Ok, i've never tried to improve upon a CCC system, but I got this idea stuck in my head and I have a creepy feeling that there's something I either don't know or that i'm forgetting. So here goes:

What if I took the module out of a CC distributor, put it into a vac adv dist with all it's associated wiring, and tried to run it? The ECM would be getting references, and the spark would advance via the vacuum.

What problems would I have? This idea seems too simple to me, so that's the purpose to this post.

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DR Stevens
1984 Trans Am 305HO L69
sucks gas, hauls ***
1991 Firebird 305 LO3
for days when I need a/c

 

interesting, it might even work, though not as you describe.
AFAIK the ecm realy only needs the reference pulses, which should be the same as the tach signal (IIRC 5V TTL), in which case you could run the reference right off the the tach terminal, no module swapping required. At worst this signal may be a 12V squre wave, in which case a simple voltage divider to get to 5V would be your answer.
The iffy part is if that is all the ecm is expecting to see, which i don't really know.
...ed

 

YES, Ed, that's exactly what I was wondering. Looking thru the trouble code chart, code 42 sets when there's a spark timing problem. If the computer doesn't like the timing curve that it's reading, then it'll probably throw that code. But if it doesn't affect my drivability, maybe that's just the small price i'll pay for better spark advance. I just hope nothing else gets whacked if this happens.

Although, I realize the ESC won't be able to work if & when there's a knock.

Whaddya think, if this works out good will I be seeing a noticeable power gain?

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DR Stevens
1984 Trans Am 305HO L69
sucks gas, hauls ***
1991 Firebird 305 LO3
for days when I need a/c

 

BTT

 

84,

From what I have been able to learn about the ESC, ECM, and EST/HEI module circuits, the ECM scans the ESC module inputs for knock indications at the normal update rate for I/O points, and constantly scans the EST/HEI inputs for the square wave output from the reluctor/coil. The ECM only expects a high reference pulse on A2 and a low reference pulse on A3.

If the ECM doesn't detect any input from the ESC module indicating a detonation situation, it will not command a retard in timing back to the EST/HEI. Whenever the ESC sends a retard signal to the ECM, the ECM sends a retard to the EST/HEI module. The signal is an analog TTL output, so zero signal should keep the timing at maximum (minimum spark retard).

I think your theory should work and is worth a try, but you will need an EST/HEI refernce signal to the ECM, whether by installing the module or dividing the tach signal into a high an low pulse to emulate the signal from the reluctor.

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Later,
Vader
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"What a Day..."
Adobe Acrobat Reader

 

Thanks Ed & Vader, I was hoping for a positive response. I've got a vac advance dist sitting in my storage closet waiting for this experiment, i'll just need to get around to doing it now.
If anyone else has any more input for me, by all means post it!!
I'll take the car to the track before I do this mod, and then after and see if I get any increases. Wish me luck.

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DR Stevens
1984 Trans Am 305HO L69
sucks gas, hauls ***
1991 Firebird 305 LO3
for days when I need a/c

 

why not get the equipment it takes to burn your own prom and set your spark timing that way? You might even get it better then the vacume advance would.

 

I was under the impression that either the equipment or the data for PROM burning on a CC-carburetor system wasn't available to the public....am I mistaken? I know some off-the-shelf companies have them, not like they do much good.
Basically i'm shooting for a smoother, wider spark curve. From what I gather, the CCC unit advances spark only every 400 rpms and it doesn't get as many degrees of advance as a vacuum unit will. Plus as a hobbyist, it would make a cool experiment.

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DR Stevens
1984 Trans Am 305HO L69
sucks gas, hauls ***
1991 Firebird 305 LO3
for days when I need a/c