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GM Gen III LS tuning with HP Tuners, O2 MV's drop below 50mv under WOT with simple basemap.

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Hello Everyone,

I've got what I am thinking is a very simple problem that I am too inexperienced to determine what is going on. I am trying to tune a friends 2003 Silverado with a 5.3 LM7 engine. We did a base datalog with the truck and everything was working great. I built a simple basemap in essentially just turning off torque management settings and enabling PE to actually kick in. During our first drive around everything seemed to be working okay until he went WOT. When he went WOT the O2 MV's dropped into the high 40's for MV readings, once he got out of WOT they went back to reading proper MV's. I flashed his stock map and retested, O2 MV's read properly. Can anyone tell me what I am doing wrong in setting up a base file that might be causing this? I'm almost a little embarrassed to ask because I'm sure I'm missing the silliest and easiest thing possible, but I'm hoping someone can help me out. I will attach a couple of logs showing the issues.

Datalog 04 is the log where the O2's drop to high 40's MV under WOT

Datalog 03 is his stock OEM file reinstalled and tested with no O2 issues

Attached Files
  • MATT.DATALOG.03-STOCK-MAP-REINSTALLED.hpl
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

  • MATT.DATALOG.04-NEW-BASE-MAP-O2-SHUT-OFF-AGAIN.hpl
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

You can't really use the narrowband O2 voltage for anything useful under WOT operation as they are only accurate at an AFR of 14.7:1. That being said, you should expect them to show rich under WOT operation so the likely scenario is that the map that you've flashed in is supplying insufficient fuel due to the MAF calibration being changed (I note that the power enrich target has been changed but that is still a sensible target to start with).

In order to tune the engine you will need a wideband AFR meter so you can see what the actual AFR is under WOT conditions. If you watch the worked examples in our Practical Reflash Tuning course you'll see how this should be dealt with.

Hi Andre,

Thank you for getting back to me. Yeah I've watched through the Practical Reflash section. I plan to do WOT tuning with a wideband, I have one ready to go. I was just doing same base driving to make sure everything is working properly and see how far off everything is before I started scaling the MAF with the wideband in. Then when I saw the o2's falling below 50mv's under wot on my file and mid 800's on the stock file I worried I was doing something wrong.

I guess my concern is why do the narrowbands go to sub 50mv's with my reflash (his stock map just enabled PE and maxed TQ management settings) under WOT, pull over and flash it back to his OEM map, and the narrowbands are back to mid 800's with his stock map? I realize the reading makes no difference because there is no wideband in, I just wanted to make sure everything is working properly before I start scaling the MAF. I just feel like I'm missing something in my base file, a file in which all I am changing is the PE engagement points and maxing out the TQ management settings.

If you believe it's a non issue, I will go back and start dialing everything in and see how it goes.

Thanks for your time Andre!

If you're running around 0.90 lambda or thereabouts then this is rich enough that the narrowbands will show a continuous voltage (it varies but let's say 800 mv for the sake of argument). If on the other hand you're actually really lean at WOT and seeing 1.05 lambda for example, the voltage from the narrowbands will drop to close to nothing. All this really shows is that the tune probably needs work and if you follow the process with a wideband you'll have it dialled in very quickly.