ChopperDoc

For this it's best to leave the TEMP out of the equation. That's why setting the EQ table at 140* and up to 1.0 is so important in getting the VE correct, otherwise you'll chase your tail a good bit, because temp changes VE. When VE changes, commanded vs WB will be incorrect, and because there is a bias, it gets complicated more than need be. Setting a baseline VE number relies on a warm engine, under operating temps in a relatively stable environment.

Here is what the PCM is trying to calculate with VE and ultimately trying to figure out for fueling on a gen III:

P (map) * V (volume per cyl in L) = n (moles.. unknown) * R (8.3145 constant) * Temp (K, bias included in normal tune)

So... P * V / R / T = moles

Moles * 28.97 = molar mass

Molar mass * VE from table in % (VE number/100) = g/cyl

Here is the complex math Bias factored in:

Temp = (IAT + (ECT - IAT) * Bias)

Bias will be from the table under "Cylinder Charge Temperature"

Example: MAP = 57 kPa, Volume = 0.875 L, R = 8.3145, IAT = 306, ECT = 364, Bias = 0.2827, n(moles) = unknown, VE table = 44.18

57 * 0.875 = n * 8.3145 * (306+(364-306) * 0.2827)

49.875 / 8.3145 / 322.40 = 0.0186 moles

0.0186 * 28.97 = 0.539 molar mass (total possible air in cylinder, in theory)

0.539 * (44.18/100) = 0.238 g/cyl <<< reality.

Now I know that gen IV is different, but still uses the same temp corrections because you cannot ignore them regardless of generation. Using commanded on the EQ table would assume that the Bias is 100% correct for your engine, when in fact 99% of the time it's just not. Especially if you have made changes that will affect the normal temps of your intake air, like chopping out the airbox as many do. Not saying it will be drastically off, but remember, GM intended MAF to be the PRIMARY method of determining airflow, not VE. Therefore it can be assumed that the EQ table isn't really precise, nor should it be included when attempting to find the commanded correction for airflow. Best to take that out, and as much other commanded changes as possible out (excluding PE or BE obviously) to get a good baseline for your VE table if you plan to use it as a primary means for fueling. If you plan to use MAF, then close is good enough in all honesty. I've done 100% MAF tunes on gen IV's just because I lacked the time to do the VE at all. It will run fine on a MAF only, no issues. I only had a few hours lol.

Wait to tune the MAF. Get the VE close first. From your log it says a 2004 express, and that is a Gen III last I checked. Unless for some reason your tune has a VVE (Virtual VE table) then all the math above applies to you. Gen III is one thing, and Gen IV is another. Since it is YOUR car and you have the time, do it right, get the VE to a good spot, and then go ahead and tune the MAF. As for your inputs, that is beyond me, but HPT absolutely supports 5v inputs. Many have used the EGR or AC pressure sensor too to get the reading into the scanner. I've always and will always have the PRO version, so like I said, I'm no authority on how to do it another way.

ChopperDoc

I will say though that the BIAS is gone if your car utilizes a MAT (manifold temp) sensor, aka, IAT in the intake manifold. I did that a long time ago, relocated the IAT to the intake and disabled the complex model. Simplifies it a bit, and I know most newer cars are now setup this way... Duh... lol. Thanks engineers for getting with the times lol.

ChopperDoc

Also, that's interesting to note about the newer PCM's not using the low octane table with a MAF fail detected. My experience has been mostly focused on Gen III and Ford, though I have tuned a number of Gen IV's, just never thought about it lol. I will say Ford has a WHOLE different approach o VE... Like holy **** different. The MAP sensor is disabled by default in the stock tune, I'll just say that. I won't even get started there... Tuning is obviously way different too.

Kevin Fodge Jr.

Well you guys gave me a lot to think about! On a side note though, I just got my wideband installed today, and fuel trims were normal both before and after. The weird thing is though, when I finally went to log my wideband(everything was fine before this) it was almost like I had pulled a ton of fuel out of the tune. My fuel trims shot up to almost 10 across the board, and my wideband was reading rich (13ish, the wideband did eventually settle down, but the fuel trims stayed high) I had to add more fuel to get them to cooperate, meanwhile the wideband sat perfectly happily at 14.5-14.8 Does anyone have any suggestions on what might have caused this? I don't believe its an exhaust leak, because as said, everything was playing well until I finally went to log the wideband in HPTuners

ChopperDoc

Your trims caused it, pretty clearly. That and the error that often exists between NB and WB O2's, especially if they have moved farther back in the exhaust on account of headers or something like that. What happened was the NB's were reading "lean" based on their switching points, which can vary especially if they were moved, which caused the PCM to think it was lean and add fuel.

The WB read correctly and showed a rich condition, because the PCM was adding 10% fuel the whole time. In addition to all of this, with a bad VE or MAF table, it's unlikely the PCM even knows how much fuel to add in the first place because the airmass calculation is simply wrong. And since the stock O2's operate on a very "Narrow Band" of reporting, often when this happens they simply max out in one direction or the other, and become wildly inaccurate. Moving the VE or MAF in that direction will eventually get them close, but you cannot trust a single number they are giving you as far as a %, because they can't read accurately when off more than a point or 2 from stoich. The WB can though, so that's why we use that to tune the tables, not the trims. Later when the Narrowbands are closer and in range, you can fine tune them so the trims are close if you intend to use them, which will be in cruise and steady state operation outside of Power Enrichment (PE).

Also, you said it behaved well until you started logging. This was most likely your LTFT learning making up for the lean condition in those cells, probably idle and light pedal. Once outside of that though, you got a taste of how far off your airflow tables actually are. On a GM PCM, LTFT's are NEVER used during tuning. STFT's are also disabled to get an ACCURATE baseline using a WB. Remember, like I said, STFT's (just think stock O2 sensors here) are very inaccurate outside a "narrow range" which is literally why they are called Narrow Band O2's.

You said that the WB "eventually" calmed back down as well, again, probably because of Long Term Fuel Trim learning. LTFT learning is the product of a history of Short Terms that were off by a wide margin, say 13% "average" for example. After some amount of time of constantly adding between say 8-15% fuel through Short Term Fuel Trims, the PCM will recognize this pattern and Create a "Long Term Fuel Trim" to bring the O2's back in a better range, and lessen the STFT corrections, again because even it knows the stock O2's are inaccurate out of a certain range.... Let's say the PCM adds 10% to the LTFT's, and now the STFT's will read -2% and +5% (8-15% off - 10% = -2 and 5). Now it's back to a "switching point" and can more accurately measure the result of trims. However, the actual AIRFLOW table (MAF is on if using LTFT's) is still 13% off at that point in the calculation.

Here's my suggestion to you if your want to get this thing running nice and the tables all tuned: Do more research, watch the videos I made or ones others have made for this topic, read the guides in the stickies, and keep asking questions when you get stuck. I'm not trying to sound like a dick or anything here, or tell you what you should do, but there is a process we have all used with success in exactly what you are trying to do. It is not terribly difficult, but at first might be some learning on your part. I'm here to help as much as I can with a keyboard. It's all I can do. The rest of it is up to you to either follow the advice or not.

Kevin Fodge Jr.

You didn't sound like a dick at all, I appreciate the input. I had my ltfts disabled as suggested. But I now need to get a serial to USB adapter since I found out the ADC converter in my Arduino isn't terribly accurate. I saw one at bestbay, but it has a male serial port on it, and I'm not sure if that makes a difference, since all the writeups I see people are using a male terminal on the wideband. I guess I'll try it out and see, the worst that happens is that I have to return it. Again, I appreciate all the advice you've given me, I've been reading up /watching videos on this for months, but it's evident I have more to learn. After all, experience is the best teacher

DFORESI

Hard to anticipate the problems you'll have before they occur. Research is good, but application of theory is always the best teacher. Just be cautious of what you do and try not to damage anything, aka, stay out of high load until you've become reasonably comfortable tuning the first 3rd of the MAP. Pretty hard to wreck anything via tuning when you stay under 3000rpm and 25% load.

ChopperDoc

Couldn't agree more here.

OP - No rush to blow up your engine for lack of experience. If you follow my video, I cover adding 15% to the fueling to mitigate any possible lean conditions while tuning. If you have a bigger cam, you can skip adding the 15% to the 400, 800, and 1200 columns on the VE table. I know you said you have a mild cam, so this might not be noticed nearly as much for you. Make sure you disable ALL the adders, get that WB working right, and go from there tuning the VE, then MAF, then Spark. If EVER you have knock retard, go ahead and reduce it in those cells and continue on, SLOW. Work your way up to Wide Open Throttle (WOT) and by then you should know what you're doing and why.

Tuning isn't for everyone and I am always excited to help someone learn. It's why I started making videos and getting more active in the forums. I really mean I am here to help, like a lot of us are. If you can learn something from my experience then I have done my job here. I'm making another video right now, as I am starting to really enjoy helping folks with this stuff in a no fluff straight to the point kind of way.

I've built cars for years, but by far tuning is my favorite thing to do. Get to sit in (or drive) fast *** cars that aren't mine and command the session in it's entirety. I don't even get dirty doing it and make decent money on the side. No complaints here lol.

Kevin Fodge Jr.

I agree, I'm in no rush to blow this motor haha, but I finally got all of the parts to log my wideband and I've done more reading up about tuning with a wideband and setting up the scanner to read it. I'm going to hook everything up tomorrow morning and try to get this tune a bit more dialed in. Once again guys, I appreciate all of the help you've given me so far!