What happens at max ESC retard with FAST B2B?

[dataangel]

I have an 87 TR with a FAST B2B. Knock sensor's working, ESC is set to 20deg max retard, all the normal good stuff. Strange thing is that, while tuning the car, we saw a bunch of KR on a couple of pulls (14deg), and then the ignition cut out entirely. Totally reproducible: KR climbs up to a threshhold, ignition cuts. If the KR stays under the threshhold, everything runs peachy.

So, the working theory is that, because we have the FAST reference timing set at 6deg, the 14deg is actually acting like 20deg and, when it tries to pull more than that, something throws a fit and shuts down spark.

Anyone know what's going on here definitively? Does the stock GM spark module flip out if you try to pull more than 20deg of timing out of it? Does the FAST B2B box have some safety strategy related to timing that could be causing it?

Thanks for any insights!

 

[HighPSI]

The 14 degrees is 14 degrees. It doesn't subtract your CRA. As far as I know, the computer can't pull the timing BELOW your CRA. So you could put 25 MAX retard, if the timing is set at 24 degrees, the most the ESC can pull is 18 which will get you to your CRA. If you have that much KR, I would look at solving that problem first. Then the other problem won't be a factor.

 

[dizzlesturbo6]

is it imperative to run the esc/knock retard on a b2b system? forgive my ignorance,just asking.

 

[dataangel]

Thanks for the quick reply Cal! Yes, I know 14deg of KR isn't what we want under any circumstance. Nevertheless, it does happen rarely when things get out of whack, either via real or false knock.

The real problem is that, when it DOES happen, the ignition cuts entirely. In an ideal world, that shouldn't be happening.

That's the interesting bit. . . if it can't pull timing BELOW the CRA, like you say, and the KR is set to 20 and the CRA is set to 6, it's right at 14 that it slams into the CRA. That's where this problem seems to happen consistently. It's a little too convenient to be a coincidence. Why is the FAST default max KR set at 20deg for a GM, and why do most Buick chips stop at 20deg of KR? Was it a limitation in the stock ECU or the stock ignition module?

Of course, I can set the FAST max retard to 13 or 14 degrees, and if the theory is correct, I should never see ignition cut again unless I adjust my CRA. I think there are several work-arounds, I'm just interested in why it's happening and why it appears to be consistent.

Thanks again for the help!

 

[dataangel]

No, you can certainly disconnect the knock sensor and shut off the ESC stuff. That said, for street driving - pump gas, different conditions, etc - it would make me uncomfortable to try to run without as I've seen even great tunes get KR occasionally. At the track pumped full of C16 and 30psi, I don't even care about it.

 

[Craig Smith]

Thanks for the quick reply Cal! Yes, I know 14deg of KR isn't what we want under any circumstance. Nevertheless, it does happen rarely when things get out of whack, either via real or false knock.

The real problem is that, when it DOES happen, the ignition cuts entirely. In an ideal world, that shouldn't be happening.

That's the interesting bit. . . if it can't pull timing BELOW the CRA, like you say, and the KR is set to 20 and the CRA is set to 6, it's right at 14 that it slams into the CRA. That's where this problem seems to happen consistently. It's a little too convenient to be a coincidence. Why is the FAST default max KR set at 20deg for a GM, and why do most Buick chips stop at 20deg of KR? Was it a limitation in the stock ECU or the stock ignition module?

Of course, I can set the FAST max retard to 13 or 14 degrees, and if the theory is correct, I should never see ignition cut again unless I adjust my CRA. I think there are several work-arounds, I'm just interested in why it's happening and why it appears to be consistent.

Thanks again for the help!

If the KR gets the target timing AT or BELOW the CRA, you will lose spark. The target timing needs to be at least 0.25 degree higher than the CRA for the FAST ECU to be able to calculate a spark angle. However, nothing in C-Com will enforce this. Now that you know it you know how to avoid it!

Good luck!

 

[dataangel]

Thanks, Craig, for the definitive answer!

One follow-on question. . .

Two different FAST ECUs with the same program appear to exhibit similar, but slightly different behavior when they hit this threshhold. The first one cuts spark entirely as described. The second one sounds more like it's cutting spark to individual cylinders: kind of sounds like a two-step. It's the exact same trigger point, so I'm sure it's the same problem. Is it possible that two different ECUs, manufactured a LONG time apart, would react differently to the same problem?