tach, fuel injector?

hi bros I am drunk..couple beers just now..all replies become complicated for me. anyway, now I know fuel injector gives vary pulses, tach gives stable higher frequencies, anyway..I guess Viper or Compustar will read frequency instead voltage of AC/DC if it is tach mode. As taught, pulses DC actually is AC, RPM is AC..so you are all right. I would prefer tach. but some vehicles, it is difficult to get tach wire. It might be hidden under engine cover. but for this question here, I am asking how to use fuel injector for engine starting signal. I guess I understand now. I did some imported vehicles, I used cam sensor. I used tach wire. I used generator wire sometimes..I havent tried fuel injector before. Be honest, I am not mechanical guy. I dont even know what fuel injector is. I appreciate that I learn a lot from you experienced teahers.

Yes - we are all "not wrong" about pulsed DC containing AC - but it depends on your definition. If DC is "unipolar", then coils & injectors are DC since they are unipolar voltages/currents. But that is too simple a defintion - DC does not have phase lag nor inductive spikes etc - only AC has that (where AC means a frequency not equal to zero). But to take from the oft referred Basic Car Audio Electronics ( bcae1.com/acdc.htm) - "You should remember" (near bottom of page):

bcae wrote: D.C. is a type of voltage which does NOT cross a point of reference at regular intervals.

(And conversely AC does.) But that's my dash for this thread. No point arguing about whether injector pulses are AC or DC unless you define what AC and DC are. And depending on those definitions, the answer will be different (and correct!). The same is true of many things.... I gave the Power Factor example where PF is often defined as cosΦ so that if (fundumental) current & voltage is in phase, PF=1. (The cosine of zero-degrees is 1.) But cosΦ may be 1 yet the PF may be 0.6 which is typical for many modern power supplies (switched-mode SMPS). The problem is the definition of PF = cosΦ is a subset of its true definition PF = W/VA which is actually cosΦ x df where df is a distortion factor that takes into account the non-linear switching etc (eg crest factors etc). Whether those that think pf is cosΦ only are wrong or not may not matter - until they design a power supply for an SMPS thinking cosΦ = 1 therefore the max current = peak current, and therefore their outputs blow up when the peak current is 1/0.6 = 1.67 times their expected peak. Ah yes, I love watching tendered equipment blow up.