Cylinder Airmass and Cam position Question

[David-L]

I made a log of a standard, every-day drive to work this morning. No heavy acceleration or anything unusual, just a leisurely drive to work. Looking at the log, there seem to be a lot of significant and abrupt changes to cam position, spark timing, and throttle position with minimal change in accelerator pedal position or driving load. Let me say, i have not done any MAF or VE tuning YET.

The first thing that seems odd to me is this screenshot. Cam position goes to 0deg and throttle position spikes to compensate. Could this be indicating that 0deg is far from optimal on a power prospective? What about fuel economy? I thought retarding the cam reduced manifold vacuum, but this makes it appear as if advancing the cam reduces it. Is this just an illusion?
1.PNG

The next thing that seems odd is this spike in throttle position and cam position. There is no change in accelerator pedal position, but the throttle, cam, and spark abruptly changed. Any thoughts what would cause this? It happens a few times during the drive.
2.PNG

The last thing, for now, that I find odd is the throttle position abruptly changes with no change in pedal position or cam angle, just spark timing. The cam position changes shortly after.
3.PNG

Are there more sensors involved here than just what I am looking at? Is this an indication that some tuning really needs to be done here? I tried attaching the log file, but I must be doing something wrong. I cannot get it to upload. Is there a size limit, its 10.1MB. I know its hard to say anything without it.

[David-L]

Does anyone have any thoughts on this? Or tips on how to upload log files. I assume 10.1MB is too large since most other logs I see on here are under 1MB. Any way to clip the log to make it smaller?

[blindsquirrel]

Any way to clip the log to make it smaller?

Use the Zoom In/Out buttons (or mouse wheel) to set the time span you want to clip out (1/2/5/10 minutes). Then, Log File > Export Log File, select Format: .hpl and Range: visible.

[David-L]

Thanks blindsquirrel.

Here's the logs...

WorkDrive-1.hpl
WorkDrive-2.hpl
WorkDrive-3.hpl

[smokeshow]

Cam is advancing while throttle is opening because it is trying to make torque. However spark is pulling it back out. What have you changed? This isn't stock behavior.

[David-L]

Cam is advancing while throttle is opening because it is trying to make torque. However spark is pulling it back out. What have you changed? This isn't stock behavior.

That is exactly what I thought... now I don't feel so crazy.

I have not changed anything on the engine yet. The only thing I have done so far is the TCC settings and shift timing. I am starting to wonder if the previous owner has done anything to it. I bought the truck from a good dealership here in SC with 61,000 miles on it. Everything looks bone stock on it though, tires and rims is the only thing that I know isn't stock.

I read the ECM from a 2017 Sierra 1500 at work that I know for sure is 100% stock and compared my original file to that truck. I could not find any differences at all other than the speedometer params. The main operating systems are the same, but the sub systems have different ID numbers. I guess my next step is to log a drive in the work truck and see if it shows the same behavior. If it does not, then I am completely lost.

[David-L]

I am a bit confused by these graphs... I thought advancing the cam increases intake vacuum and retarding lowers vacuum. It looks like the intake vacuum is actually decreasing with the advancing cam. Is this just an illusion because the throttle is opening so much trying to make up the power that the spark is pulling out? A lot is happening all at once here and I'm getting confused as to what is really happening. Is this basically showing the engine is making all the power it can at this moment, adding more accel pedal wont make more power until the tranny downshifts?

[David-L]

Looking at every channel I can log related to timing, the base advance is saying 4.6 which looks to line up perfectly with the high octane base table. But Timing Advance (SAE) is reading 1.5deg with everything else 0 except cranking advance that ready 8.5deg ALWAYS and IAT Advance at -0.4deg. So where is the other 2.7deg going???

Timing.PNG

[David-L]

And another peculiar thing i cant seem to catch in a log, i have noticed most days my 25 mile average gas mileage will be around 19.5 and power seems good, and then randomly there will be like two days where i get like 15.5mpg and it just feels sluggish and unresponsive. With no new fuel in the tank, no major weather changes, no conscious driving habit differences, no way to explain it. I never seem to have my computer with me to log it when it happens.

[TriPinTaZ]

Does the truck have a ported throttle body or aftermarket intake?

Any values you see over 0 in regards the the cam movement is the cam retarding, not advancing.

The ECU will pull timing based on Humidity as well. You cannot monitor this PID though which I found odd but I make a custom PID to view the approximate humidity spark value that is pulled out. Torque Management Advance is always REMOVING spark from the final value. As is knock retard.

I'm really not entirely sure what issue you are having. Do you have a legitimate drive-ability issue? Or are you only struggling to interpret the logs?

[David-L]

There is nothing aftermarket that i am aware of. I bought the truck with 60k on it and i have not done anything to it.

Would you mind sharing how to set up the custom PID for the humidity approximation?

Yes, definitely drivability issues. It stumbles and shudders when under load going up a hill before it kicks down a gear. This happens everywhere the throttle opens a lot in the first three graphs i posted. It can also be seen in the graph three posts before this one, but that graph has a downshift in it. And then also the random unexplainable terrible fuel economy.

What i am struggling to understand is why the timing is going so close to 0 and why it is shuddering under that load. I was hoping someone here would see something obvious that i dont. I already did a tuneup, new filters, plugs, etc so i have no reason to believe that would be causing an issue.

[TriPinTaZ]

The PID I made I just took the Total Commanded Timing and subtracted the Actual Timing and made a custom math. It helps show if there is a gap in commanded vs actual and mostly follows the humidity timing. But when you have spikes of KR or Torque Management Advance it will skew the number. I only use it for WOT operation.

You should be logging Torque Management Advance. It might help you see why timing is dropping out. You should also post the tune file.

Low RPM And heavy throttle it is normal for timing to dip really low. The hesitation and stumbling may not be an issue with the tune at all. It could easily be dirty valves, oil in the intake, coolant leak into the intake, cracked spark plugs, bad plug wire, dirty gas, clogged fuel filter, a failing coil pack, DOD lifters, etc. Try adding per cyl misfire counts as well to the log and see if it is misfiring and if it is one or more than one cylinder.

[blindsquirrel]

The SAE PIDs often disagree in odd ways with the GM-specific PIDs, which I think is a good reason not to use them if you want to trust the data you are collecting.