[Gmecm] Introduction

[Jay Vessels]

Hi there!

>> rich at idle, something I've never been able to correct.  I am 
>> converting it to a TBI system with intake manifold and throttle body 
>> from an '88-'92 Chevrolet Camaro or Pontiac Firebird.

Word to the wise -- unless you have the heads to match, ditch the stock
'88-'92 TBI intake.  It's false economy.  People will tell you that you 
can drill the four center intake bolts to fit the older heads (thinking 
it's like the TPI baseplate), but it's not worth the trouble as there is 
not much room to drill and not much meat around the holes.  You'll end 
up having to make some wedge-shaped washers to get the proper head bolt 
surface for them.  Either use a TBI adapter plate, or get an intake like 
the Holley 300-49, which is a TBI intake that bolts to older heads. 
I've used the newer intake on older heads but I won't do it again.

>> Anyway, here is a question.  The ECM I have is a 1278746 with an ANTT 
>> EPROM.  I did some research online and found that this is from an 
>> '89-'90 Firebird with 305, TBI and 4-speed automatic transmission.  I 
>> believe this is an almost ideal match for my vehicle.  

I used a very similar setup when converting an '85 Caprice 305 
Q-jet/700-R4 car to TBI.  It works very well.

>> I have read hints that the 1278746 is the "car" version of the 
>> 1227747, which is common in trucks.  I admit I have not yet started 
>> scouring the archives for more information about this, but I wondered 
>> what the differences are.  I did notice that there are no 
>> disassemblies of the '746 on the FTP site, only bins.

The '8746 has an almost identical pinout as the '7747, with the only 
real exception being the IAT sensor -- '8746 has one, '7747 doesn't.

I used an '87 Caprice as my donor car.  The dash wiring harness was 
almost identical to the TBI harness.  You'll need another switched, 
fused 12V source for the ECM (injector power?  don't remember), but I 
think that's it.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for now)