nAst1: Progress and Concepts Thread

[brian89gp]

^^This is why you are the man.

16214848? Is it true ODBII? If the knock filter circuitry is the same in a different form factor, maybe an adapter board that plugs into the PCM and has a MEMCAL style knock filter soldered to it? 192KB is a lot of code.

[caffeine]

Is there flash support for those Northstar PCMs already? Maybe the best one to start with is an LT1 PCM, since they're well supported already, support MAF and speed density, and SFI.

Now, I've recently noticed an issue with the tune on my Firebird where I'll be driving at low throttle, low rpm, and the AFRs will suddenly jump to the 9.X:1 range. A few stabs to the throttle usually makes it go back to normal, but do you have any ideas what could be causing this?

I thought at first it could be the converter over temp stuff but I think I disabled that (set the initialization coolant temp to 300*F) and it still happens. Seemingly happens at random and I can't find anything in the data stream to indicate why.

[robertisaar]

^^This is why you are the man.

16214848? Is it true ODBII? If the knock filter circuitry is the same in a different form factor, maybe an adapter board that plugs into the PCM and has a MEMCAL style knock filter soldered to it? 192KB is a lot of code.

it's in 96-99 US market cars, it has to be OBD2 as required by law. it looks like it communicates with both a VPW scheme and something similar to if not identical to ALDL. the weird two prong knock modules work identically to the older style that sit above the limp-home stuff in a MEMCAL.... or at least all of them that i have seen do. i have a 3.4 one sitting around here and a diagram someone made a long time ago showing the functions of the pins. also have a document showing the function of the pins of the older style, so no real guesswork would be involved.

and 192KB of POTENTIAL code.... i'll likely want to be able to do everything from scratch, so the sky would be the limit with these.

Is there flash support for those Northstar PCMs already? Maybe the best one to start with is an LT1 PCM, since they're well supported already, support MAF and speed density, and SFI.

Now, I've recently noticed an issue with the tune on my Firebird where I'll be driving at low throttle, low rpm, and the AFRs will suddenly jump to the 9.X:1 range. A few stabs to the throttle usually makes it go back to normal, but do you have any ideas what could be causing this?

I thought at first it could be the converter over temp stuff but I think I disabled that (set the initialization coolant temp to 300*F) and it still happens. Seemingly happens at random and I can't find anything in the data stream to indicate why.

there are programs/hardware out there that will flash them. madtuner took on that project pretty much immediately after dealing with the 93-95 P66 V6 stuff. i didn't feel up to disassembling and commenting that much code.

log the issue, we'll investigate.

[robertisaar]

made a spreadsheet for the 93-95 northstar PCM... of the 96 pins it has on the connectors, 8 are not used. or at least, they're never used in any of the 4 factory applications(seville/eldorado, deville, allante, aurora). i may check to see if the other 8 have any kind of connection on the board or if they are truly not connected to anything.

there are...... a lot of things going on. it appears that the high and low of certain outputs can be switched without harm. makes sense with magnetic sensors, since they produce an A/C signal anyways. appears that the PCS doesn't care either?

looking to do the same with the 96-99 applications in a minute.

[robertisaar]

and for the 96-99 unit.... of the 160 pins it has on it's connectors, 49 appear to be not used.

[caffeine]

If you're writing code from scratch, will you even need the space contained in the Northstar PCM? Do those northstars have VVT?

Another thing on nAst1 currently; when it comes to DFCO on my engine, sometimes it enters it when it should, and sometimes it doesn't (usually after driving for a while). I have it set to come on as quickly as possible in the current setup, but when it is working properly, there always seems to be a delay of a few seconds before it actually enters DFCO. Is there any way to make it come on instantly?

[robertisaar]

will i need the space? maybe... i'd like the option available to me at least. and no, not VVT. only the RWD northstars got that, this PCM was used on all of the FWD versions from 96-99.

there are a few different delays in the calibration for DFCO, some are even EGR related and can cause some interesting headaches.

anyways, logs of problems will certainly help determine why they're happening.

[caffeine]

nAst1: Progress and Concepts Thread

I did a couple datalogs today, but of course as soon as I give up and stop data logging, the sudden rich problem happens again . I think I may have the DFCO problem logged, but I need to check.

Again when it comes to DFCO, there is always a delay of a few seconds before entering it unless I'm at around 4000 RPM. Also the fuel takes another 3-4 seconds to ramp-out after DFCO takes effect. Since the AFR goes to 22:1 (full lean) as soon as DFCO takes effect anyway, is there a reason the ECM takes a few seconds to completely ramp out the fuel? I'm basing this on the injector pulsewidth gauge that's built into my meth controller.

EGR is disabled in my tune of course; is there any way some EGR-related code is preventing or delaying DFCO still?

[robertisaar]

there is a BPW ramp in and out function when it comes to DFCO. i imagine GM implimented it to not have an instant on/instant off feeling. if you wanted to, you could change the ramp rates to whatever you want.

with EGR disabled via setting minimum coolant temp to enable at max value, it shouldn't be in effect.... but the delay it causes could always be 0'd out just to be certain.

sounds like your "fast" DFCO settings are working well.... could always lower the RPM threshold for it instead of changing the "slow" DFCO settings, but it's really just preference at this point.

[caffeine]

Have already made it so the short timer DFCO comes on at low RPM. Also, the fuel ramp-out is actually instant (PW gauge will for example go straight from 9% PW to 0% and nothing in between), but it takes a few seconds from when the AFRs go full lean to when the fuel is actually cut off. With my current tune, the RPM threshold for short timer is set to 1500 rpm, enable time with conditions met is set to 0.2 seconds

The ramp-out factor is set to 1.0 (as high as it goes). KDFCOINC is set to 1.0, min time between DFCO events is set to 2 seconds. Guess I could set that last one to 0. But I don't see any way to make the fuel ramp-out faster. I just don't really understand why there's a delay when the car feels the same when it enters DFCO as it does when the fuel is finally cut (as in no difference in engine braking), so why bother with the delay?

Personally I want the on/off feeling; its also great for autoX where you want the engine braking to be instant because you're constantly on and off the gas pedal.

[robertisaar]

the cells that you hit in those situations, have you disabled DFCO and calibrated them? kind of sounds like it's commanding lean before DFCO kicks in.

ramp of 1.0 is why the instant transition from injecting to cut, which makes sense.
i would definitely try cutting the min time between events value as well.

also, here is something interesting:

KK13DMN1
KK13DMX1

those are in the DTC13 scalars, they're the min and max time allowed to prevent DFCO to test for DTC13(lazy O2 sensor). those could certainly cause a delay that only happens part of the time. factory values of BHAK are 2 and 3 seconds.

[robertisaar]

so i was looking at the 7727 diagrams again and noticed something familiar:

the add-on outputs i was talking about earlier: almost an identical function to what the U2 chip does, just without the inputs.

i'm not saying i would, but you could pull that from another ECM, move some of the address lines around and bam, like 12 outputs, 7 of which are PWM and 7 inputs that are time-sensitive that could be used for a lot of purposes.

[robertisaar]

and a correction:

96-97 LT1 PCMs use a 144KB BIN. must be split up quite oddly.

looking around to confirm 96-99 northstar sizes now.

[robertisaar]

96-99 northstar are 176KB. that's 88KB per processor. also split kind of oddly, but i'll have to see if i can make sense of it if/when i have a BIN.

[robertisaar]

http://www.aces.edu/~parmega/efi/thrasher/cal_hints.htm

So, why do some racers bother to switch ignition systems? It’s a
little known secret, but we’re in a generous mood - the Delco coils have lower
inductance (approx. 3.5 mH) than the Magnavox (approx. 8mH), and provide
slightly more energy. Primary winding resistance of the Magnavox unit is 0.7 ohm
vs. 0.34 for Delco. Magnavox current limit is 6.7 amps with a 3.5 msec risetime
vs. 9 amps @ 3 msec for Delco. This translates to a risetime energy of 8.58 mJ
for Magnavox and 9.87 mJ for Delco

so, less than 3mSec dwell will cause a drop in output?