Joe Perez

iTrader: (8)

Running a 12T wheel on an NB, you have two basic options:

1: Cut off one tooth (thus creating a 12-1 wheel) and run with no cam signal at all. This is essentially the same as my old setup with the 36-1 crankwheel.

You will be limited to batch injection and ignition in this mode, as you don't have an absolute cycle reference. In other words, without a cam signal, the ECU can't tell whether the #1 cylinder is at TDC on the exhaust/intake cycle or the compression/ignition cycle. And, of course, no VVT.


2: Leave all of the teeth in place, and modify the intake cam pulley (for '99-'00) or the intake cam itself (for '01-'05) to remove two of the three teeth, so that you have one pulse per cam revolution on the second sensor. This will enable you to run fully sequential spark and fuel, however this configuration will most likely not allow closed-loop VVT to work, as the crank teeth are too closely spaced, and the cam pulses will therefore cross over crank pulses as the cam advances.


IN THEORY you should be able to run a 12T crankwheel with a stock NB-style cam signal, however there is no SOFTWARE SUPPORT for such a configuration at present. Configuring the ECU to understand such a signal is a more complex task than can be achieved with the "generic wheel" configuration table, and it would thus require a custom configuration within the software itself, such as the ones which were done to support Neon/420A, Subaru 6/7, Mitsu 4G63 or '99+ Miata sensor pairings in the MS2. (In other words, the ones where you just select "99+ Miata" from a drop-down window, rather than manually keying in all the tooth data.)


So, long story short: The 12T wheel is an excellent upgrade for NA owners looking to eliminate their dependence on the CAS, and is a moderate upgrade for '99-'00 owners looking to slightly improve the accuracy of the spark prediction. For owners of VVT engines, however, there are some serious disadvantages which outweigh any potential benefits.


On '90-'93 engines, there is an igniter seperate from the coilpack, and this generates the signal to drive the tachometer in the instrument cluster. On '94-'95.5 engines, the igniter is integrated into the coils, and the tachometer signal is generated here. On '95.5 and later engines, the igniter is still integrated into the coils, however the tach signal is produced by the ECU.


If you convert to sequential spark, then by definition you are not using the stock ignition coils.

If you have a '95.5 or later car, this does not matter, as your tach signal was not in any way related to the ignition system to begin with. The ECU will continue to generate the tach signal just as it did before.

If you have a '90-'95.5 car, you will need to run a new wire from the ECU to the wire that drives the tachometer in the instrument cluster, and have the ECU start generating the tach signal just like it would in a later car.

In either case, it does not matter how many teeth are on the wheel, or whether you are using one wheel or two, or whether you are using two coils or four. The ECU simply generates one pulse on the tachometer output pin for every ignition event.


Each of your two ignition coils has one tachometer output pin which is driven by the coil's internal igniter. These two outputs are wired in parallel to the tachometer. Every time an ignition coil fires, it generates a pulse on the tach output pin. The summing together these two lines means that the tachometer sees one pulse every time either coil fires.



Right here, good buddy.

Techsalvager

By techsalvager at 2012-01-17

By techsalvager at 2012-01-17

Timing error%
diy's n top
stock on bottom

Interesting you can see its in the same area with GVE the same nearly but its way leaner on the other one compared to current which is richer. Guess its the map sensor change causing this.