I'm looking at a Chevy Tuned Port Injection (TPI) system from a 91 Camaro Z28 with a 350 cubic inch motor. Is the injection on this batch fire (fires all injectors at the same time regardless of the intake stroke of the cylinder)? The 93 LT1 motor was batch fire, then changed to sequential port injection (injectors fire in time with intake valve opening) in 94.

  • 1
    The information on various forums sure is confusing. The sure-fire way to know would be to backprobe a couple of injectors. Not sure if that's the answer you're looking for though'
    – Zaid
    Dec 19, 2015 at 13:47
  • You could, but without an ocilliscope or some way to tell the pulse rate, it would be hard to tell. Dec 19, 2015 at 15:30
  • I dug around some sources and could not find the info. You could buy two noid lights and hook them up. If they flash at the same time it is bank fired. way cheaper than a scope. Scopes open a world of testing not available any other way. Dec 20, 2015 at 5:21

1 Answer 1


According to this Corvette web site which pulled this from GM Performance:

"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".

So the answer appears to be that the TPI injection system is indeed a batch fire system which fires all eight injectors at the same time. I found several other sources which corroborate this. For instance:


There does appear to be some mis-information out there concening this. Some would say these systems fire 1/2 at a time (odd bank, then even bank, etc, four injectors at a time). This is not correct. The Reason for this mis-information is that the injectors run on two separate circuits. The only reason for splitting these as was done was to distribute the electrical load so as to not overload one circuit.

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