VE Table Tuning Issues - Negative Spark Advance

[Ben E]

Edit: Truck is a 1999 GMC Sierra with a 2002 Silverado 5.3l engine with a BTR Stage 2 Cam (212/218, .553, 113+2).

Hey folks, I first started trying to get a 0411 PCM tune for my truck but I couldn't figure that out so I am working with a Frankenstein build from a 1999 GMC Sierra PCM. Today I tried tuning for the VE table and hopefully got into speed density mode correctly and changed the tables correctly to get data from my LTFT's. I also moved my high octane table into the low octane table as a MAF failure uses the low octane table.

I reset fuel trims and started my drive whilst the truck was warm to start with and everything was going great. About 15 minutes in I had some weird knock issue and was getting zero power since the knock retard smashed my timing into the ground. Then I got food and restarted the testing but this time I restored the low octane table with the factory setting in hopes of getting better data or less knock retard. However, it seemed worse! I personally didn't hear knock or pinging other than the strange noise of -10 degrees of timing...

Now I didn't do tons of different driving like high RPM, or high load mostly regular driving to start with. There was one spot near the end of my second log where I dropped it from 4th TCC locked to 3rd and then 2nd and neither spots had knock which was strange. I was only getting knock retard on low throttle light load acceleration (normal driving.) The other strange thing is my LTFTs had nearly the same result of -13% to -16% of fuel pulled. I was expecting at least some added fuel when I had the truck in 3rd and 2nd near 4k-5k rpm.

I'm curious to know if I set up something wrong or if there is something you guys can see for me. I will post my current tune(With factory high+low octane spark tables), log 1, and log 2.

I apologize for strange file names. The build names are accurate. Build 7 is SD mode with high and low octane tables matched. Build 7.1 is SD mode with factory high and low octane tables. The Build 7 log had a good amount of 45-60 mph driving and a little bit of 75 mph highway driving. Build 7.1 log had mostly 45-60 mph driving, and this is the worse log with a huge amount of knock retard.

[5FDP]

Intake temps read -38, you can't have that. It will throw every airflow and fueling calculation off.

Do not unplug the MAF if you are. Just fail the maf like you have been, the IAT is in the MAF sensor.

Not saying that's all of your issues but it for sure could be a reason the fuel trims are trying to yank 15% worth a fuel all the time.

[Ben E]

I didn't think about the fuel issue being that -38 temp. I was only thinking about the spark. I'll have to run another test tomorrow. So all I need to do is leave the MAF plugged in, but keep it failed by keeping the MAF high frequency to fail at 0 will work the same and hopefully get better results?

[cobaltssoverbooster]

yes leave the maf plugged in, raise maf rpm enable to something you wont exceed such as max allowed value, set maf disable hz to 0, and set P0101/102/103 to Mil First Error (disable SES check box if you dont want to see the light during tuning)

if you completely remove the maf you will need to wire in an external IAT sensor that can sit in the intake. this new sensor gets wired into the iat signal feed in the maf harness so the ecu can calculate proper air density.

Your spark is negative because your IAT spark modifier at -32* is likely pulling a ton of timing as a result of -*F exceeding the axis limits of this table. The ecu forces a max default value that is likely hard coded (im not sure what it would be). If it uses the max value listed on the IAT table then its pulling at least 10* in your case.

[Ben E]

Thank you both for the help. I left my tune the same and just plugged in the sensor and it started reading correct intake temps. I got far better results than the absolute garbage I had previously. I'm not exactly sure what I'm doing but at least I feel like I'm doing something right! One thing I thought of today after doing my tests is I didn't turn off DFCO stuff so I don't know if that played games with my readings or not but we shall see in a few days when I have more time to revisit this again for more data!

I still had a bunch of KR and I just don't understand how I have so much by doing this test but not with regular driving(that I know of I guess) even with the low octane table thrown in. Now I do drive with 87 octane fuel so I'll have to do all of my VE tuning and revisit this again with some 93 or race fuel and see if I still get knock like I am now. Then go from there if it's real knock or false knock.

I'm not sure how I should go about testing WOT without the PE mode activated. Do I manually retard timing some, or just crank up the fuel to keep it safe, or is there some kind of math equation that can get me close to what I should see?

Here are my test results of today if anyone is curious to see them. Build 7.1 log was my original accurate test and the results I used the LTFT's and just added them to the table and probably should've multiplied by a percent but didn't seem like it was a big enough result. Then Build 8 log had the previous test results added in and this is what came of it.

Edit: I felt like I should add this. My knock seems to come a lot from light load, low rpm acceleration then once you're a tad higher in the RPM or throttle the knock seems to be much less or non existent like you may believe. I'm not sure if it's only me or not, but it's in the logs there.