[Gmecm] ? about pre-efi gm ecm

[Jared Ryan]

I need to mention, also, to put any thought of using the stock CCC 
carburetor harness out of your head.  The CCC carburetor and TBI 
systems are not the same.  You will end up using some of the in-dash 
wiring, and that is fine, but the under-hood part is different.

The CCC ECM for carburetors is very, very different from EFI.  You will 
want a 1227747 or 1228746 (I prefer the '746 for the El Camino since it 
is a car, and the '746 was used in cars, not pickups).

The ECMs for carburetors have edge connectors, and those for EFI have 
pin connectors.  That is one example of how different they are.

  ---> Jared Ryan <---
jryan at caminofx.org | http://www.caminofx.org

On Aug 27, 2006, at 10:46 AM, Jay Vessels wrote:

> 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)
>
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