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

  1. #46
    Fuel Injected! spfautsch's Avatar
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    The wideband was calibrated when it was installed - thinking that was around 4 months ago. It's due for it's initial 3 month re-calibration, though it hasn't seen much actual use in the time it's been installed. It's on my todo list. The only other thing that could be causing it to read less accurately is it's location in my x-pipe. The recommendations are to avoid places where the exhaust system pressure might change. Unfortunately that's the only point in the exhaust where both sides converge.

    I suppose the same phenomenon (pressure change) could be affecting the binaries which are located in the header collectors.

    However, in general I would agree and go on to state I don't think I've ever seen a binary O2 sensor actually fail. Speaking in the context of tuning there are a lot of other factors that can cause them to appear to be causing a problem. Poor individual cylinder trims, poor closed loop settings to accommodate for header and / or cam, being relocated from factory placement, etc. All these are possibilities here. But I'm probably going to replace them simply because when I installed new ones back in 2017 I saved myself $20 by getting the Bosch units instead of the AC Delco 75s.

    Before I pulled the engine apart looking for a mechanical problem I swapped back to my stock injectors. I should have reverted back to the factory tune at that point just to be sure, but for whatever reason just copied the injector and startup tables. I may repeat that test but revert back to the factory tune this time to eliminate my modded mystery injectors. I don't think they're leaking but I could have completely wrong offsets for them.

    When I had the heads off I leak tested all the valve seats and found nothing wrong other than goopy fouling on the piston tops and in the chambers. This could have been from oil getting sucked into the intake ports from the rocker stud holes. I used better sealant on these bolts when it was re-assembled. The plugs didn't show signs of fouling and in fact looked relatively good - a light tan color on the porcelains.

    Assuming it's not running miraculously better when I get back to it, and the injector swap proves fruitless I'm thinking I better start looking at the ignition system.

    I'm traveling this week so will likely have no progress to report other than the acquisition of some ethanol free fuel.

  2. #47
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    MAF sensors work on a heated wire principal. The wire is heated and then the resistance is checked, then the wire is pulsed to return i to a "known" resistance. The amount of pulses it takes to return that wire to the known or base resistance is reported to the ecm as a Hz signal. Hence the lookup table is referenced in Hz. MAF sensor performance is based on is internal processor, the supply voltage and ground.

    As for humidity, if BARO is not reading within 3 of reported actual baro, the air density calc can be off. The humidity flowing over the MAF wire cools the wire, misreporting actual airflow. We are trying to calibrate a sensor table to report a mass of air that happens to include oxygen. Temperature (iat), mass flow(MAF) BARO (key on MAP) reading and engine vacuum (VE) determine the air density being delivered to the cylinder. So the actual humidity is not that big a problem. Its impact the actual combustion process in the chamber not so much the calibration of the engine. The stfts are fast enough to handle the humidity.

    The enlarging the idle passages is for allowing the air passages to do their jobs. There is not a "closed loop idle" like there is in a GEN3 engine. If opening the idle bypass does nothing, but opening the throttle blades does, the passages need to be larger. Air in the main intake chamber (non idle passages of intake manifold) can be robbed from cylinder to cylinder if your just gonna open the throttle blades. Cylinder to cylinder fueling will need to be redone either way you choose. If you haven't adjusted the eoit i would visit that as well. Maybe stick a set of injectors in that you have excellent data for, then swap back the the njectors you need for power and adjust the injector data around the idle data from the known injectors.

    Chris

  3. #48
    Fuel Injected! vilefly's Avatar
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    I just remembered something from my obd-I days that really screwed with me at the time. Narrowband O2 sensors sometimes go nuts and put out NEGATIVE voltage on the output wire. This really made things crazy, since each computer brand reacted differently to this. The OBD-1 ecms could only see voltage differential, did not ignore the O2 sensor like they should have, skewing everything backwards. Lean became leaner and rich became richer.
    Not that this might help, but one should always check for positive voltage output from the O2 sensors on OBD-1 setups if suspicions are raised.

    I have an old injector flow tester that tests the injectors on the vehicle (with some temporary fuel line rerouting). Let me see if I can find it and check to see if the display works still. It has a faded lcd display that may or may not work.

  4. #49
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    I have an old injector flow tester that tests the injectors on the vehicle (with some temporary fuel line rerouting). Let me see if I can find it and check to see if the display works still. It has a faded lcd display that may or may not work.
    Don't waste a bunch of time messing with that - if I go to the trouble to try characterizing the injectors I think I'll find a 4 cylinder fuel rail at a junk yard and build my own test bench. I'm just not sure it's worth the trouble. A new set of 42lb Ford Racing injectors with good data is only $400. The only reason I'm going to this trouble with the ones I have is because I know they were working pretty darn well before summer.

    At the point I had to stop working on it the drivability wasn't that bad save for slightly lazy cold start (at hot ambient) and falling on it's face at hot idle. If my hot idle is still crap when I revert the last couple changes I'll probably switch back to the factory 25lb injectors and see if I have better luck.

  5. #50
    Fuel Injected! vilefly's Avatar
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    Quote Originally Posted by spfautsch View Post
    Don't waste a bunch of time messing with that - if I go to the trouble to try characterizing the injectors I think I'll find a 4 cylinder fuel rail at a junk yard and build my own test bench. I'm just not sure it's worth the trouble. A new set of 42lb Ford Racing injectors with good data is only $400. The only reason I'm going to this trouble with the ones I have is because I know they were working pretty darn well before summer.

    At the point I had to stop working on it the drivability wasn't that bad save for slightly lazy cold start (at hot ambient) and falling on it's face at hot idle. If my hot idle is still crap when I revert the last couple changes I'll probably switch back to the factory 25lb injectors and see if I have better luck.
    A quick way to test for equal injector flow w/o removing it involves a fixed injector pulsewidth with about 10 cycles or so, and a fuel pressure gauge. Pressurize the fuel system and turn off the fuel pump, send 10 x 4mS pulses to an injector, note the fuel pressure drop, write it down, and move to the next injector - repeat. This way, you can get a rough idea whether or not your injectors flow equally. The injector pulsewidth can be 4mS - 500mS. Your choice, just make sure it is enough to move the gauge far enough to get a good reading. Don't forget to WOT start the engine afterwards to clear the fuel. I bought the injector pulser tool a long time ago, before the arduino or Basic Stamp was born.

  6. #51
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    bosch sensors explain the odd readings you have, even new they are garbage and can`t switch fast enough for the superior GM pcms.
    Get a delco ones and for the sake of money savings, don`t buy anything bosch related for GM cars.

    There is a minimum keep alive blm settings, that explain the 120 blms at startup. For vettes it is set at 120, changing it to 128 must fix the lower blms at startup.

    Look at the wideband reading not as extremely accurate tool, but as a fixed constant to dial the ve and maf curves and get a match between commanded and actual afr. After that offsetting the whole tables up or down will get you the sweet spot you are looking for.


    SInce I also have elongated start times at clod startup around 25-35 C, and great start time less than 0.3 seconds at warmer engine, went through the code to see what is happening.

    The prime pulse is complex as hell, in your case you will have to adjust for new injectors along with the extra cube. The good way is to convert the stock BPW readings to grams of fuels. than add some fuel for the extra cubes and convert from grams to bpw of the new fuel flow constant. I still haven`t found the switch point between prime pulse and the crank ve calculations. There are 2 different afr crank tables that switch around 0.4 seconds of cranking, which must be the norm of cranking time around 0.3 seconds.

    The good news is that afr and delta ve mode 4 control all works in cranking mode. Changing these before cranking with igntion on will cut the guess time. Only crank spark is unchangeable. I have noticed that you set the crank spark at 12 degrees, stock is 7. Any explanation on that why it is needed.

  7. #52
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    bosch sensors explain the odd readings you have, even new they are garbage and can`t switch fast enough for the superior GM pcms.
    Get a delco ones and for the sake of money savings, don`t buy anything bosch related for GM cars.
    I wish I'd known this a couple years ago. Bosch is generally OE on my daily driver (a diesel VW) so I thought they were of decent quality. The cost differential wasn't even $20 - more like $12. AFS75s arrived couple days ago.

    Quote Originally Posted by kur4o View Post
    I still haven`t found the switch point between prime pulse and the crank ve calculations.
    I had always assumed it switched to the crank VE table after the first two low res pulses simply because the ecu should have determined sequence by that point. But your understanding of machine language trumps my theory.

    Quote Originally Posted by kur4o View Post
    I have noticed that you set the crank spark at 12 degrees, stock is 7. Any explanation on that why it is needed.
    I haven't modified the cranking spark table. This must be another Y-body specific thing.

    Code:
    12075 Crank Spark Advance vs Coolant Temp
    -40	14
    -28	14
    -16	14
    -04	14
    08	13
    20	13
    32	12
    44	11
    56	10
    58	9
    80	8
    92	7
    104	6
    116	5
    128	4
    140	4
    152	4
    After more research I'm finding that the location of my O2s (both binary and UEGO) shouldn't be causing an outright skew of AFRs - the source I'm referencing says they should still report stoichiometry accurately. Linearity above and below stoich is where exhaust pressure can affect the output. So I'm hoping they will agree once I get the new binary sensors in and some pure dino gasoline running through it.

  8. #53
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    I went through the code and there is 1 pulse on first opti event, and there is 1 more on the second opti event. All pulses are corrected with baro reading. Than it starts to calculate fuel based on crank afr and ve tables.

    First at reset a value from table $2682 is loaded for initial BPW, not sure if injectors fires with this value.

    AT first opti event a value from table $2691 is added to the initial BPW, injectors for sure fires with this BPW.
    At second opti event a value from table $26A0 is added on top of the already calculated BPW, injectors also fires.
    On second opti event injectors also fires with values from crank ve and afr tables.

    There are some other tables that seems to do nothing and are labeled with crank names.



    For the first 16 opti events[2 full engine revolutions] the $2504 crank afr table is used, AFter that the pcm switch to $25f7 crank afr tables.
    The tables are vs coolant and opti event number.

    UNtill the engine running flag is set it could be a batch fire mode or it could be sequential. It is decided from the TPU processor, which we don`t have access to the built in rom.

    Bigger cubes might need less spark advance at startup. Trying the f-body crank table could help abit.

    A healthy starting time is around 0.3 seconds. The prime pulse plays the biggest role here. Usually the crank ve and afr tables comes into play after that.

  9. #54
    Fuel Injected! spfautsch's Avatar
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    That's awesome, thanks for taking the time to research that.

    I've finally been able to spend some "quality time" methodically troubleshooting. Step one was to put my stock multec injectors in and revert to stock cranking tables and injector characterization. That made zero difference.

    Continuing on, the first thing I found is that my fuel pressure was hovering around 50-52psi while the pump was running (engine not running). After the pump switched off pressure dropped immediately to 42-44 and held. Leakdown was about 2 psi every 10 minutes. I'm kind of embarrassed that I didn't check fuel pressure sooner - I thought I had when this problem first started to materialize but I guess I didn't. Anyway, I replaced it with a 3 bar regulator I happened to have in my parts bin that fit and now the pressure maxes out at 42-44 and holds at 42 after the pump stops running.

    The other simple thing I hadn't looked at very recently was plugs. They were a little wet and fouled, but I wanted to try and salvage them since they're almost new AC double platinum 41-906s. Cleaning the first one with carb cleaner I then hooked it up with a grounding clip and tested the spark by hooking up my spare opti and spinning it by hand (with the injector and fuel pump fuses out). All I can say is I'm confused. The spark kernel was seemingly avoiding the platinum discs and jumping from the perimeter of the center electrode to the outsides of the ground electrode in an orange-ish ball. Very odd... I took some 600 grit wet or dry paper and cleaned up the platinum discs but if anything that made it worse. So a dirt cheap set of NGK TR55s were bought, gapped to 0.045 and a hot blue spark was witnessed.

    Planning to finish installing the plugs and the new O2s tomorrow, will report back soon.

  10. #55
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    That might be the culprit of the weak spark you had recently. The energy of the ls1 coils is too much for the platinum disks to handle on these plugs and the spark scatters taking the least resistance path around the platinum disk. I should say they are either defective or the ls1 coils are overkill for 41-906s. Tr55s are always better for non stock application, but they must be replaced quite often for optimal performance.

    If your fuel pump can support 60psi and you have a regulator for 60psi, go for it. Much better spay pattern and atomization with the newer ls1 style injectors.

  11. #56
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    That might be the culprit of the weak spark you had recently.
    I think I might have possibly eliminated weak spark as the problem. Read on...

    Quote Originally Posted by kur4o View Post
    The energy of the ls1 coils is too much for the platinum disks to handle on these plugs and the spark scatters taking the least resistance path around the platinum disk. I should say they are either defective or the ls1 coils are overkill for 41-906s.
    Since this is the first time I've ever used a double-platinum plug to check spark strength (normally I use a new + clean champion that I keep in my toolbox for this specific purpose) I 'm going to go out on a limb and say I think these type of spot-welded disk platinum plugs are just junk. I also dug out my old OE plugs that have been run an unknown amount (possibly original to the car) exclusively with the optispark / hei2 setup. This is the plug on top, the plug below is essentially new. Notice how the center electrode is eroded away around the perimeter of the platinum disc. Also, the ground electrode has long since expelled it's platinum.



    Quote Originally Posted by kur4o View Post
    Tr55s are always better for non stock application, but they must be replaced quite often for optimal performance.
    I just wanted something I could get cheap at the local parts house. Since I'll need to order some water pump gaskets from my favorite online parts house I'll probably buy several different exotic plugs (double iridium, ruthenium, ???) to compare. The prices there are almost $4 per plug cheaper than the local wallet sucker parts house.

    Quote Originally Posted by kur4o View Post
    ... and you have a regulator for 60psi, go for it. Much better spay pattern and atomization with the newer ls1 style injectors.
    This makes me wonder if there is a OE style 4 bar regulator that's a direct fit for this application. But unfortunately this pressure problem was with the original non-adjustable 3 bar regulator. I'm going to cut it open when all this is over and see what's going on internally, because it seems like the problem could be caused by clogging in the return section. The lines don't seem to be the problem because the new regulator doesn't exhibit this behavior.

    Anyway, as I parked it three weeks ago it wouldn't even start without giving it pedal. I wasn't sure what had happened but in my troubleshooting process I noticed I'd left the radiator cap sitting loose so I likely boiled the coolant during my last few test drives. This made me wonder if I'd burned some exhaust valves. So after the plugs and factory injectors made no difference I started out by doing a complete compression check. Every cylinder was within 2 psi, so I breathed a huge sigh of relief.

    I then installed my new binary O2s and recalibrated the UEGO, thinking all the while it may be the sixth Tuesday of the month of Never before I get to enjoy the fruits of that labor.

    After that I decided to check off a few other remedial things vilefly suggested. Hats off to you sir.

    Since it wouldn't run, I flashed a bin with 0 degrees cranking spark advance and had the wife crank her while I observed with a timing light. To my surprise I was never able to see the painted-on timing mark. After confirming by checking the opti outputs with my ignition controller's timing check mode, I found the low res pulse was retarded a massive amount. Seems like when it got hot the loctite "high temperature" sleeve and bearing retainer I used to secure the two parts of the opti hub together got soft enough to allow the hub to slip.



    I had assembled this around December of 2018 when I had bought a spare opti base and decided to do some disassembly to discover what rebuild options there were. This is the rebuilt hub that came with the car. I removed the 1/8" roll pin that originally filled the hole because according to my degree wheel it was off by about 6 degrees - 2+ of which was due to my cam needing to be installed advanced to make target ICL.

    Anyway, I'm debating putting this back together and re-drilling the hub for another roll pin. That, or looking for an adjustable MSD base I can get cheap off eBay so I won't have to trial-and-error 20+ times to get the junk opti hub installed back at zero like I did back in December 2018 (with the engine comfortably mounted on a stand).

    Thinking back along the progression of this problem, it seems highly possible this was the entire cause, and that the opti hub slipped more than once. An initial slip of a few (8-16) degrees of retard would more than explain the difficult cold start, lean readings and rich smell I was describing at the beginning of this thread. Where it's at currently is at least 30-40 crankshaft degrees retarded. I'm surprised it would start at all.

  12. #57
    Fuel Injected! vilefly's Avatar
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    Timing lights are still not obsolete, folks. It still urks me that they are fading away from the public's reach, due to the illusion that computers don't make timing errors. One of these days I am going to build a timing pointer with its own LED strobe built in. Stroboscopes used to rule the days of old due to their usefulness. Still used to balance driveshafts. Mystery solved.

  13. #58
    Fuel Injected! spfautsch's Avatar
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    I'll be sure to pass your outrage along to the dealership the next time I buy a new car. I need a damper that's keyed and marked for TDC and a dipstick on that automatic transmission or there's no deal. Pfffft!

  14. #59
    Fuel Injected! vilefly's Avatar
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    Don't forget to make sure it has more than just one keyhole in it. The new camaros are so wrong when it comes to unlocking it with a dead battery in the back. I'd just have to drill holes in it to install my own tumblers. The door handles are electrical membrane switches, no mechanicals.

    Fire that engineer.....now. And call off christmas!
    Last edited by vilefly; 09-09-2019 at 04:45 PM.

  15. #60
    Fuel Injected! spfautsch's Avatar
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    Well if you knew me the only thing funnier than my demands was the part where I said "buy a new car". Never gonna happen (unless I win powerball).

    A mechanic buddy of mine owned a '18 Camaro. Notice the past tense. Turns out the key fobs don't like cold much and he found it was damned hard to get the car to start at 5F when there's no manual ignition and the bcm isn't seeing the key fob.

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