Which component determines dwell? Igniter or ECU??

[Guest boostin]

I was having this discussion today with Reuben and Matt. I thought the ECU set the dwell, whereas Reuben thought it was the igniter. Matt was just happy playing with his infra-red key unlocking Reubens car.

This is all relative to BC/BF Legacy and V3 STI.

Can anyone confirm either way??

[Guest]

im sure in the link ecu i have i can setup the dwell times and also have them dependent on battery voltage on a table, and that the dwell time depends on the size/type of coil.

dont know how much that helps

-smurff

[log1call]

The circuit diagrams I have seen only show a simple transistor switch arrangement in the ignitor, so I'd have to say the ecu controls the dwell.

(Edit).. From a pdf manual called "Ignition diagnostic and operation",

The crankshaft position sensor is an

inductive pickup type which uses a six

tooth reluctor ring located on the crankshaft

sprocket. As the reluctor teeth

pass the crankshaft position sensor, they

cause the sensor to generate a weak

inductive voltage signal. This signal is

forwarded to the control unit, which

uses this information to determine the

proper dwell and timing advance for

changing engine operating conditions.

[Guest]

ECU - you can change dwell with aftermkt ecu's

[Durty-Sanchez]

As the engine speeds up the time period between ignition events decreases, however the charge time of the ignition coils remains constant at all speeds. Therefore the ECU is responsible for determining the dwell time, or the amount of time between ignition events.. and of course if the ECU c0cks it up and doesn't give a long enough dwell time to charge the coils then you get a crappy spark

[Guest boostin]

Right, that confirms my thinking that the igniter was basically just switching transistors for higher current.

So by changing to an ECU that uses a coil pack on top of the manifold, I will need to swap from coil-on-plug to coil pack also? From what I understand the coil charge/saturation/whatever you want to call it is different between the 2 setups. I'm guessing my igniter will still be ok as we've made the appropriate wiring mods so that its firing 1 3 1 3 1 3 1 3 instead of 1 3 2 4 1 3 2 4.

[Durty-Sanchez]

Maybe.. without knowing the electrical characteristics of the coil-on-plug devices it's hard to say if they have a suitable charge time to be used with a wasted spark setup (although I'm sure Reuben and friends have done it with their single turbo setups and have no problems). The cheapo way is just split the two ignition signals from the ECU in to two, so you have 4 signal wires again, run them to the coils and go for a thrash. If at high RPM/boost you have missfiring then chances are you've run out of time to charge the coils.

Best way would be to get the manifold based coils (as Mr. Fuji had intended it to be). At least that way you dont need to worry about expensive coilpacks (x4) dying every 4 years

[Guest boostin]

Sorry, I should have elaborated slightly. When it fires #1 now, it also fires #2, as in those 2 cylinders are now linked together, and the same for 3 and 4. So it is effectively running wasted spark coil-on-plug. This is so I can plug a coil-on-manifold coil pack into 1 pair of the coil wiring and still have it run. Otherwise it will only fire on 1 bank.

So yeah, we have done what you have said with the wiring. Now I just need to fit the ECU, AFM and MAP and see if it runs ok. We test ran it yesterday with a 3 plug TT ECU from a BG5C. It ran ok apart from throwing every TT fault code under the sun and having the AFM unplugged.

[log1call]

As far as I know, if you are using the coils on the manifold you don't need the ignitor. I thought those manifold coils had built in ignitors?

I suppose I had better have a look under the bonnet and see whether my car has an ignitor. Nah, on second thoughts, and being a mechanic, I think I'll leave the bonnet down... like I like it.

[Guest boostin]

No, the early ones (up to about V4 and BG5B?) had an igniter behind the boost solenoid bracket. N/A's have it above the pitching stopper on the firewall. The later HEI type coils had inbuilt igniters, like the 3 wire coil-on-plug coils.

[Bazza-NZ]

So you have manged to get the coil on head to coil pack conversion to work?

I remember when i did it on my BC5, i had fuel and compression but no spark

Sorry to hijack

[Guest boostin]

Not as yet. Been too busy pulling a TT engine out. Hopefully this arvo or tomorrow I should have a result.

[Bazza-NZ]

Sweet, I'd be interested in how its goes, Keep me posted as i tried to do this with mine but failed