P0300 / Tuning Mystery

[robof16]

Need a little help on this. Primarily rough idle and occasional surging to light throttle issue, sets the P0300 code even after increasing values in C5621. No expert but, looking at the log, seems like something is up with the O2 sensor system.

6.0L in a Yukon XL, small cam (-2 degree overlap), 823 heads, TBSS intake, SEP injectors (with their tune data), stock exhaust...

To this point:
- New MAF and front O2 sensors
- New plugs and wires, good spark, plugs look good/all the same
- New fuel pump, filter, etc., adj FPR, fuel pressure checks good
- Noid light check on injectors
- Good compression
- Smoke check - no apparent vacuum leak
- I've reduced the idle spark overspeed/underspeed compensation B5935/6
- Desired Airflow, VE, and MAF frequency are as close as I can get them

Check the crazy voltage readings on the O2 sensors (WB at location 11). I figure it's normal for the WB to read about 450mv steady?
I've suppressed the secondary 02 sensor DTCs and figure the CATs have lost effectiveness but the performance is so good, it doesn't seem like they could be clogged.

[nonnieselman]

IF WB is steady 450mv it is either bad or disconnected.
What are cam specs?

[robof16]

Update: Desired airflow was off a little, idles much better now. Logged misfires and even though the P0300 code is not being tripped, it's significant enough to unlock the converter. Cyl 1, 2, and 3 are the primary culprits, 2 & 3 are the worst. The log was recorded at 60ish MPH cruise. The converter locks, then as the misfires build (which you can feel), it unlocks.
In one very specific circumstance, the Check Eng light will flash - hwy speed, very light load, as you slow or reduce throttle to maintain speed down slight incline (single digit TPS). Again, no P0300 in this case, nothing in memory.
Cam: 212/212 .553" 107 LSA +3
Readout on WB and data in log looked good and seemed accurate as I did some tests with injector flow rates and saw exactly what you would expect.

[robof16]

Log file for cruise 60 mph

[statesman]

Some aftermarket injectors perform poorly in low pulse, which is where you seem to be having problems. Try swapping injectors 1-4 with 5-8 and see if the misfires follow the injectors.

[robof16]

Good call on the injectors, I'm afraid that might be it. Will do the swap then the same with coils if the injectors check OK.
Thanks.

[robof16]

Looks like it's the injectors. Coil test passed.
Misfire followed the injector and misfires pick up on the three suspect cylinders as PW drops close to 2 ms. Min injector PW is .76 so, that's disappointing.
Per data from SEP, Small Pulse Adjust does not kick in (zeros) until PW gets down to 1.033ms.
I set Default Minimum Pulse Width to the same as Min Injector PW (.76), didn't know what else to set.
Also, I left Small Pulse Threshold alone at 4.0ms.
Just hoping there's something in the tune that can be adjusted...

[nonnieselman]

Looks like it's the injectors. Coil test passed.
Misfire followed the injector and misfires pick up on the three suspect cylinders as PW drops close to 2 ms. Min injector PW is .76 so, that's disappointing.
Per data from SEP, Small Pulse Adjust does not kick in (zeros) until PW gets down to 1.033ms.
I set Default Minimum Pulse Width to the same as Min Injector PW (.76), didn't know what else to set.
Also, I left Small Pulse Threshold alone at 4.0ms.
Just hoping there's something in the tune that can be adjusted...

SEP injectors arent known for their quality.

If you want a alternative..
Ive used a few hundred sets of these and they are good stuff. They all flow the same on my bench and their spray pattern is nice.
I can get you the data if you want to go that route.

https://www.ebay.com/itm/274424906026

When someone brings me something to tune with SEP injectors or some chinesium injectors i just turn down the job.

[robof16]

Thanks!
Wondering what those injectors flow, I'm preparing to step up to FI and need at least an 80lb injector.

[robof16]

50 lb/hr at 43.5 psi?

[robof16]

Also, for anyone that reads this in the future, the tune has B9021 cax loaded, and the suspect injectors still misfire with B4003, and B4004 set to .015198.

[nonnieselman]

50 lb/hr at 43.5 psi?

50@58psi

[robof16]

Thanks. No harm in trying the injectors you suggest. PM sent.
Where do you purchase injectors if you need more flow?

[nonnieselman]

Thanks. No harm in trying the injectors you suggest. PM sent.
Where do you purchase injectors if you need more flow?

Fuel Injector Connection.
What kinda FI are you thinking? How much power?
Those "3412" injectors can flow enough for 5-6psi from a decent size turbo.

[nonnieselman]

Ive used these in several turbo trucks over the years.

https://fuelinjectorconnection.com/products/fic-72-lb-for-trucks-with-adapters-set-of-8

[robof16]

Turbo - The 3412's and 5-6psi is a great place to start and the FIC 72's will be perfect if I turn it up.
Thanks for your help.