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Thread: $ee lt1 tuning cruise and idle

  1. #1
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    $ee lt1 tuning cruise and idle

    Alright first off thanks to steveo and others for the help diagnosing the drivability of my car. 1995 firebird, rebuilt .040 over, comp 276, pacesetter midlengths, using tunerpro and winflash. Ive put several thousand miles on it, and had it to the drag strip. Only pulled a 14.069 though, i feel like it should be faster, but take off is slippery to say the least. I installed a new aem wideband gauge setup. I tuned it on the dyno with our dynojet set up and it compares within 1 point of my wideband so i feel the readings are pretty accurate. at wot im currently running about 11.8-12 through the entire rpm range. from what ive read it should be closer to 12.5-13 and i plan on adusting it more but im also working on the cruise and idle mixxture because that is where it is most off.

    Theres a lot to explain here, i dont want to make it hard to understand or over explain things. ive done a lot to the tune but im just trying to understand more mostly.

    I changed the maf tables to help adjust the blms at cruise//low airflow. by about 10% in some places and smoothed it out with the graph. I also did pretty much everything steveo suggests on his sight like adjusting the corrcl, integrator delay, 02 reference voltage and im sure im forgetting some.

    The "problem?" im trying to fix is that at idle my blms become badly split, about 114 on the left and 140 on the right. almost exactly the same everytime. the integrators will hang out right around 128. Also at cruise, even with the maf adjusted down about 10% my blms still hang a little low at around 122-124 . Also at idle and at cruise, the wideband will read from 15.5-17. of course any acceleration at all will cause it to jump more rich. and also in open loop it of course hangs out around 14-1.

    I have done a lot of searching on what it should run at cruise on a na engine in general and it seems that this is too lean, i thought that maybe it would be for fuel mileage, but from what ive read, people say that it should still hang out around 14:7-1 at cruise and even idle, although more lean at idle.

    I have also of course done extensive diagnosing to make sure there are no mechanical problems. the maf puts out about 9-10 at idle and gets up to like 260 above 5000 rpm. seems about right. The plugs do look white, the ground on the is white, but not extremely bad, but it does look lean. the fuel pressure checks around 37-42. map sensor seems to check out also tried another one. 02 sensors are both new. checked extensivley for vacuum leaks using the integrators and brake clean. ended up rebuilding my throttle body it was leaking a little. also no leaks around my wideband sensor.

    im sure ive forgotten something, and ill be glad to answer anything else, or upload my tune or a log if necissary. sorry for the long post and thanks in advance for advice and help.

  2. #2
    LT1 specialist steveo's Avatar
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    Also at idle and at cruise, the wideband will read from 15.5-17. of course any acceleration at all will cause it to jump more rich. and also in open loop it of course hangs out around 14-1
    there's no way closed loop averages over 15.5:1; something is off there.

    at wot im currently running about 11.8-12 through the entire rpm range
    that's typical for a stock PE mapping and a maf working properly, which leads me to something about closed loop being screwed up.

    or upload my tune or a log if necissary
    please do

  3. #3
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    I hadn't really realized it but it is completely to do with closed loop. In open loop its right on. 13 at idle 14-15 cruise. I guess I kind of assumed open loop should run really rich. Also something that confuses me is at cruise the blms are low indicating rich yet the wideband shows lean and my plugs show lean. Anyway thanks for the reply I'll upload a tune and log when I get to the computer tonight

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    O2 sensor compares oxygen content in exhaust and oxygen content in atmosphere. If sensors are in different locations it is possible to get different readings... combustion could continue as gases travel down exhaust pipe. Dramatically different readings is not common though.

    Not looking at specs, but...

    How much overlap in cam? Are we seeing exhaust dilution? Where is the stock sensor compared to WB sensor?

    Split BLM after cam change was a common LT1 problem once upon a time. But I once had to diagnose split BLM's on a customer's car that would go to min and max limits all the time. It took a few minutes to find the problem because it was very unexpected. For some reason the LH and RH O2 sensor wiring was swapped. Not sure how that happened but correcting the wiring fixed the problem.

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    Heres a quick idle log, and a long drive log. sorry i didnt have a chance to record a shorter one today. Also thats the current tune im running.

    what steveo said about the closed loop really has me pondering because it does seem ok in open loop.

    I did some more vacuum leak testing tonight with brake clean and using the integrators watching for change, not finding anything. I was thinking i may check to make sure an injector isnt leaking slightly as well, though i wouldnt think it would cause these problems.

    what you say about the sensors make sense and im curious about that as well. the stock sensors are in pacesetter midlength headers, so they arent far from stock postion. The headers go into a y pipe and i put the wideband about 6 inches or so after the y. so realistically its a good three feet or so from the exaust valves and a couple feet downstream of the stock 02s.

    The cam is a comp 276 ( 278? maybe) its 112 lsa and like 224/230. from searching back when i first picked it up it seems to come up as basically that c503 cam.

    thanks for everything guys

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    One of these days I should really sit down and become fluent with TP. I have an old bag of tricks that works for me but doesn't allow me to view TP logs.

    Engines like to run in the 13:1 region. It often takes more work to dial them in as the AFR is leaned out to 14.7.

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    I guess I should ask should I just kind of ignore the blms and tune with my wideband and plugs ? And then see where I end up? If so should I try and tune with the be tables or maf or what. Aldo I guess I should try running with maf unplugged and see what happens.

  8. #8
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    I have a similar car, 96 WS6 Formula m6.


    I also have a similar cam with a generous amount of overlap, and my part throttle/ cruise WBO2 readings show similar to yours, mine being closer to 14.* to 15.* with a lot of fluctuations. I don't pay a whole lot of attention to the WB readings at these cruise conditions.



    What does it drive like, and what do your plugs look like?



    As 1Project2many suggested, the O2 sensors measure O2 amounts in the exhaust stream. And with low rpm part throttle conditions and a cam that has both valves open at the same time (for a varied amount of time given different cam specs), some unburned fuel and O2 gets pushed out into the exhaust.
    Also he mentions O2 placement vs stock placement. (headers may put them further downstream) This will effect when the pcm looks at the O2 signal, thus can effect a BLM split.


    There does seem to be BLM splits in LT1 cars, but from what I remember it seems to show up after the modifications begin..headers, larger throttle bodies, etc..


    A lot of guys descreened their maf sensors, and all I remember is the driveablity issues this seemed to bring on, and maybe cause for split BLMs? I still have my screen in mine, fwiw.


    For my cam anyway (GM847) 234/242 @.50 anything below 2000 rpm and the wide band goes nuts. Part throttle/ cruise WBO2 readings are not useful for my car anyway. I tweaked my maf tables in these rpm's and got it to drive pretty well. It's fatter than the 14-15:1 the WB is showing.



    I use my WBO2 for WOT tuning. This is where it shines for tuning AFR.


    However, getting the voltage offsets set correctly for whatever injectors you are running, and the fuel pressure setting is critical to a better tune.


    I am not so sure you will be happy trying to run a closed loop tune with that cam (not sure of the amount of overlap?).


    I can get mine into closed loop, but it isn't happy with that. If your car is an automatic, you can get away with more surging My car is a 6 speed.


    HTH


    Keith
    NE Tennessee
    04 Lightning Pullies n Tune CAI
    96 Formula WS-6 m6 383 LE3-Heads/GM847/N2O/ Ford 9" 4:33/Sus Work/Stickies/TunerProRT
    93 K1500 383 LT1 with Low RPM 4x4 torque cam

  9. #9
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    That sounds pretty close to what mine does. It drives great. Gas mileage seems decent. The only thing that concerned me was the wideband reading and when I removed the plugs they were a little whiter than they should be but not real bad. I do need to check and see if my maf has been descreened. It does also seem like above 2k rpm or so the trim is more rich and any load or acceleration whatsoever and it hangs from 14-15.

    Edit: My mass air flow has been de-screened. thank you keith for reminding me to check that .I also noticed something else when i checked this, i have my opti fresh air line routed in front of the maf sensor, so thats an unmetered vacuum leak, although i plugged it with the integrators pulled up and the difference seemed insignificant. although i still think i will re route it to behind the maf.

    unplugged the maf on the way home, runs the same at idle and cruise, as keith said, the wideband really jumps around a lot in these areas. The only time the wideband holds still like i would think it should is in open loop and at wot or heavy acceleration. At all of those points its close to where it should be.

    I'm thinking maybe i should try to run in an open loop for a drive and see how it cruises and reacts throughout... and maybe tune it that way. I just dont want to throw fuel mileage completely out. I drive this car everyday and on long trips a lot.

    Edit: i looked up my cam to verify, comp 276 224/230 112 lsa. calculated the overlap came up with 3.00
    Last edited by zoomo; 01-01-2015 at 09:02 PM.

  10. #10
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    Sounds like your there!
    If your still utilizing your knock retard system, and your not seeing knock retarding in your data logs, plus your WOT plug readings look good.. ( a light brown toast colored on the porcelain )... just drive it. 8^)
    Now..you need traction. That car will do MUCH better when you get it to hook. A set of Mickey Thompson Drag radials, or the Nitto NT05R drag radials do wonders for our cars.

    I used to drive mine daily (not rainy or snowy days though).

    Keith
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    96 Formula WS-6 m6 383 LE3-Heads/GM847/N2O/ Ford 9" 4:33/Sus Work/Stickies/TunerProRT
    93 K1500 383 LT1 with Low RPM 4x4 torque cam

  11. #11
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    Yes it seems to do well all around, after a wide open run and shut down the plugs were a little brown.

    After doing way too much reading about descreening mass air flows tonight, i feel that could very well be the cause of my weird readings at idle and cruise. I;m going to pick up a used one with a screen when i come across one.

    I am still going to try running in open loop just to see how it acts. it still does make me curious that it runs so close to spec on the wideband in open loop.

    Also, i am still using the knock retard, and the table im using is doing well but i did notice at the 1/4 during the end of the run. about 4500 rpm and above in third gear i would get some knock retard of a few degrees and it would keep pulling a little timing to the end(wot timing is 30-32 and thats what im getting). This doesnt happen on the street, and was consistent at the track. I wasnt able to fix it, as i killed my pcm uploading tunes at the track that day and had to be towed home 2 hours ha. I did although lower the timing down to like 26 and still had the same thing. I dont seem to get any retard on the street, although i dont run from 0-110 full speed on the street, so i assume it was either some bad gas, or maybe some heat buildup by the end of the track? ill be curious to see if it does any better this year with headers.

    and ya i would love to hook better and get down into the 13's or even 12's , but im scared of breaking stuff ha! its a long trip to any drag strip here lol. im currently running some nitto all seasons so my 60 ft is like 2.1 seconds ha.

    anyway thanks for the help guys
    Last edited by zoomo; 01-02-2015 at 06:03 AM.

  12. #12
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    Update for whom it may concern. I have yet to find anyone with a stock lt1 using a wideband to see what the cruise air fuel ratio is. So this is just in referance to studying how various cars cruise.

    It is OK and normal to run at 16-1 when cruising. People are experimenting running up to 24-1 in light load cruise situations. Many new cars Also use what's called a lean cruise. It seems ls1s have this built in and cruise at 16-17. Also if you read about people using efi to tune a regular old SBC , they are shooting for a cruising Afr of 15-17. Many people also suggest tuning your cruise until you feel a slight lean misfire then backing off a little.

    Now, no car will be the same. As others here have advised me, The proper way to tune a car is a combination of sensors, reading the plugs, and understanding how the car is running.

    All I'm saying is if your cruise wideband seems lean at 16-17 it may be normal. Just make sure things richen up as the load increases.



    Edit: I also did lean my wot out with the maf tuning , its 12.9 the whole way. Feels like it runs better like this, I'll know more once I get it back on the dyno :))

  13. #13
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    There really isn't a simpler way to check your cruise AFR then by watching the O2 sensors. You are running at lambda =1 or stoichiometric if they are switching.

    I'm not sure why you are tuning the WOT with the MAF. You change the WOT AFR tables if you want a different WOT AFR.

    The $ee LT1 or LS1 do not have a lean cruise mode. Both of mine drive down the road in closed loop with the O2 sensors switching.
    Last edited by lionelhutz; 01-13-2015 at 03:57 AM.

  14. #14
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    I'm not sure what that means about if its switching its OK. As far as I've seen cars will still switch back and forth because of the attempt to correct themself.

    I believe most would agree the maf should be tuned throughout the rpm range.


    When I tuned it only with the pe vs rpm and temp tables I was running too rich under non-wot pe situations. There's some information on this elsewhere, I won't take the credit


    You are right lt1s do not appear to have an option called lean cruise.
    Ls1 owners seem to be tuning this feature in using HP tuners. Also just to poke a little at you, it appears the L's does not use the $ee platform.

    My car drives down the road with the 02s switching in closed loop. But my arm wideband reads 16-17.

    I appreciate the help as always I just wanted to talk about my findings.

    all I'm saying is if you are searching this thread because you are in the same boat as my, try searching about other cars besides just ours
    Last edited by zoomo; 01-13-2015 at 04:59 AM.

  15. #15
    LT1 specialist steveo's Avatar
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    i still say your wideband must be miscalibrated or something. it might 'switch' with your narrowbands a little, but if your o2s are switching, your wideband should average stoich too.

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