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Thread: $EE / LT1 Injector Swap Running Rich

  1. #1
    Fuel Injected! spfautsch's Avatar
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    $EE / LT1 Injector Swap Running Rich

    Moderately built LT1 / bored .030" over w/ ported heads and intake, moderate cam (CC 467) and 1 5/8 tube headers. Been tuning with the factory 24 lb injectors since finishing the rebuild, and have good confidence my VE tables are rock solid - at least in "normal" driving ranges (all load ranges up to about 3200 rpm). Runs great in SD mode, makes incredible power up to fuel cutoff @ 6800 rpm but hard to tune there because the rear tires aren't big enough or roads long enough.

    So having a long weekend to tinker with it, I thought I'd try installing the no name brand, auction site injectors I bought when I started the build. The specs provided claim these are 36lb/hr / 380cc/m "skinny" bosch gen 3 clones. The auction shows Bosch 0280155737 as an equivalent part #. I'm starting to think I might have wasted $90 (I know, why go cheap here). After four months of tuning this isn't the only thing I've found I shouldn't have pinched pennies on, but a poor man has to try...

    Initial start I used 36.0 lb/hr for the injector constant, and an extrapolated offset / voltage table that the seller provided. It did start and run, but with newly installed (dry) injectors and the fuel rails not completely purged of air it wouldn't last long. Subsequent start attempts seemed to flood instantly. Zeroing the injector offset adder table and cutting all the tables with "* prime pulse width vs coolant temp" (adder) tables by half made no difference. Still would only start after opening throttle to clear the flood.

    Next steps were to increase the injector constant by 1lb / hr, followed by cutting the injector offset vs voltage table by 25%. Twelve or thirteen flash cycles of the E side later I'm at offsets lower than the stock Rochester specs and 42lb / hr IFC.

    Oddly, when warming up at idle with commanded AFR of 14.0:1 the narrowbands are indicating a lean condition of ~130mv. Then closed loop / BLMs turn on and it immediately turns pig rich (~850mv average on the narrowbands over a short drive).

    This is my first injector swap, so I'm sort of grasping at the idea I must have forgotten something obvious.

    Any thoughts or ideas appreciated, including recommendations for a quality set of 32-36 pound 3 bar injectors with a known good datasheet that I won't have to sell a kidney to own. I would especially like to make these triple-C injectors function acceptably for the time being, but at this point the money lost on the junk injectors is somewhat irrelevant. I've built the valvetrain and reciprocating assembly to survive 7000 rpm. That, in addition to the cam, port work and exhaust it should be able to touch on 460-500 crank hp which is (according to what I've read) well beyond the flow capability of the 24lb factory injectors north of 6000 rpm.

  2. #2
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    Go and get known GENUINE Bosch injectors. Green giants should be OK here. I've had chinese knockoffs get stuck open suddenly and flood the engine completely. Then you try to start, and destroy the hydrolocked engine...
    Not to mention complete weirdness trying to tune that shitty injectors...
    It's really not worth it to waste your time and good engine with cheap injectors.

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  4. #4
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    Bosch D3 series injectors are well controllable at low pw, so I don't think you'd run into problems. I used them on 383 sbc that made 420hp on a dyno.
    In your case red Bosch D3's (0 280 155 759) 32lb/hr should suffice to around 430bhp...
    Those are two injectors with known good tuning data, so I'd stay with them.

  5. #5
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by spfautsch View Post
    Greens are 42lb / hr - any problem with those at hot idle on a 355ci / 5.7L LT1?
    Hi , saw the email.

    Don't know about the greens..
    I've had
    30lb Venom from TLF performance.
    30lb Modified Bosch 3(stainless later core) from Fuel Injector Connection
    42lb Modified Bosch Blue Demon 3 from Fuel Injector Connection.
    (tried several sets to rule the injectors out when I had the manifold issueand for peace of mind.).

    I did get some figures for the offsets with them but couldn't make much sense of them.

    Solomon did me an initial tune which was drivable OK but OL and I was used to BLM tuning so went closed loop.

    Since going OL with the wideband, my VE tables look nothing like they did CL and this motor likes to drink fuel.
    Solomon zeroed out the injector offsets.
    I've played with them without any better success.

    Are you using a wideband yet?
    I've always tried to get the idle right first. Currently I think my wideband needs a hard drive to get hot.
    Starting up tonight Idle was at 9:1 . After the run I'm at 11+

    Also I've had to lower my injector constant several times as I keep hitting 100+VE Table values.
    Steveo has said drop it by say 10% and the VE tables by the same amount. This doesn't seem to be accurate here. I don't know why. It takes 3-4 logs to get back to the ball park.

    A couple of points off around idle also seems to make a huge difference.


    I'd say drive the car for half an hour then start playing with the tune.

    If the car is running i'd just pull some fuel around idle.

    Are you
    Open or Closed Loop?
    Narrow or wideband ?
    Speed Density or MAF ?


    Mitch
    Who doesn't seem any further on than 6 months ago!
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  6. #6
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by dzidaV8 View Post
    In your case red Bosch D3's (0 280 155 759) 32lb/hr should suffice to around 430bhp...
    Those are two injectors with known good tuning data, so I'd stay with them.
    I'm trying to decide between the greens (0280155968), some remanned + modified blue demon 3s mentioned by mitch (very affordable), and 34 / 36lb 0280155868s. The latter were used on the 98-05 supercharged 3800 buick engines so I would think I could glean an offset table from a factory bin from one of those. They're also available new on a certain auto parts site for a very reasonable price.

    I'm at a point where I have some health issues eating into my wallet, and will have to sell another toy or two to afford this purchase (especially the greens). But I'd rather have more and not need it then have my car strapped to a dyno and find I can't feed the beast above 6000 rpm.

    Quote Originally Posted by Terminal_Crazy
    Solomon zeroed out the injector offsets.
    Do you mean the 'Injector Offset Adder' table (tunerpro)?

    Quote Originally Posted by Terminal_Crazy
    Currently I think my wideband needs a hard drive to get hot.
    Starting up tonight Idle was at 9:1 . After the run I'm at 11+
    Narrowbands are no different. Bringing the car up to temp at idle my BLM splits are horrendous. Idling after driving they're generally within 4-6 counts.

    Quote Originally Posted by Terminal_Crazy
    Also I've had to lower my injector constant several times as I keep hitting 100+VE Table values.
    Steveo has said drop it by say 10% and the VE tables by the same amount. This doesn't seem to be accurate here. I don't know why. It takes 3-4 logs to get back to the ball park.
    I would suspect the proportional relationship between injector flow constant and the fuel calculation that uses the VE table aren't 1:1.

    Quote Originally Posted by Terminal_Crazy
    I'd say drive the car for half an hour then start playing with the tune.

    If the car is running i'd just pull some fuel around idle.
    Done all that. The chinese injectors are going to get turned into keychain fobs. If they're rated at 36lb/hr and the injector constant in the tune is 46 lb/hr and I've tried a rainbow of different offset tables, something's rotten when the car won't start because it's flooding on first crank every time.

    Quote Originally Posted by Terminal_Crazy
    Are you
    Open or Closed Loop?
    Narrow or wideband ?
    Speed Density or MAF ?
    Currently SD CL with narrowbands only. I found out what I was doing "wrong" with trimalyzer and my last tune of VE seemed to be solid after logging a few hundred miles to verify. I did enable my MAF to attempt to calibrate it, but I suspect I have a wire or connector causing problems because it stopped working inside of 10 minutes.

  7. #7
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by spfautsch View Post

    Do you mean the 'Injector Offset Adder' table (tunerpro)?
    Yes.

    The voltage offsets I have are slightly higher than the stock figures at around 13V but I don't think they affect much if the motor is running well (and electrics are stable). (same sort of curve).


    If your injector constant is upto 46 on 36lb injectors they should be running _very_ lean.
    I'm now down to 38.5 on the Injector Flow Rate on the 42lb to keep the VE table within range.

    Running CL here even with a crappy VE table, the car would tune itself back happily enough.

    I hope the new injectors will cure your issue.

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

  8. #8
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by Terminal_Crazy View Post
    If your injector constant is upto 46 on 36lb injectors they should be running _very_ lean.
    You would think. The MostPlus injectors came out and stockers back in. Model # MO2A36 - if anyone is considering them save yourself the headaches and buy something reputable.

    Quote Originally Posted by Terminal_Crazy View Post
    I'm now down to 38.5 on the Injector Flow Rate on the 42lb to keep the VE table within range.
    I need to do this myself as I'm out of headroom in the bottom left corner of VE. I might try scaling with the factory injectors to see what happens. I'd hope a complete remap of VE would not be necessary. This is the primary reason I chose to wait to install the bigger injectors - I know the constants for the factory Rochester / Multecs are right, and if nothing else has changed but the injectors logic dictates you should be able to get back to where you were by simply tweaking the IFC and offset vs voltage table.

  9. #9
    Fuel Injected! spfautsch's Avatar
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    Remanned 42lb injectors showed up yesterday. Lacking any flow bench data (what happened there FIC?) I punched in 43.0 for IFC and used an offsets table I found for the injector part #s (12561462 - LS1/LS3 injectors). Initial start was ok, but it was quite a bit rich so instead of increasing IFC I took 5% off my VE table except for the 10 cells that were maxed out at 99.6. Now it's flooding when started cold (I have to pedal it to clear the flood), and sputters some when restarting hot. A short drive shows my trims are pretty close with these changes (I've been targeting 3% rich).

    Anyone have any ideas on how to prevent the cold start flooding? I haven't messed with any of the tables named "* prime pulse width vs coolant temp" since they didn't seem to have any impact on initial start pulsewidth previously.

  10. #10
    Fuel Injected! Terminal_Crazy's Avatar
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    As I've said I'm not using any offsets.
    If they aren't right, the fuel curve will be off anyway and you'll be retuning anyway to correct it.

    I've only bothered to lean out the Open Loop AFR table to lean out during startup & the Initial AFR Enrichments vs Coolant.
    I don't expect the other tables will make any huge difference to the startup.

    At idle you will be running around 2ms any small adjustment will be a relatively large jump percentage wise.
    Log and adjust VE tables or just lower the corner of the VE table from just above idle (rpm & map) ( or drop the whole table 3% first ).

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

  11. #11
    Fuel Injected! spfautsch's Avatar
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    I think you're confusing the offset vs voltage table with low pulsewidth adder. The tune you shared with me had a populated offset table. I've zeroed the low pulsewidth adder table which is what I think you're talking about.

    It's idling fairly well, not exactly like it was last month when my "long way to work" road was horribly mutilated by the Missouri Department of Transportation (we rednecks refer to it as chip-n-dip). But it's also 100F ambient and 50% relative humidity here so I haven't run it in this type of weather much to have a "baseline". Driveability is good. The seat of pants dyno says mid-range power isn't great, but again the weather may be a variable. I won't be able to collect much data to verify for quite some time, but my worst trim cell after a 10 minute drive was 5% rich so I'm not thinking a big VE remap will be in order.

    I'll experiment some and report back. I'm beginning to think there are some IPW calculations happening during cranking that don't reference the VE table or the injector flow constant.

  12. #12
    Fuel Injected! spfautsch's Avatar
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    Well color me stupid. No sooner than I clicked "post" it occurred to me there's a "Crank Volumetric Efficiency Vs. %TPS Vs. RPM" table that I hadn't adjusted to match the main VE tables.

    I'll have to test more after she cools down but it sprang to life almost as quickly as it used to (feels like within the first 180 degrees of rotation).

  13. #13
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by spfautsch View Post
    I think you're confusing the offset vs voltage table with low pulsewidth adder. The tune you shared with me had a populated offset table. I've zeroed the low pulsewidth adder table which is what I think you're talking about.

    It's idling fairly well, not exactly like it was last month when my "long way to work" road was horribly mutilated by the Missouri Department of Transportation (we rednecks refer to it as chip-n-dip). But it's also 100F ambient and 50% relative humidity here so I haven't run it in this type of weather much to have a "baseline". Driveability is good. The seat of pants dyno says mid-range power isn't great, but again the weather may be a variable. I won't be able to collect much data to verify for quite some time, but my worst trim cell after a 10 minute drive was 5% rich so I'm not thinking a big VE remap will be in order.

    I'll experiment some and report back. I'm beginning to think there are some IPW calculations happening during cranking that don't reference the VE table or the injector flow constant.
    I did say to get your data first!

    Nope, no confusion there. I've got the Voltage offsets set, I have since zero'd out the low pulsewidth adder.
    As I don't know that they are correct, close or way out, I've removed them from any interference in the data logging.

    This motor will start at 7.5:1 or less and 22.4:1 or more without any issue.

    If you do adjust your VE table i'd only adjust it fractionally from what you are calculating so it doesn't shift too far from where you are now.

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

  14. #14
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by Terminal_Crazy View Post
    This motor will start at 7.5:1 or less and 22.4:1 or more without any issue.
    You also have another 30 cubic inches of displacement, which is not insignificant.

    Quote Originally Posted by Terminal_Crazy View Post
    If you do adjust your VE table i'd only adjust it fractionally from what you are calculating so it doesn't shift too far from where you are now.
    I had the opportunity to do some more logging this afternoon and found the trims aren't very far from what they were with the factory injectors. I feel confident I'll be able to tweak the offsets and injector constant to "a happy place" without significant remapping of VE.

    The Crank Volumetric Efficiency Vs. TPS Vs. RPM table looks to have the biggest influence on my starting flood problems. Extremely rich pulsewidths on a 24 lb injector are a completely different animal with a ~43.5 lb injector setup. In addition, this cam is right on the edge of ridiculous in my book - the idle cells are around -30% from the factory tune. So far I've tried three different scalings on this table, all with extremely noticeable and some very promising results.

    I'll be happy to spend whatever time it takes to get this one just right because it's hard to describe how satisfying the sound is when the engine breathes to life within 500 milliseconds of crank start.

  15. #15
    Fuel Injected! spfautsch's Avatar
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    Is anyone aware of a "minimum injector pulsewidth" constant in $EE?

    I ask because I've removed enough of my Crank VE vs TPS vs RPM table that warm starts are coming in at 0.75ms pulsewidth and don't seem to go lower. I'm just curious because the specs on these injectors show a minimum PW of 0.52ms.

    I'm pretty sure I've run the crank VE table too lean, but it's hard to tell. It seems to be starting rough (long crank, sputtering start) when cool, warm and hot now. There seems to be a "black hole" startup spot where the ECT reads around 140f where once the valves have cooled down the difference between flooding and firing is awfully narrow.

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