Can anyone tell me if I'm understanding the following correctly?

From the ANHT hac:


***************************************************
* SPARK CALIBRATION PARAMETERS
*
***************************************************
L801A: FDB 3277 ; 300 RPM, START UP RPM
; ARG = (65536*120)/(RPM/NUM CYL)
;---------------------------------------


So, does that mean that for the above code, 300 RPM is the minimum when the ECM sends an EST signal, to take over control of spark timing from the ignition module during startup?

And if so, is there any reason why that 300 RPM value couldn't be lowered even further, to where it could essentially make for a full-time EST signal during cranking?

Thanks in advance,

Yes, once the engine is over that RPM (300 in this case) the ECM switches to EST control. It will also move from crank fueling to run fueling along with other items (IAC park to run is typically another, I haven't looked for all changes or exactly what changes the $8D mask does).

Typically there is a short delay where the engine needs to be over that RPM for a short period before the switch from crank to run is made (200 msec or so).

RBob.

There might be something eles going on behind the scenes. ie the dwell is handled differently. Or at low volts, slow cranking the module gives a more reliably timed spark. I forget what I was looking at but one of the new things didn't have an EST. it looked like the timing was all done in the PCM. I might be one of those, just in case items, so while for a million starts you might do just fine, there might be once where you get a no start for some odd reason. It would seem if there was no need for it, GM wouldn't have bothered doing it.

Thanks.

What I'm looking at, is putting an eDist on the TPI car.

I have the Vortec cam & crank sensors, that should be able to supply the signals needed to make it RUN. But, it's the startup bit that I'm concerned about.

This particular engine reliably spins to about 250 RPM off the starter. Actually, it will crank to about 300, but that's with a fully charged battery, in warm weather. So I want to retain some margin for error, in case I ever leave the lights on or something.

Up until now, I'd been trying to figure out how to incorporate an ignition module into the mix, to take care of the initial startup bit. If I could avoid that altogether with a code change to make the ECM spit out the EST signal a little sooner, that seems like it would be a lot simpler.

A related question, does anyone happen to know where (or if) a similar RPM threshold is in the $58 code? I've looked through the hac, but haven't yet found it.

RBob.

Why didn't you just say so?.

Where the coil would normally go, insert a 1K ohm resistor. Then tie a wire to the *point* side of that to use for the ref pulse to the eDist. Thank Scott Sea for that idea. Worked well on my GN.

I had seen that, but 65KHz seemed way too high, by a factor of about 2000.

i.e. 300 RPM = 5 revs/sec = 30 ref pulses per second (on a V6), or only 30 Hz.

Obviously, I'm confused.

But for an SBC application, instead of a GN, then how would you get a cam synch signal? I'm not quite clear on how you'd identify #1 TDC, using that method.

Still confused

You hadn't asked about a cam synch so far you've been asking about a ref pulse and the activation point of EST.

If you want a cam synch then you need to get a distributor that has a cam synch signal generator, and a refence pulse generator. MSD sells one. There are some dual sensor GM distributors out there, but they take some reworking to synch the signals. Or use a crank sensor, and then the distributor as cam sensor. Meaning just one trigger point in the distributor, for getting #1s position.

For an 8-cylinder:

RPM = 984030 / counts

984030 / 2711 = 363 RPM (the value 2711 is actually for a 6 cyl that is what gives the strange value for an 8 cyl calc).

So. . .

984030 / 3277 (from ANHT) = 300 RPM

RBob.

Thanks, guys. You've helped to clear up a few loose ends.

I believe I can make the Vortec pieces work without too much difficulty. I'll post results, once I've had a chance to test it out.