Tuning fuel to compensate for heat soak

[phuz]

Yesterday we had our first hot day of the year (90F) and I had the C5 out for a bit.
I thought I had my VE table dialed in pretty well in the idle and "light cruise" sections of the map until after about 45 minutes of stop and go in the heat, the AFRs started getting very lean in these same regions (~17.5-18).
I had previously done all my tuning in these areas when ambient temp was around 70F.

• Isn't the PCM supposed to be taking IAT into account for these fueling calculations?
• Do I just need to make these sections richer and let the STFT and LTFT do their thing when I re-enable them?
• Will this remedy itself when I re-enable the MAF for the low end?
• Is there something else I can adjust to help with this? (Hotsoak Enrichment?)

This post #12 looks like it might be on to something. Maybe the IAT is more heat-soaked than the engine and pulling fuel when it shouldn't be.
https://forum.hptuners.com/showthrea...l=1#post290311

[kingtal0n]

According to this GM calibrator, it will solve all your problems. Let me know if it works for you or not as I am genuinely curious if it can actually help somebody. Let me know what you think please.

https://forum.hptuners.com/showthrea...l=1#post722112

[phuz]

According to this GM calibrator, it will solve all your problems. Let me know if it works for you or not as I am genuinely curious if it can actually help somebody. Let me know what you think please.

https://forum.hptuners.com/showthrea...l=1#post722112

I don't have Matlab and thinking about this a bit more, I don't know that IAT is changing enough to cause such a large swing to the lean side, especially after seeing that you disabled yours completely and it had no effect (which is a bit unnerving in itself). I need to log the voltage too, because I didn't take notice if the voltage dipped a bit during this period as that would definitely explain it. I didn't see your previous post about this otherwise I would've piggy-backed on that (my bad!), but sort of glad to know I'm not alone.
I fully agree that I would expect to see it go rich with hotter temps, not lean.

[kingtal0n]

My worldview,
- look at system voltage and consider increasing the injector delay (delay vs pressure vs voltage table) to help with voltage is low at high vacuum regions where its running lean, high temp = low voltage = slow response
- consider adding a variable resistor to the IAT to adjust a/f ratio (about 1000ohms is what I would recommend) as desired
- if you are using a dead-head fuel rail, converting to a fully return (recycling rail) might help emphasis on might
- airflow or water cooling the injectors might help, when solenoids get hot they respond slowly, (related to temperature vs solenoid opening the injectors hotter = slower)
- remember afterstart enrichment table called "heat soak" or "hot soak" table has a timer which can enrich after hot soaking (sitting engine off while hot)
- disable CTS bias to make tuning efforts reliable and reduce variation / variability
- relocate the IAT or isolate the IAT sensor with plastic washer to prevent IAT heat soaking although the iat is only a small component of this issue
- remember fuel ethanol content in open loop will swing the a/f ratio leaner as ethanol increases, pump say 10% but you get 13% it can be that 0.3a/f difference or whatever

In my case I think the injector solenoids are getting hot and system voltage is dropping, and the fuel may be dropping density as it warms, and those together causing leaner a/f ratios. Nothing to do with IAT or IAT sensor.
I can adjust the iat back to ambient but its still lean. I can remove the iat completely and flat-line the table it but its still lean in heat soak situations which rules out IAT related.

[SiriusC1024]

This is at least the 3rd related topic within a week.

The big question here is why is the engine running non-stoich, yet no DTC's are generated?

Since we're talking out of our ass here, I'll present my worldview:
Hot day = hot oil = extra volatiles thru pcv = contaminated O2 sensor.

In my case, I run quaker state full synthetic and use denso O2's.

xD

[TheMechanic]

This is at least the 3rd related topic within a week.

The big question here is why is the engine running non-stoich, yet no DTC's are generated?

Since we're talking out of our ass here, I'll present my worldview:
Hot day = hot oil = extra volatiles thru pcv = contaminated O2 sensor.

In my case, I run quaker state full synthetic and use denso O2's.

xD

That scenario is highly unlikely. Any time a stock vehicle without mechanical or software issues doesn't run stoich it is because there is some table, adder, etc. that is modifying it.
There is one issue that might cause issues and that is case grounded/PCM grounded HO2S's. If you are sure they are right then it is a table etc.

[Alvin]

Yesterday we had our first hot day of the year (90F) and I had the C5 out for a bit.
I thought I had my VE table dialed in pretty well in the idle and "light cruise" sections of the map until after about 45 minutes of stop and go in the heat, the AFRs started getting very lean in these same regions (~17.5-18).
I had previously done all my tuning in these areas when ambient temp was around 70F.

• Isn't the PCM supposed to be taking IAT into account for these fueling calculations?
• Do I just need to make these sections richer and let the STFT and LTFT do their thing when I re-enable them?
• Will this remedy itself when I re-enable the MAF for the low end?
• Is there something else I can adjust to help with this? (Hotsoak Enrichment?)

This post #12 looks like it might be on to something. Maybe the IAT is more heat-soaked than the engine and pulling fuel when it shouldn't be.
https://forum.hptuners.com/showthrea...l=1#post290311

What were the fuel trims doing at this point? When most people talk about heat soaked IAT's they are talking about a lean restart which usually goes away in a few minutes. Not 45 min worth of driving.

[phuz]

Sorry for not mentioning it in this thread, but ALL trims are disabled. This is happening in 100% open loop.

[kingtal0n]

try afterstart heatsoak enrichment for the hot refires
hotsoak-enrichment.jpg

during run-time if it happens from sitting in traffic I can spritz water on my fuel injectors to temporarily, sort of fix the issue. Seems to help. Prob to be related to heat, voltage, injector response, idk
I've never seen anything like it using any stand-alone computer , thats what drives me nuts. Why only GM ecu? Could it just be the style if injectors we use? Or the enormous engine under the hood? I've tuned hundreds of engines but most are 4 and 6 cylinders with the hot exhaust well insulated and distinctly off to the side away from the engine.