So when im driving the Jeep after first start up, before closed loop the AFRs are now lean. Tune was dialed in really well this summer in hotter temps.
Temps in the 30s this morning, had a pretty long first crank. log and tune posted, whats the next step to compensate for lower air temps? Trying not to rely completely on closed loop.
YJ Tune 10-23-20.hplYJ Tune Final.hpt
Besides the lean spot on start up it looks like its still with in a few percent with the exception of low RPM/ Low MAP richness which is inherent in injectors with poor low pulse width control. This is during decel, and DFCO usually has the injectors off as the engine doesnt need to have fuel going through it while trying to slow down. What are you looking at for AFR error? I suggest using the predefined user math's for AFR err.
As far as cold start showing lean, its hard to trust a cold O2 sensor, but since you said it started hard, you can try adding to the cranking fuel, it may take removing some you will have to play with it. The cold engine may not actually like when commanded follows what the cold sensor is reporting. Its part of OL tuning freedom to tune the truly cold starts. Just be aware your AFR commanded is already in the 8's on startup, and it takes about 30 seconds before the WB shows a relative rich condition and AFR command is in the 12's. I really think its just sensor error. It doesnt even show a truly lean condition until nearly 8 minutes of idle warm up, even at that its only 6% lean. I would attribute this to you putting it in gear as you starting moving shortly after.
Lean start up.PNG
Last edited by murfie; 10-24-2020 at 01:14 AM.
First time starting in temps this cold so had no idea the commanded AFR was going to be so rich. I?ll mess with that.
I had the tune within 2% this summer pretty much always so I guess I?m being overly critical?
Does it hurt anything to go into closed loop sooner?
Super cold this morning, did a cold start log and a warm up log. can anyone gleam anything insightful? still long crank when cold.
93 Jeep YJ
5.3 TSP Stage 2 truck cam
Novak headers
Voltage is 11.6 and drops into the 9s while cranking. Probably need to replace the battery.
battery is less than 6 months old and I actually had the battery and alternator checked 2 days ago bc my gauge was reading low. Ill take it to another place and check again i suppose...Originally Posted by murfie
93 Jeep YJ
5.3 TSP Stage 2 truck cam
Novak headers
I'm having the same issue. A 2009 Silverado with aftermarket cam and cold air intake. I tuned the truck in the summer (about 100 degrees) and when it gets cold outside, it leans out. I don't have a tune and/or scan to share at the moment but I went from 4-5% to about 20%. I understand ambient air temp changes air density, which in return effects the AFR. I just haven't found how to compensate for the outside temp change.!?
The reason you have a intake air temperature sensor it to compensate for the change needed. I think you guys are over thinking this and/ or misreading your logs. If your AFR is changing because it is getting cold, its far more likely an electric power issue causing a fuel control issue, as you battery power reduces significantly with colder temps.
n= P*V/ R*T
n= Air mass, which gives you fuel mass from the air/fuel ratio desired.
P= trapped in cylinder pressure. This comes from your VE table, that translates the manifold pressure into a cylinder pressure through a volumetric efficiency multiplication.
T= Intake air temperature given by a sensor, there's a little heat picked up between this sensor and the air in the cylinder, but the air is moving fast so its minimal. Air slows down and picks up more heat at WOT. Compensation for the this can be done in the coolant temp bias table.
V= volume of cylinder at intake valve closing, this is constant.
R= the gas formulas constant. The value depends on the units used in the other variables, but it is a constant single value.
Nowhere in this does ambient air temperature matter. Unless you are talking about fuel rail temperature, battery temperature, or other things that their heat and temperatures are effected by ambient air temps as they touch the outside air.
I have only been into tuning for just over two years and have only 3 vehicles I can accredit myself to tuning. That being said I cannot say I am up to par on the tuning part.
I can say I am certain my issue isn?t any way related to voltage. I am running a dual battery setup and even at crank my voltage drops from 13.8 to 12.1.
As for the air, when it?s cold outside all of my vehicles run differently. So I am certain that air temp changes things. If I am understanding your post correctly, the IAT will compensate for the colder air. Now I just need to know what table and how to tune to for said compensation.
Last edited by DaNeW; 10-31-2020 at 12:33 PM. Reason: Sounds argumentative and aggressive
The ambient air temperature doesn't matter. The intake air temperature sensor reports any temperature change to the air in the manifold, the ecu calculates in cylinder air mass from that. mass per cylinder volume is the density being calculated, not ambient air density. The stoich AFR gives the ratio of fuel mass needed to be injected. No compensation needed for ambient air temp, the IAT sensor does it for you.
PV=nRT
P is a sensor, with VE correction.
T is a sensor, with ECT bias.
A cam changes VE, you correct this table and fuel will be correct no matter the ambient air is, as long as your IAT is accurate. The only big factor ambient air can effect is electronic resistance. fuel injector control, battery amp output, fuel pump output. Good grounds and wiring eliminate this as a factor. Fuel rail temperature is effected by ambient air. The other thing to keep in mind is winter blend fuels. The stoich AFR of the fuel shouldn't change 20%, but some do increase ethanol and that can move stoich a little, but that's splitting hairs at that point.
Your MAF sensor and MAP sensor need to be in agreement on what the in cylinder air charge mass is. The system is very MAF based, but if the VE is off, it can introduce error in the final calculation. When you tuned it, did you put it in MAF only mode and dial in the MAF, then put it in speed density mode by failing the MAF and dail in the VE table? Separating and tuning both independent from one another allows you to get both accurate to what your O2 sensor is reporting. If you left MAF enabled while correcting the VE table, you probably didn't get it right and the MAF compensated for some of the error, which now that it's colder the MAF isn't doing, as MAF's mass calculation Doesn't involve temperature.
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