TDC number 1

Hi- If you are running group fire injection and a distributor ignition with a G4+ does the ECU actually recognize TDC on number 1 cylinder to start its injection cycle . With a VR pickup in the dizzy i guess it knows where TDC is in relation to any cylinder but how would it find no 1 . Does it even matter with group fire injection ? And every time you start the engine does it in fact start its injection sequence at different times ? It just essentially picks a start point ( any cylinder ) and goes from there . Also if this is the case would it effect AFRs slightly ? What am i missing ? - Thanks .

Hey H8LUZN, it depends on the distributor exactly...

If its got a single reluctor sensor with 4 identical trigger points (or as many triggers as there is cylinders) then I would say no it does not tell the difference between number one. Does not matter with group fire injection/ignition as the distributor is litterally distributing the spark to each relevant cylinder as it spins... the ECU doesnt know what cylinder its firing.

I believe you correct when it comes to the fueling and the injection timing is not linked to any one cylinders crank position.

There are other distributors which are abit more advanced, Holden/Isuzu 4ZE1 2.6L for example, it has a flat disc inside with 2 rings with slots, the outer ring has 360 evenly spaced slots to give a RPM signal with its own Hall/optical sensor the inner ring has 4 evenly spaced slots but the slot for cylinder #1 is slightly shorter and has its own hall/optical sensor. Its quite a simlar setup to the Nissan CAS but it still retains a distributor rotor and cap and single coil.

When the engine starts the ecu waits until it gets a cylinder #1 signal and this may take a few revolutions for it to sync itself

Thanks Viper . That does make sense . Some back ground - I have a v8 running with a dizzy through an Atom G4+ . I have a trigger wheel (60-2 ) mounted up with a VR pickup . ( not wired up yet ) and a modified dizzy with one tooth i can use as a sync ( not hooked up yet ) My question- is there any advantage with regard to better/smoother running if i convert to semi sequential injection rather than the group fire im running at the moment? . In theory i can manipulate the firing order in the ecu to get the injectors to fire in 4 evenly ( and hopefully more accurately ) timed events . Leaving less time for the fuel to puddle in the ports . As opposed to group fire which are fired in 2 groups over the engines cycle . Have you or anyone else tried this ? Is it worth doing ? Im 90% percent there so maybe i should just try it ?

If you have a crank mounted 60-2 wheel and a sync from the cam (via the dizzy) then you can run full sequential and is only beneficial to do so...

As you said will be more consistent fueling and by tuning the firing angle you can achieve a smoother idle using less fuel and better fuel economy during cruise (assuming the atom G4+ has the function for this, im not familiar with links)

Just an update - Got the v8 running on semi-sequential injection now . The change over went perfectly from group fire . Got it timed up with the offset sorted very easily and come start time it fired right up . Starts quiet quickly - idle and runs very smooth . Thanks for your help .