We've been working on a 2GCDFIS involving a transistor trick, and have some questions we thought you guys might be able to assist with.

As far as taking a signal direct from the dizzy, what would you use to condition that signal to fire a 2nd gen ignitor? Mind you, this is not using the stock J109 ignitors from the 1st gen at all.

That's the only question for now, but it's a loaded one.

 

I've also been working on the 2GCDFIS TT Circuit Mod for a few months.

Just to help clarify.

- How does the MS circuit deal with the signal coming from a J109 Ignitor (any special diodes etc.?)

- Do you have any special circuit/componentry for interfacing the MegaSquirt ECU to run a 2nd gen ignitor/coil pack?

I'm currently building an MS too but I'm not up to that level of understanding yet.

Any ideas at all would be great!!

Cheers,

Paul.

 

If you asking how to obtain a signal from an existing ignition system, you just use the coil negative. I've found it necessary to put some resistance in the MS tach input line to prevent false triggers during coil ring.

If we're discussing MS controlling ignition, the MS reads signal from the reluctor and doesn't involve the 109 at all. I use the MS controlling a VB921 to fire a second gen leading coil directly as the stock electronics (ignitor) do some unpredictable things regarding dwell, delaying coil firing, etc. I prefer to control these parameters directly. Also, I'm firing the coil without using the ballast resistor; the coil stays cool and theoretically a full charge will be reached with a shorter dwell vs charging through the resistor.

-Mike

 

as far as I know pmrobert is also using a modded 2nd gen CAS, and not any kind of 2GCDFIS transistor trick.

Ken

 

The reason we're asking is because we seem to be getting interference through our circuit (but only with the coil connected). Everything works perfectly as expected until we plug in the 2nd gen ignitor+coil pack.

Thanks for the replies so far, it's given us a few things to think about.

 

I will try to clear this up for you guys. devitek does not have an MS. The TT ignition is just to interface between the J-109 and the 2nd gen coil without an ECU. devitek was looking at bypassing the J-109 and going straight to the TT circuit from the VR sensors. I told him about the LM1815 that he could maybe use. The problem is that there would be no dwell control for such an arrangement. It may be okay if you could find a constant dwell value that would work with the 2nd gen ignitor pack over the range of RPM.

Paul was asking about the interface between the MS and the 2nd gen coil. I know that you guys normally use the LM1815 and 2nd gen CAS for input. The 2nd gen coil, it is just connected to a regular output with a pull-up resistor to 5v.

We are getting some feedback on the TT circuit with the coil connected. There are a couple things that we are going to try to take care of that, though.

Hope that makes sense.

Kent

 

Why do you want to bypass the j109? I used Kent's circuit very successfully for several months, and it's now on my 'racecar'.
For the MS input, most everybody uses a stock CAS, either modified or stock. The stock distributor is not good for this sort of operation since it only has only 4 teeth and its sensors are not as good as a regular stock CAS, though I suppose a lm1815 circuit could be created from scratch, it doesn't seem like it'd be worth the effort.. If you did want to endure such a project, you might as well design one using a stock CAS, but after all that work, it'd be easeier to just build a megasquirt to control a stock FC ignition setup and keep your carb...

 

jayroc: which circuit are you running? The simple one, or the earlier switching one?

What we are curious about specifically:

Taking a signal directly from a stock distributor, conditioning it accordingly, and somehow feeding that conditioned signal to the 2nd gen ignitor, thus firing the 2nd gen coil. With the transistor trick, we have 2 ignitors in the equation. I'm looking to eliminate one of them, and the J109 is the weakest link.

 

I have one of the original simple circuits.
If I remember, I posed a similar question when this idea was being thought up.. The short answer is, if the only reason you have is to eliminate one of the ignitors, it's not worth the effort.
Also, the j109 doesnt have a load on it like it did stock, so it should be more reliable.

 

Yes, this is all true. The J109 (or in my case, now and HEI) has very little load on it in comparison to the stock setup. I guess you could say the idea is more conceptual than anything. After I blew out my J109, I got to thinking about the idea and decided to inquire about it. So far, it does seem as though it's just easier to go with the TT with the J109. You say you've been running the simple circuit--no problems so far with overheating of the 2nd gen ignitor? Just wondering, my simple setup blew out after a week. Probably just bad luck, but it would be good to know what people are doing with their setup, especially those that haven't had any troubles.

 

I had an ignitor go bad, actually. After a few months of use. I don't know the cause, it could have been bad grounding on my part. I heard a one or two other people had issues with that as well, and Kent was working on checking the circuit for a problem. Think it may have been too high a dwell or something but I dunno what happened with that...

When it did go bad, I didn't run it very long.. Just a warmup and drive around the block. Parked it, then it wouldn't start. Weird. Didn't even rev it high, but guess that doesn't matter in this case.

 

Yeah, high revs wouldn't do it. It's the idle that kills 'em. Mine went out at a gas station. I was about to start filling up and the idle just dropped hard. So you haven't done anything special to keep it working...interesting.

To keep temps down on the thing, I thought about pulling out the ignitor and applying some thermal paste there, and possibly putting a small fan, maybe from a laptop or something, inside the casing. I've seen some people flatten out the backing so that it will sit flush with whatever it's mounted to, but there are 4 small holes on the back that are likely there for ventilation.

 

I just replaced the whole coil pack and didn't have any issues after. Though, a month or so after, I converted to MS controlled ignition and haven't ran the racecar on it for too long. I was running the variable pulse width, IIRC... Whichever one was better for idle.