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Thread: $OD Switch from TBI to CPI - Corvair Pickup - Airflow Issue

  1. #1
    Fuel Injected! corvairnut's Avatar
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    $OD Switch from TBI to CPI - Corvair Pickup - Airflow Issue

    I know my projects are a little out there with the Corvair, but everything we do is learning (for me anyway). Its all from scratch on this end since I have to run 2 throttle bodies. I have the dual TBIs running for years now with good results... so that means its time to switch. I bought a Corvair Pickup and wanted to EFI it with MPI instead of TBI. I want to stay with GM 16196395, but wanted to do something a little different.

    I used the mini injector from 03 Vortec, so I have 6 injectors directly above in intake runner of each cyl (3 on each bank). I switched to a CPI chip and everything runs pretty good, but I'm having a idle issue and I have narrowed the "symptom" to airflow.

    Quote from another thread:
    1project2many
    Airflow is calculated using MAP, RPM, displacement, volumetric efficiency, and air temperature. This calculation is the heart of speed density.

    When my engine is idling, the lowest idle is around 1200 unless I plug the IAC opening. Idle stops are already at bottom. the IAC count is around 20, when I change to "IAC counts vs Airflow" to 0 @ 43.8% airflow, then idle drops to 750 as it closes the IAC. Trouble is, no idle under load and of course and other issues I'm sure. So this is telling me that the calculated Airflow is way out of whack.

    Why is it calculating 40%-50% airflow at idle?

    What am I missing. I started with a BPLH CPI bin and started right away after my DIS adjustments. I adjusted the injector rate to make it drivable, but I am missing something simple Im sure.
    Last edited by corvairnut; 06-21-2015 at 11:35 AM.
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

  2. #2
    Fuel Injected! corvairnut's Avatar
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    $OD Idle Mode - Non existant on the TBI to MPFI Switch

    OK.. it appears the airflow is high because it never goes into idle mode (Idle Flag = OFF).

    I think if I could get over this idle issue, this conversion from TBI to MPFI would be a snap.... but of course it never happens like that. I run the engine right now with the IAC blocked off to prevent 1500 RPM - Non idle. Everything runs pretty good except for the idle. I'm just randomly changing things now trying to find the offending setting.

    Any input would be appreciated.

    Ted
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

  3. #3
    Fuel Injected! sturgillbd's Avatar
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    What % does the TPS show when the throttle is closed? There are a few qualifiers that have to be met for the PCM be commanding idle spark and ve.

  4. #4
    Fuel Injected! corvairnut's Avatar
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    Thanks so much for jumping in on this topic.
    TPS is 0 volts/percentage. I guess maybe I the question should be what qualifiers does it take to command idle mode?
    I will post a log file this afternoon if that will help.
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

  5. #5
    Fuel Injected! corvairnut's Avatar
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    This is the latest bin and idle log file. You will notice in the log that the IAC is about 50% airflow (I have 100% set at 75 counts). I have the IAC blocked due to high idle, but the idle flag never trips. I unblocked the IAC at 3/4 of the way through... which increased idle of course and injected more fuel due to higher map. Very little has changed on the bin file except changes to make DIS work, Knock sensor, idle speed, etc. No matter what I adjust, I cant seem to get the injector pulse lower than .90 which may be the root of the issue. Using the "Async Short BPW Offset Bias" I was able to get idle to 126-130 BLM, but I notice the numbers from the O2 sensor that the swings are much lower number than the TBI.

    Keep in mind the TBI ran pretty good on this truck. One other note is that I am using a 6 Cyl CPI memcal but no jumper on the memcal since that should be only for V8 if I understand it properly.
    Last edited by corvairnut; 07-12-2015 at 12:07 PM.
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

  6. #6
    Fuel Injected! sturgillbd's Avatar
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    The CPI VE tables are quite a bit different from a TBI table. Compare the Idle VE tables from a CPI bin to a TBI bin. I also notice the TPS voltage is at 0V with the throttle closed. From everything I have looked at in your bin and datalog, the airflow % being high at idle is corresponding to the VE table. I think you are going to have to play with the VE table and fuel pressure. I also remember you having DIS and the trigger offset was odd but worked. These PCMs use timing advance and retard to help control idle speed. You are in somewhat uncharted territory and a lot of testing is going to have to take place to see what is happening.

  7. #7
    Fuel Injected! PJG1173's Avatar
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    There is a minimum PW setting that needs to be lowered.

    Minimum Synchronous BPW Allowed
    Minimum Synchronous BPW

    I had to change these in mine when I put bigger injectors in. I would love to see pic's of this setup.
    Last edited by PJG1173; 07-12-2015 at 07:26 PM. Reason: added settings
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  8. #8
    Fuel Injected! corvairnut's Avatar
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    OK..... Had another fire in the shop and I finally gave up and went back to a good running TBI setup. I have ran this setup for a couple of years and I think...maybe, it is what it is.


    One thing that I have noticed is that when in PE mode, my timing does not increase. This may be because of the changes I made to make DIS work with this setup and will use my time to figure out the TBI better before I go off on anymore wild goose chases.

    I'm going to take Marks' advise and create a new bin file from scratch and tune. I've learned a lot here over the last few years....wished I knew more.
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

  9. #9
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    do you have a balance tube like the old vw's did betwin the left and right side intake manifolds ?

  10. #10
    Fuel Injected! corvairnut's Avatar
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    Yes... The Corvair has so much reversion that a balance tube is almost required. I run the MAP and trans modulator from the Crossover to get a smoother signal.
    Ted Brown
    Anderson, SC
    68 Corvair EFI
    61 Corvair Loadside Pickup (Future EFI)

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