    -4 77
    8 70
    20 63
    32 56

    So no idea where the 130 comes from

    IAC relearn done with new iac several times. No change anywhere

    I'm going to mix it up with a new Throttle body - yay.

    How does AFR & WB compare in EEHack?

    Mine sits initially at 3.30:1 at 20C

    Jumps to 5.70 as the motor starts turning
    Jumps to 12.1 as the motor flares up 13/1400 rpm (iac at 108 so starting to control revs)
    at about 30 secs, the wideband starts recording & matching AFR at 12.6


    As Rocko350 also mentioned increasing the manifold idle ports, Who would agree it's a good idea?
    I've ordered 2 pair of gaskets for the manifold.

    Hmm the IAC does seem to control the idle though.
    It also depends on idle timing where it sits.
    As I lowered idle from mid 30's to 20 I needed to re restrict the bleed hole in the throttle body.
    When idle was in 30's the iac was hitting zero and my idle is set at 800.

    HTH
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  4. #34
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by Terminal_Crazy View Post
    Have you played with injector startup PW and crank VE tables.
    Extensively. That's really a subject for a completely different discussion - the point of this discussion is to make it stay running once it fires. But since all my threads eventually turn into into free-for-alls here's what I've learned.

    Quote Originally Posted by Terminal_Crazy View Post
    Mine cranks right away now cold but doesn't always fire right away when warm... but is ok hot.
    I had the same problem after my injector swap, before the stroker kit. It would flood when restarting warm. I spent a lot of time fiddling back then and got it "pretty good" restarting warm. Then when I looked at these tables again a couple weeks ago I realized I'd scaled the prime pulse tables in the wrong direction (made them bigger) and then compensated by removing fuel from the cranking VE tables. Totally wrong way to go about it, but it worked.

    Look at the prime pulse width tables - this is a raw pulsewidth that does not reference the injector constant. The ecu fires the injectors for this period in batch mode (I believe all 8 at once) when it sees the first low res pulse from the opti. This is to re-establish wall film in the intake ports. So you'll want to scale this table by the relative difference between your stock injector constant and your current injector size. I started with about 25% (42 / 24 = 1.75) or multiplying by 0.75, but I also factored in the additional displacement so ended up around 0.82 as the multiplier. The warm and hot cells of this table will need to be massaged by hand in hex because the stock values are like 0x02, 0x03 and 0x04 and there is very limited resolution for removing an accurate amount of fueling. You'll have to settle for "close".

    Then move on to the cranking VE table and use this to add / subtract fuel based on how it behaves in those first few firing events. The fueling calculations behind this table do reference the injector constant so you shouldn't need to factor that in. Just changes in pumping efficiency caused by cam & displacement.

    Lastly, the Crank AFR vs Low Res Pulse vs Coolant Temp can be tweaked. This is the target AFR the calculations are using with the cranking VE table for. Notice the first two cranking pulses are much leaner than the rest. I assume this is because the first and second prime pulses aren't factored into the fueling and wall film modeling. I've no idea however if this then adds to the prime pulse or what.

    Mine is far from perfect, but I'm not trying to get it perfect yet. This can be a slow & tedious process b/c you have to let it cool down to test.

    Quote Originally Posted by Terminal_Crazy View Post
    So no idea where the 130 comes from
    That's a question kur4o might be able to answer - he mentioned it a few posts back as being set to 144 but not the address for the table / constant. But long story short the ecu uses IAC for coarse idle speed control, and spark timing for fine control. So it will move the IAC as the ecu sees the need (there's a RPM Variation pid you can monitor / graph in eehack).

    Quote Originally Posted by Terminal_Crazy View Post
    How does AFR & WB compare in EEHack?
    My WB controller pulls the analog pin to ground until the warmup timer has expired (30 or 60 seconds). So it reads 0 (in units of lambda).

    Once it starts reporting AFR it's all over the place. Sometimes showing rich of the narrowbands in OL and then usually 20% lean in closed loop. I'm really not paying it much attention because at cold start, or in any other instances where you have unburned fuel getting in the exhaust the effect is lean output from the O2. For example one of the Banish tuning guides I talked to you about says at cold start you should see the widebands showing stoich because the unburned fuel isn't seen by the sensor. Only the concentration of oxygen in comparison to other gases. Bear in mind his wideband probably costs more than my car, so I doubt we'll be able to use this method to favorable results with a $200 instrument.

    Quote Originally Posted by Terminal_Crazy View Post
    As Rocko350 also mentioned increasing the manifold idle ports, Who would agree it's a good idea?
    I didn't get in a hurry to pull my intake off to try that, and I don't intend to unless nothing else gives results. I'd like to see some quasi-scientific data that compels me towards that before I jump out of that airplane. I already had a plan to fix my IAC bypass before I decided to drill it. Doing the same with the port feeds is a whole different animal.

  5. #35
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    It looks like the 02s you have are dead shot. Not swinging enough in either direction. They can crack from moisture but yours are completely dead, if something else is not going on.

    Get a good afs75 delco ones.

    Here are some logs i made showing good voltage swing. The car is perfectly untuned but you can get the idea. There is a cold start and some idle showing the IAC in stock form can easily support 15 AFGS. It has a midlength SLP headers and some tweeks in the delay times. The wideband is set at 0v-11.4 5v-16.5 at d27.


    The way you modified the injector scalar can lean the mixture alot. For the sake of experiments set it at 41 and see how it goes.

    I will have to dig out the iac tables. Sure there is one for startup counts vs iat or coolant.
    Attached Files Attached Files

  6. #36
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    Quote Originally Posted by kur4o View Post
    It looks like the 02s you have are dead shot. Not swinging enough in either direction.
    Are you saying that based solely on analyzing the two big logs from 5/31?

    Quote Originally Posted by kur4o View Post
    ... but yours are completely dead, if something else is not going on.
    Trust me, there's the possibility of a great many other "somethings" going on. Not least of which is that this is the entirety of the calibration data I received with my injectors. Be sure you zoom in because it's hard to see. At the very least I'd like to determine the main injector slope within reason through extrapolation. I know this isn't the way to do this, but hear me out.

    In a couple weeks I'll be in a state where I can buy ethanol free gas. I intend to bring 10 gallons back. I'm already braced for my wife's response when she finds out why I'm bringing two empty gas cans along for our 25th anniversary trip.

    Assuming I can tweak the ADC output and get my wideband to a spot where I feel it can be trusted to report stoich, I believe I can extrapolate injector flow in a manner more objective than guessing. Obviously I'll want to be forcing OL and AFR to 14.7:1 during this experiment, and running at a load that yields a pulsewidth above the slope knee (aka low pulse adder).

    This theory is based on the (relatively huge) assumption that my MAF transfer curve is accurate. But assuming it's in the ballpark, you should now be able to more completely understand my fascination with the effect of humidity on the MAF function. Adjusting for humidity, and assuming I have healthy enough spark for complete combustion, it should be realistic to be able to scale my injector constant based on however rich or lean of stoich the results are.

    Quote Originally Posted by kur4o View Post
    Get a good afs75 delco ones.
    When I get to fine tuning closed loop I'll likely create a new discussion. I might even break down and buy some new ACD O2s. I would be honored and grateful if you'd contribute to it. But that's not my goal for today.

    Quote Originally Posted by kur4o View Post
    The way you modified the injector scalar can lean the mixture alot. For the sake of experiments set it at 41 and see how it goes.
    Based on my faulty assumptions, that was my intention. I've discovered through experience that trying to improve on the factory MAF transfer function isn't a terribly productive exercise.

    I'm getting ready to test a cold start with 41.92 for the injector constant. Fingers (and plug wires) crossed...

  7. #37
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    No miracles were witnessed but I think I learned something. Only change to tune from yesterday was injector constant from 43.xxx to 41.92.

    Take a look at this log pls.

    Sluggish and pegged IAC from cold again. I did notice however that the BLMs ramped down from 128 to 120 in frames 14-18. If this is affecting OL fueling I'm baffled as to why. I'd just flashed the e-side with the injector constant. I always assumed that flashing a new bin (programming mode / running code from ram) reset BLM data. But even if it didn't, it hasn't run in 24 hours. If the ecu is using stale BLM data to trim startup (edit: meant to reference OL, not cranking) fueling that would probably explain the lame cold start. And it makes me ponder the question "why in the hell did they do that"?

    Edit: I've always labored under the assumption that BLM data was NOT being used to trim fueling if the BLM box in eehack wasn't green.

    Closed loop acted pretty much the same as before.

    At frame 2243 I forced open loop at 14.5:1 and immediately it jumped 50 rpms and the IAC count started falling. O2s started to read rich and exhaust smell changed from eye watering to what I imagine Steve refers to as "chemical fire". I fooled around with forced AFR a bit to see where the wideband reported stoich, but not placing much faith in accuracy when the O2s aren't being heated by moderate driving.

    I'm going to reset the BLMs in eehack and run it some tomorrow in forced OL.
    Attached Files Attached Files

  8. #38
    Fuel Injected! vilefly's Avatar
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    Wish I could take that trip, spfautsch, but I will be installing a fuel pump in the wagon and getting it ready to pass inspection. Just got the exhaust done, now this. It's doing the vapor lock stumble of death. So much for joyriding in the vette. (sigh)

    But in the meantime I will dig up some binaries from a '39 Business Coupe with a 383 lt-1 engine. I had the problem of running rich when cold, and lean at cruise. Can't remember what I changed, so I will compare bins. It had come in with a bad MAF sensor, and an untuned speed density map. It did not run lean like yours, and had a choppy cam. It looked like whoever worked on it didn't really tune it at all. Yours should have behaved in a similar fashion, but instead it is leaning out.
    When diagnostics fail, I start the testing back at the beginning again. It hurts, but it gets you there.
    Some basic questions perturb me.
    1) Timing test - make a timing mark for #1 TDC on the balancer/timing cover, and see if a timing light agrees with your scan readings. Requires a timing light with advance/retard feature or knob (or timing tape on the balancer). It will at least prove the ignition system has no logic errors, and no delays due to dwell mismatch.
    2) The bucket test - With the engine running, dump a large cup of water on the intake manifold areas, and watch for misfires or sucking noises. Injector o-rings can be dastardly vacuum leak. So can EGR gaskets.
    3) Intake manifold gasket test - remove the pcv valve from the valve cover, but leave it connected to the hose. Plug off the pcv vent and valve ports in the valve covers, and
    see if the engine pulls a vacuum in the crankcase when you open one side up. It should show slight positive pressure from blowby. If there is a vacuum, you have a intake gasket problem that will also suck oil into the intake also.
    4) O2 test - supply an alternate fuel source into the engine while watching o2 readings. (carb cleaner spray) If you can make them twitch, they work.
    5) running compression test - Install compression gauge, start engine, watch for equal readings that do not vary more than 7psi. Will tell you how well the engine is breathing, and whether or not the valves are sealing.
    6) Vacuum Reading - should be steady. If you have a bouncing needle, look for a broken valve spring.
    7) Map sensor - check with vacuum pump and scan data. Make sure it reads barometric pressure correctly, also. It calculates air density from this, so it can really mess things up if it is wrong. Yours should be making it run rich in speed density mode with a oem tune.


    With these basics out of the way, only then can we go after the software. Not that you didn't try all this, but I had to go back to the beginning, since I forget a test or two when I think I know something, and sabotage myself.
    Last edited by vilefly; 08-07-2019 at 07:25 PM.

  9. #39
    Fuel Injected! vilefly's Avatar
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    Ack. It was a 1949 truck with a 383 lt-1 in it.
    Here's the original bin and the VE modified @idle speeds.
    The pcm/engine combo is from a 1996 firebird.
    Attached Files Attached Files

  10. #40
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    Take a look at this stock log from vette calibration. The 02s are constantly running from 100-150 to 850-900 mv. Yours are barely moving from 300-650

    http://www.gearhead-efi.com/Fuel-Inj...5&d=1565148272

    It really doesn`t matter the fuel, the stoich and the tune you have. Unless the blms are maxed out you weill always get the correction close to the swing voltage settings.

  11. #41
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    Take a look at this stock log from vette calibration. The 02s are constantly running from 100-150 to 850-900 mv. Yours are barely moving from 300-650
    That's great, thanks for taking the time to post that.

    What I'm really curious about now that I've gone open loop until I figure this out is...

    Why does the BLM # drop from 128 to 120 at every start?

    I assumed this was stored trims being applied, but I've reset my BLMs numerous times and it still happens every time it's started.

    I didn't think it was trimming open loop fueling, but when it's running and I clear BLMs and see them jump from 120 to 128 immediately the IAC drops a few counts.

    I'm working on measuring the dwell time of my ignition controller tonight. I'm hoping to find a really dumb math error causing far less dwell than intended, which would explain a weak spark scenario.

    Quote Originally Posted by vilefly View Post
    Wish I could take that trip, spfautsch, but I will be installing a fuel pump in the wagon and getting it ready to pass inspection.
    No worries, it was just a ploy to get you to come out and then once you'd driven 3 hours I'd change my mind and want to re-lash the valves and then change the diff oil in my wife's daily driver. You know, work that's dirty and sucky. ;-) I was going to grill porksteaks and make you drink a couple cold adult beverages though.

    Valve lash has been re-set and even made a few laps around town. The good news is after spending $1000 on complete kit, then putting my old pressure plate back in my clutch is working better than it has in 2 years. Two different cheap chinese pressure plates exhibited the same problems - chunky engagement.

    I feel ya. Knock on wood, most of my daily driver dramas are sorted for the moment.

  12. #42
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    Mods feel free to change the thread title to something more appropriate like "Idiot attempts tuing LT-1".

    I spent a good bit of time over the weekend testing the ignition system. I haven't yet ruled out weak spark, or some mechanical issue. When I have time I'll outline all the things that have been attempted to those ends such as swapping the original injectors back in, leak testing valve seats, etc. But here's where I'm at right now.


    Item #1 - starts and then immediately dies.

    I think this might have been VATS. Since disabling it two days ago the cold start behavior has been fairly consistent.

    Unfortunately that consistency hasn't been great.. "Cold" starts have still required a bit of initial throttle to keep it from dying and expedite the warmup process.


    Item #2 - unknown injector slope

    As mentioned, I don't have an overwhelming amount of faith in the actual slope of my injectors, other than it's somewhere between 41 lb/hr and 44 lb/hr @ 43.5 psi.

    In an effort to extrapolate the injector slope based on what sensors I have at my disposal, I adjusted my wideband controller to give similar analog outputs to what kur4o mentioned a few posts back. This is what my wideband config looks like currently. Note the -0.200 afr adjustment, due to the fact that I know there is some amount of ethanol in all the pump fuel I'm able to purchase (because water dissolves in it).



    Using these settings I went for a short drive tonight to get the wideband heated by some load greater than idling, and afterwards ran a cylinder balance test. Log attached.

    However, my primary concern is determining injector slope. If there's something I'm overlooking that invalidates my theory here please point it out - I'm very much an amateur at this stuff. But...

    Assuming the wideband is within the "ball park", looking at the data between frame # 2580 and 2794 there's a block of data where TPS and AFR target were absolutely steady for nearly 20 seconds. Running at about 2150 RPM, this range of operation should be just beyond the range where cam overlap / reversion would cause unsteady airflow numbers, and subsequently wideband readings.



    What I can't seem to discount here is that the wideband is averaging 13.0:1 afr while commanded AFR is 14.3:1 through this entire stretch. Even if my assumption is correct about airmass sensors causing rich operation in humid conditions, I would think this is a bit excessively rich.

    Just looking for some honest opinions. My plan for tomorrow is to increase my injector constant from 42.114 to somewhere around 42.5 lb/hr, repeat the above test and see if the wideband comes closer to agreeing with commanded AFR.

    Edit: Running OL MAF currently
    Attached Files Attached Files

  13. #43
    Fuel Injected! Terminal_Crazy's Avatar
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    Hiya
    You running OLSD?
    Is it generally rich all over? Then increase injector constant
    What is your VE table like?


    Mitch
    Recently I had to reduce the injector flow value as my VE table was maxing out
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  14. #44
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    First attempt with 42.5 ifc looked near perfect, until I realized BLMs had reverted to 120 after initial startup. I wish I knew why this was happening.

    Third attempt looks pretty good if I remove the ethanol stoich adjustment - 42.62lb/hr injector slope w/ BLMs reset immediately after start.



    I'm noticing that my narrowbands almost never cross below 450mv except during dfco. Lean spikes hitting the limit of the wideband's analog range (16.5:1) are still really close to stoich according to the narrowbands. If they're not completely shot then my wideband must be. Though I still need to confirm that what eehack is seeing on D27 agrees with readings from the wideband controller's serial data.

    I was in a rush to get back home so there's not much in this log, but open to any thoughts if anyone cares to analyze.

    I did further tinkering and things got much worse after this log was captured - possibly because I removed too much fuel from the one cylinder that shows the largest lean delta during cylinder balance tests (#6). By the end of the day it almost wouldn't idle at all. I assumed this was because of heat soak and / or my ignition controller. I'm not completely convinced I'm not tuning around ignition problems, but driveability was very good until the idle started getting screwy.
    Attached Files Attached Files

  15. #45
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    Kind of a shot in the dark here, but if both your O2 sensors are in agreement with one another--that is, both narrowbands--then I have to ask. How long has it been since you fresh-air-calibrated your wideband? Could it simply be outside of its calibration?

    In my experience with multiple cars that have had narrowband O2 sensors fail, they tend to fail either completely by dropping out (in my case, due to physical damage from afterfire in the exhaust melting the catalytic converter onto it) or by getting incredibly lazy compared to other O2s on the vehicle. It should be fairly obvious in the log as one will flick back and forth rapidly as normal while the other sits relatively static. I've never seen an O2 sensor fail by operating "normally."

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