Cam Swap - Surge / Bucking in LS3 - HPT and HPL attached

[HX Kingswood]

I recently installed a larger cam in my LS3. I had it professionally tuned and it makes good power (470hp at hubs) but it has a lot of cam surge below 2000 rpm.

I have done a lot of research and believe the way to fix this problem it is to make the computer run open loop from 1000 to 2000rpm then increase the fuel in this area as per the image below (hope you can see that as it is tiny on my screen). The thing is I cant work out how to do it. I tried changing it by Fuel/power enrich/hot then setting enable TPS to 0% from 1000 to 2000 (screen shot below). Then I went Fuel/power enrich/power enrichment/EQ ratio and guessed a higher fuel target as a starting point (screen shot below).

This took the bucking out but now it stumbles badly going from 2000 to 3000rpm so I have done something wrong.

Is it possible for someone to have a look at my tuners original tune. Ideally also to make the appropriate changes for the open loop from 1000 - 2000 with the additional fuel.

The cam is 229/235 @50, 112 Lsa, around 580 lift. It has headers and 6 speed manual, 4'11 gears. Everything else is stock

I also attached the HPL file to show the issue

How to FIx.png

1000 to 2000 OL.png

EQ Ratio.png

[ns158sl]

You shouldnt have to put it into OL to fix the bucking for that small of a cam. Log again with the laptop connected to get better resolution.
Tune is typical MAF tune, probably most of your issues. Your over/under is very aggressive also.

[HX Kingswood]

Please find scan attached through my laptop. I put the original bucking tune back in (without the changes I tried) then ran this scan

It currently has not cats but will again next weekend. Internals on one broke so I pulled them out temporarily as I needed to drive it.

[rabbs88]

Your missing a bunch of PID's in your log for it to be useful. Also MAF only won't run as good as speed density, especially with a cam. Not really sure how your adjusting fueling without being able to see MAF frequency.

Load these PID's and get another log.

[HX Kingswood]

Hey Rabbs cannot work out how to download the .xml file Seems locked and keeps downloading as microsoft edge.
Any tips?

[blindsquirrel]

Right click, 'save as...'

[HX Kingswood]

Actually the problem is my VCM Scanner software wont read the file for some reason.

When I do a 'Save Layout As' of my own xml file (attached) it is 14kb and reads very differently to the 3.7kb file I am trying to upload.

Maybe there is a different software version issue going on.

[rabbs88]

It's not a layout file. It's a channels list

[blindsquirrel]

screenshot.12-05-2024 09.49.25.png

[HX Kingswood]

Ahh thanks got it. I will take her for a run and get a new log.

[Alvin]

This doesn't look like a very good tune at all. I'm sorry to tell you that. The timing table is very rough.. Its commanded to go super rich at WOT.

In the log its going into PE all the time.. That isn't proper. Do you have your stock file to compare to? I don't see many holdens on my side of the world.

[HX Kingswood]

Attached is a scan I took today with the new PIDs. I went WOT a couple times for reference. I have cats back in it now and they are in for this scan.

Mainly trying to get rid of the bucking under 2k (as much as possible). There are a couple other smaller items such as; sometimes harder to start when warm and also sometimes tries to stall coming off the gas before it catches itself.

I did not drive it to exaggerate the bucking but can get a scan doing that if it helps.


Alvin, yeah Holdens were in the South Pacific only I believe. They are all GM's though.

[edcmat-l1]

I did not drive it to exaggerate the bucking but can get a scan doing that if it helps.

Why? That's exactly what you need to do. Make it buck as bad as you can and point out in time stamp where you feel it. There are 2 timers at the bottom of your scanner. One is real time, the other is data log time.

[biholliday]

according to your tune this is not an LS3

[HX Kingswood]

Hi all I got a short scan doing a couple laps around the roundabout to make it buck.

If anyone can see any fundamental issues with the tune please let me know.

[edcmat-l1]

The only thing that's varying to any degree is the fuel trims. There are no timing swings, the MAP is even pretty steady so doesn't look like a ton of reversion. There's nothing that looks like bucking to me.

Why is there no speedo reading?

It has a constant flicker of knock retard it looks like.

Try using your scanner controls and turn the closed loop off and on while getting it to buck and see if that makes a distinguishable difference.

[HX Kingswood]

Ok thanks edcmat I will give that a go