JP84Z430HP

I was sitting here brainstorming and thought of something. I have the stock LG4 CC distributor in my car. We all likely know how lame the timing curve is that's provided by the ecm, right? Well, would it be possible to change the shaft to an older shaft with a mechanical advance mechanism on it and run a little mechanical advance in addition to the CC advance? I know it would take some tuning to get it right, along with limiting the amount it can mechanically advance, but if it is something that would get me by until I go fuel injected, I would be willing to try it. I have all the parts I think I would need, other than a kit for modifying the advance curve.

Your thoughts are appreciated!

Vader

I'm not sure you'd be able to accomodate teh centrifugal advance mechanism AND the reluctor and pickup coil in the housing, but if you could, you'd definitely have some more advance at RPM.

That may or may not be a good thing.

JP84Z430HP

I think it would have to fit! Isn't it the same pickup coil and reluctor ring used since the 1973 or 4 era? At least dimension wise.

I have the large cap, integral coil HEI. I'll look at a couple of them at work tomorrow, along with an idea of what I'm getting for advance the way it is. I have a feeling that I could use close to 10 degrees more!

Thanks for your input!

Jproz1167

iTrader: (3)

JP84Z

I've heard of people swapping the LG-4 esc module with a L-69 module, and this supposedly allows the ecm to to advance timing from the LG-4's max of 32 degrees to 36 degrees, this module is mounted on a firewall bracket by your relays and has like 7 wires going to it.

Ed Maher

You are crazy and trying to make things way too dificult on yourself. 2 ways to do what you want

1.) Run a regular distributor outright, no hybridization necessary. You just need to patch the tach signal to the reference pulse input to the ECM so that it still knows the engine is there. Other than that, this will even work on EFI cars. Thirdgen GM ECMs don't have the slightest clue that they are controlling the timing, and thus they don't care if they're not.

2.) Run a TBI ECM standalone to control the distributor. Patch the code a bit so it doesn't care about fuel delivery and run a MAP signal.


Option 1 lets you tune a dizzy the old fashioned way. Option 2 gives you the ability to write a much cooler advance curve. On the other hand, a bastard hybrid mechanical / computer dizzy would leave you never knowing what your total timing was, nevermind that it would be quite a piece of work to fabriacte.

JP84Z430HP

Hmmm.... Now I have more to think about! That does make sense to just ditch the computer control all together. So all I need to do is splice the tach wire into the ref wire, which should be purple with a white tracer? What to do about the SES light from the bypass not being there? I get over that stumbling block, and I'll do it to it!

It would be nice if I was able to just burn my own chip! That's why I'm planning to go with fuel injection!

My other option is the MSD timing controller. I haven't look into it all that much yet, but it looks like a viable option.

Jproz,
The 1984 LG4 doesn't use ESC (if it did, I would be cranking up the initial timing more!) I think 86 is when they put ESC on the LG4. I think the L69 had it pretty much all along.

Thanks for the help, and if anyone has more ideas, please add them!

Oh, BTW..... Ed, I love making things difficult for myself!

five7kid

iTrader: (14)

We may be wrestling with semantics, but computer control is Electronic Spark Control. What you may be thinking about is the knock sensor and its associated control module.

Knock sensors were added to the LG4 in 1985 when then compression was raised to 9.5:1 with the use of flat-top pistons.

Ed Maher

Unfortunately, i've never actually done the stadard dizzy / computer thing myself, so i can't say for sure. The only time i had a chance to ask questions f someone who did it, i only asked about the tach - reference pulse thing.

My best WAg would be that you'd have to tie the ref low and bypass connections off, either high or low. Probably OK floating the EST control wire, but it might need a resistive load on it.

archives at diy-efi or something might be helpful to be sure though. Wish i knew more details for sure. I do know that if i ever had another CCCS car this is what i would be doing.

JP84Z430HP

Yeah, I think we are dealing with semantics here, but as detail oriented as I am, I have to elaborate....

ESC is the knock sensor and module. They provide an input to the ECM to retard the timing under a spark knock condition. EST (Electronic Spark Timing) is on all the cars that have computer controlled timing. They are 2 different systems, that work together. The module in the earlier post I was referring to when saying that the 84 didn't use ESC is the ESC module, and it uses the knock sensor to determine when to tell the ECM to retard the timing.

Anyway..... I may do some more research to figure out how to do this, but it will have to be a way that will keep the SES light off!

I have other issues to deal with at the present time, so this may get put off for a week or 2. I need to get fuel to the carb more consistantly first!

Thanks again!