2.5 DIS mod using stock ECU timing?

[SolReaver]

I was spending some quality time today with the 924S with the cap and rotor setup. I wanted to bounce a few ideas of of you folks and ask what you thought of them.

I always wanted to install a dual coil pack using the wasted spark method. I am aware that Micro spark has some really interesting options and I might go that way but wanted to keep things as simple as possible and use the existing ECU for timing. (it does a pretty good job, at least so far)

The problem as I see it is pretty simple. I currently have one distributor that distributes to 4 plugs and a signal wire that fires the coil on that plug with a signal generated by the ECU. I want the signal from the ECU to fire one or the other bank of a GM coil pack. IOW, the current signal to the coil would have to alternate between coil packs.

Is it possible to use a photo sensor (or other sensor) reading the camshaft (or crankshaft) hooked up to a simple circuit that switches the signal from the ECU between coil banks? I was thinking of a simple photo switch reading the cam sprocket with heavy duty transistors switching signal between the banks.

This way I could use my stock ECU for timing and replace the cap and rotor with solid state circuitry. If the cam (dist rotor) is on 1 or 3 three, signal goes to the first bank. If the cam is on 2 or 4, the signal goes to the second bank. All I need is a yes or no from any sensor I use.

SO my question is....are....

What kind of signal comes off the ECU to fire the coil? How much power does it draw and what would be a good way to switch signal between two circuits?

What power spark do I need to drive? IOW is the spark from the current coil, divided by four cylinders, equal to the spark from one of the coils in the pack, spread out between two cylinders? how are coils rated?

IS a photo switch a good idea for the on/off signal I will need to drive the transistors? I would like to use a magnetic sensor, but those only put out square or sine wave pulses and the logic to decode them is a bit more involved that I want to go. I just need an on/off like that of a photo eye.

[Schumi]

Look into MegaJolt. Do a search on this forum, a member has done a lot of work with it including posting some nice ignition maps.

By the time you work out and build any circuitry needed for what you describe, you could have a MegaJolt. If you built the kit yourself, done on the cheap, it probably would cost less than $120.

[SolReaver]

Hey Schumi: I will check them out as a reference source. Are the stock ignition maps THAT bad? I was thinking of using the current signal from the ECM and using the current maps.

As far as cost..I was thinking it would come in well below the cost of a few distributors. A few transistors, an Led and a photoresistor or photodiode could switch between banks and the current ECU would supply signal.

Let me see what the megajolt people are up to.

[SolReaver]

Yea, the megajolt people use a 32 -1 pick up plate and a sensor to get signal and essentially replace the stock ecu timing. I was thinking of something that only replaced the distributor with a coil pack. IOW it is not that I don't like the current engine timing management, but rather I don't like the moving parts of the distributor itself. The current ECU is doing a good job of timing from my POV and I just wanted to have a high speed coil bank selector to put the signal into.

I didn't want to make it into a MAJOR project. Lord knows I have enough of those. The current setup works reasonably well and I was hoping I could improve it's reliability by going solid state on its one moving component.

Of course, I have to ask myself is this trip really necessary? Is replacing the distributor cap that important? It is not like it is particularly difficult to Inspect, test, diagnose, and replace a cap. Will the benefit of replacing the cap outweigh the cost of doing the work and being able to troubleshoot the ignition system should something fail? Do caps and rotors fail at all? Would the mod I am talking about make the car more or less dependable?

And of course, cost. It has to be pretty cheap. The Mega Jolt goes for 200 for the kit, I am sure with trigger wheels and sensors it will get to 300 without too much of a problem. I am budgeting a LOT less. A coil pack from a junkyard, a couple of heavy duty switching transistors, some led's a phototransistor or photodiode. From a cost benefit analysis, it shouldn't go over the cost of 2 distributors with rotors. That gives me 100 as a budget redline.

Would the laser and pickup off an old CD work? How about the light and sensor off an old scanner?

[SolReaver]

After researching it, I decided to drop the optical sensor to a hall effect sensor for durability. I was thinking of placing a magnetic strip on the inside of the cam shaft sprocket and placing the sensor on the inside of the plate where the distributor mounts. The voltage difference in the sensor will be used to switch the packs back and forth via transistors.

How many watts does the signal wire draw?