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Thread: 94 F-body LT1 solving problems/tune

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  1. #1
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    Yes, I'm not sure LT1's ever had an EGR circuit that was active, however, all other ecm's have quite a few separate "tables" when the EGR is active. Or I should say, when the ecm thinks the egr is active.

    I read all the time where people block their egr and wonder why they have a part throttle lean and knock issue. IF THE COMPUTER THINKS THE EGR IS OPEN IT PULLS FUEL AND ADDS TIMING!!! These are tuneable events and corrections. Changing a cam/exhaust/heads etc drastically alters the egr qualities.

    Some egr's are basically on or off, other later ones are pulse width modulated and there are even more fuel tables and spark tables to work with that.
    Last edited by In-Tech; 08-26-2021 at 12:34 PM.
    -Carl

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    I've found only timing corrections due egr is opened. But can't find where the condition is leaner with egr engaged. Hit me to that table please.

    Also should I correct o2 swing table with cat removed?
    Mine o2 swing table is default. I tried to raise the values in this table to get some power in closed loop, but it seems the car accelerates even harder.

    How far should I move timing with 93 octane?

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    Are you using the EGR circuit?
    I haven't followed this thread closely, can you post the stock .bin you started with so I can find stuff? Most stuff I have seen can usually accept 5 more degrees of timing on a stock timing table if the engine is stock. If much has been changed you have to tune accordingly. Hopefully more experienced LT1 guys can chime in with how much is acceptable, shoot, they have a pretty aggressive timing table from the factory due to the reverse cooling so I creep up on it and do a lot of logging.
    -Carl

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    Quote Originally Posted by In-Tech View Post
    Are you using the EGR circuit?
    I haven't followed this thread closely, can you post the stock .bin you started with so I can find stuff? Most stuff I have seen can usually accept 5 more degrees of timing on a stock timing table if the engine is stock. If much has been changed you have to tune accordingly. Hopefully more experienced LT1 guys can chime in with how much is acceptable, shoot, they have a pretty aggressive timing table from the factory due to the reverse cooling so I creep up on it and do a lot of logging.
    The stock is in the very first message of this thread. Mod list is there too.
    I've disabled egr, but hadn't removed it manually. It is installed, but not working because of PCM.

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    Quote Originally Posted by yoheer View Post
    The stock is in the very first message of this thread. Mod list is there too.
    I've disabled egr, but hadn't removed it manually. It is installed, but not working because of PCM.
    Whether you are using MAF Sensor or Speed Density, if you've disabled the EGR Valve operation in the pcm, then it will not apply the EGR spark timing table modifiers.
    O2 sensors take care of the rest, provided they are working well.

    In the long run, your intake manifold will appreciate that you installed an EGR blockoff plate.

    Until you've personally calibrated your spark & fuel tables so that your LTFTs are all between 123 & 133 (123 is slightly better), leave the O2 sensors working.
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    Quote Originally Posted by LeMarky Dissod View Post
    Until you've personally calibrated your spark & fuel tables so that your LTFTs are all between 123 & 133 (123 is slightly better), leave the O2 sensors working.
    Yes to the 123, most stock cal's are like this!!! The engine will always respond better with the slightly richer mixture while the computer attempts to remove fuel rather than add.
    -Carl

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    Quote Originally Posted by In-Tech View Post
    Yes, I'm not sure LT1's ever had an EGR circuit that was active, however, all other ecm's have quite a few separate "tables" when the EGR is active. Or I should say, when the ecm thinks the egr is active.

    I read all the time where people block their egr and wonder why they have a part throttle lean and knock issue. IF THE COMPUTER THINKS THE EGR IS OPEN IT PULLS FUEL AND ADDS TIMING!!! These are tuneable events and corrections. Changing a cam/exhaust/heads etc drastically alters the egr qualities.

    Some egr's are basically on or off, other later ones are pulse width modulated and there are even more fuel tables and spark tables to work with that.
    By comparing the 1996 LT1 tables (which had an EGR) with the 1996 LT4 tables (which did not), we can see how the LT1's PCM handles EGR events.

    The obvious differences are the EGR-related error codes. Easy enough to disable, but only gets rid of the MIL. The LT4 sets the enable temperatures high to disable EGR but otherwise leaves the settings within sane ranges (Min MAP 22.2 kPa, Min RPM 900, Max RPM 2300, Enable Speed 8 MPH, Disable Speed 6 MPH...Enable Coolant Temp 151.25C). EGR Spark Advance is set to between 0.0 and 1.0 (odd they didn't just zero out the table). Those are the only differences between the two calibrations with regards to EGR operation.

    It would appear that merely making sure that the EGR enable values are out of a sane range is enough to disable all EGR-related changes. GM certainly seemed to think so.
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    Well if it is so, then i've disabled it correctly.
    What about CAT?

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    Quote Originally Posted by yoheer View Post
    What about CAT?
    Asked & Answered.
    Quote Originally Posted by LeMarky Dissod View Post
    GM uses the following values for vehicles that were never equipped with catalytic converters:

    Min Coolant Temp for CAT Protect = 150°C
    CAT OverTemp Threshold (Low Baro) = 1065°C
    CAT OverTemp Threshold (Mid Baro) = 1065°C
    CAT OverTemp Threshold (High Baro) = 1065°C
    CAT OverTemp Air Fuel Ratio = 12.2 AFR

    (Although I'd raise the CAT OverTemp Air Fuel Ratio to 14.7 AFR without any fear.)
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  10. #10
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    Quote Originally Posted by LeMarky Dissod View Post
    Asked & Answered.

    Oh that is clear. I'm talking about back pressure, so O2s can read different parameters without CAT. Any issue or just disabling cat protection(already done) and that's it?
    I mostly ask about fuel and timing modifications.

  11. #11
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    Quote Originally Posted by yoheer View Post
    Oh that is clear. I'm talking about back pressure, so O2s can read different parameters without CAT. Any issue or just disabling cat protection(already done) and that's it?
    I mostly ask about fuel and timing modifications.
    Should be totally fine. The O2 sensors care about what's in front of them, not what's behind them.
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    I know, that f-body and y-body engines are the same. 92-94 vette and 93-93 fbody. Same cam and all other stuff is the same. (Correct me if not)
    Just headers and intake differs a little bit. And 2 knock sensors instead of 1
    So is it good idea to take vette calibration and move all timing and fuel tables to my pcm? Tables differ a little bit. I compared em.
    What do you think about it?
    Last edited by yoheer; 08-31-2021 at 07:20 PM.

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    Quote Originally Posted by NomakeWan View Post
    By comparing the 1996 LT1 tables (which had an EGR) with the 1996 LT4 tables (which did not), we can see how the LT1's PCM handles EGR events.

    The obvious differences are...Forget about any kind of static ratio pertaining to a dynamic environment. Enable Coolant Temp 151.25C). EGR Spark Advance is set to between 0.0 and 1.0 (odd they didn't just zero out the table). Those are the only differences between the two calibrations with regards to EGR operation.
    edited above
    -Carl

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