Misfire Desensitizing

[SloppyRob]

I changed the idle and low rpm tables per Cyl all to 32,767. This should help with my misfire codes correct?

[Screamn03]

I believe that 32767 is what they are stock. I believe the number you change them to is 32000. Does any one know why or what 32000 or 32767 is in units?

[SloppyRob]

Im probably wrong but it has something to do with time between each cylinder fire?? 32,767 is in there but only for certain rpms or temps (cant remember). By changing the entire low rpm table to this i think it raises the threshold at low rpms.

[jimmyblue]

32767 is a 16-bit binary "clip" limit (signed integer).
32000 or 32767 probably doesn't matter. I know
I've seen numerous discussions about misfire
adjusts (usually revolving around big cams and
converter unlocking) on LS1Tech.com PCM forum
but I haven't paid enough attention to know what's
what; however, there's some other (threshold?)
limit that I think is what you're really after - I'm
guessing that it's something about how much
crank jerk gets called a misfire instead of ignored,
and I recall the units being 100-150, not the higher
count?

[Screamn03]

it almost seems like the 32000 or 32767 is a unit of time or something based on how I read the charts. I guess I still don't get it.

[Screamn03]

[Screamn03]

[SloppyRob]

I think the 32,000 represents crankshaft rotation counts. I looked at my service manual and it contained a page of really confusing info but i believe the misfire routine reports back to the pcm every 32,000 rotations if it's set to 32,000. I'll see if i could possible type up some of the info for you guys to look at.

[jimmyblue]

Is this the Helm manuals? I'd like to read up on this,
can you give me a pointer?

[SloppyRob]

Yeah, I dunno if it's helms but it's the full service Manual for GM 2002 F-body. It's actually 3 Manuals. The Information regarding Misfire's is located in the Engine Manual under Engine controls. It actually shows how a misfire is generated.

[jimmyblue]

I have the 3-manual GM service set but the Engine
Controls section runs to 300+ pages just on the 5.7
part; index does not point to anything. If this is the
fat green set, can you narrow down for me where the
misfire info hides? All I've found is a pretty light bit at
the P0300 code section, and a bit in the "Scan Tool
Data Definitions" (pg 6-1431).

That bit indicates there is one misfire counter that is
short term ("Misfire Current&quot, on a per-last-200-
firings basis and one long term ("Misfire History&quot that
runs 0-65535 and gets updated only when current
misfires have tripped the DTC0300, and then every 200
firings I guess it adds Misfire Current to the tally?

So it would appear that you'd want to elevate the
misfire current threshold above 200 to eliminate any
DTC trip, or somewhat less if you wanted this to
catch a real misfire problem. The history, I don't know
what it does (code-wise). And I don't know whether
the misfire settings in the tuning menus pertain to
the current (/200) or history counters(65535)?

[SloppyRob]

Yes, it's the green service set. I dunno if you've found the section im talking about or not? I think on the second page of what im talking about there's a diagram of how each cylinder notifies the cpu. It looks like a bunch of file cabinets. Is this where you were looking? Im at work so Im not near the manuals. I'll let you know tonight if you haven't seen these pages.