Lean burn to GM TBI/Microsquirt conversion

[R.W.Dale]

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.

 

[Mikes5thAve]

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.

 

[R.W.Dale]

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.

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.

 

[Mikes5thAve]

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.

 

[R.W.Dale]

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.

 

[Duke5A]

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.

 

[R.W.Dale]

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.

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

 

[R.W.Dale]

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.


View attachment 42587

View attachment 42586

View attachment 42588

 

[89.Fifth]

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

 

[R.W.Dale]

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?

 

[FredMcJoe]

...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!

 

[Mikes5thAve]

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

 

[Gearhed]

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

 

[R.W.Dale]

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

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

 

[Gearhed]

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

 

[BudW]

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.

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

 

[R.W.Dale]

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.

 

[BudW]

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

 

[R.W.Dale]

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

 

[R.W.Dale]

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.