I only looked at the MPH, and things that change the MPH like throttle position, so I noticed the low TPS volts - that's the only reason I mentioned it.

Didn't plan to do a full review, but I can if you want. Again just looking BRIEFLY at the LTFT's I would strongly recommend you stop beating on it before it goes into closed loop. That's when it runs almost exclusively in Cell 18, and that cell is totally screwed up with the 180 LTFT. It could be running running super rich (O2 sensor maxed out), and you may damage the engine, washing down the cylinder walls

Is there some reason you have chosen to DIY tune rather than have a knowledgeable tuner set it up initially?

 

Fred, I will answer your last question first. Yes indeed there is a very good reason why I've "delved" into DIY tuning, and, if you really want to here my horror story about mail order tuning with "knowledgeable" tuners...... send me a PM, and ...... I'll spell out all the details.

Now, on to your other comment about that possibility of running super rich on bank 2 of my engine. Here is where the picture gets "muddled". Right now I have about 120-130 miles on the new engine mostly/all to data log and DIY tune it. When I started seeing high BLM's on bank 2, I pulled all four spark plugs on that side and, they looked .... perfect! Just the slightest light tan color with NO evidence of either carbon or oil fouling anywhere on those plugs! Also, since the exhaust system was also brand new with the engine re-build, there is no evidence of soot/carbon staining even at the tail pipes!

Now, I'm assuming since I haven't made any major changes to the fueling table (yet!) from the tune for the 350 motor, that the PCM was just (probably?) commanding more fuel to feed the additional 46 cubic inches (i.e. 13%) of engine displacement? At this time I've only been focusing on the timing tables to check for and/or eliminate any knock retard, while running this 12.5:1 static compression ratio engine on 93 octane pump gas. (If you do look at the data logs I sent, you will see some instances of the PCM pulling 3 to 5 degrees of knock retard). My general thinking here was to pull ignition timing to prevent any detonation, that might/would harm the engine, (after that major step up in compression ratio!), and then get into the VE tables to fine tune fueling. But, I did make a slight 2% richer scalar adjustment to all the values in the old 350 VE tables, just to "get in the ball park".

If you do have time to dig deeper into the logs I sent, of course that would be greatly appreciated, but, the car is not a daily driver by any means and, once the roads get snow covered ....... it probably won't even leave the garage till Spring.

And, as always, thanks for all your insights into this.

 

I'm not a tuner. I don’t even use a stock PCM. My approach is to look at the end results in the data log. Recognizing the limits of the narrow band O2 sensors, to me it appears that the 1.00+ V right bank O2 sensor readings in open loop, when you roll into the throttle, are not good to see. My point was not to drive it hard in open loop. Maybe the brief period you spent in open loop wasn't enough to foul the plugs. But it could be enough to wash the cylinder walls, particularly in an engine with possibly limited break in time.

The problem with Cell 18 is that it is mathematically derived based on the what happens in the other sells in closed loop. It's mostly used at coast down, or low throttle operation. But in open loop it's use whenever the engine is under load, and the PCM cannot use the STFT'S to correct for over or under fueling. Seemed important to point this out, but maybe not.

I saw the 5.00 deg of knock retard several times when you hit the throttle in closed loop. Have you set the maximum possible knock retard to that value? Are you still running the EVAP system? PCM is attempting to operate it. EGR appears to be tuned out. The more radical the engine build, and the further you depart from “stocking” tuning, the less I can extract from the logs. Not sure there’s much to be gained from additional review.

 

Fred, as always your "pearls of wisdom" have inspired even more thinking at this end, sooooo ...... let's tackle your most recent questions and/or comments!

Have you set the maximum possible knock retard to that value? No, I have not even touched the two (2) Max Retard Tables (yet!) but, in re-examining my last "professional" tune, (on the old heads and cam 350 set up), which I used as a starting point for my current tune, you are TOTALLY correct on that call. The Max Retard was set to 5 degrees by that "knowledgeable" tuner in the "pro" tune I started with. I will set this max value to 8 degrees in my next DIY tune, and see where it goes in the next data log. Thanks for spotting that!

Are you still running the EVAP system? Yes, I have not touched, (or modified), the EVAP system in any way. It's still there and fully functional to the best of my knowledge.

EGR appears to be tuned out Yep, the EGR system is long .... gone. I know it doesn't really affect performance, but to "dress up" the engine bay, use long tube headers without EGR provisions, and take some weight off the nose of the car ..... all EGR components are .... gone, gone, gone, and ..... tuned out.

Not sure there’s much to be gained from additional review. Don't worry, you've done enough already. Don't feel obligated to continue looking any more. You've given me some things to think about for both my next DIY tune, and some mechanical stuff I want to work on too. My "action plan" now is to 1) re-set my TPS to that 0.50 volt value you've suggested, 2) swap right and left O2 sensors and see if the bank 2 (180 pegged) BLM reading follows the O2 sensor, 3) change that Max Retard value to 8 degrees and also re-set the Max BLM setting back to 160 in my next DIY tune, and finally, 4) try and look for any loose VSS connections on the trans or trans harness to try and figure out why (???) Scan 9495 WON'T read true vehicle MPH ...... even when the speedometer IS reading correctly. (???)

 

Okay, I need a brief "sanity check" here. If the base VE tables for an engine tune are waaaaayyyyy lean, then we should expect to see LTFT's pegged at 160, because ..... the feedback from the O2 sensors are still (correctly) reading a lean engine condition, which the ECM is then trying to compensate for by adding fuel ...... right???

Also, what are the percentage limits that correspond to a maximum 160 LTFT. When "pegged" at the stock 160 maximum setting, is the ECM adding 5%, 10%, 15%, 20% etc., etc. more fuel??? And finally, if we raise the LTFT maximum limits to say 180 or even 200 in the tuning table for "MAX" LTFT ..... will the ECM continue to add even more fuel???

As always, TIA for any replies.

 

If it's actually running lean, the average O2 sensor readings will be below 450 millivolts. First the PCM raises the short term (not stored) fuel corrections (STFT). The STFT are temporary corrections, and are actually toggled back and forth from a little bit lean to a little bit rich to make the cats work.

If the PCM sees the STFT's adding fuel. (STFT averaging more than 128) the PCM increases the long term fuel correction (LTFT) above 128 to add more fuel “permanently”. The LTFT will be increased step by step until the average O2 sensor reading are 450 mV, and the STFT's are averaging 128.

To get the percent of fuel being added or subtracted, divide the LTFT by 128, and subtract 1. The factory tune sets the maximum LTFT at 160.

160 / 128 = 1.25

1.25 - 1 = 0.25

0.25 x 100 = 25% extra fuel being added.

The lower limit is 108

108 / 128 = 0.844

0.844 - 1 = -0.156

0 156 x 100 = -15.6 fuel being subtracted.

Yes, if you raise 160 upper limit to 180, it allows the PCM to add 40.6% extra fuel. At 200 it would be adding 56.2% extra fuel.

What are you interpreting as the VE tables being tuned “wayyyy lean”?

Is your tune 100% speed-density?

 

First off, Fred, (as usual), you comments here are pure gold! I "got" all the info you explained above about how to convert LTFT "numbers" into % rich or lean. Now on to your two questions, before I ask more of my own!

What are you interpreting as the VE tables being tuned “wayyyy lean”?

Here's the scenario. Since nobody sent me a base 396 VE table (or tune) to use as a starting point for my DIY tune, (as I asked for both here and on LTX Tech) ........ I started with my "Professional" 350 heads and cam, LT headers, bigger throttle body, yada,yada,yada, modifications tune. But, that "Pro" tune, (despite my numerous calls and/or complaints), always ran .... rich. So, since I already had a rich base tune on the 350 motor, I just added 2% additional fueling for the 396 tune, to use as a starting point. The intent here was to get the base fueling "into the ballpark" where the PCM could add enough fuel to get to "stoich" without pegging the LTFT's to 160, and then I could back calculate how much fuel the PCM was adding, and ..... update the VE table. Now, I assumed a 13% increase in engine displacement (i.e. from 350 to 396), based on an already rich 350 base tune with 2% added .... might just do that?

Also, while I might not know much about PCM tuning, (after all that's why I'm posting here), a physical inspection of spark plugs, O2 sensors, piston tops (using a bore scope camera), and exhaust pipes, all show the engine running either lean or slightly lean, with the LTFT's pegged at 160. Finally, let me ask this. When I datalog the O2 sensor output the sensors do "swing" from 100 to 900 mv, sooooo ..... the only way to calculate the average O2 reading, would be to note the time spent at those limit readings right? In essence you want a timed average of 450 mv, right? Is there any PID on Scan9495 that would show this?

Is your tune 100% speed-density? Nope, still trying to use closed loop tuning with those narrow band AC Delco AFS-75 O2 sensors.

 

OK. I'll show my “tuning” ignorance? I honestly do not know with absolute certainty the answer to this question - When does an MAF tune use the VE tables?

Speed-density requires an accurate assessment of volumetric efficiency. (VE). That's because VE is on of the factors the PCM needs to calculate the mass air flow, along with manifold absolute pressure and manifold absolute temperature. The engine designer runs the engine on a dyno to get enough data to back-calculate the VE table.

Running an MAF sensor eliminates the need to calculate the mass air flow. The MAF sensor directly measures mass air flow. Now the tricky part is calibrating the MAF sensor - in this case the translation of the frequency output of the MAF sensor vs. the actual mass air flow. That calibration is very sensitive to the physical layout of the ducting in front of the sensor, and the ducting after the sensor.

Look at this description of when speed-density (VE used) in the operation of the engine. It sort of answers my question, but still shows he is not exactly sure (or not telling) when VE table is required:

LT1 PCM Tuning - Tips & Tricks for DIY Tuning!

Scroll down to the “Idle - VE Tables” section. You've likely seen this before - maybe this is where you got your “professional tune”.. He indicates it's used in cold start. Maybe at idle? ? ? He's vague on that. Next look ar “Part Throttle - VE Tables”. He indicates this is an “either or” situation. You either program is for speed-density (VE) or for MAF (calibration). If you run MAF, you only need the VE tables to e accurate enough to give you decent results if the MAF sensor fails and the system defaults to speed-density.

When you get to “WOT” it again appears it’s the “either or” situation.

My thought here that trying to change fueling using the VE tables, when the PCM is running in MAF is not going to accomplish anything.

Yes, he vaguely suggests speed-density may indirectly affect running in MAF, but he way it is written, he either doesn’t know, or he is keeping that info as “proprietary” to his tuning skills.

As an aside, have you tried using VEMaster?

 

Fred, we've got a lot of ground to cover here, soooooo ....... let's get started and see where we agree, (on your now highlighted statements/questions above), or ...... agree to disagree!

Let's start with my "general thoughts" on MAF tuning:

Every (non electric!), vehicle that leaves an OEM manufacturer today, has some sort of EFI system on it that utilizes both O2 and MAF sensors to "control" fueling. Stock OEM "tunes" are all feedback systems, based on an initial VE table, (that you so accurately described is indeed "set up" by engine design engineers via dyno testing). That "tune" is then programmed into all PCM's with a common powertrain.

Now these engineers long ago realized that they could not determine true stoichiometric (Sp?) fueling for all the varying conditions of engine wear, fuel quality, operating temp, humidity, altitude, etc., etc., etc., soooooo they said ........ here's an idea! Let's program in an initial (read "middle of the road") baseline VE table, and then set up say +25% and -15% limits on the feedback control that the PCM uses to get to "stoich" fueling. Within these fueling limits the PCM is free to add or subtract fuel to maintain, (or get to), stoich. And if, for whatever reason the PCM exceeds these fueling limits ..... have it set a Check Engine/MIL light and corresponding DTC, and ..... we'll have a human being look into it.

Sooooo to answer one of your questions "When does an MAF tune use the VE tables?" Simple answer ..... always!

Even when it's in OPEN loop, where it defaults back to that initial/baseline VE table, (because it lacks O2 and MAF sensor inputs until they "warm up"), or at WOT (i.e. power enrichment), where those design engineer's original/initial VE table programing "intercedes" to prevent any unanticipated conditions where serious engine damage could/might occur. And, when in CLOSED loop operation, the PCM is now using feedback from it's sensors to control fueling within the limits it's allowed to again ......... based off that initial VE table.

On to your next comment "My thought here that trying to change fueling using the VE tables, when the PCM is running in MAF is not going to accomplish anything".

My thought here is that by changing/re-programming those baseline/initial VE tables (due to extensive engine mods, of course!), that the PCM uses as a starting point ..... that the PCM is now better suited to get to "stoich" fuel tuning within the +25% -15% fueling limits imposed upon it.

And finally some quotes pulled right from the website you linked (Thanks! for that by the way) which appear to support my thinking on this:

"BLM stands for "block learn multiplier." As mentioned above, the PCM uses the grid of cells referenced by engine load and speed to correct for discrepancies due to air and fuel quality. The PCM will be expecting the engine to run a certain way depending on the MAF sensor calibration or the VE tables."

The only reason I think (?) he used the word "or" instead of "and" is because he knows the VE tables are defaulted to in both open loop and WOT operation, where the MAF sensor input is ignored, but is still used as the starting point for BLM "tweaks". I think it's better understood if the end of that sentence concludes ......depending upon the MAF sensor calibration AND the VE tables which are always used as a starting point, (at the very least), for BLM adjustments.

And, the "smoking gun" quote:

"The BLM can also show a need for a change in the PCM tune; if the VE tables are set too high (low BLMs) or too low (high BLMs), ..."
And .... I rest my case here!

Finally, "As an aside, have you tried using VEMaster?" No, not ......... yet.

 

He used “or” because he separated tuning methods based on whether you are running speed-density tune (VE), or an MAF tune.

Beyond that, we're so far apart that I will just drop it. Apparently I'm just not capable of comprehending all this.

 

Nevertheless ..... Thanks (again) for all your comments, questions, and the links you've supplied, as well as having Gary Doug answer that question about his Scan9495 data logging program. You've steered me in the right direction on this, and I do truly appreciate that.