Do you think it would work? I was looking back at the spark retard based rev limiter I did and decided it just wasn't practical. Basically what you'd end up with is flames shooting out the exhaust instead of a good rev limiter. Which is still fun, but a good way to ruin parts at full throttle. So would setting the dwell to something super short so the coil doesn't charge work? Or is there something in the icm that will screw up my plans? I'm using DIS with a modified version of 6E.

 

It might, if you can get a short enough dwell. Isn't cutting the fuel the normal way to do it?

 

How do you propose to adjust the dwell?

The dwell is controlled by the ICM.

 

Yea, but that's a no no with n2o.

I was looking through the 6E hack briefly and noticed some dwell related stuff... I thought the icm was what did the dwell too but that got me wondering.

 

Ultimately it would be nice to have a spark based rev limiter but aside from something goofy like wiring up a relay to kill power to the icm, finding a way to change dwell is the only way to do it... more research tomorow... bedtime now.

 

Here's what I was looking at. Still not entirely certain what this does.

; ZERO VAL'S
; EST DWELL, EST PULSE WIDTH
;
CDE2: CLRA
CDE3: CLRB
CDE4: STD L3FDC ; TO SPK Dwell Cnt'r
CDE7: JSR LF4EE ; SHORT DELAY

CDEA: STD L3FE6 ; SPK Dwell Cnt'r
CDED: JSR LF4EE ; SHORT DELAY

CDF0: STD L3FE8 ; CURRENT EST FALL-LAST EST FALL
CDF3: JSR LF4EE ; SHORT DELAY

CDF6: STD L3FF6 ; EST FALL CNT'R
CDF9: JSR LF4EE ; SHORT DELAY

CDFC: LDX L3FEC ; B Cnt'r last ref
CDFF: JSR LF4EE ; SHORT DELAY

CE02: STX L3FE4 ; B Cnt'r Bgn nxt Dwell
*****************
* Compute Dwell
*****************
;
; IF LOAD CHANGE DURING LAST
; 25 msec > 10 LV8 SET DWELL
; to $FFxx & Br to LCEC8 ...
;
CE05: LCE05 LDAA #255
CE07: LDAB L0064 ; LD VAL
CE09: SUBB L0063 ; NORMALIZED LOAD, 25 Msec OLD
CE0B: BCS LCE12 ; BR IF OLD G.T. NEW
; ... else

CE0D: CMPB LC01B ; Ld Val vs Dwell Limit
CE10: BCC LCE1D ; br if G.T.
; ... else
;----------------------------------------
; IF DELTA RFPER > DYNAMIC DWELL
; set DYNAMIC DWELL = -2 * DELTA REFPER
;-----------------------------------------
CE12: LCE12 LDD L009B ; OLD REF PER
CE14: SUBD L0099 ; CURRENT MNR LOOP DRP PERIOD
CE16: ASLD
CE17: SUBD L009D ; DYNAMIC DWELL
CE19: BMI LCE1F

CE1B: ADDD L009D ; DYNAMIC DWELL
CE1D: LCE1D STD L009D ; DYNAMIC DWELL

;------------------------------
; Limit DYNAMIC DWELL to
; REF PERIOD/8, (11 DEG FOR V8)
;------------------------------
CE1F: LCE1F LDD L0099 ; Current Minor LP Ref Period
CE21: LSRD ; DIV BY 8
CE22: LSRD
CE23: LSRD
CE24: SUBD L009D ; DYNAMIC DWELL
CE26: BCC LCE2C

;
; IF DYNAMIC DWELL > REFPER/8 set DYNAMIC DWELL to REFPER/8
;
CE28: ADDD L009D ; DYNAMIC DWELL
CE2A: STD L009D ; DYNAMIC DWELL
CE2C: LCE2C LDD L0099 ; Current Minor LP Ref Period
CE2E: STD L009B
CE30: LSRD ; n/2
CE31: SUBD #229 ; 3.49 Msec, (15.25 Msec/bit)
CE34: BCC LCE3B ; BR IF D G.T. 3.5 Msec,
; ... else

CE36: ADDD #0308 ; ADD 4.697 Msec
CE39: BRA LCE4B ; EXIT via BATTERY COMP


CE3B: LCE3B LSRD
CE3C: SUBD #0295 ; 4.5 Msec
CE3F: BCS LCE46 ; BR IF D L.T. 4.5 Msec
; ... else

CE41: ADDD #0382 ; ADD 5.825 Msec
CE44: BRA LCE4B ; EXIT via BATTERY COMP


;---------------------------
; D = 1/4 * (D + 23.3 msec)
;---------------------------
CE46: LCE46 ADDD #1527 ; 23.3 Msec
CE49: LSRD ; n/4
CE4A: LSRD

 

I'd be tempted to experiment and watch the waveform on the ignition scope. I don't know by what means the ECM would communicate the desired dwell to the module, though.

 

There's a few disfunctional or carryover code sections in 6E that look like something gm planned to implement but didn't. The power steering logic is another example that just doesn't work, but it's there taking up space... I need to build an ecm test bench to test this stuff out quicker.

 

You could also use spark retard. Basically as the engine approaches its cutoff RPM, you rapidly pull spark. This would effectivly arrest the engine in a more controlled manner rather than cutting fuel or spark. Another option, if your diving into the code, is to allow the ECM to control the N2O. A few hundred RPM before the cutoff is approached, you cut the flow of nitrous. When the RPMs have stabilized, you then restore the flow. This will also allow the ECM to control the additional fuel directly, so the mixture can be enriched prior to adding the nitrous. Makes it less likely that you will blow the intake off when you hit the button.

How much coding are you planning on doing? There are some other improvements that you can make to the 6E as well.

 

Also, are you using the 6E code on a 6 cyl.? IIRC, the 6E code is explicitly designed for an 8 cyl, and assumes that 8 cyls. are present in the fueling logic if my memory serves me right. You can use it on a 6, but the MAF calcs will not be correct as the fuel is calculated as a duty cycle, rather than as actual mass of air per cylinder like modern MAF systems.

 

That happens in every embedded assembly project.

 

Yep, v6 with 6E. The maf is from a '97 thunderbird so recalibrating was a given. I've been recalibrating what was an ARAP base for sevral years now so it runs like a watch. The LV8 calc has a scalar that needed to be changed and I had to set the # cyls & fueling mode to v6 but other than that I haven't found anything that makes it v8 specific.

There's a few simple code changes like wbo2 input and extended the main spark table to 6400 rpm that were done over the years but I only recently took on the challenge of rewriting all the LV8 stuff for a 3bar map, n20 controlled by the egr table, writing launch spark retard code and a bunch of other stuff I have planned. It's going to be something along the lines of BAUJP, but flexible enough for any type of power adder.

I did a spark retard rev limiter but decided against it, ended up as a flamethrower. Cutting the nitrous is a good idea, I should have thought of that. The problem I keep running into is finding space for new stuff. I also need to figure out a way for the LV8 calc to repalce the map incase the map fails. The simple solution was leaving LV8 alone & having the map write to the same location, but that makes reading the datalog kinda hard as the signal constantly switches between the two. Doesn't appear to effect spark though.

 

Have you made a compilable hack yet? Thats how i start my projects. Something the size of the $6E can be made to compile in about 1-2 days of work. After that, you can delete and change things at will as the addressing can be made inherent, which allows you to relocate blocks of code. You could then also add things like a true 16-bit single table MAF lookup and fuel calcs for better resolution, or replacing the LV8 SA with true MAP based SA.

 

The '7165 ECM is capable of using a '256 kb PROM, stock.

RBob.

 

I haven't made it compileable/relocateable yet. I was going to get rid of the factory test stuff then see how much more space I need.

Are you telling me there's a crapload of unused space I never knew it could read with a 256 prom???

 

Yes, it has 15 address lines run to the PROM portion of the MEMCAL.

RBob.

 

 

I would use the ecm to control it like the 4th gens do. cutting spark or the rev limiter as a nitrous saftey? sorry to come off mean but your asking for broken parts. the solenoids are still going to be dumping nitrous and fuel while the eng is off for a few split seconds guess whats going to happen!!

 

I think shutting it off a few hudred rpm ahead would be enough for the lines to empty. Spark cut is the better way to go but so far there really isn't a way to do it with these ecm's. Even if you kill the signal the icm will still fire at base timing, so the only way is to command either less spark or shorter dwell and dwell is controlled by the icm. Other ideas?

 

The GM fuel cut and power adders just don't work well together. N2O can be coded to shut-off at a certain RPM before pulling fuel. Not so with Turbo/Supercharger. It is a more difficult problem. It requires spark being cut.

Don't dwell at all for a given pseudo-random spark event with cut spark. You could also use the scheme of cutting power to the coil like the EDIS requires for cutting spark. Yeah, with the EDIS that is the only way to cut spark. At least with the GM dizzy you can cut the icm control signal.

I currently start adding a little more fuel and pull timing once the rev limit is hit as a means to slow down the rate at which the engine revs. It is not a rev limiter, but is the next best thing.

 

That's probably the best compromise. It may shoot flames without a catcon but it gets the job done without hurting stuff.