mazzerman

I have a nasty little misfire on random cylinders under acceleration that i cant figure out.
Iv attached some Tech2 data shots to see if anyone can spot something.
it's a 2005 LS2 with no mods except for Vararam intake.
on the plot you can see i am accelerating so not on a decel open loop scenario, and the downstream O2's are dropping right down in MV which i would expect to see on decel in open loop but on acceleration i would have thought they would be stable higher on the scale.
Fuel trims look OK and up streams are switching OK. On the misfire i also hear a light metallic ping like a lean condition engine ping but it looks to me like its running rich and trims are leaning it slightly?
Any ideas where i should be looking most appreciated.

BlindSpot

First of all, ignore both sensor 2s they're not offering your anything. Second, the LTFTs look to be correcting a 3% lean condition. Third, you're going to leave CL and enter OL in PE. So, open loop occurs both on acceleration (approx. above 4KRPM) and on deceleration. The "misfire", and associated with what you are hearing sounds like Knock to me. But no screen data shows KR.

mazzerman

Looking at the snapshot the LTFT's fluctuate between -15 and +3 for very short instances so dont think i'm looking at a fuel issue because under load i would see fuel trims going + to compensate wouldn't i? I mostly see - numbers on playback....
Any ideas where i should check with another run and Tech2?
would ignition degree info tell me anything?

BlindSpot

Not following you - snapshot and LTFTs -15 to +3?? That is a huge swing and not sure what you're looking at there.

+ FTs are correcting a lean condition; - FTs are correcting a rich condition. Not likely FTs are swinging in that big a range.

Suggest you track KR, RPM, Load. KR is what I suspect you're getting

BlindSpot

Let me put one more in here - serious misfires or chronic random misfires will show up in CELs as P0301 through P0308s, or P0300. Since you're not seeing any of these CELs, I think KR.

Where are you located? Outside air temps? This problem recent and related to higher outside temps?

mazzerman

I probably didnt explain it to well what i was seeing so here is a link to a video clip of the data i captured.
It's the switching on the LTFT's i was trying to explain, they seem to jump around quite frequently which may or may not be normal.
I cant find anywhere on the Tech2 to monitor knock, only misfire data.
https://www.dropbox.com/s/j20dvxoi9w...pshot.mp4?dl=0

Temps here in southern Spain are around 73f and nothing adnormal with temps here.
Does anyone know a good way either with Tech2 to monitor KR?

BlindSpot

yeah, a Tech 2 is probably not the best device to DL. Since there is no other information on that screen, if RPM were captured in the same screen, I am thinking you are generating the high - LTFTs on DFCO. If so, ignore that and only focus on FTs if you are holding a steady or increasing % throttle command. Not deceleration. That said, if you're staying in a range then of +5% to -5% LTFTs, this is considered pretty normal FTs. The steady +3%s that I see are good, but I personally prefer mine to be slightly -, and I hold -2% to -4% going into PE. That way I'm not dragging FT corrections into PE.

If you could switch off to a more comprehensive DL device, it would probably be better for you in analyzing the tune. Don't want to sound like an HPT sales person, but that would be far better, even a Diablosport DLs pretty well. If your Tech 2 is a clone, I believe you can set up a data collect on a PC so you can capture live data from several screens that you cannot catch on the fly just looking at the tech 2 windows. I wouldn't be satisfied in your case, until I could see KR.

mazzerman

Yeah i might need to look at HPT,
I will do a few more runs, a steady RPM cruise then a brisk acceleration, then a hard acceleration run and look at the trims and misfire data.
Thanks for the advice, much appreciated.