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Firing order and cam sensors

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  • Firing order and cam sensors

    I'll probably end up flooding this section with dumbass questions - bare with me please...

    I'm having a visualization problem with firing order and how to set the cam sensor. As far as I can tell from my reading, all it does it locate TDC for number 1. Working off of this, and Chevy firing order and cylinder numbering, I'm a little confused on where to set the cam sensor. #1 TDC on an LSx is #5 TDC on a Ford, but after that they follow the same firing order.

    Should I set the cam sensor to read #1 TDC for #5 on the Ford? If I understood any of this, the actual ignition is going to come from the crank trigger, and the "synchronizer" is just to tell the ECM that we hit TDC on number 1, then the ECM calcluates spark from the crank trigger?

    /edit - I think I figured it out but a sanity check would be great. I want to use an 96-98 Explorer distributor, it's a 5v Hall effect sensor. I think I can just put it on TDC #5 instead of #1 and drop it in, then use the Ford tool to locate it.
    Last edited by Beagle; August 29, 2011, 03:02 PM.
    Flying south, with a flock of bird dogs.

  • #2
    Pretty much every EFI system works the same.

    There will be a TDC output pulse from the cam angle sensor, and pulses for each individual cylinder either from the cam angle sensor, or a separate crank angle sensor.
    The engine management system has an internal electronic counter that just counts the individual incoming cylinder pulses up to however many cylinders there are, then starts around again again at cylinder number one.
    But as all these incoming cylinder pulses look the exactly same, the engine management unit has no way of knowing which incoming pulse corresponds to which cylinder when the engine first starts up.

    That is where the TDC pulse comes in.

    It synchronizes the electronic counter in the engine management unit with the camshaft, so the engine management unit knows exactly which cylinder corresponds with each incoming cylinder pulse.

    So all you need do is make sure the TDC pulse corresponds to when cylinder number one is at TDC firing stroke with both valves shut.
    The engine management unit then knows the next incoming cylinder pulse will be number two, then number three, and so on....

    It needs that information to fire the injectors and igniter coils in the correct sequence.


    • #3
      a) spambot - thanks Bruab or Chad or whoever removed that!

      b) I should probably clear this up a bit. I'm putting an LS style 12200411 GM ECM on top of a Ford 331 - the firing order is the same essentially with a small exception. Number 1 on a Chevy is number 5 on a Ford, using the respective manufacturer's number system. What I'm trying to verify is this -

      Assuming the Chevy computer wants a CPS signal for number one to start it's injector sequencing, I have to make the CPS start at number 5 on the Ford engine. I'm using a Ford sending unit that wants to be aligned to it's number one, but for it to speak Chevy, I'll have to make it start on 5, not 1.

      I am pretty sure I just answered my own question... just looking for a sanity check.
      Last edited by Beagle; August 30, 2011, 05:57 AM.
      Flying south, with a flock of bird dogs.