Im using a 98 fbod pcm in my carbed LS2 and im wondering what method GM uses to limit rpm to 8000 rpm? The lower rev limits are fuel cut, but what about 8k limit? Ignition kill?

 

The PCM doesn't have calibration options BEYOND this RPM. Its the limit of the stock PCM according to the stock tune calibration. There are no more fields beyond this rpm...no data to reference...no worky!

 

Im not trying to turn past 8k, im asking how pcm disables 8k and up rpm?

 

Rev limiter cuts fuel. Fuel is then turned back on at an rpm you choose which is typically -100rpm below the cut limit. i.e. cut @ 6,500rpm, back on @ 6,400rpm.

Hp Tuners Example:

VCM Editor> Engine > Fuel > Cutoff, DFCO > Fuel Cutoff > RPM Limit. (Max available in stock tunes is usually 12,800rpm) BUT again there are no other supporting tuning tables past 8,000rpm.

 

In the crazy high RPMs the crank sensor "pulse" becomes static. Maybe that will shed some light.....

 

i think it just uses the table values at 8k for anything past that.

 

the pcm will use the last values in the cells as it goes past 8k...
RPM limits are 12800... its a pcm resolution thing..

 

^ exactly. How far is the res on the newer pcm's? the...is it green and blue connnectors? i cant remem the numbers. haha

I can tell you mines seen 8200 more than a few times..of course, it also blew up eventually haha

 

the newer pcms are higher resolution, but they limit to 8192...
which is pretty screwed up if you ask me..

but hey, twice the data rate of ls1 pcm's

 

its 2 ^ 13. 8192. gotta understand the chip(s) and programming