[Gmecm] ? about pre-efi gm ecm

[Rick McLeod]

Thanks, Jay. You've answered and confirm'ed some of my base questions.
I believe my route at this point is:
1227747 ECM (very common unit)
Painless Harness 60101 (they engineered wiring based on a 90 Chevy P/U)
Painless TBI adapter 60118 (solves the bolt pattern match issue)
Painless VSS Adapter 60115 (gets 2PPM from mechanical speedo cable)
TB from same size engine or modify cal on PROM to change inj size
PROM from same size engine (I can modify to suit)
Sensors/inputs: Knock, TPS, Temp, MAP, Spark, Speed
        I intend to make a plate to mount fuses, relays, MAP, etc onto to make installation clean, similar to the Painless plate
* Knock sensor exists
* TPS should be part of the TBI
* Coolant sensor (this is still an outstanding question, will the existing one suffice - I think so, if not acquire correct one)
* MAP sensor (this is still an outstanding question, will probabally have to acquire correct one) My sources show a valid 90 TBI 305 P/U part # as  OEM to be 16137939 but the parts houses show it to be 16137039, so am a little puzzled here
* Vehicle has large HEI dizzy, so Painless harness should plug right up
* VSS will be from the Painless VSS adapter
The last area that I'm not yet sure of is EGR and AIR (not A/C):
* I'm hoping the existing EGR controls will adapt to the new ECM w/ no changes, any help/comments here welcomed.
* AIR, haven't spent much time under the hood yet, so I don't know what is there in this area if any, may not need to go here at all. We'll wait to figure this one out when I see if the hardware is ther now.
 
If anyone has a good reliable source of pulled TBI's I'd appreciate that, otherwise car-parts.com search has turned up quite a few, and the swap may also discover one, so we'll see there.
 
If I have overlooked something, anyone please comment. I'm on my way on this, it looks like a rather simple project to pull off!
 
----- Original Message ----
From: Jay Vessels <jay at vessels-clan.com>
To: Rick McLeod <dunvegan at sbcglobal.net>; gmecm at diy-efi.org
Sent: Sunday, August 27, 2006 10:46:03 AM
Subject: Re: [Gmecm] ? about pre-efi gm ecm


Hi there!

> My objective is simply to get this vehicle to EFI with absolutely as
> little modifications as possible.

I understand that.  I did a similar swap on an '85 Caprice, from CCC 
Q-jet on a 305 to TBI, grabbed from an '87 Caprice 305.  It wasn't that 
bad.  The pre-existing dash wiring is nice since with some small changes 
you can re-use it.  The rest of the CCC harness is scrap.  The existing 
O2 sensor can be re-used, as can the knock sensor/module and CCC 
distributor.

> I was under the impression GM's initial TBI was essentially the next
> step in evolution from carb to EFI, transitioning through the CCC
> (short lived) phase

CCC wasn't short-lived enough.  It should have never seen the light of 
day.  GM knew how to do EFI before unleashing CCC on the world, and they 
were doing TBI as early as 1982.

TBI is just as valid an EFI system as port injection (MPI/TPI/SFI) and I 
like it a lot.  It has some advantages.  Simplicity and compactness come 
to mind.  Port injection certainly brings a lot to the table, but a 
properly-tuned TBI system isn't bad.  Check out the Ultimate TBI stuff 
going on over at Thridgen.org.

> Will the throttle body for a TBI directly replace the CCC carb, or is
> it absolutely necessary to lift the manifold and replace it?

Stock GM TBI units have three bolts in a roughly triangular pattern, so 
it will not bolt to a stock intake.  You can get/make an adapter plate 
to put the TBI on a carb. intake.

Your other choice is to get a TBI intake.  GM used TBI on cars and light 
trucks from around 1985-mid '90s.  Later model (1987+) intakes have the 
center four bolts angled differently than the older intakes.  There are 
ways around this, none of which are fun.  I redrilled a newer intake but 
was never really happy with it.  If I were going to do it again, I'd 
either get the adapter plate or I'd get something like the Holley 300-49 
TBI intake for older heads.  Knowing me, I'd probably spring for the 
Holley ;)

> If I can use the existing manifold, shouldn't all the linkage and
> kickdown cables essintially just hook up

It depends on your donor, but the answer is "probably".  When I get 
parts from a donor, throttle/TV/cruise cables are on the list.

> We've a local show and swap event next weekend, so I'd like to have a
> 'shopping list' in my pocket of things to try to find. With that in
> mind, will the 846 work w/ most any GM throttle body from an
> equivalent engine, ie from a truck w/ 305 or can I expand my search
> to include throttle body units from the 350 as well.

Almost all 2-barrel GM TBIs are the same mechanically and electrically, 
with the exception being throttle bore size and injector flow rate. 
4.3/305/350 all share the same bore, using different injectors.  Some 
4.3 systems have injectors with two different flow rates, so be careful. 
  The 454 TBI has a larger throttle bore than the 4.3/305/350, and the 
2.8 TBI has a smaller bore.

If you use a TBI from a different engine size than yours, you'll either 
need to change the injectors or change the cal to know what injectors 
you've got.  Either choice is pretty simple.

The TPS sensor changed physical plug style sometime in the early '90s, 
but it's electrically the same.

> carburetor.  It is much easier to remove the entire factory harness 
> for the feedback emissions system and use the Painless harness. That 
> is what I did.  The factory ECM harness is accessible by unbolting 
> and moving the right front inner fender.

I have used stock ECM harnesses and the Painless harness, and both are 
good choices.  The stock harness has some rather oddball wiring routing 
choices, but it's not that bad to use.  The Painless harness is nice but 
doesn't usually contain provisions for AIR, etc. and the instructions 
with my harness had some bad advice (i.e. hooking up the P/N wire to 
avoid having to use a VSS sensor is bad advice).  The harness itself is 
pretty decent, though.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)