LS6 DBW to DBC conversion starts but won't idle

Hey everyone,

Wondering if anyone might be able to shed some light on an issue that I ran into with my build.

I'm using a LS6 from a 2004 CTS-V for a miata swap and have also swapped to an LS3 style MAF and switched the DBW throttle body out for a DBC throttle body from an express 3500 with new IAC valve and TPS (all delco). I am running this from the factory CTS-V PCM which is capable of driving the IAC (I can see in VCM scanner that I am in fact seeing the position reading change for IAC) with the factory OS. I can see the TPS reading correctly from 0.4% - 100% with the throttle pedal as well.

One odd thing to note is that O2 B1S1 is reading as "not ready" while B2S1 seems to be "ready" with no issues. They both have voltage.

I finally got to the point of the first test start and it does start just fine but won't find an idle and drops out/stalls pretty much right when it would want to settle into idle.

So far in HP tuners, I've:

• Turned off VATS
• Changed 1 to 0 in ETC column under System Options
• Did my best to copy the idle tables from the express 3500 tune to the CTS-V tune
• Removed the emissions systems from the DTCs under Engine Diagnostics
• Removed secondary O2 sensors

Anyone have any ideas where to turn from here? This is my first car I've worked with Hp tuners on so I'm fairly new to the interface, I'd always used megasquirt for the car in the past.

Here's my tune file as well as two logs I took while trying to start the car today (the second one to monitor the O2 sensors and make sure they were working):
Attachment 96684
Attachment 96685
Attachment 96686
Attachment 96687

On the second log its long enough you can see the IAC is opening more as the idle is dropping so its is trying to idle and use the IAC like a DBC setup. At this point it seems like it is working so it may just be a matter of adjusting your startup / idle tables to get the car to idle. The MAF is also reading and looks like its working.

What happens if you use the throttle to keep the motor on? I'd be curious to see if you could warm it up a little and then slowly come off the throttle and see if it will idle. You should see the IAC and spark adjusting to keep the idle where you set it.

I would set it to idle at 1200 at and under 68 degrees then tamper off from there to 950 and see if it idles and everything is working and then if you like cut it down from there. Also could try adding startup airflow and some delay on the camshaft revs before it starts to decay startup air. Also checking what desired idle air once its idling will be helpful in the scanner to know how much air to put in the base idle air flow table.

Thanks for the input GoatCheese.

I tried upping the rpm to 1200 and still got more or less the same result. It's not very happy if I try to keep it alive with the throttle, it wants to start up pretty nicely and everything seems alright but as I try to keep it alive it starts running rougher and rougher until it wants to stall out.

Here's a log of a startup without throttle input after the change and with throttle input after the change, and with desired airflow and a few other hopefully more useful parameters added to the log:
Attachment 96688
Attachment 96689

Your TPS voltage it too high, you are not in the idle fuel trim cell. Your ECU is not running on the idle tables. you need to log your fuel trim cell and lower your TPS voltage until you are in the 19 cell or 18 with the AC on.

Quote:

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Originally Posted by 1970ss8.1

Your TPS voltage it too high, you are not in the idle fuel trim cell. Your ECU is not running on the idle tables. you need to log your fuel trim cell and lower your TPS voltage until you are in the 19 cell or 18 with the AC on.

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So what your're saying is basically I probably need to re-adjust the throttle blade set screw to lower the TPS voltage until the fuel trim cell is sitting at 19 with AC off and 18 with AC on? I just set up the table and graph to also record the fuel trim cell so I'll give it a test start just to grab a log and see where the fuel trim cell is at before making the change.

Also, will the IAC and Idle Desired Airflow work/show a good value if the engine's not running on the idle tables? I noticed they seem to be reading alright.

You need to be in the idle cell to use the idle tables.

I'm sorry I'm pretty confused being an HP tuners noob. Is there any chance you can expand on that a little? I'm having trouble finding any good information online that has enough concise information in one place to get up to speed.

When you are in fuel trim cell 19 or 18 the ECU will reference the idle tables. If you are in cell 20/21/22 it will use other tables such as decel, PE, steady state. If you are not in the idle cell it will ignore all the idle tables. Mine gets out of the idle cell at .62 volts then it starts using normal driving tables or decel.

So I think you may definitely be onto something here because looking at the log trying to start it again, I see that the fuel trim cell is staying at 20, and then goes to 21 with some throttle input.

I did try to reduce the TPS voltage as much as possible but that doesn't seem to have an effect on changing the fuel trim cell to 19. I'm almost out of real estate on the throttle set screw and I'm sitting at 0.55v for TPS but am still in cell 20 for fuel trim. Is there a table or setting that dictates what TPS voltage switches it to idle fuel trim?

Here's a log of attempting to start it with TPS voltage set back to 0.55v to see if there was a change in fuel trim cell:
Attachment 96714

I believe 20 is an idle cell in open loop. and 21 is decel and 22 is wot PE. These are open loop. If you go closed loop it would be 19. I?m tuning closed loop first.

https://www.ls2.com/forums/showthrea...-by-MaP-vs-RPM

I looked at your last log. Your IAC counts are really high and your commanding 9.5 stioch. Check your after start enrichment. It shouldn?t be commanding that low unless your running e85 or higher. Your stioch is set to 14.68 and your PE is only at 13.88 so you need to find why it is commanding such a low stioch.

Thanks for checking it out. It does seem to have some pretty high IAC counts and the you're right that 9:1 for AFR seems pretty darn rich. I can get the IAC counts down by tighetning the throttle set screw and re-learning the TPS to still read 0-100% so I think that might have been an effect of closing the set screw a little to get to 0.55v on the TPS reading.

What have you seen to be good for LS motors as far as startup AFRs? Theres a few spots where it's getting multipliers in the after start enrichment settings so it does seem to be wanting to be rich at least at start

Well I think I had at least a slightly more succesful attempt at idling today.

I ended up re-writing the entire stock program back to the ECU with as few changes as possible to start fresher and see what would change.

I changed:

-ETC, Oil Pressure, and Brake TqMgt from 1 -> 0
-Turned off VATS
-Increased the Base Running Airflow by 25%
-Opened up the throttle blade screw until my TPS reached 0.78V, then re-taught the TPS (still reads 0-100%)

The engine ran for a little longer than it had previously but still wanted to sputter out and die.

I did see the commanded AFRs go to something much more reasonable and also saw some more favorable stuff in the log such as the O2 sensor voltage actually starting to read and the IAC reading actually starting to drop and stabilize some.

Here's a log of the attempt:

Attachment 96781

Now that I have the stock tune sent I still need to re-remove the emissions systems and rear O2 sensors and such but I'm wondering if maybe there's something else I'm missing.

Mine starts at 12.5 and jumps to 13.5 fairly quickly. Too much fuel will wash the cylinder walls.

Now I've got it where it starts off around 9:1 right at startup and then quickly increases to close to 12:1 within 3-4 seconds. Still maybe a little rich on the startup? At least now I think my risk of washing the cylinder walls is slightly less so that makes me a little more comfortable.

Starting back with the stock tune with just those few things removed, I now wonder if it's something emissions related or potentially even oil pressure sensor related that's killing it? It does seem like a MUCH more normal startup cycle after re-writing (I did do write entire) but does still seem to be dying out in a way that the throttle won't keep it alive which makes me think it's cutting fuel for some reason.

Post a log with the new tune.

I finally got it to hold its own idle!!!!

I ended up noticing that while the MAF Frequency tables seemed pretty close in some areas between a CTS-V MAF and the LS3 card style MAF, it was actually somewhat different over the whole range and had a slightly different shape/concavity to the graph. This wasn't something that jumped out at me at first because over the numerous compare files that I opened that had settings for the LS3 style MAF, none of them had fully matching ranges for the MAF frequency tables, and instead of highlighting the cell red to show there's a difference VCM suite didn't react or show any cell differences. Honestly, when I did the compare I naively thought that I'd just lucked out and that the MAF tables were a match and went on.

I went ahead and interpolated the MAF frequency tables from an 07 Z06 into my current tune table (figured that would match my airbox/MAF setup the best from what stock tunes I could find - I have a Z06 airblox/filter which is why I am using the LS3 MAF) and now it fires right up and holds a pretty nice seeming stable idle. I let it sit and idle for a little longer than a minute and also blipped the throttle slightly to see what I was working with and it stayed pretty steady.

I did notice that the O2 sensor reading for bank 2 is a little erratic so I'm not sure what's going on there. Ended up starting to burn off some manufacturing oil in the exhaust so it was smoking out the garage pretty bad so I had to shut it off.

Here's my current tune and a log of the succesful idle:
Attachment 96825
Attachment 96826