Temp effect on AFR?

[98WS6_JPM]

Sirs,
I have been logging for a few weeks and cannot seem to nail down a consistent Open Loop SD tune. I have noticed that the same tune reacts differently at different times.

Example.
This morning IAT averaged 55 F (52-66), AFR averaged 14.68 (12.50-16.81).
This evening IAT averaged 100 (91-111), AFR averaged 15.08 (12.64-16.82).
Both runs were ~30-45 minutes under mixed daily driving, no WOT, same tune.

1. How much does temperature effect AFR?
2. Are these differences temp related or something else?
3. If temp related, what map should I change to compensate?

thanks! (also posted on ls1tech...)

[caver]

I have noticed the same thing. Now I try to make sure the ia temps stay about the same. Also found if you do the tune process over a few days that you chase yourself around in circles with some sites alternating between rich and lean on succesive tunes.

[Blacky]

We are currently testing some new/custom IAT based correction tables for SD tuning. Results look promising...

Regards
Paul

[SSbaby]

Sirs,

1. How much does temperature effect AFR?
2. Are these differences temp related or something else?
3. If temp related, what map should I change to compensate?

thanks! (also posted on ls1tech...)

Temperature should affect AFRs. The higher the temp the thinner the air, therefore the mixtures should be theretically richer. In any case, the PCM should force the tune to go richer to protect the engine from detonation as the more fuel supplied, the cooler that incoming charge. If you don't run a MAF, then the PCM has no real way of knowing how dense the air is. :(

If you avoid running an engine cover of use an OTRCAI, this would help to lower the IATs by at least 20-25*F. This means better performance as less timing is pulled as a result of the cooler incoming air.

[98WS6_JPM]

I fully understand the "hot should be richer" idea, but the results for my car are repeatable, hotter = leaner, almost 0.1 AFR per 10 degrees F (see below).

Yesterday morning IAT averaged 55 F (52-66), AFR averaged 14.68 (12.50-16.81), ECT averaged 166, spark average 29.9.
This morning IAT averaged 62 F (61-66), AFR averaged 14.52 (12.76-16.28), ECT averaged 174F, spark average 28.5.

Yesterday evening IAT averaged 100 (91-111), AFR averaged 15.08 (12.64-16.82), ECT averaged 195, spark averaged 26.6.
This evening IAT averaged 115 (108-120), AFR averaged 15.15 (10.47-17.39 WOT-run skewed min/max), ECT averaged 222, spark averaged 27.4.
All runs were ~30-45 minutes duration under mixed daily driving, same tune.

So the ECM in open loop still must adjust for temperature. My question is what table/group of tables change AFR based on temperature? I'm sure that the answer is buried in multiple variables. I'll shoot for a happy medium and go back to closed loop. That should still get the LTFTs to average close to zero. Then readjust the tune when the average temp is different this winter or when the LTFTs go beyond +/-5.

thanks!
Jason

[SSbaby]

Jason

Sorry, I should have been clearer. I was only making a general comment pertaining to temp and its effects on the tune.

But if you are running open loop, what are your PE settings? There is a temperature (both IAT {B3641} and ECT{B3617}) contribution to PE. Maybe look at richening those tables up in the relevant range with increasing temps?

[SSpdDmon]

Maybe we're looking in the wrong place saying the IAT is the culprit for leaner results in warmer temps?? I have a theory that may be worth looking into. How many of you have been out logging and stopped to get gas in the middle of your log? Did your fuel trims take a dive as you're pulling away from the gas station and slowly begin to recover about 30-45 minutes later? Well, why wouldn't the temp of the gas in our tanks affect AFR? They store it in tanks quite a few feet under ground where I'm sure it's nice and cold. I'm not the best when it comes to chemistry, but I know cooler things generally tend to have a greater density to them whether they be gases or liquids. So if our cars open the injectors for a given period of time regardless of fuel temps, could we be letting a greater amount of fuel into the cylinders if the gas is colder? This could explain why we run leaner on warmer days and richer on cooler days....just a thought.

[98WS6_JPM]

I have only performed the AutoVE steps from the tutorial and modified the VE table. I will tweak the IAT and ECT tables that you specified and report the results after a few days of logging. Thanks for the suggestion!
Jason

[oztracktuning]

Charge temperature is supposed to effect AFRs. It says it calculates it from IAT and ECT - so if it calculates it then what does it do.

My car also is much leaner when hot and richer when cold.
But the leaness at idle is more extreme than the leaness at higher speed and rpm. I want to tweak my charge temp blending to get it all in balance. The IAT correctio has got it quite close - but idle is more extreme so there isnt a balance in the correction.

This may also have something to do with heat soak and IAT sensors saying the air is hotter than it really is.

[carneb]

Maybe we're looking in the wrong place saying the IAT is the culprit for leaner results in warmer temps?? I have a theory that may be worth looking into. How many of you have been out logging and stopped to get gas in the middle of your log? Did your fuel trims take a dive as you're pulling away from the gas station and slowly begin to recover about 30-45 minutes later? Well, why wouldn't the temp of the gas in our tanks affect AFR? They store it in tanks quite a few feet under ground where I'm sure it's nice and cold. I'm not the best when it comes to chemistry, but I know cooler things generally tend to have a greater density to them whether they be gases or liquids. So if our cars open the injectors for a given period of time regardless of fuel temps, could we be letting a greater amount of fuel into the cylinders if the gas is colder? This could explain why we run leaner on warmer days and richer on cooler days....just a thought.

SSpdDmon I've been thinking along the same lines. The temperature of the air is taken into account in the VE calculation and so shouldn't have an affect. The PCM doesn't alter fueling based on the temperature of the fuel though (or does it?) So hotter fuel = less dense = less fuel mass = lean.

[joecar]

Maybe we're looking in the wrong place saying the IAT is the culprit for leaner results in warmer temps?? I have a theory that may be worth looking into. How many of you have been out logging and stopped to get gas in the middle of your log? Did your fuel trims take a dive as you're pulling away from the gas station and slowly begin to recover about 30-45 minutes later? Well, why wouldn't the temp of the gas in our tanks affect AFR? They store it in tanks quite a few feet under ground where I'm sure it's nice and cold. I'm not the best when it comes to chemistry, but I know cooler things generally tend to have a greater density to them whether they be gases or liquids. So if our cars open the injectors for a given period of time regardless of fuel temps, could we be letting a greater amount of fuel into the cylinders if the gas is colder? This could explain why we run leaner on warmer days and richer on cooler days....just a thought.
The PCM doesn't alter fueling based on the temperature of the fuel though (or does it?) So hotter fuel = less dense = less fuel mass = lean.
Welcome, mate.

You're right, the PCM does not know the temp. of the fuel.
This looks interesting, looks like you two maybe onto something.

[jfpilla]

Might as well throw one other thing into the mix, particularly, if you have bigger injectors. Manifold vacuum and voltage changes will change IPW and therefore AFR. Also, the battery charging system will tend to put out more volts after the car has been sitting overnight and affect IPW. More volts decreases IPW resulting in leaning, if the IPW table is not corrected. Try logging GM.Manifold Vacuum and Battery Voltage and I think you will see it. I set up a LTFT MAP versus those parameters and it becomes pretty clear.

[carneb]

After a bit of research it seems that the volume of the fuel only increases by approximately 1% for a 10 degree C increase in temperature. This wouldn't be enough to have a huge effect on AFR's I wouldn't think.

[SSbaby]

After a bit of research it seems that the volume of the fuel only increases by approximately 1% for a 10 degree C increase in temperature. This wouldn't be enough to have a huge effect on AFR's I wouldn't think.

True, But a difference of 30*C ambient temp is enough to have your car stall if your mixtures richen up by 3%.