This is just a general "out of curiousity" question...

As I understand it, TPI systems employ a batch fire mechanisim wherein only either the odd numbered injectors or the even numbered injectors can actuate at a time. Thus, while only one cylinder is in need of fuel at a given point in time, a total of four injectors will be fueling four cylinders--three of which do not need fuel.

Is my understanding of this system correct?

If it is, it just seems terribly wasteful to me. It seems like, among other things, it would dramatically increase fuel consumption and decrease fuel economy. I mean, of the fuel that's going into the four cylinders being sprayed, only one cylinder turns that fuel into power--what happens to the fuel in the other three?

Also, what would have compelled GM to use batch-fire in the first place? Just to simplify wiring? Or was the computer technology at the time perhaps not ready to keep up with when to fire each individual injector?

Like I said, this is just a general curiousity question. I'm not trying to start a flame war or anything--I've just always been curious as to why the batch-fire system was used when sequential-fire seems so much more intuitive.

Thanks

 

Batchfire..all 8 injectors fire at once..

Fuel mixture is still suspended until the valve opens.

I'd assume cost was the factor, maybe technology at the time as well.

 

sancho you were correct, only one bank at a time, not all 8 like mike said..the reason its not wasteful is because the fuel only enters the chambers with open intake valves.. and the technology was in fact around at the time.. ford had sfi on fox body stangs' in the 80's

 

No, actually, he was not correct. TPI fires all 8 injectors at the same time, period. I know there are 2 wires, and 2 fuses for the injectors, but I can assure you that they lead to exactly 1 spot in the ECM for control.

And batch fire isn't wasteful because it is only injecting the right amount of fuel. It's not injecting all 8 inectors everytime a cylinder fires. It's firing 8 inectors (for 1/2 the needed time) every 4 cylinder firings. So every cylinder gets exactly the right amount of fuel.

While not quite as efficient as SFI, SFI won't make a real difference even in MPG, and it doesn't do anything for power production.


BTW, sequential, while 'more intuitive' also adds unnnecessary complexity. With SFI you need a cam sensor as well as 8 individual injector drivers, as well asa little more complex code to control them. And in the end, you don't get much for all the extra work. Cars all use it these days because everything is needlessly complex on mdern cars, and ever tightening emmisions standards necessitate going for that every little bit helps mentality too.