You are trying hard to earn that 12 pak! Thank you for the ideas.

This morning I tried disabling "Cylinder Charge Temperature Blending" as MY64 mentioned previously. Went to our usuall Sunday morning breakfast place about 15 freeway miles away. I have the Callaway CAI with the maf and IAT sensor right up at the TB. Thought I'd mess with that and do some logging and see how that reacts. Even with the AC on I couldn't quite get the temp high enough to matter. I want to finish messing with this.

Ok, To answer your questions....Yes I have a wideband, HPTuners and Real Time Tuning. No changes in AFR or fuel trims in closed loop when the car transitions into it's rougher running mode when oil temp starts to exceed 200+. A fueling issue was my first suspect as well.

Nothing to do with the fans, they don't run at freeway speeds. AC on or off, it still does it....

The motorboating will occur with the cruse control on or just regular driving thru town w/o cruise just as long as the temp rises up there.
No it's not a TCC issue, I have the transmission dialed in right where I like it. A TCC unlock problem feels more like a inconsistant stumble or a miss. When this motorboating starts it's constant... the exhaust note gets deeper as well as the car having a slight rough running feel like you would get with being bogged down but just slightly....no RPM drop detected, fueling is constant, spark constant. Or it's like the PCM is trying to blend two tables that don't react well with each other??? Or like I mentioned when I first started this thread, vaccume in the gas tank and fuel pump not maintaining constant pressure??? I thought this was more of a mechanical problem because I couldn't see it in the tune. It's strange and that's why I've asked for your help.

I'm going to a new PE table so I'm going to do another VE tune (Open Loop Speed Density) soon and of coarse an Open Loop MAF tune right afterwards. I'm anxious to see if running SD open loop only with stop this issue like you mentioned.

Still open to ideas, thanks
Bob

 

Hi----I just thought of another table that is temp or heat related that can affect both timing and fuel--- The COT system---( cat overtemp)
This sytem monitors the cat heat with the rear 02's--If it thinks the cats are overheated it will dump fuel to cool them off and subtract timing---
Even if you have LT's or have the rear 02's removed--if you didn't disable the COT system in the ECM it could be false triggereing----
The COT system can be enabled during closed loop cruising or even at WOT runs--This would explain the mototboating sound---as it subtracts timing and the added UN-burnt fuel would tend to gather in the exhaust and lite off
I have seen the COT system activate randomly or become overly sensitive to heat with damaged cats or exhaust pipes -- dented or leaking or too many miles or years on the clock try dis-abling the COT--it is a one line entry in the program--report back-----

 

Thanks tblu92 but I've had COT disabled for some years now. Again fueling and timing don't even change a little bit when the symptoms start up.
I'm still not thru with messing with the "Cylinder Charge Temperature" and it's "Bias" table yet. The LTFT's were richer when disabling that and richer yet when enabling it back and making the Bias table all 1.00's. Driving the car last weekend I didn't get the oil temp over 198* so can't tell yet if that will help. This weekend I'll get the temp up there and see if this changes anything.
Also I've been wanting to re-do my PE table so hopefully this week I'll be running SD only and making VE changes. We'll see if the Vette behaves normally in open loop SD.

 

So it's been right at a month since your last post. Did you find anything?

 

I was just getting ready to finish off this thread with the answer so I'm very glad you asked!

my64 was right. Turns out this was a tuning issue after all. The cure was in changing the "Cylinder Charge Temperature Bias Table" from it's factory setting of being very bias towards IAT to much more bias towards ECT.

I spent quite a bit of time researching this table on tuning forums. When moving the bias to ECT the car runs richer. Turns out it becomes a major PITA to tune this table as you have to redo your MAF, VE and this "Bias Table" tune a couple of times to bring the fueling back in line again. I wanted to change my PE table anyway so this gave me the chance to do that at the same time.
I have looked at quite a bit of tunes from modified cars and only one of them had this Bias table modified.

I still don't understand how my car was so affected by this table as my trims always were pretty close. That's why I was so stumped and started this thread in the first place.

All I can say is the car runs smooth now even with oil temps in the 220's. Problem solved! It's still a mystery to me as to what was going on in the PCM to make my car feel how it did.

I'm am still in the process of finishing up with my tuning, hopefully tomorrow I'll be done. AND I owe my64 a 12 pak of beer!!!

 

Excellent news! Congrats to you and to my64 for the fix

 

BCSEITZ, sounds like you and my64 might have found the problem. Once you have it nailed for sure, please post up by what factor you ended up changing that table. Mine starts at .60 and drifts down to .04. I suspect raising the higher gms/sec values (currently .04) to something like .2 or .4 is what you're talking about.

 

Here is where I'm at right now. With continuing to modify the VE and MAF tables this might change.

1.38770 1.39404 1.39551 1.39063 1.38086 1.36719 1.34766 1.32227 1.29150 1.25732 1.22217 1.18555 1.14697 1.10498 1.05957 1.00732

Table starts at 1.38770 and arches down to 1.00732

For all those that don't know, GM's table Min. Value is 0.00000 and Max. is 2.00000

Everyone's Bias table will end up being different based on the mods on their car (ie. Cold air intake, thermostat temp. ect.) and also the climate that they live, not to mention driving conditions.
A Value of 0 is 100% bias toward IAT (Inlet air temp.) and 2 would be 100% bias toward ECT (engine coolant temp.)
This is a linear table representing Dynamic Cylinder Air (g/sec) and is segmented into 16 cells - from 0 - 150 g/cyl (note 16 values above)

You can see from above that all my values in the Cylinder Charge Temperature Bias table are now above 1 (the halfway point) and are more bias toward ECT.

Here are the bone stock LS1/LS6 table values.

0.79980 0.41992 0.28271 0.24365 0.21973 0.20264 0.18848 0.17578 0.16455 0.15381 0.14355 0.13428 0.12451 0.11523 0.10645 0.08984

You can see that this table with all of it's values are below 1.00000. This would certainly be bias towards IAT.

I don't believe early C5's operating systems even had this table. Not sure what year GM started using this calc in their PCM's.
C6's tables range was only 0.00000 tp 1.00000 making their halfway point .50000.