Turn off misfire detection under 2000 rpm

With the big cam and all I'm wondering if it's playing with your timing tables

 

His timing stays steady and normal, at least in the log I seen. When he says light throttle he means light throttle, like no load damn near. Its like 3.0-3.5MS Injector pulse when it happens.

 

Are the injectors going below their minimum pulse width? It may be commanding an ontime, but the hydraulic operation can't happen in that amount of time (and it may be harder to detect if some of them are still working and others aren't). This will get worse as pressure goes up and commanded on-time shrinks. How big are the injectors?

 

That is possible.

With the new fuel system my pressure is actually lower than it was with the stock returnless system.

This happens at such light load simply because thats when you bump up against 1400 the softest and sit there the longest. It will do it on decel with the converter locked as well. I think it will do it under a heavier load with the converter locked too. At such a low RPM I can only put so much load on it before the converter unlocks and i flash to a higher RPM.

I'm absolutely not ruling out fueling, but I think its more of an RPM thing than it is a specific pulse width thing. How does RPM effect firing of an injector that would make it break up from about 1400-1600 and clear up above 1600? Maybe at such a low RPM and quick fire they are having trouble opening and closing that quickly for such a short period? I see a similar pulse width while cruising on the highway at 60 at 2000+ RPM with no signs of breaking up. Maybe the faster RPM has a way of making the injector timing less important?

I have played with my idle timing tables a lot lately... something keeps bringing me back there despite the timing looking find in the logs. There are certain tables that store a history in the tune file and can mess with it even if current settings are correct. Our PCM's are a fickle beast...

 

If it was a low pulse width correction issue, you would see it regardless of engine speed, but it may have some minor voltage dependency. I doubt it is your issue if you don't see it leaning out first and if it isn't present at other engine speeds with similar pulse widths.

 

You should get a snout like this for your JS setup, helps with throttle response too:

 

They sure aren't cheap. Have you run one, or are you just basing it off what Joe says?

The entire blow off through that tiny little port, huh? Maybe thats why it improves response.

 

The original idea came from Kenny Duttweiler many years ago.........I happened to be in his shop one of the times he and Joe were testing Joe's LSx/Magnuson motor and he(Duttweiler) mentioned this mod and wondered if somebody might manufacture it as a way to increase airflow. The concept is sound as a means to increase airflow as far as I know; a similar design is used in the older chevy inline 6 motors in what's called a "lump port".....check it out: Things you need to know about Your L6 Head Before Installing your Bolt in Lumps

We are talking max effort here, Joe's motor was making power in the low/mid 900's before he started to manufacture this mod if I remember correctly........obviously, he would have the more accurate facts on this.

anyway....that's what I know/or remember

 

Yeah thats my SS sedan setup in the pic above. She is just a daily driver that i take to 1/4 on fridays, road course once a month, and pick on the ctsv's and vettes on my commute to work all while rowing the gears. This is basically the only mod to the car besides 2" primary headers and its right at 600whp fuel limited.

Duttweilwer and leftcoast run this piece on their 1000hp js2300 390. There are similiar snouts for tvs front drive setups and lsa also, but dont think joe and friends made those.

The tiny port is for the bypass port thats used under low load/boost. So i guess you might be giving up some mpg on freeway cruising but the improvement in the intial boost ramp, and the dyno tq graph the drop was pushed back so it pulled longer up top when the rotors are spinning at full tilt. (Currently running underdrive cog now, so rotor speed is probably only 20k)


My SS saw roughly 45 hp improvement with just that mod on a stock ls3 wIth headers. I should have done the nw102 and intake to get full potential, but didnt want to go through additional tuning headache of dbw tb as was short on time.

 

45 HP gain is pretty legit! I had heard it was a lot but I was unsure if it was due to the larger throttle body or the inlet design itself.

What is your pulley combo on the SS currently? 20k is a lot if you currently have it set up to be under driven. This could be something for down the line... but at the moment I want to get it running right first. How much is it if you don't mind me asking.

As far as the misfire issue goes I doubt I'll be able to play with it for about a week. I leave town tomorrow morning for a few days. I do have a few tuning tricks I will try to see if those help me out at all.