The MPFI on 2.8's is batchfire ? and SFI on a 3.4 is sequential fuel inj. ? I don't have info. on these specific systems but on FI in general and it states:Both are port fuel-inj; Little if any difference in peak power but sfi gives better mid-range power and response,emissions and fuel economy . Is the 3.4 open loop or closed? Do you know of a publication that give detail knowledge on either of these systems?

 

2.8/3.1 - Batch fire, open loop till O2 is warmed, then closed loop.

3.4 SFI - Sequential setup... same looping as the 2.8/3.1

 

As far as I've ever heard, any fuel injection system, or any carbureted system that uses a computer, will have an oxygen sensor, and will have closed loop functionality. Was there any injection that didn't? Maybe the old mechanical injection?

 

There's also a mandatory engine temp for closed loop operation, around 150, if I recall.. it's been a while.. I usually assume with my 8 that it's closed loop when the converter starts locking up.

 

The 'ol GM service manual says that the coolant temp has to be at least 70 degrees, and the computer must see a changing value from the oxygen sensor. For those that don't know, until an oxy sensor warms up, it gives off one value. So when the computer sees a changing value, it knows the oxy sensor has warmed up enough to allow for closed loop operation.

 

Tech...your converter is dependent on your coolant temp?? Mine locked no matter what...as long as the speed was high enough in either third or fourth gear...