LT5 TB upgrade tuning issues

I added a LT5 TB and I'm getting negative timing at idle. I did a search and some say to get the MAF and MAP side of things in order first before attempting anything else and I ran into another issue. MAF tuning went fine, got it within 1-2%. MAP tuning started out fine, it was very close to begin with at idle but after driving about 5 miles when I came to a stop at a light it started surging pretty good. I threw it in neutral and it still surged, drove fine home but started to surge again when I parked the car. I updated the tune with the log data I got and it still surged, the surging stopped once I turned on the MAF and put it back into closed loop and drives normal with an exception to the negative idle timing.

I'd like to see if someone could check out my tune and log file and see if there is a reason for it to start surging like this. I'd also like to see if someone can point me in the right direction to deal with the negative timing at idle and the TM going on at this time. I'm assuming the VTT needs adjustment but not sure if the MAF and MAP idle is in good shape.

Short log of surging attached and MAP tune and normal tune in closed loop

Attachment 107917Attachment 107918Attachment 107919

try this tune and see how it idles

Attachment 107933

I've noticed that it only happens with OEM upgrades. If you go to a katech or NW 103 it doesn't do the whole negative idle thing...

Thanks for checking it out. It did seem to help, I'm at 3-5 degrees now. What did you change?

I got a recommendation from a facebook group that said to start over and just use my stock VVE table and that got me around 3 degrees at idle.

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Originally Posted by HeavyChevy305

I've noticed that it only happens with OEM upgrades. If you go to a katech or NW 103 it doesn't do the whole negative idle thing...

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They do it too unfortunately. Had a '21 camaro recently that I had to tune like a cammed car to make it work right.

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Originally Posted by jasonz28camaro

Thanks for checking it out. It did seem to help, I'm at 3-5 degrees now. What did you change?

I got a recommendation from a facebook group that said to start over and just use my stock VVE table and that got me around 3 degrees at idle.

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You can use the compare file to see what was changed. I changed the Virtual Torque in the idle areas. You may need to change it more in the same direction I did but aim more for the actual idle area. Only the logs and drive-ability will tell you what needs to be done. You can also tune some of the idle tables but I always found it easier to use Virtual Torque and then the ECU's idle values will work just fine.

Cool, I see it now. Did you subtract in the area by a percentage or take an actual torque number out? I see you only did the e85, is it good practice to do pump gas areas in the VVT too now or wait until I have pump gas in it to see what it does?

Im on a facebook page and someone suggested I change the TB max area from 5054 to 5136 and this change alone (not including your changes) got me to around 6 degrees at idle. I will try a combination of both later and see what it does and or take more torque out.

Another guy suggested to alter the idle torque external load table. I logged the zero pedal and it seems to match up pretty well with the delivered engine torque. I just have no idea how to change that table, the upper limits listed in there are very high compared to what I'm logging. This is my next step I guess if I cannot get the VTT to work out like you suggested.

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Originally Posted by TriPinTaZ

You can use the compare file to see what was changed. I changed the Virtual Torque in the idle areas. You may need to change it more in the same direction I did but aim more for the actual idle area. Only the logs and drive-ability will tell you what needs to be done. You can also tune some of the idle tables but I always found it easier to use Virtual Torque and then the ECU's idle values will work just fine.

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So I still cant tell exactly what you did. When you compare it shows you changed the coefficient tables but is that just showing the changes to the VTT trickled down to the coefficients? I guess I'm asking if you changed the VTT itslef or did you just mess with the coefficients?

After your change and changing the TB area again I'm getting around 5-6 degrees at idle, is this acceptable or should I keep at it and lower the tq more to achieve >10 degrees at idle?

you will need to post log, these newer PCMs are torque based

ideally at idle you should see close to zero torque, if its reporting higher it will reduce spark.

try doing a tb cleaned relearn.

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Originally Posted by jasonz28camaro

So I still cant tell exactly what you did. When you compare it shows you changed the coefficient tables but is that just showing the changes to the VTT trickled down to the coefficients? I guess I'm asking if you changed the VTT itslef or did you just mess with the coefficients?

After your change and changing the TB area again I'm getting around 5-6 degrees at idle, is this acceptable or should I keep at it and lower the tq more to achieve >10 degrees at idle?

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I used Virtual Torque to make the changes. The Virtual Torque tool then applies the changes to the coefficients. There is too much to explain how this all works and it has already been discussed in very large and multiple threads on here. I don't say this being a smartass, but you should take time to search and read all of the discussions. It will answer many of your questions and possibly create more questions. But this is why none of the people on here that grasp the torque based system will give you a multi paragraph summary. It's already been discussed.

5-6 degrees is on the low end of acceptable but it is out of the danger zone for glowing red exhaust manifolds at idle. As Sultan said, logs and corresponding tune file to the CURRENT operating state(with 5-6 degrees at idle) would allow people to help you. There may be other tweaks needed, specifically to get the ECU to close the throttle blade a little more at idle so that it can use a bit more spark to control torque which would increase idle spark into the acceptable 10-20 degree range.

Thanks for the reply. I get how the torque works, I?ve just never adjusted it and was curious to see how exactly you did it.

I?ll try to get some logs up and have y?all check them out soon.

Here's the current tune with the tq changes TriPinTaZ made and the TB max area set to 5136. I've also included an idle log, cold start to around 17X degrees.

Attachment 108005

Attachment 108006

Try this and see if it improves.

Attachment 108007

I went to VT E85 Airmass and subtracted 15% from the .20 airmass and lower in the idle rpm range, then I blended up to 1200 rpm so that it wasn't a sharp change. I also did the E85 MAP in the 40KPA and lower rpm range the same way. Since you have Flex Fuel enabled, the ECU uses the E85 tables exclusively. Then this time I actually subtracted a value of 20 from the same areas to get more of a drop in torque in those areas vs %. Then I made some minor changes to idle torque.

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Originally Posted by TriPinTaZ

Try this and see if it improves.

Attachment 108007

I went to VT E85 Airmass and subtracted 15% from the .20 airmass and lower in the idle rpm range, then I blended up to 1200 rpm so that it wasn't a sharp change. I also did the E85 MAP in the 40KPA and lower rpm range the same way. Since you have Flex Fuel enabled, the ECU uses the E85 tables exclusively. Then this time I actually subtracted a value of 20 from the same areas to get more of a drop in torque in those areas vs %. Then I made some minor changes to idle torque.

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Thanks for the detailed description. This is more or less what I had thought you did, I tried to mimic it and my numbers did not come out exactly like yours, I think I took out 5-10% in the same areas and also tried to just subtract tq values to try to match yours. I never did try to alter the numbers and run it though.

Here is an attached log with the changes you made. You can see the delivered torque at idle are closer to zero now but the timing did not change too much, it might have went down a degree or so. I'm not too familiar with the torque limits and how they work but I'll look into them so I can get a better understanding of what you changed. Goatrope garage has a video on youtube talking about these two tables and touches on them a bit but his changes are strange compared to what you made.

Attachment 108009

It's all about trial and error sometimes. Try this one where I only change the External Load. If this doesn't help then I would take the External Load in the opposite direction. If that doesn't help then we would reduce the Virtual Torque some more even though its lined up pretty good now. Normally I only reduce VT for a larger TB but this one is taking a little more effort. Normally you don't need to mess with External load unless there is an idle target issue. This may not make it better at all but I want to see how it reacts.


Attachment 108041

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Originally Posted by TriPinTaZ

It's all about trial and error sometimes. Try this one where I only change the External Load. If this doesn't help then I would take the External Load in the opposite direction. If that doesn't help then we would reduce the Virtual Torque some more even though its lined up pretty good now. Normally I only reduce VT for a larger TB but this one is taking a little more effort. Normally you don't need to mess with External load unless there is an idle target issue. This may not make it better at all but I want to see how it reacts.


Attachment 108041

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Thanks for taking the time with this. I?m out of town for work for the next month but I?ll jump right back on this when I get back and let you know how it goes.

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Originally Posted by TriPinTaZ

It's all about trial and error sometimes. Try this one where I only change the External Load. If this doesn't help then I would take the External Load in the opposite direction. If that doesn't help then we would reduce the Virtual Torque some more even though its lined up pretty good now. Normally I only reduce VT for a larger TB but this one is taking a little more effort. Normally you don't need to mess with External load unless there is an idle target issue. This may not make it better at all but I want to see how it reacts.


Attachment 108041

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I went with the trial and error route that you suggested. I started over form scratch and I read more on this and came across a post saying to uncheck the box that links the TQ tables and tackle if in each timing table instead. By removing more from the -10 to 0 degrees and less above 0 degrees it happened to like it without changing anything else. I'm now getting 10-12 degrees of timing at idle in neutral and drive. I think playing with it more may get even better results but for now this will suffice.

Thanks for all the help!

Good to hear