I am running firmware version 3.2.1 on a 350 Chevy V8 single ignition coil, dizzy, standard dwell. I was starting to get a pretty good tune done but when I approached 5000+ rpm I started getting misfires. I had previously had a almost new ignition coil go bad that took a while to diagnose and in process experimented with dwell and had noticed that my new coil would quit firing at about 1ms dwell. So when I started getting missfires at higher rpms I kinda thought dwell might be the problem. In tunerstudio I have the dwell set at 3.5ms and spark duration set to 1.8ms. To check this out I connected my oscilloscope to my spare ms2 and using my stim I discovered the the spark duration was simply being subtracted from the available dwell time so at 6000 rpm the available dwell time is 2.5ms subtract the spark duration of 1.8ms leaving .7 ms dwell resulting in no spark.
The patch below implements a proportional decrease in both dwell and spark duration allowing for more dwell at higher rpm. The rational is that at higher rpm there is not enough time to fully charge the
coil (dwell )therefore less time is needed to discharge the coil ( spark duration).
Again at 6000 rpm the available dwell time is 2.5ms by proportional reducing dwell and spark duration the resulting dwell is 1.65ms and spark duration is .85ms. I checked the code on my spare ms2 and it seems to be working correctly so I updated the ms2 in my car I made a couple of passes at 5500+ rpm without any missfires.
I am mostly familiar with lower end processors so I am used to avoiding division at all cost and wrote this patch using a subtract loop. After reviewing the capabilities of the HCS12 processor this was probably pretty silly, wow I didn't realize how fast this processor is. I have rewrote the patch using multiply and divide. I have tested it on the bench and seems to work so I am planning on testing on the car this weekend.
if the test goes well I will post that version of patch.
[EDIT]
I had a little extra time today and was able to test the new patch in the car and seems to work.
Hopefully this will be up to standards.
I am semi-interested here; I have noticed occasional misfires on my HEI-equipped engine that revs to 6000 RPM. My engine is a V6, so probably not as bad as with V8. I've been looking through version 3.2.2.
So lets go over the basics here with how standard dwell is "supposed" to behave.
At low RPM, dwell is fixed duration.
Above some critical RPM, dwell becomes fixed angle, just like with breaker points.
There's a problem with the patch. It uses flash4.max_coil_dur directly in its calculations. If the battery correction is not 100%, there will be a discontinuity at the critical RPM for dwell as a function of RPM.
It should use ( flash4.max_coil_dur * battery_correction_factor ) instead. As a user, I would expect the dwell battery correction to be applied uniformly, smoothly under all conditions of engine RPM. I understand that at high RPM, the alternator should be putting out the nominal 14.5 V or so, so the battery_correction_factor is near 100%, but it's preferable to have code that always does what you think it does, cleanly.
Feel free to inform if I'm not making any sense here.
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Something I noticed while looking at the dwell stuff, the dwell "Acceleration Compensation" setting:
flash4.DurAcc
It doesn't seem to be doing anything in the code, a "dead" variable. I don't really care for it.
However, if we want to use the setting, then the most intuitive(in my mind) dwell duration calculation would be as follows:
I thought I was going crazy. Now I think I'm going to be fine. I couldn't get my missfire @4000rpms to tune out for nothing. When will the MS2 verson be available?
jsmcortina wrote:I've applied a fix to the latest MS2/Extra and MS3 codes.
The MS3 is released, the MS2/Extra is pending.
James
James, I have MS3, which release version has this code? Could you look at my post "A few questions before putting car on Dyno", is this code relevant to my dwell issue? Thanks,
David
oldskool wrote:James, I have MS3, which release version has this code? Could you look at my post "A few questions before putting car on Dyno", is this code relevant to my dwell issue? Thanks,
David
