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So out of a combination of boredom and curiousity... lol... I started datalogging again..
One thing I noticed is some huge variability in BLMs at 35 kPa and below...
In the tables below, you can see I have my BLM's pretty good.
The first picture is the running maximum.... you can see that there are a lot of 140's at 35 kPa and below. In the second picture, the running minimum, where a lot of those 140's are now 126's and 128's (more in line with the typical BLM's elsewhere). I'd like to get those 140's to disappear, but I'm not sure what to attack. If I modify the VE table to richen those MAP/RPM cells, the 126/128's will drop to like 110 or something.
I'm thinking it's some sort of decel enlean or DFCO or something, but I'm not able to see in the data what's actually triggering it. Would someone be able to take a look? Maybe I'm missing something...
Altho I had my injectors tested for IB, I still get the proverbial “bathtub” in the area of idle along w the dreaded split BLM on my LT5 which no doubt contributes to bathtub curve. The motor is cammed, ported and has headers. Any thoughts on what could be adjusted in the tune vis a vis injectors, or is that just the way it is?
Cells 3 & 7 are next to each, delineated by the MAP value. The cell borders aren't a solid number, there is hysteresis involved. Stock AXCN is +- 2 KPa.
Yep they can vary wildly in that area. I tried tuning them and it's all over the place. So I just don't care anymore. After many datalogs and analysis, I realized it was the area of DE/DFCO/In between shifts/Light throttle going down hill. Hard to tune. I have my BLM cells divided to isolate the area now. As long as it doesn't go too wild, I don't touch them.
In fact I got rid of BLM all together. I run on INT only and never had a problem. First off it's way easier to isolate a problem with VE that way.
My personal preference, no saying anything else than that.
If you want to know what is going on, you'll have to extract the data one by one to find a pattern. Then you'll see what causes the BLM to get elevated and stuck to 140. BTW, Max and Min are useless as Cells get cross contaminated with BLM of other cells when transitioning.
TunerPro will allocate data not exactly following your boundaries. It almost "cut the pie in half". I know for a fact because I used my own excel spreadsheet and my allocations were quite different than TunerPro.
Example:
MAP value of 40 45 50 60 in table
45 means 40.1 to 45
50 means 45.1 to 50
60 means 50.1 to 60
In TunerPro History
MAP value of 40 45 50 60 in table
45 means 42.5 to 47.5
50 means 47.5 to 55.5
60 means 55.5 to 65.5
It's not exact but you get the idea. Do a comparison and you'll see what I mean.
It is bad or rather just flat wrong injector data causing the problem. At very low pulsewidth the injector data is causing the fueling to be inconsistent hence the variations you see. Log the actual pulsewidth in the affected area. The lower the PW, the more impact wrong data will have on the fueling.
I always modify VE in the boundary cells as well for that reason. One of the things I do once the VE adjustments is made to a particular cell after a datalog, is to compare the new VE table(s) with the old. I then highlight the cells where the changes were made and then use the graph to show me if there are cells between the modified cells that appear contrary to the overall contour of the VE curve. I then modify that cell to fit into the overall curve doing a manual smoothing.
After doing a bunch of searching online, I came across some threads regarding NB O2 sensors with stainless steel exhaust systems and how you should run a 4-wire sensor due to the relatively poor electrical properties of the stainless steel and how that impacts the grounding for O2 sensors. I've been running stainless headers since the mid-late 90's.
Several years ago, I had read something O2 grounding vs stainless steel, but didn't see anything on the 4-wire sensor. What I ended up doing then was using a hose clamp to attach a braided ground strap to the sensor body and then running that ground strap to the stud where the ECM is grounded. It seemed like it helped a bit at the time, so I figured that was good enough.
But this BLM variability thing got me thinking about that electrical grounding some more and then I found the 4-wire sensor discussions. Ended up buying an AFS-75 and then wiring it in. The AFS-75 has a ground wire dedicated to the sensor element such that it's not dependent on the exhaust system for electrical ground. The heater has it's own ground as well.
I've had the car out a few times now to verify consistency in the results, but now instead of variation between 126 and 140 like in the tables above, the 140's came down to ~130.
Overall the car still runs about the same, but I still like solving mysteries like this. The sensor was actually pretty reasonably priced too.. about $70 at Autozone.
03-21-2023, 09:17 PM
