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Thread: Cheap Alternative for LT1 Opti Issues

  1. #1
    Senior Member Grass-Passer Supercharged111's Avatar
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    Cheap Alternative for LT1 Opti Issues

    So this guy 411 (late LS1 PCM) swapped his 93 TA and used a 4X 96-97 OBDII LT1 reluctor/timing cover. He used an operating system from an Express van which was the only platform to receive this PCM and still have the older 5.7 engine. I'm using this PCM in both my 1500 and 3500. I guess it runs without the 1X cam sensor thus making it easier to fit to an LT1. A supposed consequence is that the engine then fires the injectors in batch mode vs multiport. Only thing we'd need to do for CMC is guinea pig it. If it has merit, we could have a spec CMC tune. Just as easy to cheat here as it is on pretty much any other car so I don't think we'd be opening up Pandora's box. These computers also came in jillions of trucks, so they're super easy to find. Just a red and blue connector 512k LSX PCM.
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  2. #2
    And there it is again, the beast of magic and foreboding....the wizardry of GM personified.....slayer of dreams.....confuser of the blue oval clan......dah dah daaaa, The Opti (so special even the T is capitalized)

  3. #3
    Senior Member Carroll Shelby Fbody383's Avatar
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    You have a source for more details?
    #39 CMC Camaro
    Orange is Fast!
    CMC-NT01 FTW!

  4. #4
    Senior Member Grass-Passer Supercharged111's Avatar
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    No, was hoping to not be the only one who saw this. What I can do is experiment with running on no cam sensor on my truck to mimic this phenomenon. Same operating system this Camaro is using.
    RM CMC Director

  5. #5
    Senior Member Grass-Passer y5e06's Avatar
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    I've looked into this in the past, and have seen the videos.
    Edit: he used a vortec type distributor in back, instead of the front mounted cam sensor, because he had the parts on hand. I saw the same videos. Not terribly expensive, but it is some work.
    Edit There is a different route for sequential fire & front mount cam sensor:
    basically, the top two items in this table:
    https://www.eficonnection.com/home/c...efi-24x-lt1lt4
    you could do it fairly cheaply; junk yard/craiglist 411 PCM & ignition coils, '96-'97 front cover (for crank sensor), Efi Connect components, and some time to re-pin the harness. the re-pinning doesn't look to bad, actually. the one catch is finding and agreeing to a standardized program.

    guy with the videos used this instead of the front cover mounted parts:
    [edit:deleted. I listed wrong part]. He used the vortec style distributor with plug wire terminals.

    https://www.youtube.com/playlist?lis..._BiVMa4pEUpWoD

    oh, 411 doesn't need to come from the van. lots of vehicles used it... including LS1 4th gens.
    Edit: vortec/van setup is batch fire. the '93 was batch fire. '94+ lt1 is sequential. 411 swap can be sequential if using LS type of setup and not vortec SBC stuff.
    edityou also, as shown from EFI connect, don't need to use the distributor in back (i.e. modify lt1 manifold) but the opti location for a cam sensor instead.
    edit edited incorrect details above. more investigation is warranted if there is interest. I wouldn't sign up to modify the manifold and mount a distributor in back (what a PITA that would be) but instead prefer the front mount cam sensor with coil-on-plug ignition. Perhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc. *maybe* you could do a sync only type of *distributor* in back and only have to mount the *distributor* ala LT1Intakes small cap HEI conversion. a sync distributor is not really a distributor as it doesn't distribute the spark to the cylinders but instead is just a position sensor.
    Last edited by y5e06; 01-08-2019 at 12:04 PM. Reason: Edited some incorrect details in my original post.
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  6. #6
    Senior Member Grass-Passer y5e06's Avatar
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    partial list of 411 PCMs, from another web source. accuracy TBD
    ADILLAC ESCALADE 2002
    CADILLAC ESCALADE EXT 2002
    CHEVROLET ASTRO (2001 - 2002)
    CHEVROLET AVALANCHE 1500 2002
    CHEVROLET AVALANCHE 2500 2002
    CHEVROLET BLAZER (2001 - 2002)
    CHEVROLET BLAZER TRAILBLAZER 2001
    CHEVROLET C3500 PICKUP HD 2001
    CHEVROLET C3500 PICKUP HD CHASSIS CAB 2002
    CHEVROLET CAMARO SS (2001 - 2002)
    CHEVROLET CAMARO Z28 (2001 - 2002)
    CHEVROLET CORVETTE (2001 - 2003)
    CHEVROLET CORVETTE Z06 (2001 - 2003)
    CHEVROLET EXPRESS 1500 (2001 - 2002)
    CHEVROLET EXPRESS 2500 (2001 - 2002)
    CHEVROLET EXPRESS 3500 (2001 - 2002)
    CHEVROLET S10 PICKUP (2001 - 2002)
    CHEVROLET SILVERADO 1500 (2001 - 2002)
    CHEVROLET SILVERADO 1500 HD (2001 - 2002)
    CHEVROLET SILVERADO 2500 (2001 - 2002)
    CHEVROLET SILVERADO 2500 HD (2001 - 2002)
    CHEVROLET SILVERADO 3500 (2001 - 2002)
    CHEVROLET SUBURBAN 1500 (2001 - 2002)
    CHEVROLET SUBURBAN 2500 (2001 - 2002)
    CHEVROLET TAHOE (2001 - 2002)
    GMC C3500 PICKUP HD (2001 - 2002)
    GMC JIMMY 2001
    GMC JIMMY ENVOY 2001
    GMC JIMMY SLS 2002
    GMC SAFARI (2001 - 2002)
    GMC SAVANA 1500 (2001 - 2002)
    GMC SAVANA 2500 (2001 - 2002)
    GMC SAVANA 3500 (2001 - 2002)
    GMC SIERRA 1500 (2001 - 2002)
    GMC SIERRA 1500 HD (2001 - 2002)
    GMC SIERRA 2500 (2001 - 2002)
    GMC SIERRA 2500 HD (2001 - 2002)
    GMC SIERRA 3500 (2001 - 2002)
    GMC SIERRA C3 2001
    GMC SONOMA (2001 - 2002)
    GMC YUKON (2001 - 2002)
    GMC YUKON DENALI (2001 - 2002)
    GMC YUKON DENALI XL (2001 - 2002)
    GMC YUKON XL 1500 (2001 - 2002)
    GMC YUKON XL 2500 (2001 - 2002)
    OLDSMOBILE BRAVADA 2001
    PONTIAC FIREBIRD FORMULA (2001 - 2002)
    PONTIAC FIREBIRD TRANS AM (2001 - 2002)
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  7. #7
    Senior Member Carroll Shelby
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    Quote Originally Posted by y5e06 View Post
    IPerhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc.
    I will say that when I LS swapped my car, the LT1 MAF I was using for my 96+ OBD ECU carried right over to the 99-02 LS1 harness/ECU no problems.

    Same MAF I believe was used 94-97 right?

    That's one less thing possibly, although what the tune is looking for in regards to MAF reading vs RPM/Throttle is a different story...

  8. #8
    Senior Member Grass-Passer Supercharged111's Avatar
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    Quote Originally Posted by y5e06 View Post
    I've looked into this in the past, and have seen the videos.
    Edit: he used a vortec type distributor in back, instead of the front mounted cam sensor, because he had the parts on hand. I saw the same videos. Not terribly expensive, but it is some work.
    Edit There is a different route for sequential fire & front mount cam sensor:
    basically, the top two items in this table:
    https://www.eficonnection.com/home/c...efi-24x-lt1lt4
    you could do it fairly cheaply; junk yard/craiglist 411 PCM & ignition coils, '96-'97 front cover (for crank sensor), Efi Connect components, and some time to re-pin the harness. the re-pinning doesn't look to bad, actually. the one catch is finding and agreeing to a standardized program.

    guy with the videos used this instead of the front cover mounted parts:
    [edit:deleted. I listed wrong part]. He used the vortec style distributor with plug wire terminals.

    https://www.youtube.com/playlist?lis..._BiVMa4pEUpWoD

    oh, 411 doesn't need to come from the van. lots of vehicles used it... including LS1 4th gens.
    Edit: vortec/van setup is batch fire. the '93 was batch fire. '94+ lt1 is sequential. 411 swap can be sequential if using LS type of setup and not vortec SBC stuff.
    edityou also, as shown from EFI connect, don't need to use the distributor in back (i.e. modify lt1 manifold) but the opti location for a cam sensor instead.
    edit edited incorrect details above. more investigation is warranted if there is interest. I wouldn't sign up to modify the manifold and mount a distributor in back (what a PITA that would be) but instead prefer the front mount cam sensor with coil-on-plug ignition. Perhaps you can use an LS1 type tune but would have to adjust for firing order and make sure correct for stock LT1 MAF etc. *maybe* you could do a sync only type of *distributor* in back and only have to mount the *distributor* ala LT1Intakes small cap HEI conversion. a sync distributor is not really a distributor as it doesn't distribute the spark to the cylinders but instead is just a position sensor.
    The EFIConnection stuff is 24x, the LT1 was 4x and the Vortec was also 4x but used a 1x cam sensor. While the computer doesn't need to come from a van, its 4x operating system will. The problem with just yanking the cam sensor is the engine doesn't know when a cylinder is on its compression stroke or not. I'm not sure why his motor ran fine without and I haven't tried yanking the cam sensor on my truck, but the way it misfires is characteristic of a cam sensor on its way out.

    Quote Originally Posted by Pranav View Post
    I will say that when I LS swapped my car, the LT1 MAF I was using for my 96+ OBD ECU carried right over to the 99-02 LS1 harness/ECU no problems.

    Same MAF I believe was used 94-97 right?

    That's one less thing possibly, although what the tune is looking for in regards to MAF reading vs RPM/Throttle is a different story...
    Same MAF. In order to get the MAF data right it needs to be pulled from an OBDII LT1, not sure if HPT supports this PCM or not. I know EFILive does not. No guarantee if you do snag the MAF data from an OBDII LT1 PCM that its reference points will be the same which means the data is then worthless. The only thing that should affect the MAF settings are MAF placement and intake plumbing. I know when I swapped my trucks from the black box to the 411 that the MAF data was different and used different data points. In the case of the 1500 it was on the same engine so it should have matched, but did not because of the different airbox setups between those 2 platforms.
    RM CMC Director

  9. #9
    How does the airbox impact MAF data? I mean...as long as everything going into the engine is going through the MAF the layout of the plumbing should have no impact.
    Al Fernandez
    CMC National Director

  10. #10
    Senior Member Grass-Passer Supercharged111's Avatar
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    It does. Bends create turbulence and different diameters of tubing affect velocity.
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