Lean burn to GM TBI/Microsquirt conversion

Engines, Exhaust and Fuel Systems

  1. R.W.Dale

    R.W.Dale Well-Known Member

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    Thanks for the add fellas. New member making a pretty technical first thread.

    I have been collecting parts and in the next couple of weeks I will be taking my 88 Fifth Ave out of action to convert it from all original lean burn to Gm TBI with a microsquirt.

    I’m a hot rodder at heart but in this case I just want a reliable smooth fuel efficient daily cruiser. I’m trying to make this conversion happen in the easiest least invasive way possible. Performance is very much down my list

    parts list so far
    1995 Chevy van TBI unit (rebuilt)
    Mitsubishi/mopar 3.0 coil
    Stock lean burn distributor
    Gm 7 pin hei module
    Microsquirt pcm
    Honda injector resistor box
    Airtex E2000 fuel pump
    Jeep 258 to tbi carb adapter


    My plan is to use the stock fuel and return lines and in-line the pump at the rear.

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  2. Mikes5thAve

    Mikes5thAve Well-Known Member

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    Sounds like an interesting project. I've thought of trying to use the throttle body injection from a 350 on my 360 before.
    The factory fuel line isn't meant to hold pressure so you might want to change it for safety. Even with tbi gm converted their lines over.
     
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  3. R.W.Dale

    R.W.Dale Well-Known Member

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    The steel line will be fine. The soft parts will get replaced with efi rated hose.

    The line pressure will be under 15 psi at all times so it’s not nearly as dramatic a change as with multi point injection 65ish psi.
     
  4. Mikes5thAve

    Mikes5thAve Well-Known Member

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    Also check the lines where they run over the frame by passenger wheel. They are prone to rusting out and leaking there from dirt accumulation holding dampness against them like a sponge.
     
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  5. R.W.Dale

    R.W.Dale Well-Known Member

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    10/4 I will inspect that area. Thankfully this is a 100% rust free southern car. Even the battery box still has paint on it.
     
  6. Duke5A

    Duke5A Well-Known Member

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    Very interesting project indeed. If you do end of needing to replace hard line then I would opt for the nickel copper stuff. Very easy to bend/flare and is corrosion proof. I'm using it in my fuel injected system.
     
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  7. R.W.Dale

    R.W.Dale Well-Known Member

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    Copper nickel is very good and easy to work. the aluminum I used on my turbo LS truck was pretty easy too. If I had a favorite though it is nylon like modern cars use.

    But I plan to do this swap on the CHEAP and fast. It’s going to be EFI rated rubber and hose clamps.

    another thread of mine showing using nylon. TheSamba.com :: Performance/Engines/Transmissions - View topic - Krochus’s turbo 2165 Baja Bug sequential EFI swap
     
  8. R.W.Dale

    R.W.Dale Well-Known Member

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    Minor progress. There’s really no way to hook a tbi to a rubber hose without a pile of oddball expensive fittings.

    so being the creative cheapskate I am I tig welded/blobbed some stainless steel barb fittings to the TBI fittings that thread directly into the injector pod.

    it’s ugly but cheap hopefully it’s going to clear everything. I did dye pen the welds to make sure they weren’t porus.


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  9. 89.Fifth

    89.Fifth Well-Known Member

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    I love progress posts. Can't wait to see what you do with it.
     
  10. R.W.Dale

    R.W.Dale Well-Known Member

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    I’m still working around the edges until my microsquirt arrives and the real progress starts.

    I mounted a few components namely the Honda injector resistor box which is required to use a microsquirt with low resistance injectors to prevent over amping the injector drivers. Also mounted was a part I have had for quite awhile an edelbrock “ignition amplifier” which is nothing more than a Gm 7 pin hei module in a fancy branded box/heatsink

    one question I have for you guys is about how the lean burn system and stock ignition is powered. I’m trying to decide if I need to run new wiring and fuses to power my EFI stuff. Do you know, is the lean burn power supply fused somewhere?


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    Last edited: Mar 16, 2021
  11. Mr Volare Imperial

    Mr Volare Imperial Well-Known Member

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    ...why do I recall something about the GM HEI system running on more voltage than a stock non-LB mopar distributor pick-up coil runs which overheats and burns up the HEI... I think it was the guy's webpage who sells the vacuum advance limiter plates. I seem to recall he made ignition control boxes, too. Good question you posed :) Keep it up!
     
  12. Mikes5thAve

    Mikes5thAve Well-Known Member

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    The power for the computer is dark blue wire and fused. Its normal 12v.
     
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  13. Gearhed

    Gearhed Well-Known Member

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    I've thought about eventually doing this, only I'd try and hide the microsquirt inside the original case from the lean burn computer, for stealth purposes
     
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  14. R.W.Dale

    R.W.Dale Well-Known Member

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    I thought about that but you can’t use the stock 2bbl breather

    I just snagged the breather from the donor van to use for the time being
     
  15. Gearhed

    Gearhed Well-Known Member

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    Gm tbi units do have a tendency to interfere with most air cleaner setups. What you could always do is take a stock assembly from a tbi car, cut the center out of it, and weld that into a mopar assembly
     
  16. BudW

    BudW Moderator Staff Member

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    If this is for a manual transmission car, I see no (to very little) issues with what you are doing and eager to see how it goes.

    That said, Chrysler automatic cars, have a few technical issues that “GM designed” carburetors/FI's were not designed for.
    “GM designed” carburetors have the throttle stud located at 10:30 o-clock position when at idle and a 1:30 o'clock position when at WOT (Wide Open Throttle).
    Chrysler designed carburetors (any) have the throttle stud located at 11:30 o'clock (idle) to 2:30 o'clock (WOT). This all has to do with kickdown linkage controls (when action starts and rate of control).

    I can't tell you how many times I have had to fix a customers transmission not shifting correctly concern when only change to vehicle was the installation of a “GM designed” carburetor. That small amount of change makes a big difference – even when kickdown linkage is adjusted correctly. In all of those cases, installing a Chrysler carburetor adapter then readjusting the throttle cable/kickdown linkage fixed the problem.
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    The Chrysler based throttle body injection vehicles have the throttle stud in correct location – but adapting that style throttle body might be a lot more work.
    BudW
     
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  17. R.W.Dale

    R.W.Dale Well-Known Member

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    Bud you just hit on one of the main considerations I took into account for a couple weeks trying to decide if I wanted to use a GM based throttle body or a Dodge one with an intake swap.

    in the end I decided that since the throttle cables would be wrong on either setup I would go with the cheaper much more available GM unit.

    I’m not going to show it in detail yet because it’s crude and I’m not sure if it’s correct yet but I removed (read cut) the Gm linkage provisions from the TBI unit and tacked on a bracket to use a mopar throttle stud and match the carbs geometry as much as possible.

    plan B will be to cut the throttle arm off the carb and TIG weld it onto the TBI unit.

    this is something I won’t be able to hash out fully until I take the car out of action which will be after I finish my microsquirt harness and get a wideband guage delivered. Probably another week or so.
     
  18. BudW

    BudW Moderator Staff Member

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    A person might be able to take a (any) Chrysler carburetor, cut off the arm and adapt it to your throttle body.
    I have a few Thermoquad's that are locked up (I bought, cheap, for parts). If you want to pay for freight, I can send you an arm (or the whole baseplate). That ... might ... be a good solution (maybe).
    BudW
     
  19. R.W.Dale

    R.W.Dale Well-Known Member

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    I appreciate the offer I’ll let you know if that becomes necessary but my feedback carb should be able to make the ultimate sacrifice if necessary
     
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  20. R.W.Dale

    R.W.Dale Well-Known Member

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    You know I was cleaning the grease ball engine today getting ready to start “de smogging” prior to the swap and I keep looking at that EGR valve that I had originally planned on deleting, I’m beginning to think I’ll keep it and later down the road try to work up a switching/tuning strategy for it it to assist in very lean burn cruise tuning later to maximize mpg.