Rich Spike @6400rpm

[LSxpwrdZ]

I've been racking my brain trying to figure out what it is in the tune files that is causing this. It's not only on one car but every Gen3 car I still have a datalog file for. At 6400rpm you can see the Pulsewidth spike slightly and react on the wideband usually within .2 of a second with a rich spike. My Formula does it, my Camaro that I spun to 7500rpm does it as well as a handfull of other car's. Just wondering if anyone else has looked this closely to the logs and observed similar.

[Ben Charles]

Maybe fuel to wall impact factor under transient fuel needs to be decreased at that MAP value?

[LSxpwrdZ]

It is defineately fueling related because airflow doesn't really change abnormally when that spike occurs. You can see this in the injector pulsewidth at that RPM.

I've looked at C5's and multiple Fbody's that I have tuned and they all seem to have that particular spike. Also it doesn't matter if it's SD or MAF either which concludes it's not an airflow calculation issue.

[CancerJCC]

My guess which is based upon nothing more than speculation is that it might be something hard coded into the PCM we can't see. I know my V has the limiter set at 6500 and perhaps GM threw some extra fuel right at redline. It would make sense considering you can see it on multiple gen III vehicles.

Again an uneducated guess based upon nothing from a noobie.

[LSxpwrdZ]

Bump this back up. Over the last 2 years I have been observing this issue on all gen3 applications I have done. This pulsewidth spike is really obnoxious, mainly because I'm a perfectionist and I would mainly like to know what is causing it. I've logged dynamic airflow, MAF and none of the airflow related tables cause this little spike right at 6400rpm. It is only shown on the pulsewidth, duty cycle and wideband as a result.

[Bluecat]

Lol, I mentioned this years ago. Everyone acted like I was crazy especially in PM's. I see it every damn day and just work around it on genIII stuff. g/cly and cmdAFR don't change when it happens. It just litterally adds a little to the injector pw when it does it. Not just at 6400, there are other points you can see it happen, just not as bad or as impacting. There is a table somewhere we cant see that does it, but have no idea what it is. Dosent interpolate either. Like a switch at the rpm points it happens.

[Bluecat]

http://www.hptuners.com/forum/showthread.php?t=19426

And now after another 4+ years of looking at it, I can say for sure EVERY and I mean EVERY genIII pcm ive tuned does this!

I need to do a sim test with a static ve table and sweep the rpm. Inj pw should be strait across a rpm sweep. Would show the break points of missing table easily then. But 3200 and most definatly 4800 and 6400 there is something happening.

[jimmyblue]

Interesting that it happens at those even boundaries.
In data converter design we worry about "major carry"
nonlinearities (like '00000001 -> '10000000) and maybe
this is an artifact of cell boundary transitions and the
interpolation method?

[LSxpwrdZ]

Like you I've seen it for a long time and have wasted alot of time looking through tables to see if I could remedy it with no luck. Figured someone with more coding knowledge could shed some light on it.

[waz89]

http://www.hptuners.com/forum/showthread.php?t=19426

And now after another 4+ years of looking at it, I can say for sure EVERY and I mean EVERY genIII pcm ive tuned does this!

I need to do a sim test with a static ve table and sweep the rpm. Inj pw should be strait across a rpm sweep. Would show the break points of missing table easily then. But 3200 and most definatly 4800 and 6400 there is something happening.

8 years has past, has anything happened regarding this?

Or is it still unexplained.

[ryan_axberg]

I have a P01 ecu that is in 3 bar speed density and I was just looking at different logs and I don't have anything weird going on at 6400. I was also looking at a couple other vehicles I have tuned both just maf and neither one of them had anything odd going on at 6400 either.

[waz89]

I was about to make a new thread but thought i'd just piggy back off this. Can someone have a look and spot anything?

p01 with 2bar OS. mp112 at 7~psi.

[LSxpwrdZ]

Still happens. I have a injector tap that my dyno logs the raw PW from the injector and it shows a spike in a few different places throughout the graph. I have still not found out what causes it either. It's worse on some cars than others for some reason.

I assumed it was something to do with desoot or some other parameter in the background that we don't currently have access to outside of user defined parameters.