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Thread: Narrowbands Reading Super Lean at WOT ($EE / LT-1)

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    Fuel Injected! spfautsch's Avatar
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    Narrowbands Reading Super Lean at WOT ($EE / LT-1)

    Disclaimer: I have no wideband(s) and don't really intend to make that leap. I have cats that I'd have to remove to make a wideband in my x-pipe meaningful, and I'm not sure I want to spend $300-$400 for a wideband, welding in a bung and cat "delete" tubes just to learn I wasted $300-$400. My tuning methodology has been to tune SD and then MAF with the PE TPS threshold jacked way up. I've been using Steveo's eehack + trimalyzer and targeting 2% rich for everything. As far as I can tell this has worked very well. Read on.

    For more background (see mods in sig) I started out tuning my LT-1 build with the factory multec / rochester injectors. Once I was happy with the overall SD tune, and after striking out with some Cheap Chinese Cr@p eBay injectors, I swapped to some 42lb bosch d3 injectors from FIC. Racetronics 255l/hr fuel pump.

    After a few weeks I come to a nice SD baseline tune that runs very well with the bigger 42lb injectors. All the while I've been noticing this anomaly during WOT (super lean narrowband readings) that I never noticed before swapping from the stock 24lb injectors. I didn't really think much of it at this point because I wasn't "done".

    Skip ahead another month or so and I notice kur4o's post about a pump shot adder for $EE that works as a MAF adder / multiplier. This is the nudge I need to finally switch my MAF back on and get it tuned in (same method mentioned earlier of setting PE TPS threshold really high). 600-700 miles of logging later I'm at a point the MAF tune runs great, and I haven't even bothered to mess with the pump shot tables. Driveability is great everywhere - parking lot manners are as good as could be expected with 50+ degrees of overlap and it will suck you into the seat at will. But still noticing aforementioned anomaly.

    So I've reached a point I don't think there's any progress to be made tuning airflow. While I'm sure I'm asking for a barrage of "you should tune to a wideband" posts, I'm not sure it will help. What I'd like to do from here on is to get my PE AFR targets where I want them - ramping down from 14.0:1 at lower rpms to 12.8:1 at rev limit (6800 rpm) and tune for best performance. I'm relatively confident my SD and MAF curves are within +/- 2% at airflows above 70 gm/s.

    The only concern I have is the anomaly (note O2 voltages in screenshot).

    low-o2-at-wot-edited.png

    log: drivelog-10-20-2.eedata

    I've checked fuel pressure with a mechanical gauge during WOT passes and see no discernible loss. Also, I'm seeing zero PE knock above 2800 rpm. Additionally, the O2 readings don't stick at these low values - 7 frames after the one above when I'm letting off to shift, O2s are reading 901mv (left) and 848mv (right) at commanded 12.3:1. Also, preceding these low readings I see 835mv (left) and 808mv (right) at commanded 13.4:1 immediately after stabbing the throttle.

    My theory here, which I'm hoping to have confirmed or dismissed - is it possible my narrowband O2s are getting fouled with raw fuel causing them to read ridiculously lean here? Normally I would expect to see the O2 voltage floating steadily around 800-900 mv like I used to see with the factory injectors, but these numbers are DFCO low. If there's any possibility I'm actually running this lean I'd like to resolve the problem or at least confirm the cause. But short of connecting a fuel pressure transducer to a spare analog input on the ECM to verify that the fuel pump is keeping up, I'm sort of drawing a blank. Has anyone seen anything like this or have other thoughts / suggestions?
    Last edited by spfautsch; 4 Weeks Ago at 08:41 PM.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

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