Sequential fires makes sense to me Fire one injector on the intake stroke of each cylinder; but firing all 8 injectors at once dosen't make sense to me. Can someone please explain this to me?

Thanks

 

They fire in pairs.

 

technically, the TPI engines are a type of batch fire called bank to bank



each bank fires 4 times per crank rev, although at only a 1/4 the P/W, the fuel spray collects above the intake valve, then the valve opens and pulls the complete(4x 1/4=1) air/fuel charge needed

this is not as efficient as sequential, as sequential is a more atomized charge, due to no "fuel puddling" or lag time between the injector cycle/pulse and the valve opening

bank to bank/batch is easier electronically, since cam position/cylinder ID is not requried, only RPM

 

I still find it hard to believe that after all the posts on this board and the TPI board at thirdgen.org and all the thirdgen boards in the world, that people still think the injectors fire four at a time.

There are two separate fuses and two banks, but there is only one injector driver circuit in the computer. All eight injectors fire at the same time. I've proven it with a computer on a test bench and 8 test lights hooked up. I've also seen the schematic of the computer which shows it.

Batch-fire was what GM used in the 80's because the technology wasnt there to make sequential-fire work until later. Plus, batch-fire is simpler and cheaper so of course they used it for as long as they could.

 

F car TPI uses right/left batch fire and "all" batch fire. The r/l batch is used most of the time, "all" batch is used near
WOT. These are called double fire and single fire by GM.

There are some small gains in emissions for sequential fire at or near idle
operation.

 

The schematics show two connections for the injectors.
1,3,5,7 go to D15 on the ECM connector
2,4,6,8 go to D16 on the ECM connector
On the inside of the ECM it looks like only one drive controller and both sets of injectors are tied togother internally inside the ECM.
It is on page 6E3-A-14 of my 1988 Firebird Service Manual.

The V6 Cars have 2 Injector controllers,
Page 8A-20-5
V8 TPI have 1,
Page 8A-21-7

 

That is what I heard as well. SFI has negligible performance gains vs batch fire MPFI, but that the small emissions advantage is the reason GM switched to it.

 

Lesson to Kevin, he knows his stuff!!!