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Thread: '94 Corvette Dyno Run Analysis

  1. #1
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    '94 Corvette Dyno Run Analysis

    Hey all,

    The other day I finally had a chance to get my Corvette dynoed on a dynojet. There were six run attempts, but we lost three due to the ground cable on the dyno falling off the car and dropping signal as a result. I had my laptop plugged in and running EEHack the whole time because I was using it to lock the car in 3rd gear, but when I went to close the program it warned me about saving the log. I totally forgot it logs passively in the background as long as you're connected. So I saved the log. The dyno shop wouldn't let me have the dyno data but they did let me at least take a photo of the dyno screen, so here we go:



    The dyno looks pretty noisy which could be the ground or could legitimately look that odd, I'm afraid I'm too new to the LT1 and 4L60E to be able to tell at a glance. My only real concern was the massive dip at the end of the first run, but it never appeared in any other runs, so I treated it as an anomaly.

    I did have a crack at inspecting the EEHack log, but again my inexperience in how this engine works made it difficult to interpret since I'm not sure what "normal" looks like for this type of operation. I did notice knock retard going on a lot at WOT, but not usually tied to an actual knock count event. In fact a few knock count events coincide with supposed ECU errors that only appear for a single frame, which makes me think they're serial data glitches rather than actual events. In addition the EEHack log analyzer seems to suggest I'm dangerously lean at WOT, and yet Trimalyzer's analysis suggests reducing several VE cells by 50% which seems to suggest running the engine significantly leaner for those cells?

    I understand that the experts here are pretty darn busy, and I'm not looking to be spoon-fed if no one has the time to run their own analysis of my logs and break it down for me. I'm perfectly content with being pointed in the right direction in terms of reading material and spending my own time reading up on how to interpret these logs and know what exactly I'm looking at in terms of operating parameters. That said, any help is appreciated as I'd love to become more familiar with this system and start making worthwhile changes. I do plan on going for an extended drive with EEHack connected later so that I can also have a log of "normal" driving parameters in addition to the dyno runs.

    Thank you all!
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  2. #2
    Fuel Injected! steveo's Avatar
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    hey glad you're enjoying my software

    a preliminary glace shows something seriously wrong with your fueling or maybe you have a miss at WOT. the eehack log analyzer is not wrong here. the reason you don't see that in trimalyzer, is good ol' trimalyzer is (rightly) filtering out WOT events, you can't tune power enrichment fuel with a narrowband, but you CAN use it as an indicator if you're going lean.

    in your case they are going totally nuts during power enrichment. could be a misfire (a misfire looks like a lean condition to an o2 as that cylinder just pumps air into the exhaust)

    but something is fishy there, i'm not used to seeing closed loop switching-like events during power enrichment.

    the only other thing i can think of is that someone or something has jacked around with the parameter controls in eehack or maybe even something in the bin so it's actually trimming during WOT which would explain the switching.

    I do see the integrator going crazy which I don't seem to remember being normal.

    any idea why that would be happening? ...did you force closed loop in the eehack parameter controls during the dyno run?

    see attached graph of abnormal behavior
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    just fyi and so we're clear a 'normal' log would be both o2 sensors pegged @ high voltage during the green area

    the reason your o2 voltage is dead low in between those events is the dyno is winding down so you're in DFCO (fuel is cut right off) (look at your MAP during that time and it's pulling heavy vacuum and inj. pw is zero)

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    Hey steveo, thanks for taking the time to respond. As I've mentioned before, yeah, I really do enjoy your software!

    During the dyno run, the only parameter I personally clicked was the button for 3rd gear. I left every single other "active test" parameter alone, so assuming EEHack isn't doing something odd in the background that shouldn't be it. The ROM on board is one I created based on a stock EE_16200891.bin, having brought over all the differences I deemed relevant to the old ROM. The changes, according to the difference tool in TunerPro, are to the following entries:

    >VIN number
    >Fan Enable Coolant Temp (Lowered to 183F/192F)
    >Main Spark Advance
    >Extended Spark Advance
    >Max Knock Retard
    >Max Knock Retard in PE
    >PE AFR Correction

    The altered tables look like this:
    changedmaps.jpg

    I couldn't find any difference that would explain the car being in closed loop correction during PE, at least with TunerPro using the EEXTRA definition. I thought it was weird to see closed loop behavior outside of cruise as well, but like I said, I don't know anything about LT1s. Good to know I wasn't going crazy, but now I'm a little worried that my dyno session might've done something nasty. Definitely would want to get to the bottom of this.

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    Fuel Injected! steveo's Avatar
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    well with that torque graph and intermittent lean id expect a miss under load to be causing this. an engine that is quite lean at wot is going to peg the o2 sensor low. all you know now is that theres too much oxygen in the exhaust, gotta find out why. maybe add some fuel and do some wot pulls to see if it gets better. dont need a dyno to do wot pulls.

  6. #6
    Fuel Injected! steveo's Avatar
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    you know looking at your screenshots, maybe your power enrichment table is just too lean. did you develop that table with a wideband? there's knock at WOT too. compared to stock bin you're like 7-8% leaner. the corvette calibrations aren't that rich to begin with. combined with the fact that your engine, injectors, ignition, fuel pump are probably ancient, you might have pushed it over the edge.

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    The table actually came with the car, so I had left it alone. When I get home from work today I'll go ahead and flash a stock ROM back to the car minus the coolant temp and BLM Locker parameters and go for a nice long drive while logging. Will post the results then. Thank you again!

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    Okay, just got back from a test run driving around some backroads and mashing the gas a bit. Starts in my garage, drives around, then as I get near to my house again I pulled off, used EEHack to lock the car in 3rd, then did some WOT pulls with it locked just like it was on the dyno for kicks. Then I put it back on auto, parked, and disconnected from the car.

    Before this test run I did flash a new BIN to the car, this time EE_16200891 except with Siderail Serial, 0E14, VIN, Calibration Part Numbers and Fan Enable Temp copied from the original BIN, and BLM Locker enabled. Everything else was stock. Flashed fine with WinFlash, and passive entry worked fine afterwards this time around.

    I had a look at the graph and it still looks very similar to the dyno run log. Not sure what I should attack from there. Spark plugs were last replaced in 2015, wires were last replaced...at some point, so I could get a set of wires and plugs and do that job I suppose. Not sure if that would explain what's going on, but at least now I've ruled out the tune as the culprit. EEHack wasn't on the "Control" page until the very end, so I don't think that would have anything to do with it either.
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    Power seems pretty low

    Check the wire that runs along the back side of the water pump to the opti spark.
    The 1994 production had issues with the long connector that plugs into the optispark.

    When these came out they pulled pretty much the same curve every time.
    70HP loss may be time for overhaul.

    The Knock Module in these cars should be upgraded to 16214681 and new knock sensors.

    Get a set of cheap 1.6 roller rockers
    ditch the cats or replace with High flow.
    Get some 26LBS injectors
    should bring you up over 300WHP

    1995 was the sweat spot for these engines 1996 went Communist OBDII.
    Most all the issues where worked out in the 1995 Model year for the LT-1 the power loss and reduction in drivability in 1996 prompted the CAC to build a late production LT-4 version to get back some of the losses.
    The 94 optispark I think has the old style Timing cover however the Corvette usually had the next version from the rest of the cars.
    If you are using Cats to tune you can take the 91C cop car tune an port over it will improve response an bring the torque up earlier.

    10134358 valve springs
    COMP Cams Magnum Steel Roller Tip Rocker Arms 1418-16

    I also Have a set of 280cc Wildly ported Cast Iron heads for these engines leave me a message if interested.
    Avatar is my motor 800 RPM 184ft Lbs Torque 18 inches x 18 inches x 9 inches thick external combustion engine.

    98 WS-6 full tube chassis rally car Aluminum Block LS2 (soon to be LSX 376)(in Storage)
    95 Suburban 6 inch drop, Pioneer DVD in Dash 5.7 TBI, 220cc 2.02x1.60 64cc heads, Stainless longtube headers 2.5 crossover 3 inch exhaust, LT-4 roller cam.
    2002 Seville STS

  10. #10
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    Quote Originally Posted by daveosx View Post
    Power seems pretty low
    News to me. I thought this was about what the LT1 was good for, based on some Googling I did. I have an automatic, and people say the 4L60E is good for about 18%~20% drivetrain loss, so I figured the engine was still healthy. But you guys would know better than I would.

    Quote Originally Posted by daveosx View Post
    Check the wire that runs along the back side of the water pump to the opti spark.
    The 1994 production had issues with the long connector that plugs into the optispark.
    Will do. The Opti has been replaced twice in the car's lifetime already, with the latest replacement being 2004.

    Quote Originally Posted by daveosx View Post
    The Knock Module in these cars should be upgraded to 16214681 and new knock sensors.
    Noted, will put that on the short list since that shouldn't be too expensive.

    Quote Originally Posted by daveosx View Post
    Get a set of cheap 1.6 roller rockers...10134358 valve springs...COMP Cams Magnum Steel Roller Tip Rocker Arms 1418-16

    I also Have a set of 280cc Wildly ported Cast Iron heads for these engines leave me a message if interested.
    No head work is going to be done until my dad and I make a decision. We're not going to do small things with the heads; if we're doing heads, we're gonna really tear into them and do the whole shebang, plus a cam. So that's not going to happen short-term. In addition we're sticking with aluminum heads and shooting for a stock idle that doesn't ruin emissions, so I'm afraid we won't be needing those.

    Quote Originally Posted by daveosx View Post
    ditch the cats or replace with High flow.
    Already a full Magnaflow exhaust including Magnaflow catalytic converters.

    Quote Originally Posted by daveosx View Post
    Get some 26LBS injectors
    I'll do that if I notice duty cycles getting over 80% or so. Until then it doesn't make much sense to upgrade injectors.

    Quote Originally Posted by daveosx View Post
    1995 was the sweat spot for these engines 1996 went Communist OBDII.
    Most all the issues where worked out in the 1995 Model year for the LT-1 the power loss and reduction in drivability in 1996 prompted the CAC to build a late production LT-4 version to get back some of the losses.
    The 94 optispark I think has the old style Timing cover however the Corvette usually had the next version from the rest of the cars.
    If you are using Cats to tune you can take the 91C cop car tune an port over it will improve response an bring the torque up earlier.
    I'm using TunerPro to tune, WinFlash to flash, and EEHack to do realtime stuff. Until I figure out what's going on with the tune that's on the car, which is stock as stock can be and should be running fine, I won't be adapting any other tunes. Thank you for the tip, though, I may look into it later.

  11. #11
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    1994-95
    Typical brand new would run closer to 290-300 RWHP
    In house the LT1 is known to make 1hp per cube at flywheel open headers.
    The 18-20% is about right.
    In 1996 the commiepinko and his hag signed a tax in I think it was anything less than 11lbs for 1hp so THEY DETUNED.

    I have built a couple 9 of these motors for various reasons one that I ran for 8 years 200K was 600 hp at 6800 rpm and tacked out to 9000.
    The bottom end was 4340 crower and balanced two bolt with girdle.
    TRW 1157 old fashioned pistons.
    Zero Gap secondary rings (Now available from Total Seal by phone)
    MH55V pump 80psi spring
    GMPP Hot Cam from parts catalog #6
    Timing chain tensioner https://www.ebay.com/itm/New-SBC-Sma...-/261872111036
    1.6 rockers self aligning no guide plates Hard pushrods
    The orange valve springs
    Crower Rev kit https://www.crower.com/valve-train-c...12-offset.html
    Extremely ported stock heads 2.02x1.6 (the web beweencylinder almost complete removed only .07 thick. The whole head wedged 5 degrees and intake side cut back to allow LT-4 manifold to fit.
    Under cut valves with sodium filled exhaust
    44lbs EV-1 5 hole injectors 42PSI
    True Try -Y headers and crossover at 52 inch from valve
    MSD optispark with Jacobs Electronics Module and Coil.
    TCI megaRaptor 1800rpm stall.
    This motor sounded like a bike engine when out of gear.

    The chain stretches at HIGH Rpm most guys use heavy spring and get shitty throttle response.
    Let it stretch just take up the slack. The lighter spring makes the throttle really crisp the crower rev kit takes care of the bulk of the Mass so no valve float.
    When these springs where introduced in @1990 they where engineered for NASCAR they are a low moment of inertia Alloy of Chromium Silicon.
    When you compress a spring and release the alloy has a period that it takes to react to the change.
    Guys use heavier valve springs to lower the length of period.
    The cheap price of the orange spring is intentionally misleading so that it can be used on claimer engines in racing as well.
    GMPP stocks them as part of their racing support.

    From 91 on We would put the rockers and springs on every vette when the owner complained of lack of power.
    Stock cam stock tune wakes engine up.
    rockers are available for @130 the springs for @80 <<<Do this you'll love the throttle response change
    The injectors will also make a big jump I used Ford Eco boost 26lbs on one of my LT1 not the latest direct port but the yellow ones EV1 style they FOG instead of squirt.

    I have two sets of Speedmaster 220cc heads in my office now.
    1 set going on my truck with an LT-4 cam.
    The other set I am modifying slightly to fit one of my LT1 blocks.
    After close examination all that is necessary to convert these heads is to the reverse flow is to pipe plug or weld over the oil drain back hole and notch the deck at the front and rear steam hole.
    I have used three sets of these heads they make power.
    Avatar is my motor 800 RPM 184ft Lbs Torque 18 inches x 18 inches x 9 inches thick external combustion engine.

    98 WS-6 full tube chassis rally car Aluminum Block LS2 (soon to be LSX 376)(in Storage)
    95 Suburban 6 inch drop, Pioneer DVD in Dash 5.7 TBI, 220cc 2.02x1.60 64cc heads, Stainless longtube headers 2.5 crossover 3 inch exhaust, LT-4 roller cam.
    2002 Seville STS

  12. #12
    Fuel Injected! steveo's Avatar
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    why are we talking about performance mods for an engine that is obviously broken or mis-tuned in some way?

    just fix the thing

    also i dont care what the dyno reads vs some other dyno.. huge variations are possible. the modulation on the torque output graph is the only thing i'm concerned with there

  13. #13
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    Quote Originally Posted by steveo View Post
    why are we talking about performance mods for an engine that is obviously broken or mis-tuned in some way?

    just fix the thing

    also i dont care what the dyno reads vs some other dyno.. huge variations are possible. the modulation on the torque output graph is the only thing i'm concerned with there
    My Express van was doing something similar. The valve springs had about 50 lbs on the seat and 110 @ .480. It was floating the valves so bad it lost 40 rwhp between 5,150 and 5,300.

  14. #14
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    Quote Originally Posted by steveo View Post
    why are we talking about performance mods for an engine that is obviously broken or mis-tuned in some way?

    just fix the thing
    My thoughts exactly, but as I'm new to V8s in general and the LT1 in specific, I would like help in figuring out where to look. I did upload a new log, and the "closed-loop-like" O2 operation during PE was still present across the board. Since this is clearly not normal operation, but since the tune now on the car is 100% stock save for the fans kicking in sooner and the BLMs locked at WOT, what exactly would this indicate?

    Thank you again.

  15. #15
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    With the blm locker the blm and INt must read 128 in any PE event. If it reads something else the locker might not be applied properly.

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